Water Global Practice Lesotho WEAP Manual m A Water Global Practice Lesotho WEAP Manual m A © 2017 International Bank for Reconstruction and Development / The World Bank 1818 H Street NW, Washington, DC 20433 Telephone: 202-473-1000; Internet: www.worldbank.org This work is a product of the staff of The World Bank with external contributions. The findings, interpretations, and conclusions expressed in this work do not necessarily reflect the views of The World Bank, its Board of Executive Directors, or the governments they represent. The World Bank does not guarantee the accuracy of the data included in this work. The boundaries, colors, denominations, and other information shown on any map in this work do not imply any judg- ment on the part of The World Bank concerning the legal status of any territory or the endorsement or acceptance of such boundaries. Rights and Permissions The material in this work is subject to copyright. 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Contents Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . v Abbreviations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vi 1 The Water Evaluation and Planning (WEAP) System Basics . . . . . . . . . . . . 1 WEAP System Capabilities. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 General Modeling Approach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 WEAP Calculations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 Note . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 2 Lesotho Application of WEAP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Hydrology of Lesotho . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Key Water Management Features of Lesotho. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Building the Model for the Orange-Senqu River. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 Re-Calibration of Hydrology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 Notes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 Figures 1.1 Conceptualization of Integrated Hydrologic Processes and Water Management Operations in WEAP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 1.2 Developing a WEAP Application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.3 Diagram of the Two-Bucket WEAP Hydrology Model. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 1.4 Reservoir Zones. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 2.1 Two-Step Process for Developing Lesotho WEAP Model. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 2.2 WEAP Schematic Showing Catchment Objects Used to Simulate Basin Hydrologic Processes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 2.3 Climate Grid Points Used to Construct Climate Time Series for WEAP Model. . . . . . . . . . 10 2.4 WEAP Schematic Showing the Linkage of Water Supplies (Blue Lines) and Demands (Red Circles). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 2.5 LHWP Water Transfer Targets to South Africa. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 2.6 WEAP Schematic Showing Configuration of Lowland Demand. . . . . . . . . . . . . . . . . . . . . . . 15 2.7 WEAP Schematic Showing Configuration of Lowland Demands. . . . . . . . . . . . . . . . . . . . . . 16 2.8 WEAP Schematic Showing the Configuration of Metolong Dam. . . . . . . . . . . . . . . . . . . . . . 19 2.9 Metolong Dam Volume-Elevation Relationship (Metolong Authority 2015). . . . . . . . . . . . . 19 2.10 Simulated versus Reported Crop Production (1999–2005). . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 2.11 WEAP Schematic Showing Streamflow Calibration Locations. . . . . . . . . . . . . . . . . . . . . . . . . 26 2.12 WEAP versus ORASECOM Results for D11 A-F (Inflows to Katse Dam). . . . . . . . . . . . . . . 27 2.13 WEAP versus ORASECOM Results for D17A (Inflows to Mohale Dam) . . . . . . . . . . . . . . . 27 2.14 WEAP versus ORASECOM Results for Matsoku River. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 2.15 WEAP versus ORASECOM Results for Senqu River Flows into Polihali. . . . . . . . . . . . . . . . 28 2.16 WEAP versus Observed Makheleng River Flows at Qaba. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 2.17 WEAP versus ORASECOM Results for D21E. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 2.18 WEAP versus ORASECOM Results for D21H. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 Lesotho WEAP Manual iii 2.19 WEAP versus ORASECOM Results for D22C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 2.20 WEAP versus ORASECOM Results for D22H. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 2.21 WEAP versus ORASECOM Results for D23E. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 2.22 WEAP versus ORASECOM Results for D23J. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 Maps 2.1 Lesotho Highland Water Project. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 2.2 Location of Intakes for Lowland Demands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 2.3 Quaternary Catchments Used for Hydrological Routines. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 2.4 Population Density (CIESIN 2011). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 Tables 2.1 Dams Included in WEAP Model as Part of Lesotho Highlands Water Project . . . . . . . . . . . 12 2.2 Location of Intakes for Lowland Demands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 2.3 Demand Projections for Domestic, Industrial, and Institutional Consumers 2005–35 . . . . 17 2.4 WEAP Inputs for Domestic and Industrial Water Demands . . . . . . . . . . . . . . . . . . . . . . . . . . 18 2.5 Monthly Instream Flow Requirement from Metolong Dam (Metolong Authority 2015). . . . 20 2.6 Flood Requirements (Metolong Authority 2015). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 2.7 Maximum Potential Yield and Yield Factors for Irrigated Crops. . . . . . . . . . . . . . . . . . . . . . . 21 2.8 Crop Factor Coefficients throughout the Years. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 2.9 Total Area Planted, ha (2007). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 2.10 Total Yield, Tonnes (1999–2005). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 2.11 Statistics for Observed Data Used for WEAP Calibration. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 iv Lesotho WEAP Manual Acknowledgements This work represents one in a series of three reports documenting the findings of a program of  support to the Government of Lesotho aimed at enhancing the capacity for water resources modeling and management, and the assessment of climate-related vulnerabilities. The World Bank team was led by Marcus Wishart (Senior Water Resources Management Specialist) and Ijeoma Emenanjo (Natural Resources Management Specialist). Model develop- ment and analysis was undertaken by the Stockholm Environment Institute, led by Annette Huber-Lee, and included Brian Joyce, David Yates, and Stephanie Galaitsi, along with David Groves, James Syme, and Zhimin Mao from Evolving Logic. The program was implemented under the guidance of Asad Alam (Country Director), Guang Zhe Chen (Country Director), and Jonathan Kamkwalala (Practice Manager) of the World Bank. The program in Lesotho was coordinated by the Ministry of Energy, Meteorology and Water Affairs in collaboration with the Ministry of Agriculture and Food Security and the Lesotho Highlands Development Authority. The three reports represent the culmination of a series of virtual meetings, physical workshops, and reverse missions over the course of the program that included representatives from a wide range of national institutions, such as the office of the Commissioner of Water, the Department of Water Affairs, the Lesotho Meteorological Service, the Crops Department of the Ministry of Agriculture, and the Lesotho Highlands Development Authority. Specifically, we are grateful for the participation