بـررسی پتـانسیل اثـرات تغییر اقلیـم بر خشکسـالی‌های‌ آینـده کشـور با استفـاده از خروجی مـدل‌های گـردش عمـومی جـو

A Study of the Potential Impact of Climate Change on the Future Droughts in Iran by Using the Global Circulation Models as Outputs Gholamreza Roshan Assistant Professor in climatology, Department of Geography, Golestan University, Gorgan, Iran Mohammad Saeed Najafi  MSc Student in Climatology, Faculty of Geography, Tehran University, Tehran, Iran. Extended Abstract 1- Introduction The development of urbanism and the expansion of cities, coupled with the rapid increase in population and intensification of industrial activities, have led to irregular patterns of consumption of fossil fuels (Roshan et al., 2010), which has caused disarrangement of climate system balance and heightened the climate anomalies. Climate change is often measured by changes in primary climate variables such as global surface air temperature and precipitation (Blenkinsop & Fowler, 2007). Recent and potential future increases in global temperatures are likely to be associated with impacts on the hydrologic cycle, including changes to precipitation and increases in extreme events such as droughts. By developing Atmosphere–Ocean General Circulation Models (GCMs), a modeling of the possibility of future precipitation changes have been provided. In this study the first aim is to assess the emissions scenarios for choosing the best scenario for Iran and the second goal is to analyze the potential changes of drought in the future global warming in Iran. 2- Data & Methods In this study, in order to assess Iran's droughts, two datasets have been used. The first one is Climate data for 70 synoptic and climatologically stations as experimental dataset and the second one is GCM data. To estimate potential future climate changes in droughts in Iran, we used data from the IPCC AR4 General Circulation Model (GCM) simulations. Any one model simulation of future climate may represent only one of many possible future climate states, so for simulating the precipitation climate parameter as results of two Global Circulation Models (GCM), CNRM-CM3 and GISS-EH outputs have been used. In order to introduce proper scenarios, 18 scenarios have been chosen and among this, P50 scenarios have been offered that agree with the condition of greenhouse gas emission in Iran. To analyze the changes in precipitation in the future, mean precipitation amounts were calculated for the years 1961–1990 and compared with each of the GCM control integrations. In addition to, for assessing Iran's droughts, Standard Precipitation Index (SPI) has been used. In current study, we used two time scales, past to now (1976-2005) and future (2025, 2050, 2075, and 2100). The correlation and regression methods for determining the trend of drought in context of time have been used. For the purpose of forecasting and simulating precipitation parameter changes as a result of greenhouse gases dispersion increase, the MAGICC SCENGEN compound model has been used. For developing the drought maps and analyzing them, GIS software and IDW method were used. 3- Results & Discussion Results of the study in 1976-2005 show the most quantity of drought occurrence in 43 studied regions in Iran, was first in winter and then in spring and autumn, which are nearly contrariwise for simulation data. Because of the effect of the global warming occurrence, the most drought risk potential respectively will be in spring, autumn, and winter. But precipitation simulated issues and concerning yearly and long-time mean (1961-1990) beside this mean, show that there will be an increase of rains in all simulated periods. The average change in annual precipitation in the entire country starts with 30.09 mm in 2025, precipitation in 2050 increased about 52.83, in continuation of these changes, 43.73mm is amount of precipitation changes during the 2075, and in finally increase of precipitation ends in 88mm in 2100. The calculation of droughts for simulated data in the future for autumn, the mean of SPI was calculated 0.61 for 2050, 2075 (SPI=0.58), 2025 (SPI=0.53) and in 2100 SPI calculated 0.47 respectively. The results of SPI simulated output in autumn show that the most studied areas are near normal. In winter, the most SPI value was calculated for the year 2100 (SPI=1.16). In this season, 2050 (SPI=1.08), 2025 (SPI=1.01), 2075(SPI=0.99) were calculated. In winter, as in autumn, the most studied areas are near normal. In winter, the minimum of SPI was calculated for northern Khorasan and north of Khorasan Razavi and the Maximum of SPI was calculated for the west of Caspian area and Guilan, west of Kermanshah and Ilam. In the spring, the mean of SPI in 2100 was -0.4, 2050 (SPI=0.11), 2075 (SPI=0.19) and in 2025 (SPI=0.22). So, the risk of drought in spring in comparison with other seasons has increased. 4- Conclusion The general conclusions from the observed data for drought and wet periods that can reach to this result, that’s the ratio of occurrence in significant increasing trend in droughts for a variety of seasons, are greater than wet periods. The results show that in all years and seasons that have been simulated, most wet years will be in the west of Caspian area and Guilan, west of Kermanshah and Ilam furthermore, most risks of drought occurrence for years and seasons have been simulated in northern Khorasan and north of Khorasan Razavi. 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