بررسی اثرات تغییر اقلیم بر خشکسالی هواشناسی و هیدرولوژیکی (مطالعه موردی: حوضه آبریز بختگان)

drought is transient phenomenon , slow , repetitive and integral part of the climate of each region. drought begins with a substantial reduction in precipitation over the long-term average rainfall and over time, reduced soil moisture and surface and ground water resources will continue to decrease. this phenomenon is the most important in bakhtegan basin because of its importance in strategic areas, agricultural lands and associated tashk and bakhtegan lakes is more. increasing greenhouse gases in recent decades and the resulting temperature rise due to the balance of the earth s climate and climate change in most regions of the global. studies suggest that this phenomenon may have a negative impact on various sectors including water resources , agriculture , natural resources and environment, health , industry and economy. thus, that will decrease in precipitation , relative humidity and increase temperature and due to the drought crisis severe losses to agriculture and the economy. to study the effects of climate change on meteorological droughts in future periods (2074-2045 , 2044-2015) were used the output of general circulation models hadcm3, gfdlcm2.1 and csiromk3.5 published under the two scenarios a2 and b1. lars – wg model was used for statistical downscaling output of the three models. the model of rainfall - runoff ihacres was used to simulate daily flows in future periods. drought indices used in this study is the standardized precipitation index (spi) and standard discharge index (sdi). result shown that catchment area of study has been involved from 2007 to 2010 years with extensive meteorological drought. the highest very severe drought in all the time scales occurs at stations located in the south west catchmen. the highest very severe hydrological drought in all the time scales occurs at shoor- shirin basin and roodsefid basin has been involved from 2008 to 2010 years. in the future period, 2015- 44, 2045 -74under the three models and two emission scenarios , the overall maximum temperature rise caused them to march, april , may and minimum temperature occurs in january and october. rainfall increases during the months of september to january and deacrease in the months of february to june. the highest minimum flow in future periods (2045-2074 , 2015-2044) for jamlbeig station ( shuor kharestan ) in april and jamlbeig station ( shirin ) in february , march and april ,also dehkadeye sefid in march and april. the results shown that scenario a2 have meteorological and hydrological drought frequencies higher than the b1 scenario. the results shown that risk analysis of meteorological and hydrological drought characteristics , the probability of duration and magnitude specified time period in future is equal to or less than the current time.