of Commission of Water colleagues Lebohang Maseru, Matebele Setefane, Khotso Mosoeu; Department of Water Affairs ­colleagues Nthati Toae, Phaello Leketa, Molefi Pule, Thabo ‘Mefi, Thabiso Mohobane, Motoho Maseatile, Neo Makhalemele; Ministry of Agriculture colleagues Mahlomala Manoza, Lebone Molahlehi, Moeketsi Selebalo, Tsitso Marabe, Tiisetso Monyobi, Tsoanelo Sekoiliata Ramainoane; Lesotho  Meteorological Service colleagues Kabelo Lebohang, Pheello Ralenkoane, Mathabo  Mahahabisa, Tseole Charles, Tsekoa Maqhanolle; Leshoboro Nena from the Lowland Water Supply Unit; and from the Lesotho Highlands Development Authority, Fred Tlhomola, Khojane Lepholisa, and Thelejane Thelejane. The team also acknowledges the peer reviewers who contributed to the study: Ademola Braimoh (Senior Natural Resources Management Specialist), Ana Bucher (Climate Change Specialist), Raffaello Cervigni (Lead Environmental Economist), Mukami Kariuki (Lead Water and Sanitation Specialist), and Regassa Namara (Senior Water Resources Economist). Lesotho WEAP Manual v Abbreviations DC deep conductivity DWC deep water capacity FAO United Nations Food and Agricultural Organization LHWP Lesotho Highlands Water Project MCM million cubic meters NSE Nash-Sutcliffe Efficiency ORASECOM Orange-Senqu River Commission PBIAS percent bias PFD preferred flow direction RDM robust decision making RRF runoff resistance factor RSA Republic of South Africa RZC root zone conductivity SC sub-catchment SEI Stockholm Environment Institute SWC soil water capacity WEAP Water Evaluation and Planning vi Lesotho WEAP Manual Chapter 1 The Water Evaluation and Planning (WEAP) System Basics WEAP System Capabilities Water management and allocation models are often used to help water managers make informed decisions. To support the robust decision making (RDM) process in Lesotho, this project used the Water Evaluation and Planning (WEAP) model to examine hydrologic dynamics in the Orange-Senqu river basin. This section describes the WEAP model’s broad capabilities and the process for implementing the model in Lesotho. The WEAP system provides an integrated approach to water resources planning by linking hydrologic processes, system operations and end-use within a single analytical platform (Huber-Lee et al. 2003).1 The RDM process depends upon stakeholders engaging with the development and analysis of results. In additional to its complex operation capabilities, WEAP provides a comprehensive, flexible and user-friendly tool for water resources planning and policy analysis. As part of the Lesotho Project, team members lead capacity building trainings in WEAP both to provide Lesotho planners with the tool and to include them in the project’s processes and results inter- pretations. WEAP’s transparent structure facilitates the engagement of stakeholders in an open process to evaluate water development and management options, and consider the mul- tiple and competing uses of water systems. To model a water system’s operation, WEAP integrates both water demand and supply by placing demand-side issues on an equal footing with supply-side dynamics. Demand esti- mates emerge from data regarding water use patterns, equipment efficiencies, re-use strategies, costs, and water allocation schemes, among others. WEAP models supply by reproducing both its managed components (streamflow diversions, groundwater pumping, reservoirs, and water transfers) and its natural components (e.g., evapotranspiration demands, runoff, base- flow) and its managed components. WEAP operates on the basic principle of a water balance and can be applied to a single watershed or complex trans-boundary river basin systems. At the most basic level, WEAP’s integrated hydrology/water allocation framework (Yates et al. 2005a, 2005b), recognizes that water supply is defined by the amount of precipitation that falls on a watershed (see figure 1.1). Further, this basic supply is depleted through natural water- shed processes, where the watershed itself is the first significant point of depletion through evapotranspiration (Mahmood and Hubbard 2002). The water remaining in excess of evapo- rative demands throughout the watershed is the supply available to the water management system. Thus, as in the physical realm, there is a seamless link in the WEAP framework between climate, land use/land cover conditions, and the management of the water system (Purkey et al. 2007). Lesotho WEAP Manual 1 Figure 1.1  Conceptualization of Integrated Hydrologic Processes and Water Management Operations in WEAP Precipitation ET Runoff Runoff ET ET Runoff s Infiltration ee Tr ity Infiltration C ps ro C Groundwater discharge into stream Aquifer General Modeling Approach WEAP is an integrated water resources planning tool that is used to represent current water conditions in a given area and to explore a wide range of demand and supply options for balancing environment and development objectives. WEAP is widely used to support collaborative water resources planning by providing a common analytical and data man- agement framework to engage stakeholders and decision-makers in an open planning pro- cess. Within this setting, WEAP is used to develop and assess a variety of scenarios that explore physical changes to the system, such as new reservoirs or pipelines, as well as social changes, such as policies affecting population growth or the patterns of water use. Finally the implications of these various policies can be evaluated with WEAP’s graphical display of results. Steps in Developing a WEAP Model The development of the WEAP application in this study followed a standard modeling approach (see figure 1.2). The first step in this approach is the study definition, wherein the spatial extent and system components of the area of interest are defined and the time horizon of the analysis is set. Following this initial assessment, the “current accounts” is defined, which is a baseline representation of the system—including the existing operating rules for both sup- plies and demands. The current accounts serves as the point of departure for scenarios that characterize alternative sets of future assumptions pertaining to policies, costs, and factors that affect demands, pollution loads, and supplies. Finally, the scenarios are evaluated with regard to water sufficiency, costs and benefits, compatibility with environmental targets and sensitivity to uncertainty in key variables. The steps in the analytical sequence are described in greater detail in the following sections. 2 Lesotho WEAP Manual Figure 1.2  Developing a WEAP Application Study definition Spatial boundary System components Time horizon Network configuration Current accounts Demand Pollutant generation Reservoir characteristics Resources and supplies River simulation Wastewater treatment Scenarios Demographic and economic activity Patterns of water use, pollution generation Water system infrastructure Hydropower Allocation, pricing and environmental policy Component costs Hydrology Evaluation Water sufficiency Ecosystem requirements Pollutant loadings Sensitivity analysis Study Definition Evaluating the implications of managing diversions and impoundments along a river requires the consideration of the entire land area that contributes to the flow within the river—the river basin. Within WEAP, it is necessary to set the spatial scope of the analysis by defining the boundaries of the river basin. Within these boundaries there are smaller rivers and streams (or tributaries) that flow into the main river of interest. Because these tributaries determine the distribution of water throughout the whole basin, it is also neces- sary to divide the study area into sub-basins such that we can characterize this spatial vari- ability of river flows. Current Accounts The current accounts represent the basic definition of the