The Environmental Impact of Hirmand River and Sistan 120 Days Winds Interactions

Sistan basin is located in an arid zone with less than 60mm precipitation per year. The life of region to be indebted to the Hirmand river and its embranchments inflows that import more than billions cubic meter of water and can support the survive of Hamoon international wetland and the population of the regions. The occurrence of periodic fluctuations in the water inflows and the potential climatic، geomorphologic and hydrologic conditions that expose the surface to wind erosion. In Sistan basin wind blow throughout the year، but during the June to September the wind is more important in respect to direction، frequency and intensity. This wind distinguished as 120 days winds and is one of the most famous meso scale wind systems in the northern hemisphere. The effects of these winds can observe in eastern regions of Iran، west and southwest of Afghanistan and northwest of Pakistan. The blow of winds has unavoidable effects on all ecologic، economic and social aspects. High temperature especially during the periods of 120 days winds، lack of precipitation and physical aridity of environment prepar the favorite conditions for winds erosion. These situations accompanying with reduction of soil moisture can increases the possibility of dust storm. In this paper، the relationships between the hydrologic fluctuations and principle components of 120 days winds are studied. The results suggested that the days with visibility less than 2 km، calm conditions and dust conditions in Sistan basin have a significance difference with other regions of Iran and a significant correlation exists between these climatic elements and periodic fluctuations of discharge of Hirmand river، stability of Hamoon lake. These facts are substantiated based on the non-parametric and parametric tests and multivariate regression analysis. By decreasing the water inflow to Sistan basin، the calm conditions significantly decrease، horizontal and vertical visibility reach to minimum and dust storm violently increases and subsequently the environmental problems arising from dust also aggravated.