A novel regional irrigation water productivity model for complex cropping patterns in arid regions coupling soil water and salinity dynamics, irrigation and drainage, and shallow groundwater movement

Abstract

Abstract. The temporal and spatial distribution of regional irrigation water productivity (RIWP) is crucial for making agricultural related decisions, especially in arid irrigated areas with complex cropping patterns. Thus, we developed a new RIWP model for an irrigated agricultural area with complex cropping patterns. The model couples the irrigation and drainage driven soil water and salinity dynamics and shallow groundwater movement, to quantify the temporal and spatial distributions of the target hydrological and biophysical variables. We divided the study area into 1 km×1 km hydrological response units (HRUs). In each HRU, we considered four land-use types: sunflower fields, wheat fields, maize fields and uncultivated lands. And we coupled the regional soil hydrological processes and groundwater flow by taking a weighted average of the water exchange between unsaturated soil and groundwater under different land-use types. The RIWP model was calibrated and validated using eight years of hydrological variables obtained from regional observation sites in a typical arid irrigation area of North China, Hetao Irrigation District. The model reasonably well simulated soil moisture and salinity, groundwater table depths, salinity, and discharge, and regional evapotranspiration. Sensitivity analysis indicates that soil evaporation coefficient and specific yield are the key parameters for RIWP simulation. The results showed that, from 2006 to 2013, RIWP decreased from maize to sunflower to wheat. It was found that the maximum RIWP can be reached when groundwater table depth is in the range of 2 m to 4 m, regardless of irrigation water depths. This implies the importance of groundwater table control on RIWP. Overall, our distributed RIWP model can effectively simulate the temporal and spatial distribution of RIWP and provide critical water allocation suggestions for decision makers.