water system as it currently exists. Establishing current accounts requires the user to “calibrate” the system data and assumptions to a point that accurately reflects the observed operation of the system. The current accounts include the specification of supply and demand data (including defini- tions of reservoirs, pipelines, treatment plants, pollution generation, etc.). This calibra- tion process also includes setting the parameters for WEAP’s rainfall-runoff module such that WEAP can use climatic data (i.e., temperature and precipitation) to estimate water supply (i.e., river flows, aquifer recharge) and demand (evaporative water demand) in the delineated basins. Lesotho WEAP Manual 3 Scenarios At the heart of WEAP is the concept of scenario analysis. Scenarios are self-consistent story-lines of how a future system might evolve over time. The scenarios can address a broad ­ range of “what if ” questions. This allows users to identify unintended changes in the system and evaluate how these changes may be mitigated by policy and/or technical interventions. The result of these analyses guide the development of response packages, which are combina- tions of management and/or infrastructural changes that enhance the productivity of the system. Evaluation Once the performance of a set of response packages has been simulated within the context of future scenarios, the packages can be compared relative to key metrics identified by stakehold- ers in the XLRM activity of the RDM process. Often these relate to water supply reliability, water allocation equity, ecosystem sustainability, and cost, but any number of performance metrics and be defined and quantified within WEAP. WEAP Calculations At each time step, WEAP first computes the hydrologic flux, which it passes to each river. The water allocation is then made for the given time step, where constraints related to the charac- teristics of reservoirs and the distribution network, environmental regulations, and the prior- ities and preferences assigned to points of demands are used to condition a linear programming optimization routine that maximizes the demand “satisfaction” to the greatest extent possible (see Yates et al. 2005a for details). All flows are assumed to occur instantaneously; thus a demand site can withdraw water from the river, consume some, and optionally return the remainder to a receiving water body in the same time step. As constrained by the network topology, the model can also allocate water to meet any specific demand in the system, without regard to travel time. Thus, the model time step should be at least as long as the residence time of the study area. For this reason, the Lesotho project adopted a monthly time step for our study. Rainfall-Runoff (aka Streamflow Generation) WEAP offers three methods to simulate watershed hydrological processes such as evapotran- spiration, runoff, and infiltration. These methods are (1) the Rainfall Runoff and (2) the Simplified Coefficient Approach, and (3) the Soil Moisture Method. This study used WEAP’s Soil Moisture Method to estimate the rainfall-runoff processes at the sub-basin level through- out Lesotho. The Soil Moisture module in WEAP is spatially continuous, with a study area configured as a contiguous set of sub-catchments that cover the entire extent of the river basin under exami- nation. This continuous representation of the river basin is overlaid with a water management network topology of rivers, canals, reservoirs, demand centers, aquifers and other features (see Yates et al. 2005a, 2005b for details). Each sub-catchment (SC) is fractionally subdivided into a unique set of independent land use/land cover classes that lack detail regarding their exact 4 Lesotho WEAP Manual location within the SC, but which sum to 100% of the SC’s area. A unique climate-forcing data set of precipitation, temperature, relative humidity, and wind speed is uniformly prescribed across each SC. A one-dimensional, quasi-physical water balance model depicts the hydrologic response of  each fractional area within a SC and partitions water into surface runoff, infiltration, evapotranspiration, interflow, percolation, and baseflow components (see equation 1.1 and ­ figure 1.3). Values from each fractional area within the SC are then summed to represent the ­ lumped hydrologic response, with the surface runoff, interflow and baseflow being linked to a river element and evapotranspiration being lost from the system. Equation 1.1  Soil Moisture Model dz1, j  5 z - 2 z1, 2 j RRF 2 2 Rd j = Pe (t ) - PET (t )kc , j (t )  1, j  - Pe (t )z1, j j - f j kz , j z1, j - (1 - f j )kz , j z1, j dt  3  WEAP offers a default method for calculating the potential evapotranspiration that uses a modified Penman-Montieth equation or an alternate method that allows the user to define his/her own equation(s). Because the Penman-Montieth relies on variables that were not easily obtained for the suite of climate futures used in our analysis (i.e., wind speed and relative humidity), we chose to use a modified Hargreaves equation developed by Droogers and Allen (2002) that required only estimates of temperature and precipitation. Figure 1.3  Diagram of the Two-Bucket WEAP Hydrology Model Pobs Et = f(zfa, kcfa, PET) Pe = f(Pobs, Snow Accum, Melt rate, Tl, Ts) surface runoff = f(Zfa 1, cdfa, Pe) Ufa Lfa Wcfa Zfa interflow = f(Z1,j, Hcfa, 1 – f ) Percolation = f(Zfa, Hcfa, f ) WC Z Baseflow = f(Z, HC) Source: Yates et al. 2005a. Lesotho WEAP Manual 5 Water Allocation Two user-defined priority systems are implemented to determine allocations of water supplies  to demands (i.e., urban and agricultural), for instream flow requirements, and for ­ reservoirs—demand priorities and supply preferences. filling ­ Demand priorities allocate water among competing demand sites and catchments, flow requirements, and reservoir storages. The demand priority is specified for every demand site, catchment, reservoir, or flow requirement. Priority numbers in WEAP range from 1 to 99, with 1 being the highest priority and 99 the lowest. Many demand sites can share the same priority, which is useful in representing a system of water rights, where water users are defined by their water usage and/or seniority. In cases of water shortage, higher priority users are sat- isfied as fully as possible before lower priority users are considered. If priorities are the same, shortage will be shared equally (as a percentage of their demands). When demands sites or catchments are connected to more than one supply source, the order of withdrawal is determined by supply preferences. Similar to demand priorities, supply pref- erences are assigned a value between 1 and 99, with lower numbers indicating preferred water sources. The assignment of these preferences usually reflects some economic, environmental, historic, legal and/or political realities. In general, multiple water sources are present when the preferred water source is insufficient to satisfy all of an area’s water demands. WEAP treats the additional sources as supplemental supplies and will draw from these sources only after it encounters a capacity constraint (expressed as either a maximum flow volume or a maximum percent of the demand) associated with the preferred water source. WEAP’s allocation routine uses demand priorities and supply preferences to balance water supplies and demands. To do this, WEAP must assess the available water supplies at any given time step. While total supplies may be sufficient to meet all of the demands within the system, it is often the case that operational considerations prevent the release of water to do so. These regulations are usually intended to hold water back in times of shortage so that delivery reli- ability is maximized for the highest priority water users (often urban indoor demands). WEAP can represent this