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Climate changes are the main motivation for destruction of ecosystems; in fact the effects of these changes on biodiversity and ecosystems are considered as the most challenging cases in present century. Therefore, since the lakes are the most important services and functions of ecosystems, the effect of climate change on water level fluctuations of Tashk and Bakhtegan Lakes was analyzed as a natural ecosystem in this essay. For this purpose, the data related to six parameters of temperature, precipitation, evaporation, sunshine hours and snowy days were selected during 25-year statistical period , and Mann-Kendall test was used to determine the trend of changes in each time series. Inflow system of the lake, the volume of evaporation and area of water were simulated and fluctuation of lake was also assessed by using dynamic analysis method and to achieve to lake level and analysis of its fluctuations in period under study, the satellite images of Landsat 7 and ETM 5-1 were used in two high waters of April 1987 and April 2010. Results indicate that the lake level has been dropped 6 meters in 2010 compared to the similar period of 1986; in wet years that the rainfall is more than 618/5 mm, high water level is the lake conditions in all months of the year; unlike in most years when rainfall occurred under average of 365.4 mm, lake is faced with dry condition that is mainly due to the reduce of icemaker area, rainfall reduction, increase in evaporation and temperature. These conditions show the extent to which the lake is fragile and affected by climatic conditions that the most obvious evidence of it is decline of genetic storages such as Tashk and Bakhtegan lakes and subsequently instability of the region and reducing of services and ecosystems' functions.

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