Simulation modeling at different scales to evaluate the productivity of water

With the increasing scarcity of water and the need for real water saving measures, a clear understanding of the productivity of water is essential. For a basin in western Turkey, simulation modeling was performed at three different scales (field, irrigation scheme, and basin level) to obtain all terms of the water balance. These water balances were used to calculate the Productivity of Water (PW) at the three levels. Four PW indices were considered: PW_irrigated (yield / irrigation), PW_inflow (yield / net inflow), PW_depleted (yield / depletion), and PW_process (yield / process depletion), all expressed in kg yield per m³ water. Two cotton fields were considered at the field scale and it was found that the more upstream field performed better than the field at the tail-end since runoff from the upstream field was used by downstream users and was not considered as a loss. At the irrigation scheme level PW_irrigated was higher than at the individual cotton field level, since non-irrigated crops were also included. Other PW values were lower as crops more sensitive to drought were also found in the irrigated areas. Basin scale PWs were lower than those at the irrigation scheme, as large areas of the basin were covered with less productive land types. This study demonstrates that the PW indices provide quantitative measures of water dynamics. Models provide a useful methodology for extending field observation for the estimation of the indicators.