Hydrological Thresholds of Urmia Water Basin.

Space is a multidimensional, boundless realm in which the relative position of phenomena is reflected. During the last few decades, the water level of Lake Urmia has decreased drastically. Lake Urmia, as a geographical device and a complex system, has been affected by natural and anthropogenic factors, as visible and hidden layers. In order to check the water storage threshold of dams in reducing the water level of Lake Urmia, we first prepared the desired data bank: DEM of the basin, data from climatology stations, discharge of hydrometric stations and dam information. We estimated the linear relationships between altitude and Temperature and precipitation and altitude in SPSS software. Considering climatology stations and dams as output points, we extracted several sub-basins. We estimated the volume of water inflow into the basins without a hydrometric station using Justin's method; We also analyzed the percentage of annual discharge compared to annual precipitation and changes in the water storage volume of dams. The results indicate that the reservoir volume of 46 dams in 12 sub-basins (1628.68 million cubic meters) accounts for about 21% of the total volume of basin runoff; This number was 13% until 1996 and reached 21.8% in 2013. In 1970, with the construction of the Mahabad dam with a reservoir volume of 197.8 million cubic meters, the reservoir volume of the dams exceeded the environmental threshold; it caused the lake's water level to decrease irreversibly. Examining the volume of the dam reservoir according to the volume of water intake and the volume of rainfall in the basins of the dams shows that out of the 41 dams, the reservoirs of 28 dams are built according to the rainfall potential of the basin. The ratio of reservoir volume to rainfall volume of 33 dams has very favorable conditions, and 6 dams have favorable conditions. [ABSTRACT FROM AUTHOR]