Evaluation of 30 Years Changing of River Flow Discharges in Urmia Lake Basin

Changes in the amount and distribution of flow discharge are a remarkable manifestation of climate change. Reducing or increasing the amount of flow discharge affects many other climatic and environmental phenomena such as runoff, flood, humidity and also affect many human activities such as agriculture, economics, the fight against soil erosion and so on. In this study, the trend of river flow discharge in the Urmia lake basin was investigated in two annual and monthly scales using modified non-parametric Mann-Kendall test (MMK) with complete removal of the self-correlation structure. In this study, 26 hydrometric stations were surveyed in the Urmia Lake basin during the statistical period of 1984-1984. Also, a non-parametric Pettett test was used to determine the time of change in flow trend. The results of the study of the trend of the studied stations at the Urmia lake basin showed that the course of the changes in the flow of water is decreasing in most months. On a yearly scale, at all stations, there was a trend of decreasing flow at the basin level. Also, the trend of flow discharge decline is more intense in both autumn and winter. The time of change in the decreasing trend of the flow discharge in the Urmia Lake basin was also taking place between 1994 and 1998. With evaluation the time of changing in the trend of the Urmia Lake water level and its hydrometric stations found that the decreasing trend of Urmia Lake water level data occurred one year after the decreasing trend in flow data.