controlled release of stored water using its built-in reservoir object. WEAP uses generic reservoir objects that divide storage into four zones, or pools (figure 1.4). These include, from top to bottom, the flood-control zone, conservation zone, buffer zone and inactive zone. The conservation and buffer pools together constitute the reservoir’s active stor- age. WEAP will ensure that the flood-control zone is always vacant—i.e., the volume of water in the reservoir cannot exceed the top of the conservation pool. The size of each of these pools can change throughout the year according to regulatory guidelines, such as flood control rule curves. WEAP allows the reservoir to freely release water from the conservation pool to fully meet withdrawal and other downstream requirements. Once the storage level drops into the buffer pool, the release will be restricted according to the buffer coefficient, to conserve the reser- voir’s dwindling supplies. The buffer coefficient is the fraction of the water in the buffer zone available each month for release. Thus, a coefficient close to 1.0 will cause demands to be met more fully while rapidly emptying the buffer zone, while a coefficient close to 0 will leave 6 Lesotho WEAP Manual Figure 1.4  Reservoir Zones Total storage Flood control zone Top of conservation Conservation zone Top of buffer Buffer zone Top of inactive Inactive zone demands unmet while preserving the storage in the buffer zone. Water in the inactive pool is not available for allocation, although under extreme conditions evaporation may draw the reservoir into the inactive pool. Note 1. WEAP has been developed for the past 20 years by the Stockholm Environment Institute, (SEI) working in partnership with a number of agencies and organizations. WEAP is used by a large community of researchers, government officials, professionals, students and non-government organizations. They share their WEAP experiences in a User Forum (www.weap21.org). ­ Lesotho WEAP Manual 7 Chapter 2 Lesotho Application of WEAP This project developed a WEAP model to represent the main water supply and demand fea- tures for the Kingdom of Lesotho. The model was developed at a spatial scale appropriate to simulate major hydrologic flows; to represent major demographic trends; and to evaluate the effects of water management responses. Monthly observations between 1950 and 2005 were used to calibrate WEAP (See Annex A) to enable it to consider future climate and water man- agement scenarios from 2010 to 2050. The model is designed to evaluate the performance of water supply reliability for different water use sectors across a range of future climate conditions. These water use sectors include domestic and industrial water users, rainfed and irrigated agriculture, hydro- power, instream flow requirements and water transfers to South Africa. For purposes of water allocation, the model assigns transfers to South Africa the highest priority. After that, the domestic water users have the highest priority for water deliveries; industrial water users the second highest priority; irrigation the third highest priority; instream flow requirements the fourth highest priority; and surface water storage behind dams holds the lowest priority for water. In the model, the current water supply system disconnects the demands in the Lesotho lowlands from the water supply system of the Lesotho Highlands Water Project (LHWP). Thus, under current operations, the deliveries to South Africa from the LHWP and the associated hydropower production are independent of water allo- cation in the lowlands. The Lesotho WEAP model was developed using a two-step process (outlined in figure 2.1). The first step of this process focused on developing the rainfall/runoff routines and calibrating Figure 2.1  Two-Step Process for Developing Lesotho WEAP Model Rainfall data and calibration parameters Historical development and Hydrological A Observed flow for rainfall/runoff model calibration Agreements/Conventions/ Law allocation strategies B Naturalized or virgin runoff Water balances Rainfall and evaporation Dam storage trajectory reservoir data System yield System analysis Dam and river characteristics model Flow regime compliance Water use scenarios Environmental requirements met? Environmental flow requirements User satisfaction Source: Juizo and Linden 2010. 8 Lesotho WEAP Manual these to observed historical streamflow timeseries. The second step focused on adding repre- sentations of the existing and planned water management infrastructure to the model. These steps are explained further in the following two sub-sections. Hydrology of Lesotho In general, we used quaternary catchments from the South African Department of Water and Sanitation1 as the basic unit used to define the spatial resolution of the hydrologic simulation. These catchments were often combined to form larger areas in cases where multiple catch- ments lay upstream of control points. For example, we combined quaternary catchments D11A through D11F, because they all lie upstream of Katse dam, which is the first control point that this study considered on the Malibamatso River (figure 2.2). This approach resulted in 34 catchments used in the WEAP model to represent hydrological processes within Lesotho. An additional 12 catchments were used to represent the hydrology of areas within South Africa that discharge into the Caledon River. Each of the catchments shown in figure 2.2 contain climate data that are used as drivers for the routines that estimate the hydrological response (i.e., rainfall-runoff and baseflow) and the potential evapotranspiration for rainfed and irrigated agriculture. These data Figure 2.2  WEAP Schematic Showing Catchment Objects Used to Simulate Basin Hydrologic Processes Lesotho WEAP Manual 9 Figure 2.3  Climate Grid Points Used to Construct Climate Time Series for WEAP Model include time series of historical and projected monthly precipitation (mm), average ­temperature (deg C), minimum temperature (deg C), and maximum temperature (deg C). To construct these timeseries, we used historical climate data from 1948 to 2008, devel- oped by the Terrestrial Hydrology Research Group at Princeton University (Sheffield et al. 2006). These data include climate sequences of monthly temperature and precipita- tion, spatially averaged for each hydrologically connected catchment. This dataset was developed at the 0.5 degree scale, resulting in 20 grid cells that overlay the Kingdom of Lesotho (figure 2.3). To calculate climate inputs for each catchment, we used weighted averages based on percentage of catchment polygons within each climate grid cells. This involved using GIS to intersect the grid cells with the catchment polygons. Key Water Management Features of Lesotho The model includes representations of the major water use sectors within Lesotho and the existing and planned infrastructure that serves them. The linkage of these supplies and demands is show in figure 2.4. ­ gure 2.4, Inter-basin water transfers to the Republic of South Africa (RSA), shown in orange in fi represent the largest single water use within the basin and are served by the LHWP. In fact, the main purpose of the LHWP is to provide water supply to South Africa and to generate 10 Lesotho WEAP Manual Figure 2.4  WEAP Schematic Showing the Linkage of Water Supplies (Blue Lines) and Demands (Red Circles) hydropower for Lesotho. According to the treaty between Lesotho and South Africa, water transfers to South Africa from the LHWP increase with subsequent phases of the project. Currently, the project supplies 27.5 m3s−1 (867 MCM/year) to South Africa and is expected to supply 40 m3s−1 (1,261 MCM/year) once Phase 2 is fully operational. Transfers are expected to be capped at 70 m3s−1 (2,207 MCM/year) once the project is fully developed. The project was originally