Investigating the Effects of Climate Change on Water Resources in the Chahardoli Plain

Investigating the Effects of Climate Change on Water Resources in the Chahardoli Plain
Introduction

Global warming caused by the increase in greenhouse gases, which leads to climate change, is known—based on various studies—to be a result of industrialization. One of the consequences of climate change is the alteration of water resources as well as changes in the general circulation of the atmosphere, temperature, and precipitation. Iran, located in the arid and semi arid belt, is not exempt from this phenomenon. Since most of Iran’s surface water resources are rapidly declining due to population growth and agricultural expansion, the pressure on groundwater resources is increasing. Climate change reports and modeling efforts in this regard can assist researchers in simulating the current and future states of aquifers and surface water resources, enabling them to make informed decisions regarding their management.
Materials and Methods
In this study, to assess the condition of groundwater resources in the Chahardoli plain during the period 2006–208 (most likely 2006–2080), the MODFLOW hydrological model was used. For climatic components such as precipitation and maximum and minimum temperature, the GFDL ESM4 and MIROC ES2L climate models were applied, using observed data covering 1988–2018 under two scenarios: SSP126 and SSP585. The long term monthly averages of climatic parameters (precipitation, maximum and minimum temperature) were compared between observed and simulated data. In this research, the groundwater level for the coming months was simulated for all piezometers, and the unit hydrograph of the Chahardoli aquifer was plotted for the current state as well as for the reference and SSP126 and SSP585 scenarios.
Results and Discussion
In this study, the sixth assessment report of the Climate Model Intercomparison Project (CMIP6) was used to predict future temperature and precipitation. To validate and evaluate the accuracy of general circulation models and their data fitting, the statistical indices RMSE, MAE, and NS were employed. Considering model uncertainty, a single model is not sufficient for validation and enhancing prediction accuracy; therefore, two models—GFDL ESM4 and MIROC ES2L—were applied under two scenarios, SSP126 (optimistic) and SSP585 (pessimistic).
The analysis of climate change impacts over the region indicated that precipitation will decrease while maximum and minimum temperatures will increase during the upcoming period (2026–2040). Simulated groundwater levels under different scenarios for 19 piezometers in the Chahardoli aquifer revealed that, in the SSP585 climate change scenario, groundwater levels in the central and southern parts of the aquifer were lower compared to the other scenarios. This decline corresponds to reduced precipitation and continuous extraction from 954 existing wells. Furthermore, when analyzing groundwater level decline and plotting the unit hydrograph of the Chahardoli aquifer under various scenarios, the SSP585 (pessimistic) scenario showed the greatest decline about 3 MCM. The simulation results demonstrated that the aquifer deficit is expected to increase by approximately 0.15 million cubic meters over the next 14 year period, with the aquifer water balance remaining negative.
Conclusion
The results regarding aquifer depletion are consistent with previous studies conducted on the Qorveh, Dehgolan, and Chahardoli aquifers. Moreover, a comparison between the obtained results and earlier studies carried out in other regions of the country and around the world indicates that climate change, together with human activities, has contributed to the decline in groundwater levels. If the current trend of excessive groundwater extraction continues, along with reduced recharge due to decreasing precipitation in future years, aquifers in all regions are likely to continue facing depletion relative to their present conditions. Given these changes, proper water resource management considering agricultural, domestic, industrial, and environmental aspects can mitigate the adverse effects of human activities and climate change on regional water resources. In recent years, numerous studies have examined the impacts of climate change on groundwater levels across different parts of the world, confirming the undeniable influence of climatic variations and the choice of climate models and emission scenarios on groundwater resources.
Keywords: Chahardoli Plain, MODFLOW, Groundwater Level, Unit Hydrograph
Investigating the Effects of Climate Change on Water Resources in the Chahardoli Plain
Introduction

Global warming caused by the increase in greenhouse gases, which leads to climate change, is known—based on various studies—to be a result of industrialization. One of the consequences of climate change is the alteration of water resources as well as changes in the general circulation of the atmosphere, temperature, and precipitation. Iran, located in the arid and semi arid belt, is not exempt from this phenomenon. Since most of Iran’s surface water resources are rapidly declining due to population growth and agricultural expansion, the pressure on groundwater resources is increasing. Climate change reports and modeling efforts in this regard can assist researchers in simulating the current and future states of aquifers and surface water resources, enabling them to make informed decisions regarding their management.