WEAP is a software tool for integrated water resources planning that
attempts to assist rather than substitute for the skilled planner. It provides a
comprehensive, flexible and user-friendly framework for planning and policy
analysis. A growing number of water professionals are finding WEAP to be a
useful addition to their toolbox of models, databases, spreadsheets and other
software. This introduction presents WEAP's purpose, approach, and
structure; a detailed technical description of WEAP capabilities is available in
a separate publication, the WEAP
User Guide.
Background
Many regions are facing formidable freshwater management challenges.
Allocation of limited water resources, concerns regarding environmental quality,
planning under climate variability and uncertainty, and the need to develop and
implement sustainable water use strategies are increasingly pressing issues for
water resource planners. Conventional supply-oriented simulation models are not
always adequate for exploring the full range of management options.
Over the last decade, an integrated approach to water development has emerged
which places water supply projects in the context of demand-side management, and
water quality and ecosystem preservation and protection. WEAP incorporates these
values into a practical tool for water resources planning and policy analysis.
WEAP places demand-side issues such as water use patterns, equipment
efficiencies, re-use strategies, costs, and water allocation schemes on an equal
footing with supply-side topics such as stream flow, groundwater resources,
reservoirs, and water transfers. WEAP is also distinguished by its integrated
approach to simulating both the natural (e.g., evapotranspirative demands,
runoff, baseflow) and engineered components (e.g., reservoirs, groundwater
pumping) of water systems, allowing the planner access to a more comprehensive
view of the broad range of factors that must be considered in managing water
resources for present and future use. The result is an effective tool for
examining alternative water development and management options.
WEAP operates in many capacities:
Water balance database: WEAP provides
a system for maintaining water demand and supply information.
Scenario generation tool: WEAP simulates
water demand, supply, runoff, streamflows, storage, pollution generation, treatment and
discharge and instream water quality.
Policy analysis tool: WEAP
evaluates a full range of water development and management options, and
takes account of multiple and competing uses of water systems.
The WEAP Approach
WEAP operates on the basic principle of a water balance and can be
applied to municipal and agricultural systems, a single watershed or complex
transboundary river basin systems. Moreover, WEAP can simulate a broad range of natural and
engineered components of these systems, including rainfall runoff, baseflow, and
groundwater recharge from precipitation; sectoral demand analyses; water
conservation; water rights and allocation priorities, reservoir operations;
hydropower generation; pollution tracking and water quality; vulnerability
assessments; and ecosystem
requirements. A financial analysis module also allows the user to investigate
cost-benefit comparisons for projects.
The analyst represents the system in terms of its various supply sources
(e.g., rivers, creeks, groundwater, reservoirs, and desalination plants); withdrawal, transmission and wastewater
treatment facilities; water demands; pollution generation; and ecosystem
requirements. The data structure and level of detail can be easily customized to
meet the requirements and data availability for a particular system and
analysis.
WEAP applications generally include several steps.
Study definition: The time frame,
spatial boundaries, system components, and configuration of the problem are
established.
Current accounts: A snapshot of actual
water demand, pollution loads, resources and supplies for the system are
developed. This can be viewed as a calibration step in the development
of an application.
Scenarios: A set of alternative
assumptions about future impacts of policies, costs, and climate, for
example, on water demand, supply, hydrology, and pollution can be explored.
(Possible scenario opportunities are presented in the next section.)
Evaluation: The scenarios are
evaluated with regard to water sufficiency, costs and benefits,
compatibility with environmental targets, and sensitivity to uncertainty in
key variables.
Examples of WEAP Scenario Analyses
Scenario analysis is central to WEAP. Scenarios
are used to explore the model with an enormous range of "what if"
questions, such as:
What if population growth and economic development patterns
change?
What if reservoir operating rules are altered?
What if groundwater is more fully exploited?
What if water conservation is introduced?
What if ecosystem requirements are tightened?
What if a conjunctive use program is established to store
excess surface water in underground aquifers?
What if a water recycling program is implemented?
What if a more efficient irrigation technique is implemented?
What if the mix of agricultural crops changes?
What if climate change alters demand and supplies?
How does pollution upstream affect downstream water
quality?
How will land use changes affect runoff?
WEAP Development
The Stockholm Environment Institute provided primary support for the development
of WEAP. The Hydrologic Engineering Center of the US Army Corps of Engineers
funded significant enhancements. A number of agencies, including the
UN, World
Bank, USAID,
US EPA,
IWMI,
Water Research Foundation (formerly AwwaRF) and the
Global Infrastructure Fund of Japan have provided project
support. WEAP has been applied in water assessments in dozens of countries,
including the United States,
Mexico, Brazil, Germany, Ghana, Burkina Faso, Kenya, South Africa,
Mozambique, Egypt, Israel, Oman, Central Asia, India, Sri Lanka, Nepal,
China, South Korea, and Thailand.
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