The impact of climate change on groundwater level changes in future periods based on fifth report of ICCP (Case study: Razan Aquifer)

Climate change is one of the major challenges affecting the environment especially groundwater resources. In this study, the effect of the climate change on the Razan plain groundwater level in two 20-year periods is investigated. To simulate the aquifer, the GMS groundwater model is validated and verified for two 18-year period, respectively. To examine the climate change impact on groundwater level variations in the upcoming periods, the CMIP5 models are utilized by three scenarios including Rcp, Rcp 8.5, Rcp 4.5 and Rcp 2.6. To consider the uncertainty of the prediction of the climate change models, the probability level method for precipitation and temperature changes are used. In the probability level method, the combination of 6 climate change models and three mentioned scenarios for each month, 18 values of predictions for ∆T and ∆P changes in the next year are estimated. Then, using the proper distribution in each month, the next ∆T and ∆P are estimated in the probability levels of 90 and 50 percent and the general circulation uncertainties are evaluated in these two probability levels to forecast climate variables including precipitation and temperature. The results of forecasting climatic variables for the Rcp 2.6, Rcp 4.5, Rcp 8.5 scenarios and two levels of probability of 90 and 50%, respectively, display changes in the average temperature of + 0.65, + 0.653, + 0.653, - 0.04 and +6.6 ° C and changes in average precipitation are -0.15, -0.06, +2.25, -30.2 and -0.095 percent during the period 2045-2018. Finally, using the GMS model, the effect of climate change on aquifer level changes under these scenarios are determined. The results show that the groundwater level under the combined scenarios Rcp 2.6, Rcp 4.5, Rcp 8.5 and two probability levels of 90 and 50% for the next period 2018-2045 compared to the base period of 1991-1998 will drop between -55.5 to -1.83 meters on average.