envisioned in four phases that are described in the left of map 2.1 and shown in red in the map. The first phase of the project (including Phase Ia and Ib) has been completed and includes Katse and Mohale dams as well as diversion structures to divert water into Katse from the Matsoku River and Mohale dam and a transfer tunnel to send water from Katse dam to Muela dam and subsequently South Africa. Phase II of the project, which is now under implementation, has been reconfigured to include a dam, Polihali, which was not part of the original design. It is expected to be complete by 2020. Further phases of the project face greater uncertainty and presently there are no reliable estimates for completion dates. For the purposes of the current study, we consider that the next phases will include the three dams planned for the main stem of the Senqu River downstream of the current facilities and they will be commissioned at regular intervals after the completion of Phase II. These are summarized in table 2.1. For the purposes of this project, we assumed that these “transfer targets” to South Africa would be adjusted following the construction of each new facility and that they would increase over a five year period during the filling period of the new facility. Figure 2.5 shows the demand curve for South Africa water transfer targets. Lesotho WEAP Manual 11 Map 2.1  Lesotho Highland Water Project Table 2.1  Dams Included in WEAP Model as Part of Lesotho Highlands Water Project Storage capacity Inactive storage Instream flow Dam Start year (MCM) (MCM) requirement (MCM/year) Katse 2001 1,950 433 65.86 Mohale 2003 938 87.5 30.44 Polihali 2020 2,322 418 22 Mashai 2030 3,305 0 47 Tsoelike 2035 2,224 924 53 Ntoahae 2040 1,432 720 63 12 Lesotho WEAP Manual Figure 2.5  LHWP Water Transfer Targets to South Africa 2,500 Ntoahae Tsoelike Polihali Mashai 2,000 RSA transfer target (MCM) 1,500 1,000 500 0 26 32 38 44 50 10 12 14 16 18 20 22 24 28 30 34 36 40 42 46 48 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 Largely disconnected from the LHWP, most of the water usage within Lesotho is in the low- lands and is served by local surface water supply sources. Currently, there is another large water project in Lesotho—the Lesotho Lowlands Water Supply Scheme—that aims to enhance water supply reliability for the domestic, industrial, and agricultural water needs of the low- land districts. To define the location and pattern of water demands in the lowlands, we used data from the feasibility report for this project (2004), which organized demands in the low- lands into eight zones. Figure 2.6 shows the configuration of the lowlands water demands within the WEAP schematic. Essentially, each zone consists of a pair of demand nodes (red circles)—domestic ­ and ­industrial, which allows for WEAP to assign a higher priority to domestic users than to industrial/institutional users in each zone. Transmission links (green lines) connect demands to various water sources. The Lowlands Water Supply Scheme feasibility study identified eight zones and five intakes from which water will be abstracted. These are summarized in table 2.2 and shown graphi- cally  in map 2.2. These abstraction points correspond to the diversion locations shown in figure 2.6. Lesotho WEAP Manual 13 Table 2.2  Location of Intakes for Lowland Demands Zone Service area Water source Coordinates (proposed intake) 1 Botha Bothe Hololo river Lat: 28°41’44.6”S Lon: 28°21’47.2”E 2&3 Maputsoe/Leribe Hlotse river Lat: 28°54’49.06”S Lon: 28°6’54.49”E 4&5 Maseru, TY, Morija Metolong Dam Lat: 29°21’10.81”S Lon: 27°44’20.24”E 6&7 Mafeteng, Mohale’sHoek Makhaleng Lat: 30°5’9.70”S Lon: 27°26’15.36”E 8 Quthing Senqu Lat: 30°21’59.21”S Lon: 27°43’14.84”E Map 2.2  Location of Intakes for Lowland Demands N Legend Intakes W E Contour S 1,500 Hololo 1,750 2,000 Hlotse 2,250 2,500 2,750 3,000 3,250 Metolong Makhaleng Senqu 14 Lesotho WEAP Manual Figure 2.6  WEAP Schematic Showing Configuration of Lowland Demand Building the Model for the Orange-Senqu River The WEAP model used in this study is a modified version of a tool developed for a p ­ revious World Bank project that examined the resilience of infrastructure throughout Africa in the face of climate change (Cervigni et al. 2015). A complete description of the development of this model, including descriptions of the spatial disaggregation of the basin and the main water management features, can be found in a forthcoming World Bank Report: Enhancing the Climate Resilience of Africa’s Infrastructure: The Power and Water Sectors. This Annex pro- vides a description of the enhancements made to the WEAP model under the current project to better represent water management in the Kingdom of Lesotho. Lowland Demands As part of the feasibility study of the Lesotho lowlands water supply scheme (2004), water demands were estimated for eight demand zones out to the year 2035. The location of these zones is shown in figure 2.7. The data are summarized in tables 2.3 and 2.4. These data were reformatted to provide input to the WEAP model for Lesotho. Specifically, we calculated per capita water use by dividing the total domestic water demand by the popula- tion.  Per capita waster use is then combined with population in WEAP to estimate total Lesotho WEAP Manual 15 Figure 2.7  WEAP Schematic Showing Configuration of Lowland Demands domestic demands. This formulation was used so that we can explore different scenarios that adjust population and per capita water usage independently. Additionally, we applied a popu- lation growth rate of 1.5 percent after the year 2035, which generally continues the trend in the data between 2005 and 2035. Industrial demands were estimated by taking the sum of industrial and institutional demands from table 2.3. Percent losses were estimated by dividing the total losses by the sum of domestic, industrial, and institutional demand. This resulted in a consistent estimate of 25 percent loss. Metolong Dam Project Metolong dam is represented in the WEAP model as a reservoir on the Phuthiatsana South River. It receives inflow from a catchment that is 348 km2 large. The dam was commissioned in 2015 and came online in 2016. It has a storage capacity of 36.5 MCM (i.e., storage at 1,671 m elevation) and a dead (or inactive) storage level of 7.275 MC (i.e., storage at 1,635 m eleva- tion). Its volume-to-elevation relationship is presented  in ­ figure  2.9. It is configured in the WEAP model to supply water to zones 4 and 5 (see figure 2.8). It is configured in the WEAP model to supply water to zones 4 and 5. In WEAP, the priority to store water in Metolong dam (priority 13) is set up such that it releases water only to meet domestic (priority 3) and indus- trial (priority 4) demands in zones 3, 4, and 5 and instream flow requirements (priority 5) on the Phuthitsana South river below the reservoir. 