In recent decades, the increase in water demand on the one hand and the pollution of water sources on the other hand have threatened groundwater resources. The purpose of this research is to investigate the impact of management scenarios of preserving the groundwater resources of Marvdasht-Kharameh plain and its effect on improvement of the aquifer volume reduction process using dynamic system approach.
The current conditions of the aquifer during the statistical period of 1384-1398 were simulated in Vensim PLE software and recalibrated according to the observed values of the aquifer volume. In this study, in order to investigate the effect of climate change on precipitation, temperature and recharge of the Marvdasht-Kharameh aquifer during the period of 1400 to 1425, four atmospheric general circulation models available in the sixth report CMIP6, including GFDL-ESM4, IPSL-CMA6-LR, MPI-ESM1- 2-HR and UKESM1-0-II were used under the influence of two scenarios SSP1-2.6 and SSP5-8.5 from the ISI-MIP Fast Track project for the two synoptic stations of Doroudzan dam and Takhte Jamshid from the ESGF portal. Considering the unsettled conditions of water resources in the plain, 3 scenarios were considered. Scenarios were adopted in three ways: examining the effect of climate change, changing the amount of water allocated to farmers from Doroudzan dam, and changing the cultivation pattern in order to reduce the area under rice cultivation by 30%, 50%, and 100%. Changing the cropping pattern for climate change conditions was applied under two scenarios SSP1-2.6 and SSP5-8.5.
In order to evaluate and diagnose the efficiency of GCM atmospheric general circulation models, the correlation coefficient index (R2) and the root mean square error (RMSE) between observational data and historical data obtained from the models in the base period (1989-2014) were calculated. The precipitation data, minimum temperature and maximum temperature of the GFDL-ESM4 model are in good agreement with the observational data of two synoptic stations of Doroudzan dam and Persepolis. Then the precipitation and temperature variables of GFDL-ESM4 model were considered for the period from 1400 to 1425 under two scenarios SSP1-2.6 and SSP5-8.5. By examining the impact of climate change and release from Doroudzan dam under two scenarios SSP1-2.6 and SSP5-8.5, it was shown that in the SSP1-2.6 scenario, the reduction of 50 and 49 million cubic meters respectively in the volume and supply of groundwater and also in the SSP5-8.5 scenario, 54 and 67 million cubic meters is decreased respectively in the volume of groundwater and its recharge. Also, by removing the rice crop from the cultivation pattern of Marvdasht-Kharameh plain in the future climate conditions under two scenarios SSP1-2.6 and SSP5-8.5, which will add 495 and 207 million cubic meters to the aquifer volume respectively, the greatest effect in increasing the aquifer volume will be achieved, instead of the 30 and 50 percent reduction in the area under rice cultivation.
In the last few decades, the exploitation of groundwater in Marvdasht-Kharameh plain has been on the rise and due to the lack of proper feeding of the aquifer of the plain and excessive harvesting, especially the increase in the construction of unauthorized wells, the drop in groundwater in this plain has increased. On the other hand, with the increase of human activities in the upper part of the plain, the decrease in rainfall has led to a decrease in water storage and release from the Doroudzan dam, and the agricultural potential of the plain has not been well secured. According to the three applied scenarios, the effect of climate change with the current conditions of water release from the dam has reduced the volume of the Marvdasht-Kharameh aquifer. However, the simultaneous effect of climate change and release from the Darudzen dam in the future will be much greater than the current conditions of release from the dam. With the decrease in precipitation and increase in temperature, a sharp drop in the aquifer level in the future will be observed. Also, changing the cultivation pattern has had a significant effect in reducing the volume of the aquifer in the future period, and by removing the rice crop from the cultivation pattern, the replacement of wheat cultivation in the future climatic conditions will have the greatest effect in increasing the volume of the aquifer.