Indus Basin Model

With population approaching 200 million, Pakistan’s food security and economy heavily relies on agriculture. Extensive agriculture is made possible by an elaborate irrigation infrastructure, referred to as the Indus Basin Irrigation System (IBIS), and is the largest contiguous irrigation system in the world. Irrigated agriculture covers 16.2 million hectare (74%) out of the total cultivated area of 22 million hectare. Irrigated agriculture is a lifeline of Pakistan’s economy as it uses 94% of the available water, provides over 90% of agricultural produce, accounts for 25% of GDP, earns 70% of the export revenue and employs 50% of the workforce directly and another 20% indirectly.

indus-basin-diagram

Figure 1. Line diagram of Indus Basin Irrigation System showing rivers, link canals, barrages, and major canals taking off from barrages.

The existing Indus Basin Model (IBM) is a very sophisticated optimization tool, and is the best mathematical representation available of the water, economy and agricultural sectors of Pakistan. However, IBM runs for a single-year at monthly time step. Current and any future year runs are compared to explore changes in agriculture production in response to external stressors. Because the model only runs for one year, operation of storage reservoirs is not included in the model. Flooding is also not considered.

To better serve on the ground needs in Pakistan, USPCAS-W will develop a dynamic simulation model, a decision support system (DSS) that will be able to explore several “what-if” scenarios to support future water management and planning decisions in the basin. This DSS will be able to capture the inter-relationships among the climate, water, population and agriculture sectors.

This will be a county level model, covering entire IBIS up to canal command area. Infrastructure shown in Figure 1 will serve as the basis for the model. A node-link system will be used to represent the entire river and canal network. The model will be developed using the software tool WEAP.

WEAP uses water demand and supply information to perform mass balance. It can calculate runoff, infiltration, crop requirements, stream flows, reservoir storage, pollution generation, water treatment, waste water discharge and instream water quality under varying hydrologic and policy scenarios. Using a dynamic link WEAP can be integrated with other models such as QUAL2K, MODFLOW, MODPATH, PEST, Excel and GAMS.