عنوان مقاله [English]
نویسنده [English]چکیده [English]
In the world, groundwater resources are counted the second freshwater resources after polar glaciers. Investigating changes in groundwater levels in any region has an important role in planning and sustainable water resources management. In the present research, trend analysis was conducted on groundwater level of 31 piezometeric stations in the monthly and annually scales in the period of 2002-2011 using Mann-Kendall non-parametric test. Trend line slope was estimated by using Sen’s estimator for each time series. Homogeneity of trend was tested using the Van Belle and Hughes method. The results showed that the trend of groundwater level for all stations was negative and the negative trend in 1% probability level was significant for 56 percent of the stations. The investigation of trend line slopes revealed that in average, the groundwater level of Urmia plain has been decreased about 19.9 cm/year. Also, the results of homogeneity test of trend in 5% probability level showed that the trend was non-homogeneous for different months and heterogeneous for various stations.