| Abstract: | For water-stressed regions/countries, like Iran, improving the management of agricultural
water-use in the wake of climate change and increasingly unsustainable demands is of utmost
importance. One step further is then the maximization of the agricultural economic benefits, by
properly adjusting the irrigated crop area pattern to optimally use the limited amount of water
available. To that avail, a sequential hydro-economic model has been developed and applied to
the agriculturally intensively used Zarrine River Basin (ZRB), Iran. In the first step, the surface
and groundwater resources, especially, the inflow to the Boukan Dam, as well as the potential crop
yields are simulated using the Soil Water Assessment Tool (SWAT) hydrological model, driven
by GCM/QM-downscaled climate predictions for three future 21th-century periods under three
climate RCPs. While in all nine combinations consistently higher temperatures are predicted, the
precipitation pattern are much more versatile, leading to corresponding changes in the future water
yields. Using the basin-wide water management tool MODSIM, the SWAT-simulated water available
is then optimally distributed across the different irrigation plots in the ZRB, while adhering to
various environmental/demand priority constraints. MODSIM is subsequently coupled with CSPSO
to optimize (maximize) the agro-economic water productivity (AEWP) of the various crops and,
subsequently, the net economic benefit (NEB), using crop areas as decision variables, while respecting
various crop cultivation constraints. Adhering to political food security recommendations for the
country, three variants of cereal cultivation area constraints are investigated. The results indicate
considerably-augmented AEWPs, resulting in a future increase of the annual NEB of ~16% to
37.4 Million USD for the 65%-cereal acreage variant, while, at the same time, the irrigation water
required is reduced by ~38%. This NEB-rise is achieved by augmenting the total future crop area
in the ZRB by about 47%—indicating some deficit irrigation—wherefore most of this extension will
be cultivated by the high AEWP-yielding crops wheat and barley, at the expense of a tremendous
reduction of alfalfa acreage. Though presently making up only small base acreages, depending on
the future period/RCP, tomato- and, less so, potato- and sugar beet-cultivation areas will also be
increased significantly. |