The Role of Average Discharge Variations of Urmia Lake Rivers on Water Level Drop of the Lake

Due to the importance of trend study of rivers discharges, in this paper, the trend of average discharge variations of the rivers in Urmia Lake basin was analyzed. Investigating the role of discharge changes, entering to the lake on lake’s surface reduction was another goal of this study. For this purpose, the recorded data of 65 hydrometric stations (during 1978-2011) were analyzed. Non-parametric Mann-Kendall method considering autocorrelation effect was used for trend analysis in this paper. On the basis of the obtained results, discharge time series was significant at 95% confidence level in more than half of the stations (41 stations) having autocorrelation with 1-year lag. Also, more than half of the stations (58 stations) had a descending trend and this trend was significant at 95% confidence level in 38 stations. The average volume of surface water entering the lake have been reached from 4654 MCM in years before 1995 (the starting year of drying) to 2134 MCM in years after 1995. The time series of surface water entering the Urmia Lake had a decreasing trend and on the basis of t-student, the difference between average discharges during the two periods (after and before 1995) was significant at 95% confidence level. The results of this study shows a reduction in the surface waters across the whole basin area discharging to the Urmia Lake during the years after 1995 and the role of this phenomenon on the lake’s water level fall. This emphasizes that the proper management of water resources in different consumption sectors including agriculture should be considered due to climatological governing situations.