ارزيابي اثرات تغيير اقليم و تغييركاربري اراضي بر پاسخ هيدرولوژيك حوزه آبخيز اسكندري

Evaluation of the Impacts of Climate andLand Use Changes on Hydrological Responses of EskandariBasin in the Future Decade

علاوه بر تغيير اقليم، تغيير كاربري اراضي به عنوان يك عامل جانبي اثرات مهمي بر سيلاب دارد. لذا پيش-بيني اثر اين دو پارامتر بر وضعيت سيلاب دهه هاي آتي، راهگشاي مقابله با اين پديده خواهد بود. هدف از مطالعه حاضر پيش بيني وضعيت هيدرولوژيكي حوزه آبخيز اسكندري در دهه آتي تحت اثر تغيير اقليم و تغيير كاربري اراضي مي باشد. جهت بررسي تغييرات اقليمي دهه 2020، برونداد مدل HadCM3 تحت سناريوهاي A2 و B1 توسط مدل LARS-WG ريزمقياس گرديد. پس از بررسي تغييرات كاربري-اراضي گذشته، دو سناريو جهت پيش بيني تغييرات آن در آينده طراحي شد. در انتها با تغيير هايتوگراف بارش و كاربري اراضي در مدلHEC-HMS كه براي دوره گذشته كاليبره و اعتبارسنجي شده، اثر تغيير اقليم و كاربري اراضي بر سيلاب منطقه مطالعاتي مورد بررسي قرار گرفته شد. نتايج نشان دهنده افزايش 2/7 تا 9/10 درصدي بارش متوسط سالانه دهه 2020 مي باشد. افزايش توأمان دماي حداقل و حداكثر منطقه مطالعاتي در تمامي ماه ها موجب افزايش 82/0 تا 02/1 درجه سانتي گرادي دماي متوسط سالانه خواهد شد. افزايش دبي اوج و حجم سيلاب در ماه هاي مارس، اكتبر و فوريه و كاهش آن در ماه آوريل پيش بيني شده است. به طوري كه در صورت تغيير كاربري اراضي همراه با تغيير اقليم اين افزايش شديدتر خواهد بود

. Introduction Climate change is a change in the statistical distribution of weather patterns which can last for an extended period of time. Climate change may refer to a change in average weather conditions, or in the time variation of weather around longer term average conditions. Changes in temperature and precipitation patterns under climate changes have serious impacts on the natural disaster, especially in arid regions. Flood is one of the most important disasters on which climate change has effect. The primary effects of flood include loss of life, damage to buildings and other structures including bridges, sewerage systems, roadways, and canals. Floods can also frequently damage power transmission and sometimes power generations. Damage to roads and transport infrastructure may make it difficult to mobilize aid to those affected or to provide emergency health treatments. Flood waters typically inundate farm land, making the land unworkable and preventing crops from being planted or harvested, which can lead to shortages of food both for humans and farm animals. In addition to climate change, the land use changes, as an ancillary factor have impact on floods. Thus, evaluation of the impacts of climate change and land use change on flood situation in the coming decades will open a new way to deal with this phenomenon. The first comprehensive review of climate change and its effects on flooding and runoff was reported by the Intergovernmental Panel on Climate Change. 2. Study Area Study area is Eskandari basin that is located in west of Isfahan province. Latitude and longitude are 33 °11´to 32° 42´ N and 50° 40´ to 50° 02´. This area is crucial because it is the water resource of Isfahan city.Zayandehroodriver flows in this catchment.It starts in Zard-Kuhsubrange of Zagros Mountains in Chaharmahal and Bakhtiariprovince. It flows 400 kilometres (249 mi) eastward before ending in the Gavkhouni swamp, a seasonal salt lake,southeast of Isfahan city.The water ofZayandehrood gives life to the people of central Iran mainly in Isfahan. 3. Material and Methods This research has three phases;the climatic phase, land use phase and hydrologic phase.In the first phase, to study the effects of climate change in the2020s in Eskandari basin, daily temperature (minimum and maximum) and sunshine along with daily precipitation (1965-2008) were downscaled with LARS-WG. LARS-WG is a model simulating time-series of daily weather at a single siteunder both current and future climate conditions. These data are in the form of daily time-series for a suite of climate variables, namely, precipitation (mm), maximum and minimum temperature (°C) and solar radiation (MJm-2day-1).It utilizes semi-empirical distributions for the lengths of wet and dry day series, daily precipitation and daily solar radiation. The semi-empirical distribution Emp= { a0, ai; hi, i=1,.…,10} is a histogram with ten intervals, [ai-1, ai), where ai-1