Quantifying the impact of climate change and irrigation management on groundwater in an arid region with intensive groundwater abstraction (Case study: Neishaboor watershed, Iran)

The impact of climate change and irrigation management on groundwater resources is of special concern in arid and semi-arid watersheds with intensive irrigation. Additionally, an integrated assessment of groundwater resources is essential to protect aquifers from over-exploitation. This study uses the integrated surface/subsurface hydrologic model SWAT-MODFLOW to quantify the impact of climate change and irrigation pumping schemes on groundwater drawdown for the Neishaboor watershed, Iran. Land use in the Neishaboor watershed is predominantly agricultural, therefore, irrigation plays a crucial role in the water resources balance in the study area. Within the integrated SWAT-MODFLOW model, the pumped groundwater, simulated by MODFLOW, is applied as irrigation water to the cultivated fields within the SWAT plant growth routines, with deep percolation from the soil profile bottom given to the MODFLOW cells as recharge. The developed model was calibrated and tested for the 2000–2010 and 2010–2012 periods, respectively, against measured groundwater level and streamflow data. The tested model is used to investigate the impact of climate change and groundwater pumping on groundwater drawdown under two scenarios: (1) the RCP8.5 pathway (the most pessimistic greenhouse gas emission scenario) and the continuation of the current irrigation trend, and (2) the RCP8.5 pathway with a 40% reduction in irrigation by 2035. Between 2020 and 2035, scenarios 1 and 2 produce a spatially averaged decline in groundwater levels of 20 m and 9.5 m, respectively. The model provides a framework to determine the best management practices for groundwater resources management in the region while minimizing drawdown.