پديد آورندگان :
الوانكار، رضا دانشگاه آزاد اسلامي واحد تهران جنوب - دانشكده مهندسي عمران - گروه عمران آب , نظري، فرزانه , فتاحي، ابراهيم پژوهشكده هواشناسي، تهران
كليدواژه :
HadCM3 , LARS-WG , خشكسالي , AOGCM , SPI , ايران , تغيير اقليم
چكيده فارسي :
امروزه معتبرترين ابزار جهت توليد سناريوهاي اقليمي، مدلهاي AOGCM ميباشد. از جمله مدلهايي كه براي ريز مقياس نمايي مبتني بر روشهاي آماري استفاده ميكنند مدل LARS-WG ميباشد، در اين مطالعه بر اساس مدل HadCM3 و دو سناريوي A1B، A2 براي دوره پايه ( 1961- 1990) و دوره پيش بيني (2040- 2011) در مقياس روزانه فرايند ريز مقياس نمايي انجام شد. و داده هاي مقادير مجموع بارش روزانه براي ايستگاههاي منتخب توليد شد. بعد از كاليبراسيون مدل و اطمينان از توانمندي مدل در ساخت سري هاي زماني بارش كه با مقايسه داده هاي شبيه سازي شده با مقادير بارش در دوره پايه در سطح اطمينان 95 درصد صورت پذيرفت، جهت بررسي وضعيت خشكسالي، شاخص استاندارد شده بارش (SPI) بكار رفت. نتايج نشان داد كه ميزان بارش نسبت به دوره پايه طي دورههاي آينده نزديك تحت خروجي هاي مدل گردش عمومي جو HadCM3 و دو سناريوي A1B، A2 تغيير معنيداري در بيشتر مناطق كشور خواهد داشت. بيشترين درصد تغيير مربوط به جنوب شرقي كشور مي باشد كه براي هر سه تداوم زماني 3، 12 و 24 ماهه افزايش خشكسالي را نشان ميدهد بطوريكه براي براي تداوم زماني 12 ماهه و 50 ساله شدت خشكسالي دوره پايه 13/82 بوده ولي در دوره آتي سناريوي A2، 15/05 و در دوره آتي سناريوي A1B ، 18/39 را نشان ميدهد. در غرب و شمال كشور نيز بطور مشابه در كليه تداوم هاي زماني شدت خشكسالي در دوره هاي آتي بيشتر از دوره پايه است، بطوريكه در دوره 24 ماهه و دوره بازگشت 50 ساله شدت خشكسالي پايه 16/31 ولي در دوره آتي A2 ، 18/65 و در دوره آتي A1B، 19/55 را نشان ميدهد. در مناطق جنوب، مركز و شرق كشور مقادير شدت خشكسالي پايه و آتي با تداوم زماني 24 ماهه و در دوره برگشت 50 ساله همگي حدود 18/8 بوده و شدت خشكسالي تغييرات زيادي را نشان نميدهد. شدت خشكسالي در شمال غرب كشور و جنوب غرب كشور در هر سه تداوم زماني 3، 12 و 24 ماهه در دورههاي آتي كمتر از دوره پايه خواهد بود بطوريكه در تداوم زماني 24 ماهه شدت خشكسالي با دوره برگشت 50 ساله پايه 23 ولي در دوره هاي آتي 18/44 را نشان ميدهد. در نهايت، اگرچه در پيش بينيهاي بدست آمده از ريزمقياس گرداني خروجي هاي مدل هاي اقليمي عدم قطعيت هايي وجود دارد كه اين امر به علت ساختار مدلهاي گردش عمومي جو، داده هاي مشاهداتي و ... مي باشد اما از آنجايي كه مدل هاي اقليمي به عنوان معتبرترين ابزار توليد سناريوهاي اقليمي مطرح مي باشند، ضروري است مديران و تصميم گيران بخش هاي مختلف منابع آب و كشاورزي نتايج حاصل از چنين پژوهشهايي را نيز مد نظر قرار داده تا امكان برنامه ريزهاي بلند مدت ميسر شود.
چكيده لاتين :
Due to the growth of industries and factories, deforestation and other environmental degradation as well as greenhouse gases have been increasing on the Earth's surface in recent decades. This increase disturbs the climate of the Earth and is called climate change. An Increase in greenhouse gases in the future could exacerbate the climate change phenomenon and have several negative consequences on different systems, including water resources, agriculture, environment, health and industry. On the other hand to evaluate the destructive effects of climate change on different systems, it is necessary to initially study the area affected by climate change phenomena. One of the most important effects of climate change on water resource is Drought. On the other hand, one of the most serious consequences of climate change is how it will affect droughts and water resources.
Drought along with warmer temperature and less precipitation will threaten the water supplies for the crop irrigation, which will directly reduce the production of crops.The climate of the 21st century will very likely be quite different from the climate we observed in the past. The changes will continue to be large in the future period with increasing carbon dioxide emissions. Analyzing and quantifying the signal of climate change will be much in demand considering the above sectors, which are highly relating to the sustainability and human living. In the past several decades, global climate models have been used to estimate future projections of precipitation [Intergovernmental Panel on Climate Change (IPCC), 2007], and have led to future estimation of drought, to quantify the impact of climate change and comparing the duration and intensity of droughts under future climate conditions with current climate by using Atmospheric-Ocean General Circulation Models AOGCMs to predict future Precipitation. Global circulation models namely, coupled Atmosphere-Ocean Global Climate Models (AOGCMs) are current state of the art in climate change research. in This study aims at investigating the impact of climate change on droughts conditions in Iran using the Standard Precipitation Index (SPI). The precipitation time series have been used for the estimation of Standardized Precipitation Index (SPI) for three timescales, 3, 12 and 24 months, for the region. The outputs of HadCM3-A2 and A1B were applied for the assessment of climate change impact on droughts. One of the major problems in using the output of AOGCMs , is their low degree of resolution compared to the study area so to make them appropriate for use, downscaling methods are required. In this study we have used lars WG for downscaling monthly average of rainfall of AOGCM-HadCM3, and The HadCM3 outputs were downscaled statistically to the study area for a future period 2011-2040.then, was evaluated by the coefficient of determination (R2) between observed and downscaled data. A method has been used for the estimation of annual cumulative drought severity-time scale-frequency curves. According to the rainfall results, in the 2011- 2040 period rainfall would decrease to compared to baseline period in the study area. The SPI time series were estimated (2011-2040) and compared with the respective time series of the historical period 1961-1990. Results revealed that there are decreases in the frequency of severe and mild droughts for the three examined SPI time series while there are increases in the duration of moderate droughts. This implies that droughts will be a concern in the future during the growing season (for the dominant crop) which should be considered in water resources management. specially in the west station of Iran. Also, these frequency ratios were mapped by GIS on study area. Results showed that generally in the future periods, frequency of droughts ratio of three months drought time- scale will be increase in the North, North West and some parts of the south Alborz mountains and, The Ratio of long ( 24 months) drought for scenario A2 compare to the current climate shows increasing drought in the parts of the North khorasn, sistan and baluchestan and kerman provinces and parts of South West of Iran. scenario A1B shows increasing drought in the parts of the East of Mazandaran , Tehran , Horozgan and parts of Fars and Yazd provinces. Finally ,further more analysis of drought, AWCDS-Timescale-Return Periods computed. These curves integrate the drought severity and frequency for various types of drought. The AWCDS time series were estimated for basic period and 2011-2040 under scenarios A2 and A1B. The comparison indicated the three types of drought intensity increases for the three examined SPI time series in the South East of Iran.