16 Lesotho WEAP Manual Lesotho WEAP Manual Table 2.3  Demand Projections for Domestic, Industrial, and Institutional Consumers 2005–35 2005 2010 2020 2035 2005 2010 2020 2035 2005 2010 2020 2035 Year Zone 1—Butha-Buthe Zone 2,3—Hlotse, Maputsoe Zone 3—Teyateyaneng Total population 86,765 92,776 106,831 130,440 141,410 157,196 193,251 264,891 85,319 89,107 95,357 106,534 Domestic (m3/day) 4,586 5,052 6,154 8,007 8,061 9,264 12,032 17,553 4,402 4,662 5,081 5,822 Industrial (m /day) 3 5,000 9,000 20,160 20,160 4,200 6,970 8,710 8,710 100 1,380 2,100 2,100 Institutions (m3/day) 259 299 394 554 675 760 948 1,309 593 631 696 810 Losses (m /day) 3 2,392 3,519 6,608 7,111 3,172 4,186 5,360 6,831 1,253 1,648 1,948 2,162 Total demand (m /day) 3 12,237 17,870 33,316 35,833 16,108 21,180 27,050 34,403 6,349 8,321 9,825 10,895 Zone 4—Maseru Zone 5—Morija, Matsieng Zone 6—Mafeteng Total population 396,469 465,202 613,678 929,709 72,570 73,383 75,659 81,217 65,904 71,729 82,820 104,853 Domestic (m3/day) 32,442 39,230 53,875 85,057 2,737 2,775 2,881 3,134 3,906 4,364 5,240 6,983 Industrial (m /day) 3 20,405 24,330 31,530 31,530 0 0 0 0 5,000 5,220 5,220 5,220 Institutions (m3/day) 5,566 6,652 8,990 13,917 152 159 177 215 243 280 352 495 Losses (m /day) 3 14,452 17,401 23,447 32,475 674 685 716 789 2,246 2,425 2,662 3,133 Total demand (m /day) 3 72,865 87,613 117,842 162,979 3,564 3,620 3,774 4,138 11,395 12,290 13,473 15,832 Zone 7—Mohale’sHoek Zone 8—Quthing Total all zones Total population 40,514 44,539 52,216 67,486 41,047 42,079 44,253 48,542 929,998 1,036,013 1,264,065 1,733,673 Domestic (m3/day) 2,491 2,808 3,414 4,623 1,804 1,857 1,973 2,208 60,429 70,013 90,648 133,387 Industrial (m /day) 3 2,000 11,860 31,000 31,000 0 0 0 0 36,705 58,760 98,720 98,720 Institutions (m /day) 3 296 341 429 603 234 244 271 329 8,019 9,367 12,265 18,233 Losses (m3/day) 1,176 3,732 8,690 9,036 496 512 547 621 25,861 34,108 49,979 62,158 Total demand (m /day) 3 5,963 18,741 43,532 45,261 2,534 2,613 2,792 3,158 131,015 172,248 251,604 312,498 17 18 Table 2.4  WEAP Inputs for Domestic and Industrial Water Demands 2005 2010 2020 2035 2005 2010 2020 2035 2005 2010 2020 2035 Year Zone 1—Butha-Buthe Zone 2,3—Hlotse, Maputsoe Zone 3—Teyateyaneng Domestic Total population 86,765 92,776 106,831 130,440 141,410 157,196 193,251 264,891 85,319 89,107 95,357 106,534 Water use rate (m /hd/yr) 3 19.29 19.88 21.03 22.41 20.81 21.51 22.73 24.19 18.83 19.10 19.45 19.95 Industrial Total demand (Mm3/yr) 1.920 3.394 7.502 7.561 1.779 2.821 3.525 3.657 0.253 0.734 1.021 1.062 Losses Loss rate (percent) 24 25 25 25 25 25 25 25 25 25 25 25   Zone 4—Maseru Zone 5—Morija, Matsieng Zone 6—Mafeteng Domestic Total population 396,469 465,202 613,678 929,709 72,570 73,383 75,659 81,217 65,904 71,729 82,820 104,853 Water use rate (m /hd/yr) 3 29.87 30.78 32.04 33.39 13.77 13.80 13.90 14.08 21.63 22.21 23.09 24.31 Industrial Total demand (Mm3/yr) 9.479 11.308 14.790 16.588 0.055 0.058 0.065 0.078 1.914 2.008 2.034 2.086 Losses Loss rate (percent) 25 25 25 25 23 23 23 24 25 25 25 25   Zone 7—Mohale’sHoek Zone 8—Quthing Total all zones Domestic Total population 40,514 44,539 52,216 67,486 41,047 42,079 44,253 48,542 929,998 1,036,013 1,264,065 1,733,673 Water use rate (m3/hd/yr) 22.44 23.01 23.86 25.00 16.04 16.11 16.27 16.60 23.72 24.67 26.17 28.08 Industrial Total demand (Mm /yr) 3 0.838 4.453 11.472 11.535 0.085 0.089 0.099 0.120 16.324 24.866 40.510 42.688 Losses Loss rate (percent) 25 25 25 25 24 24 24 24 25 25 25 25 Lesotho WEAP Manual Figure 2.8  WEAP Schematic Showing the Configuration of Metolong Dam Figure 2.9  Metolong Dam Volume-Elevation Relationship (Metolong Authority 2015) Volume Elevation (MCM) (m) 0 1605 1,690 0.049889 1610 1,680 0.371365 1615 1.063319 1620 1,670 2.327759 1625 1,660 Elevation (m) 4.324348 1630 7.275344 1635 1,650 11.16614 1640 1,640 15.99169 1645 21.82331 1650 1,630 28.86547 1655 1,620 37.43851 1660 1665 1,610 47.87276 60.61116 1670 1,600 76.20036 1675 0 20 40 60 80 100 94.75504 1680 Volume (MCM) Lesotho WEAP Manual 19 Metolong Instream Flow Requirement An instream flow requirement exists below Metolong dam that is designed to provide low- flows and floods as specified in tables 2.5 and 2.6. Irrigated Agriculture Unfortunately, little data exist to describe the farming practices within existing irrigation schemes. It is known that farmers generally use sprinklers as a means of irrigation. However, no data were available to identify what crops are grown. Fortunately, ORASECOM maintains a water information system for the Orange-Senqu basin2 that contains some general infor- mation on irrigated crops within twelve agro-economic regions throughout the basin (ORASECOM 2013). A screen capture of the tool is shown in figure 2.10. The United Nations Food and Agricultural Organization (FAO) publishes information on many crop types that describe their crop water requirements, yield response to water, and crop water productivity information.3 We used these data to describe the maximum potential yield and yield factors for each irrigated crop type. These are summarized in table 2.7. Table 2.5  Monthly Instream Flow Requirement from Metolong Dam (Metolong Authority 2015) Number of flood events Month Low-flow m3s-1 Class 1: 2.2 m3s-1 Class 2: 4.5 m3s-1 Class 3: 9.1 m3s-1 OCT 0.06   1 NOV 0.13     DEC 0.21   1 JAN 0.25   1 FEB 0.31   1 MAR 0.31     APR 0.34     MAY 0.31 1     JUN 0.27     JUL 0.13       AUG 0.07       SEP 0.05       Table 2.6  Flood Requirements (Metolong Authority 2015) Daily average Duration Volume Flood type Number requested Months peak (m3s-1) (days) (MCM) Class 1 2.2 3 0.6 2 Oct-Nov and Apr-May-Jun Class 2 4.5 1.5 0.76 2 Dec-Jan and Feb-Mar Class 3 9.1 3 2.1 1 Dec-Feb 20 Lesotho WEAP Manual Figure 2.10  Simulated versus Reported Crop Production (1999–2005) a. Maize b. Sorghum PBIAS = –3% PBIAS = –2% 250,000 50,000 200,000 40,000 Yield (tonnes) Yield (tonnes) 150,000 30,000 100,000 20,000 50,000 10,000 0 1999 2000 2001 2002 2003 2004 2005 0 1999 2000 2001 2002 2003 2004 2005 c. Wheat d. Beans PBIAS = –6% PBIAS = –4% 60,000 12,000 50,000 10,000 Yield (tonnes) Yield (tonnes) 40,000 8,000 30,000 6,000 20,000 4,000 10,000 2,000 0 1999 2000 2001 2002 2003 2004 2005 0 1999 2000 2001 2002 2003 2004 2005 e. Peas PBIAS = 1% 7,000 6,000 Yield (tonnes) 5,000 4,000 3,000 2,000 1,000 0 1999 2000 2001 2002 2003 2004 2005 Reported WEAP Note: Calibration metric is based on percent bias (PBIAS), which is a measure of the model’s ability to match the overall production. Table 2.7  Maximum Potential Yield and Yield Factors for Irrigated Crops Crop Maximum potential yield (kg/ha) Yield factor Maize 6,000 1.25 Wheat 6,000 0.85 Vegetables 25,000 1.10 Pasture 3,500 0.90 Alfalfa 2,000 1.10 Lesotho WEAP Manual 21 Rainfed Agriculture The African Development Bank publishes data on crop production in Lesotho.4 These data were obtained for five primary crop types (maize, sorghum, wheat, beans, and peas) and are summarized in the table 2.8. These data are generally consistent with FAO estimates of cultivated land,5 which was 209,000 ha in 1994. FAO data also suggest that the vast majority of these lands are rainfed. For this reason, we used the data in table 2.9 to estimate areas for rainfed agriculture throughout Lesotho. However, the data in tables 2.8 and 2.9 are reported for the ten districts within Lesotho, whereas WEAP ­ represents rainfed agriculture at the scale of quaternary hydrologic catch- map 2.3. ments, shown in ­ The simplest approach to allocating the areas from map 2.3 would be to assume that the crops are uniformly distributed within each district. However, given the topography of the  country and the concentration of people within the lowlands, it is more likely that cropped areas are positively correlated to population density. For this reason, we used Table 2.8  Crop Factor Coefficients throughout the Years Crop Crop factor Crop mix (%) Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Maize 30 0.91 0.30 n/a n/a n/a n/a n/a n/a n/a 0.51 0.91 1.10 Wheat 20 n/a n/a n/a n/a n/a 0.15 0.34 0.79 1.00 0.87 0.18 n/a Vegetables 20 0.99 1.00 0.65 n/a n/a n/a n/a n/a n/a n/a 0.29 0.70 Pasture 20 0.80 0.80 0.80 0.70 0.60 0.50 0.50 0.50 0.60 0.70 0.80 0.80 Alfalfa 10 0.80 0.80 0.70 0.50 0.40 0.30 0.30 0.40 0.50 0.70 0.80 0.80 Note: n/a = not applicable Table 2.9  Total Area Planted, ha (2007) Maize Sorghum Wheat Beans Peas Total (ha) Berea 32,535 9,776 3,131 4,289 545 50,276 Botha-Bothe 8,176 2,482 360 2,710 32 13,760 Leribe 29,616 6,397 6,807 7,279 718 50,817 Mafe-teng 26,519 6,008 5,488 3,245 1,505 42,765 Maseru 26,134 8,082 3,409 4,891 534 43,050 MohalesHoek 31,777 6,762 3,128 3,276 789 45,732 Mokho-tlong 6,482 460 1,837 768 462 10,009 Qacha’s Nek 6,970 2,168 1,116 765 59 11,078 Quthing 8,415 2,265 2,866 1,986 211 15,743 Thaba-Tseka 13,974 3,791 