Assessing the impacts of large‐scale substitution of pressurized irrigation on basin hydrology through a water accounting framework

Abstract

AbstractAs the main challenge to water resource management, the impacts of irrigation method improvement need to be addressed in regional hydrological processes. This study investigates the hydrological impacts of developing pressurized irrigation systems at the basin scale using the WEAP–WA (water evaluation and planning system–water accounting) coupling approach. Regarding the development of pressurized irrigation systems since 2006, two separate periods can be mentioned for surface irrigation (1998–2006) and for pressurized irrigation development (2006–2013) in the intermediate basin of Ahar‐Chai in Iran. All major water resource elements of the region were found and constructed in WEAP as predefined object‐oriented elements. The simplified soil moisture method was adopted to model the rainfall‐runoff process in irrigated areas. This model was calibrated and validated using PEST (parameter estimation tool) with acceptable statistical criteria. To understand water balance components, the water accounting framework (WAF) was employed, and the results indicated that modernizing the irrigation system increased water depletion and usage. The results indicate an increase of 26% in actual evapotranspiration in pressurized irrigation compared with surface irrigation (50% of the irrigated area). Actual evapotranspiration and nonbeneficial evapotranspiration per unit area also followed the same trend. However, pressurized systems have higher crop productivity and denser crop patterns. In contrast, the basin runoff during pressurized irrigation was 42% less than that during surface irrigation, which is due to fewer return flows caused by pressurized irrigation. Therefore, the basin surface runoff can be influenced by the type of irrigation. The results obtained by this study suggest an adverse effect of altering the surface irrigation methods in pressurized systems.