Why WEAP?

An integrated, practical framework for water resources planning and policy analysis.

Overview

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.

Thousands of water management professionals find WEAP to be a useful addition to their toolbox of models, databases, spreadsheets and other software.

This introduction presents the purpose, approach, and structure of WEAP; 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.

The integrated approach that WEAP provides allows the user to represent the entire water resources system, including rainfall-runoff hydrology, demands of varying complexity (e.g., extensive irrigated agriculture), and existing and planned water infrastructure.

WEAP places demand-side factors such as water use patterns, equipment efficiencies, re-use strategies, costs, and water allocation schemes on an equal footing with supply-side components such as stream flow, groundwater resources, reservoirs, and water transfers.

This allows 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 and practical tool for examining alternative water development, management, and policy 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.

It simulates a broad range of natural and engineered components, including rainfall runoff, baseflow, groundwater recharge, water conservation, allocation priorities, pollution, and ecosystem needs.

A financial analysis module allows cost-benefit comparisons.

WEAP applications generally include the following 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.
Scenarios: A set of alternative assumptions about future impacts of policies, costs, and climate on water demand, supply, hydrology, and pollution can be explored.
Evaluation: The scenarios are evaluated with regard to water sufficiency, costs and benefits, environmental targets, and sensitivity to key variables.

Examples of WEAP Scenario Analyses

Scenario analysis is central to WEAP. Scenarios are used to explore the model with a wide range of what if questions.

What if demographic or economic patterns change?
What if water conservation is introduced?
What if ecosystem requirements are tightened?
What if the mix of agricultural crops changes?
What if groundwater is exploited more?
What if reservoir operating rules are altered?
What if climate change alters demand and supply?
How will changes affect financial costs and benefits?
How does pollution affect water quality?
How do short-term weather forecasts affect supply?
How will rising CO2 levels affect crop yields?