1,671 4,574 51 24,061 Total (ha) 190,598 48,191 29,813 33,783 4,906 307,291 22 Lesotho WEAP Manual Map 2.3  Quaternary Catchments Used for Hydrological Routines Legend Districts Quaternary catchments 2010  population density maps from Columbia University (CIESIN 2011) to estimate the distribution of crops within each district (map 2.4). We then intersected these estimates with quaternary catchments to estimate the total cropped area for each crop within each catchment. The African Development Bank also provides data on total crop production for a few recent years (table 2.10). These data were used to calibrate the agricultural yield routine within WEAP (figure 2.10). Re-Calibration of Hydrology The WEAP models are often calibrated to historical streamflows using a combination of manual methods and computer algorithms, such as the PEST software (Doherty 2002). In general, eight land use parameters are adjusted to achieve calibration to streamflow. These parameters are the evapotranspiration coefficient (Kc), soil water capacity (SWC), deep water capacity (DWC), runoff resistance factor (RRF), root zone conductivity (RZC), deep conductivity (DC), and preferred flow direction (PFD). Model simulations are most sensitive to SWC, RZC, RRF, and PFD. Thus, initial Lesotho WEAP Manual 23 Map 2.4  Population Density (CIESIN 2011) Legend Districts Population density value High : 138323 Low : 0 Table 2.10  Total Yield, Tonnes (1999–2005) Crops 1999 2000 2001 2002 2003 2004 2005 Maize 118,679 124,549 194,338 158,194 111,205 85,032 80,898 Wheat 29,641 15,426 15,545 50,755 26,250 21,805 16,216 Sorghum 22,815 33,340 26,807 45,354 11,919 11,953 11,482 Beans 8,376 9,273 10,740 7,860 4,360 3,701 4,831 Peas 4,904 6,429 4,800 6,429 3,825 2,717 1,496 calibrations should focus on these four parameters. Further refinements to the shape and timing of the resulting hydrographs may be accomplished by adjusting the remaining parameters. The Nash-Sutcliffe Efficiency (NSE) coefficient is commonly used in hydrologic modeling to evaluate how well modeled stream flow matches observed data. The NSE indicates how well a plot of observed versus simulated data fits to a 1:1 line. NSE ranges from −∞ to 1.0. If NSE = 1, 24 Lesotho WEAP Manual there is a perfect match between the observed and modeled, if NSE = 0, the modeled is only as good as the observed mean of the data, and NSE <0 indicates the model performs worse than the mean. Generally in hydrologic modeling, NSE > 0.6 is desired, while NSE > 0.8 is good. The mathematical form of NSE is: ∑ (Y n  2   i obs - Yisim )  NSE = 1 -  i =1 2  ∑ (Y ) n obs   i =1 i - Y obs   Where Yiobs is the ith observation, Yi sim is the ith simulated value, Y obs is the mean of the observed data, and n is the total number of observations. While NSE is a useful one-value indicator of model performance, it is biased by high flows. Additionally, it only captures certain aspects of the model flow deviations from observed. To fully understand and evaluate model performance, NSE must be used in conjunction with other metrics that consider seasonal variation, flow duration curves, and annual totals of the modeled and observed flows. To this end, we often consider the ratio of the root mean squared error to the standard deviation (RSR) as a measure of how much the simulated flows deviated from the observed hydrographs. We consider the ratio of simu- ­ lated versus observed flow standard deviation (SDR) as a measure of how well the simu- lated flows match the flow variability within the historical record. Lastly, we consider the  percent bias (PBIAS) as a measure of the model’s ability to match the total volume of flow. In general, the model can be judged as satisfactory if the NSE ≥ 0.5, PBIAS ±25%, RSR ≤ 0.7, and 0.9 ≤ SDR ≤ 1.1 (Moriasi et al. 2007). The equations for PBIAS, RSR, and SDR are as follows: ∑ (Y - Y n   i =1 i obs i sim )  PBIAS = 100 *   ∑ (Y ) n obs  i   i =1   2  ∑ (Y n  - Yi sim )  obs RMSE i =  i =1 RSR = STDEVobs  2  ∑ (Y ) n obs  i - Y obs   i =1    ∑ (Y ) n 2 sim STDEVsim  i - Y sim  =  i =1 SDR = STDEVobs ∑ (Y ) n 2 obs i =1 i - Y obs There are a number of stream flow-gauging stations within the basin that are operated by either DWA or the Lesotho Ministry of Water (see figure 2.11). The data from these stations were used as the basis for calibrating the hydrology of the basin. The results of this calibration are summarized in table 2.11 and figures 2.12–2.22. Lesotho WEAP Manual 25 Figure 2.11  WEAP Schematic Showing Streamflow Calibration Locations Table 2.11  Statistics for Observed Data Used for WEAP Calibration WEAP Annual Site Records used NSE SDR RSR comparison bias (%) Katse inflow ORASECOM 1949–2000 0.16 −2.1 1.07 0.92 Mohale inflow ORASECOM 1949–2000 0.27 0.03 1.01 0.85 Matsoku weir inflow ORASECOM 1949–2000 0.02 6.7 0.92 0.99 Polihali inflow ORASECOM 1960–96 0.20 1.0 0.93 0.89 Makhaleng river Observed 1981–2007 0.4 −3.5 0.97 0.07 at Qaba D21E ORASECOM 1960–89 0.23 3.0 1.11 0.88 D21H ORASECOM 1960–89 0.31 −2.1 1.14 0.83 D22C ORASECOM 1960–89 0.31 0.2 1.18 0.83 D22H ORASECOM 1960–89 0.33 0.6 1.21 0.81 D23E ORASECOM 1960–89 0.43 7.0 1.23 0.75 D23J ORASECOM 1960–89 0.54 7.5 1.22 0.68 26 Lesotho WEAP Manual Flow (MCM) Flow (MCM) Flow (MCM) Flow (MCM) 0 100 200 300 400 500 600 700 800 900 0 50 100 150 200 250 0 50 100 150 200 250 300 350 400 450 19 Oc 1,000 1,400 1,200 0 200 400 600 800 5 Oct - 19 19 9 Mar 59 5 Mat-59 6 19 9 Au r-61 Aug-61 6 g 19 1 Jan-62 6 Jan-62 19 1 6 19 3 - Ju -64 6 Jun 64 19 3 Non-65 19 5 Nov-65 6 Apv-66 6 - 19 5 Apr 66 6 Se r-68 p 19 7 - 19 7 6 Sep 68 6 Feb-69 Mohale Dam) 19 9 Feb-69 19 9 Jul -71 7 -71 Jul- 7 De -72 19 1 19 1 7 Dec 72 7 M a c-73 y 19 3 Lesotho WEAP Manual 19 3 Oc - 7 5 7 May-73 7 Ma t-76 19 5 Oct-75 19 5 7 - 7 Au r-78 Mar 76 19 7 g 19 7 7 Ja -79 7 Aug-78 - 19 9 Ju n-81 19 9 Jan 79 8 Non-82 8 - 19 1 v (Inflows to Katse Dam) 19 1 Jun 81 - 8 Ap -83 8 c. Annual flow 19 3 Se r-85 a. Monthly flows Nov 82 c. Annual flow 19 3 - 8 p-8 a. Monthly flows 8 Apr 83 - 19 5 Feb 6 19 5 Sep 85 8 Ju -88 8 Feb-86 19 7 8 De l-89 19 7 - 19 9 Mac-90 8 Jul-88 9 y 19 9 Dec 89 19 1 Oc - 9 2 9 9 Ma t-93 19 1 May-90 19 3 Au r-95 9 Oct-92 9 g - 19 5 Jan-96 PBIAS = 0.3% 19 3 9 Mar 93 9 NSE = 0.27 Jun-98 19 5 Aug-95 19 7 -99 9 99 NSE = 0.16 WEAP Jan-96 PBIAS = –2.1% 19 7 - 99 Jun 98 -99 Flow (MCM) WEAP Flow (MCM) Flow (MCM) Flow (MCM) 0 10 20 30 40 50 60 70 80 90 100 0 50 100 150 200 250 300 350 400 450 O ct 0 0 10 20 30 40 60 50 100 150 200 250 50 O 5 ct N Observed ov 10 N 5 ov D 15 Observed 10 ec D 15 20 ec 20 25 Ja 25 n 30 Ja n 30 Fe 35 b Fe 35 40 b 40 M ar 45 M 45 ar 50 50 Ap r 55 Ap 55 Percent Percent r 60 60 M M b. Flow duration ay 65 b. Flow duration ay 65 Figure 2.12  WEAP versus ORASECOM Results for D11 A-F 70 70 Ju d. Average monthly flows n d. Average monthly flows Ju 75 75 n 80 Ju 80 Ju l l 85 85 Au 90 Au 90 g 95 g RSR = 0.85 95 SDR = 1.01 RSR = 0.92 Figure 2.13  WEAP versus ORASECOM Results for D17A (Inflows to 10 Se Se 0 p 10 0 p 27 SDR = 1.07 Flow (MCM) Flow (MCM) Flow (MCM) Flow (MCM) 28 0 500 0 0 50 100 150 200 250 300 350 400 0 50 100 150 200 250 100 200 300 400 500 600 700 800 900 19 2,500 1,000 1,500 2,000 3,000 19 5 Oct - 5 Oct - 19 9 Mar 59 19 9 Mar 59 6 Aug-61 6 19 1 19 1 Aug-61 6 Jan-62 6 Jan-62 19 3 - 19 3 - Jun 64 6 Jun 64 6 Nov-65 19 5 Nov-65 19 5 6 - 6 - Apr 66 Apr 66 19 7 - 19 7 - 6 Sep 68 6 Sep 68 19 9 Feb-69 19 9 Feb-69 7 -71 Jul- 7 -71 Jul- 19 1 19 1 7 Dec 72 7 Dec 72 19 3 May-73 19 3 May-73 7 Oct-75 7 Flows into Polihali - Oct-75 19 5 19 5 - 7 Mar 76 7 Mar 76 19 7 Aug-78 19 7 Aug-78 7 - 7 - Jan 79 Jan 79 19 9 - 19 9 8 - 8 Jun 81 Jun 81 19 1 - 19 1 - 8 Nov 82 - 8 Nov 82 - c. Annual flow c. Annual ow a. Monthly flows a. Monthly ows 19 3 Apr 83 19 3 Apr 83 8 - 8 - Sep 85 Sep 85 19 5 19 5 8 Feb-86 - 8 Feb-86 - 19 7 Jul-88 19 7 Jul-88 8 Dec 89 8 Dec 89 19 9 19 9 9 May-90 9 May-90 19 1 