Abstract (Times New Roman, 12 Bold)
Introduction: Environmental problems in the world are a manifestation of unsustainable and inconsistent development with the capacities of the earth. Climate change is among all the problems, due to the global impact on the scale of the earth and effects such as floods, storms, unusual rain showers, increasing intensity, duration and volume of droughts, heat waves, melting of polar ice, rising sea water levels and going under water, loss of coastal lands, increase in minimum and maximum temperature in most areas, increase in evaporation and transpiration and water requirement of crops and Baghi, more evaporation of surface water and reduction of available fresh water sources, reduction of precipitation, increase of erosion and dust storms have attracted the attention of countries more than before. Iran, as one of the countries influencing the increase of greenhouse gases, is trying to increase adaptation and reduce the risk of climate change risks in order to manage surface and underground water resources, agriculture and improve the level of food security, natural resources and biodiversity (biological resources) and health of the country. In this regard, it is necessary to establish the governance of climate change in the policies and executive measures of the country at different national, regional, provincial and local levels in such a way that adaptation to it is implemented as a part of the country's daily life and development environment and as a result of increasing the level of environmental resilience, social, economic and cultural, all classes will benefit from its results. Climate change is one of the important factors that will affect different parts of human life on the planet and will have harmful effects on environmental, economic, social and especially water resources. For a long time, the change in meteorological characteristics of different regions of the world has been proven for researchers. The reduction of precipitation, reduction of surface currents and changes in the production and performance of agricultural products can be felt in many regions of the world. Our country is also facing many issues in this regard. Climate change has a significant impact on water resources and environment, which in turn is reflected in agriculture, society and economy.The increase in the concentration of greenhouse gases in the last few decades and the resulting increased temperature have led to significant changes in meteorological elements. Global warming, climate change and changes in temperature and precipitation parameters have now become one of the most important environmental challenges in the world. The reason for this is that these changes will cause droughts or severe, short and long term floods in the future. Therefore, one of the ways to reduce the effects of climate change is to evaluate its effects on rainfall and temperature in each region.
Methodology: In order to simulate the climatic data, at first, the observational data of Arak synoptic station including minimum temperature, maximum temperature, precipitation and daily sunshine hours in the statistical period of 1980-2005 were obtained from the country's meteorological organization. Also, CanESM2 global model data under RCP2.6, RCP4.5 and RCP8.5 scenarios along with observational data related to National Center for Environmental Variables Prediction (NCEP) were downloaded from this center's website. In order to scale the output data of CanESM2 and HadGEM2-ES models, LARS-WG model was used. LARS-WG model is also one of the statistical exponential microscale models. This model is one of the most famous meteorological data generation models, which is used to generate daily data of maximum and minimum temperature, precipitation and sunny hours in a station under current and future climate conditions (Alizadeh et al., 2013). In this research, the 6th version of this model was used to scale the output of the HadGEM2-ES model. In the LARS-WG model, after receiving the daily observation data (minimum temperature, maximum temperature, precipitation and sunny hours), the statistical characteristics of the data were extracted. Then, in order to ensure the ability of the model, a series of artificial data was produced in the base period (1980-2005) and compared with the observational data. In order to calibrate and ensure the accuracy of LARS-WG model performance, simulated variables and real data were evaluated. The results show that the LARS-WG model has a good accuracy (R2=0.99) in simulating the minimum and maximum temperature. Also, the accuracy of the model in simulating precipitation (R2=0.98) is acceptable.
Conclusion: Based on the results of the model under the RCP8.5 scenario, the LARS-WG model shows a decrease in rainfall in all three periods, which is consistent with the assumption that the continuation of global warming will lead to a decrease in rainfall. Based on the results, LARS-WG model has predicted minimum temperature increase in all three scenarios and all three periods. Regarding the annual maximum temperature, the results of the LARS-WG model have increased in all three scenarios and all three periods compared to the base period. The minimum temperature and the maximum temperature simulated by the LARS-WG model increase under all three scenarios to reach the maximum value in the RCP8.5 scenario, which indicates the effect of the intensity of carbon dioxide emission concentration in the atmosphere as well as other It is a greenhouse gas. Also, the results showed that the most changes in the maximum temperature related to the RCP 8.5 scenario (from 23.12 in the first period to 26.51 degrees Celsius in the third period), the most changes in the minimum temperature related to the RCP 8.5 scenario (from 8.71 in the first period to 60/11 in the third period) and the most precipitation changes are related to the RCP 8.5 scenario. The period studied in this research was 2021-2040 (first period), 2041-2060 (second period) and 2061-2080 (third period). The modeling results show a decrease in rainfall in all three periods, which is consistent with the assumption that the continuation of global warming will lead to a decrease in rainfall. The minimum and maximum temperature changes showed that in most cases, the minimum and maximum temperature will increase in the future. The maximum temperature increase was more than the minimum temperature, so that the highest temperature increase occurs in the month of February by 1.89 degrees Celsius compared to the base period. Examining the changes in the amount of rainfall also showed that the lowest amount of rainfall in the coming period will be observed in the month of June in the amount of 07.07 mm. A decrease in rainfall on the one hand and an increase in temperature on the other hand can indicate that the increase in evaporation and transpiration and the decrease in snow cover can move the water balance towards land and reduce water reserves.