The sequence of some hydrological factors has been analyzed in detail since the mid century.The result shows that the precipitation has not shown any increase in the basin,but in the eastern zone against the wind the precipitation has been increasing.The reason is that the rise of temperature resulted in the increase of evaporation.In addition,glacier melting increase may be an another reason for the increase in precipitation.In fact,the runoff feeding the lake has not increased since the amount of water was expanded under irrigation.The plough irrigation is responsible for the evaporating area and evapjoration as well, Part of evaporating vapor has come back to the lake in the way of precipitation,the left has passed over the boundary of the basis to the outside,leading to decline of the lake level.