Estimation of groundwater recharge and its relation to land degradation: case study of a semi-arid river basin in Iran

Abstract

Groundwater extraction is one of the most important criteria of land degradation especially land subsidence in arid and semi-arid areas. Understanding the relationship between water extraction and recharge of groundwater can lead to better watershed management. For the estimation of groundwater recharge in Razan-Ghahavand watershed in Central Iran the Soil and Water Assessment Tools was used. Model calibration was done by using SUFI-2 based on monthly river discharge and annual crop yield, where crop yield was used to better estimate the evapotranspiration term, which consequently increased our knowledge on estimating aquifer recharge. The calibration results were satisfactory: The Nash-Sutcliffe model efficiency ranged from 0.53 to 0.63 for calibration and from 0.42 to 0.72 for validation. The results showed that, although the groundwater level was decreasing about 1 m per year, the groundwater recharge did not change significantly leading to a net withdrawal causing land subsidence over time.