Effects of climate change on groundwater level variations affected by uncertainty (case study: Razan aquifer)

Abstract

In this research, the impact of the human factors and climate change on groundwater level fluctuations affected by uncertainty within 27-year upcoming period (2018–2045) in the Razan Plain is examined. To simulate the aquifer performance, the GMS model is calibrated and verified for two 18-month periods, respectively. To forecast climate variables changes in the future time-frame, six CMIP5 models with three scenarios Rcp 2.6, Rcp 4.5 and Rcp 8.5 are utilized. To study the prediction uncertainty of the climate change models, the method of probabilistic levels of precipitation and temperature changes were used. In this technique, by combining 6 climate change models and 3 mentioned scenarios for each month, 18 prediction values for ∆T and ∆P in upcoming years were approximated. After that, by implementing appropriate distribution for each month, next values of ∆T and ∆P in the probabilistic levels of 50% and 90% are estimated. Finally, in two probabilistic levels of 50% and 90% considering the uncertainty of general circulation models, the climate variables of precipitation and temperature were forecasted. Eventually, based on the probabilistic level technique and using the GMS model, the influence of the human factors and climate change on the groundwater level variations under these scenarios are determined. Results showed that climatic factors have a lesser contribution in reducing the groundwater level in the plain, and the largest contribution is related to human factors and excessive withdrawal from the aquifer. The contribution of climate change in the reduction of the groundwater level in probability scenarios of 0.9 and 0.5 and emission scenarios Rcp8.5, Rcp4.5 and Rcp2.6 is about 40.8, 24.3, 32.3, 27.6 and 22.2 percent respectively. Based on these results, the first priority for aquifer planning and management should be focused on human activities and controlling the amount of withdrawal from the aquifer. These results clearly show that the main cause of creating sinkholes and the sharp reduction of the groundwater level in the region is the excessive extraction of groundwater resources as a result of human activities, including agriculture and industrial demands, and not climate change.