The Investigation of the Impact of Climate Change on Water Balance Caused by Precipitation in Tasuj Aquifer for the Period of 2017-2030

In the recent decades, the growth of the industrial activities and the increase in greenhouse gases have imbalanced the Earth's climate which is called the phenomenon of the climate change. This phenomenon directly affects the hydrological parameters. While climate change directly affects surface water resources through changes in the major long-term climate variables such as air temperature, precipitation, and evapotranspiration, the relationship between the changing climate variables and groundwater is more complicated and difficult to quantify. The large amount of water is needed in different parts of arid and semi-arid regions provided through groundwater resources. In recent decades, the quantity and quality of water resources have been reduced by unprotected exploitation. In addition, climate change and global warming increase the severity of the problem. Therefore, the predicted effects of climate change on groundwater recharge play an important role in the management of these resources in the future. In this study, Global circulation models, HadCM3 under A2 and B2 scenarios, were used for investigating the impact of climate change on groundwater recharge rates between 2017 and 2030, in the Tasouj aquifer.

In this study, to investigate the climate change in Tasouj basin, the required data were obtained from two sources including Global model output AOGCM which was based on the HadCM3 model and the observed data of the precipitation and temperature of Tabriz synoptic station with the statistical length of 1961 to 2016. To downscale the general circulation modal, the statistical method of SDSM was used. The Hydrologic Evaluation of Landfill Performance model (HELP) simulates all of the important processes in the hydrological cycle including surface runoff, evapotranspiration, vegetative growth, soil moisture storage, and vertical unsaturated drainage for each discrete layered soil column. In general, the modeled hydrologic processes by the program can be divided into two categories of surface and subsurface processes. The modeled surface processes are snowmelt, interception of rainfall by vegetation, surface runoff, and evaporation of water. The modeled subsurface processes are evaporation of water from the soil, plant transpiration, vertical unsaturated drainage. Vegetative growth and frozen soil models were also included in the program to aid modeling of the water routing processes. The required general data included growing season, average annual wind speed, average quarterly relative humidity, monthly normal mean temperatures, maximum leaf area index, evaporative zone depth and latitude.

According to the simulation of Hadcm3 model, during the period of 2017-2030, the average monthly temperature in all months of the year will increase in the studied area. The highest amount of heating in the average temperature will happen in July about 2 degree Celsius. The highest decrease in precipitation will occur in April and May about 9 mm than the base period. The highest percentage of precipitation in Tasouj basin is used for evaporation. During 14 years of the prediction, the year 2020 has the highest and the year 2029 has the lowest amount of evaporation. In terms of runoff caused by precipitation, the year 2023 with 9.69 percent of precipitation will have the highest runoff. The lowest and highest amount of recharge will respectively happen in 2021 and 2027. The depth of water precipitation is significantly affected by soil moisture and with increasing soil moisture; the depth of water percolation to soil will decrease. The soil moisture content is negative in 2027.  Consequently, the highest amount of recharge due to precipitation will happen in Tasouj basin. In the base period, the year 1990 had lowest precipitation and the year 1963 had the highest precipitation. Due to having a negative soil moisture storage in 1990, of 148 mm of annual precipitation, about 76.28 mm was spent for recharge. The amount of runoff is almost zero in this year and the rest of precipitation is evaporated. Despite the high annual precipitation in 1963, due to the high moisture content of the soil, the amount of recharge is only 4 percent of precipitation and most of the precipitation changes to runoff and evaporation. The status of evaporation, runoff and recharge in 2022, as the forecasted most precipitation year, is similar to 1963.

In recent years, the climate change has led to significant changes in the weather and the condition of surface and underground water resources in different locations. The response of the groundwater resources to drought and climate change is not as rapid as that of the surface water, but considering that the renewability of these resources takes much longer than that of the surface water, the impact of long-term drought on groundwater resources is much more serious than that of the surface water resources. Therefore, the monitoring of the condition and maintenance of the sustainability of these resources is important.  In this way, by using a step by step approach, the impact of climate change on recharge, evaporate, and runoff for the 2017-2030 period was investigated and the simulation result showed that with increasing temperature and decreasing precipitation, of three parameters of evaporation, recharge, and runoff, the evaporation dominated the other parameters. But the high consumption of basin and the increase of temperature and precipitation decrease prevented Tasouj aquifer from returning to its balance. Therefore, a principle planning to control the harvest and treatment of aquifer by underground dam and artificial nourishment is necessary