Groundwater Resources Management of Qom-Kahak Aquifer Using Simulation and Application of Different Management Options

Background and Objectives
Previous researches show that the situation of underground water tables in Iran is dire. Therefore, it is necessary to make changes in the current management of water resources. Also, in the discussions related to the application of water resource management options, the effect of climate change and its related uncertainty have either not been considered or have been rarely considered. The aim of this research was to management of underground water resources of Qom-Kahak aquifer under different options. First, the groundwater flow of the study area was simulated and calibrated using GMS software. Then, 10 management options were applied to the model considering the effects of climate change and without considering these effects, and the aquifer balance status was investigated under the effect of these management options. In order to obtain a suitable solution to balance the water of aquifers, the implementation of this research can be of great help to water resource managers and planners.
 
Methodology
In this study, using GCM and GMS models, climatic variables and Qom-Kahak aquifer were simulated and calibrated in a 16-year observation period (2001-2007). Ten different management options, (1) 15% increase in withdrawal without climate change, (2) 15% increase in harvest withdrawal in terms of climate change (HadCM3-A2), (3) 15% increase in withdrawal in terms of climate change (Hybrid-A2), (4) 15% increase in withdrawal in terms of climate change (HadCM3-B2), (5) 15% increase in withdrawal in terms of climate change (Hybrid-B2), (6) 15% decrease in withdrawal in terms of climate change, (7) 15% decrease in withdrawal in terms of climate change (HadCM3-A2), (8) 15% reduction in withdrawal in terms of climate change (Hybrid-A2), (9) 15% decrease in withdrawal in terms of climate change (HadCM3-B2), (10) 15% reduction in withdrawal in terms of climate change (Hybrid-B2), was defined and the effects of their application on groundwater level were analyzed.
 
Findings
The results obtained from the application of the management options of 15% increase in harvesting due to the effects of climate change by the developed Hybrid model and the HadCM3 model showed that the reduction of the underground water level under the A2 scenario is more than the reduction of the level obtained under the B2 scenario. Also, by applying the management options of 15% reduction in harvesting due to the effects of climate change, it was determined that the increase in the aquifer level under the A2 scenario is less than the increase in the level under the B2 scenario. This issue is due to the lower predicted rainfall of these models under the A2 emission scenario. Finally, after examining the results of applying the management option without the effects of climate change and assuming the continuation of the current rainfall trend, it was found that with a 15% reduction in harvesting, the increase in water level is more than other options, and by increasing this amount of harvesting, the reduction in water level is less than that of other options. As a result, it can be concluded that among the management options presented in this research, the options of increasing and decreasing the harvest by 15% without considering the effects of climate change are the best management options and the results indicate a positive reaction of the aquifer to this management option, and in contrast to the management option of increasing and harvest reduction in terms of climate change effects by the developed Hybrid model and the HadCM3 model under the A2 scenario are the worst options.
Conclusion
Using the results of these management options, researchers and users of the Qom-Kahak aquifer can understand the effects of reducing and increasing harvesting and take the necessary solutions and decisions to prevent possible losses. According to the obtained results, applying the option of reducing the harvest by only 15% can be considered as a suitable management solution to improve the situation of the Qom-Kahak aquifer. There are solutions to reduce harvesting in the area, which can be mentioned saving and optimal water consumption in the agricultural sector, preventing the harvesting of unauthorized wells and preventing the digging of new wells, artificial recharge of the aquifer through the drilling of injection wells, continuous monitoring of water consumption, making managers and operators aware of the value of underground water resources, using the results of research conducted in the field of water resources management and cultural works such as making people aware of the value of water through national media, including materials in the field of students' awareness to prevent water wastage, preventing water contamination, etc.
In this research, in order to manage the Qom-Kahak aquifer, the underground water flow was first simulated and calibrated using the GMS model during the observation period (2001-2017). Then, with the aim of improving the condition of the aquifer, different management options of crop change without the effect of climate change and considering these effects were evaluated. The results of applying these management options showed the high importance of harvesting on the water level situation in the future periods. Because after applying the management option of 15% reduction in harvest due to climate change and decrease in rainfall, the underground water level in all observation wells increased.