Oct-92 19 1 Oct-92 9 - 9 - Mar 93 Mar 93 NSE = 0.20 19 3 19 3 NSE = 0.02 PBIAS = 6.7% 9 9 PBIAS = 1.0% Aug-95 Aug-95 WEAP 19 5 Jan-96 19 5 WEAP 9 - 9 Jan-96 Jun 98 - 19 7 -99 19 7 Jun 98 99 99 -99 Flow (MCM) Flow (MCM) Flow (MCM) Flow (MCM) Observed 0 2 4 6 8 0 20 40 60 80 100 120 140 0 100 200 300 400 500 600 700 800 900 10 12 14 16 18 20 40 60 80 100 120 140 0 O O Observed ct ct 5 5 N 10 N 10 ov ov 15 15 D 20 D 20 ec ec 25 25 Ja Ja n 30 n 30 Fe 35 Fe 35 b 40 b 40 M 45 M 45 ar ar 50 50 Ap 55 Ap 55 r r Percent Percent 60 60 M M b. Flow duration b. Flow duration ay 65 ay 65 70 70 Ju Ju d. Average monthly flows d. Average monthly ows n 75 n 75 Figure 2.15  WEAP versus ORASECOM Results for Senqu River Ju 80 Ju 80 l 85 l 85 Figure 2.14  WEAP versus ORASECOM Results for Matsoku River Au 90 Au 90 g 95 g 95 RSR = 0.89 SDR = 0.93 SDR = 0.93 RSR = 0.99 Se 10 Se 10 p 0 p 0 Lesotho WEAP Manual Flow (MCM) Flow (MCM) Flow (MCM) Flow (MCM) 0 20 40 60 80 100 120 140 160 180 200 0 10 20 30 40 50 60 70 80 19 Oc 0 100 200 300 400 500 600 700 800 900 1,000 0 50 100 150 200 250 300 t 19 Oc 1959 No -59 v 1981 Se t-81 1960 De -60 c-6 1982 p Au -82 1961 Jan 1 83 g 19 1962 Feb-63 Jul-83 84 1963 Ma -64 19 Jun-84 1964 r Ma -85 Ap -65 1985 y 1965 r Ap -86 Ma -66 1986 r 1966 y Ma -87 Jun-67 1987 r-8 1967 Feb 8 1968 Jul-68 1988 Jan-89 Au -69 1969 g 1989 No -90 v Se -70 1970 p Lesotho WEAP Manual 1990 De -91 1971 Oc -71 c t 1991 Oc -90 1972 No -72 Se t-92 v 1992 p-9 1973 De -73 Au 3 1974 c-7 Jan 4 1993 g 1994 Jul-94 1975 Feb-76 Jun-95 1976 Ma -77 1995 Ma -96 r y c. Annual flow 1977 Ap -78 1996 Ap -97 a. Monthly flows c. Annual flow r r a. Monthly flows 1978 Ma -79 1997 Ma -98 1979 y-8 r-9 1980 Jun 0 1998 Feb 9 1981 Jul-81 2099 Jan-00 Au -82 De -01 1982 g 2000 c Se -83 No -01 1983 p 2001 v 1984 Oc -84 Oc -02 t 2002 Se t-03 1985 No -85 v p NSE = 0.23 PBIAS = 3.0% 2003 Au -04 NSE = 0.40 PBIAS = –3.5% 1986 De -86 g WEAP 1987 c-8 2004 Jul-05 Jan 7 1988 Feb-89 2005 Jun-06 89 Ma -07 WEAP -90 2006 y-0 07 8 Flow (MCM) Flow (MCM) Observed Flow (MCM) Flow (MCM) 0 2 4 6 8 10 12 0 10 20 30 40 50 60 70 80 0 10 20 30 40 50 60 70 80 0 50 100 150 200 250 300 O ct O 5 ct Observed 5 N 10 N 10 ov ov 15 15 D 20 D ec ec 20 25 25 Ja n 30 Ja n 30 Fe 35 35 b 40 Fe b 40 M 45 M 45 ar ar 50 50 Ap 55 Figure 2.17  WEAP versus ORASECOM Results for D21E Ap r 55 Percent r Percent 60 60 M M b. Flow duration ay 65 65 b. Flow duration ay 70 70 Ju d. Average monthly flows n 75 Ju d. Average monthly flows 80 n 75 Ju 80 l 85 Ju l 85 Au 90 90 Au g 95 g 95 RSR = 0.88 SDR = 1.11 RSR = 0.07 SDR = 0.97 Se 10 0 10 Figure 2.16  WEAP versus Observed Makheleng River Flows at Qaba Se p p 0 29 Flow (MCM) Flow (MCM) Flow (MCM) Flow (MCM) 30 0 200 400 600 800 1,000 1,200 150 50 100 0 200 250 300 350 400 200 0 100 300 400 500 600 700 0 200 400 600 800 1,000 1,200 1,400 1,600 1,800 2,000 195 Oct Oct - 195 - 1969 Nov 59 Nov 59 1969 - 1960 - 1960 Dec 60 Dec 60 - 1961 - 1961 Jan 61 Jan 61 - 1962 - 1962 Feb 63 Feb 63 - 1963 - 1963 Mar 64 Mar 64 1964 -65 1964 - Apr Apr 65 1965 - 1965 - May 66 May 66 1966 - 1966 - Jun 67 Jun 67 1967 - 1967 - Jul-68 1968 Jul-68 1968 Aug 69 1979 Aug 69 1979 -70 -70 Sep 1970 Sep 1970 - - Oct 71 1971 Oct 71 1971 - - Nov 72 1972 Nov 72 1972 - - Dec 73 1973 Dec 73 1973 - 1974 Jan -74 Jan 74 - 1974 - 1975 Feb 76 Feb 76 1975 - 1976 - Mar 77 Mar 77 c. Annual flow 1976 c. Annual flow -78 -78 a. Monthly flows a. Monthly flows Apr 1977 Apr 1977 - 1978 - 1978 May 79 May 79 - 1989 - 1989 Jun 80 Jun 80 -81 1980 -81 1980 Jul- Jul- 1981 Aug 82 1981 Aug 82 1982 - 1982 - Sep 83 Sep 83 1983 - 1983 - Oct 84 Oct 84 1984 - 1984 - Nov 85 Nov 85 - - PBIAS = –2.1% NSE = 0.31 1985 WEAP PBIAS = 0.2% NSE = 0.31 1985 Dec 86 Dec 86 1986 - 1986 Jan -87 Jan 87 WEAP 1987 1987 Feb-89 Feb-89 1988 -90 1988 -90 9 9 Flow (MCM) Flow (MCM) Flow (MCM) Flow (MCM) Observed 150 50 100 0 10 20 30 40 50 60 200 250 300 350 400 200 0 0 10 20 30 40 50 60 70 80 90 100 100 300 400 500 600 700 0 O Observed ct O 5 ct 10 N 5 ov 10 N 15 ov 15 20 D D ec 20 ec 25 Ja 25 Ja 30 n n 35 30 Fe 35 Fe 40 b b 45 40 M M 50 ar 45 ar 50 Figure 2.18  WEAP versus ORASECOM Results for D21H 55 Figure 2.19  WEAP versus ORASECOM Results for D22C Ap Ap r 55 Percent Percent r 60 M 60 M 65 b. Flow duration ay b. Flow duration ay 65 70 Ju 70 Ju 75 d. Average monthly flows n d. Average monthly flows n 75 80 Ju Ju 80 l 85 l 85 90 RSR = 0.83 SDR = 1.14 RSR = 0.83 SDR = 1.18 Au Au 90 g 95 g 95 Se 10 p 0 Se p 10 0 Lesotho WEAP Manual Flow (MCM) Flow (MCM) Flow (MCM) Flow (MCM) 0 500 1,000 1,500 2,000 2,500 3,000 3,500 4,000 4,500 0 200 400 600 800 1,000 1,200 1,400 1,600 1,800 0 500 1,000 1,500 2,000 2,500 3,000 3,500 0 200 400 600 800 1,000 1,200 195 Oct - Oct 195 - 1969 Nov 59 Nov 59 1960 - 1969 - Dec 60 1960 Dec 60 1961 -61 - Jan 1961 Jan 61 1962 - - Feb 63 1962 Feb 63 1963 - 1963 - Mar 64 Mar 64 1964 -65 1964 -65 Apr Apr 1965 - 1965 - May 66 May 66 1966 - 1966 - Jun 67 Jun 67 1967 - 1967 - 1968 Jul-68 Jul-68 Lesotho WEAP Manual Aug 69 1968 Aug 69 1979 -70 1979 -70 Sep Sep 1970 - 1970 - Oct 71 Oct 71 1971 - 1971 - Nov 72 Nov 72 1972 - 1972 - 1973 Dec 73 Dec 73 - 1973 - 1974 Jan 74 Jan 74 - 1974 - 1975 Feb 76 Feb 76 1976 - 1975 - Mar 77 1976 Mar 77 - - c. Annual flow c. Annual flow a. Monthly flows a. Monthly flows 1977 Apr 78 1977 Apr 78 1978 - - May 79 1978 May 79 1989 - 1989 - Jun 80 Jun 80 1980 -81 1980 -81 Jul- Jul- 1981 Aug 82 1981 Aug 82 1982 - 1982 - Sep 83 Sep 83 1983 - 1983 - Oct 84 Oct 84 1984 - 1984 - Nov 85 Nov 85 1985 - - PBIAS = 7.0% NSE = 0.43 WEAP PBIAS = 0.6% NSE = 0.33 Dec 86 1985 Dec 86 1986 - 1986 - 1987 Jan 87 Jan 87 Feb-89 1987 Feb-89 1988 -90 -90 9 1988 9 WEAP Flow (MCM) Flow (MCM) Flow (MCM) Observed Flow (MCM) 0 50 100 150 200 250 0 20 40 60 80 100 120 140 160 200 400 600 800 1,000 1,200 1,400 1,600 1,800 0 200 400 600 800 1,000 1,200 0 O ct 5 O 5 N 10 ct 10 Observed ov 15 N 15 D ov ec 20 20 D Ja 25 ec 25 n 30 Ja 30 Fe 35 n 35 b Fe 40 40 M b ar 45 45 50 M 50 Ap ar Figure 2.21  WEAP versus ORASECOM Results for D23E r Figure 2.20  WEAP versus ORASECOM Results for D22H 55 55 Ap Percent Percent M 60 r 60 ay 65 M 65 b. Flow duration b. Flow duration Ju 70 ay 70 n 75 Ju 75 d. Average monthly flows d. Average monthly flows Ju 80 n 80 l Ju 85 85 Au l g 90 90 RSR = 0.75 SDR = 1.23 RSR = 0.81 SDR = 1.21 Au Se 95 g 95 p 10 10 0 Se 0 p 31 Figure 2.22  WEAP versus ORASECOM Results for D23J a. Monthly flows b. Flow duration NSE = 0.54 SDR = 1.22 2,000 2,000 1,800 1,800 1,600 1,600 Flow (MCM) Flow (MCM) 1,400 1,400 1,200 1,200 1,000 1,000 800 800 600 600 400 400 200 200 0 0 Nov 59 Dec 60 Jan 61 Feb 63 Mar 64 Apr 65 May 66 Jun 67 Jul-68 Aug 69 Sep 70 Oct 71 Nov 72 Dec 73 -74 Feb 76 Mar 77 -78 May 79 Jun 80 Jul-81 Aug 82 -83 Oct 84 Nov 85 Dec 86 Jan 87 Feb-89 -90 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 105 0 9 - - - - - - - - - - - - - - - - - - - - - - Oct Jan Apr Sep Percent c. Annual flow d. Average monthly flows PBIAS = 7.5% RSR = 0.68 5,000 250 4,500 4,000 200 3,500 Flow (MCM) Flow (MCM) 3,000 150 2,500 2,000 100 1,500 1,000 50 500 0 0 1969 1960 1961 1962 1963 1964 1965 1966 1967 1968 1979 1970 1971 1972 1973 1974 1975 1976 1977 1978 1989 1980 1981 1982 1983 1984 1985 1986 1987 1988 9 ct ov ec n b ar r ay n l g p 195 Ju Ap Ja Fe Ju Au Se O M N D M WEAP Observed Notes 1. https://www4.dwa.gov.za/wma/. 2. Orange-Senqu Water Information System: http://wis.orasecom.org/. Information on irrigated agri- culture was obtained from http://wis.orasecom.org/irrigation-water-demand-management-wp6/. 3. FAO Crop Water Information available at http://www.fao.org/nr/water/cropinfo.html. 4. Sources: World Bank - WDI Nov. 2014; ADI 2013; FAO - Production Statistics Aug. 2014; Food Balance Sheets 2014 http://lesotho.opendataforafrica.org/rqgdlhd/lesotho-agriculture-sheet. 5. http://www.fao.org/docrep/v8260b/V8260B0z.htm. 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