Trend Analysis of Reference Evapotranspiration (ET0) and Precipitation at Some Synoptic Stations of the Lake Urmia Basin

In present study, the trend analysis of precipitation and reference evapotranspiration (ET0), as the most important input and output variables of the Lake Urmia basin were investigated. The analysis was based on monthly meteorological data at five synoptic stations located in the basin consist of Urmia, Tabriz, Khoy, Saghaz, and Mahabad during 1976-2005 data period. At first step, monthly ET0 rates at each station were estimated using a newly developed model, known as PMF56-Hybrid. Then the non-parametric Mann-Kendall and the Theil-Sen slope tests were applied. In addition, the sequential Mann-Kendall test was used to detect abrupt changes in the time series. Annual trend analysis on precipitation data showed that there is a decrease trend at all station except Mahabad. Furthermore, annual ET0 data at 5% level at the same period did not show any significant increase, The Theil-Sen test results showed the highest positive slope rate at Khoy station (3.44 mm/year). In addition, the minimum and maximum of the Sen-slope rates were 4.2 and 2.88 mm/year at Khoy and Tabriz stations, respectively. The Sequential Mann-Kendall test revealed that Khoy and Tabriz stations faced a abrupt change with decreasing trend in annual precipitation data but non-significant at 5% except at Khoy station. For the PMF56-Hybrid based ET0 time series data, abrupt changes are not significant at all stations during 1976-2005. In present study, the trend analysis of precipitation and reference evapotranspiration (ET0), as the most important input and output variables of the Lake Urmia basin were investigated. The analysis was based on monthly meteorological data at five synoptic stations located in the basin consist of Urmia, Tabriz, Khoy, Saghaz, and Mahabad during 1976-2005 data period. At first step, monthly ET0 rates at each station were estimated using a newly developed model, known as PMF56-Hybrid. Then the non-parametric Mann-Kendall and the Theil-Sen slope tests were applied. In addition, the sequential Mann-Kendall test was used to detect abrupt changes in the time series. Annual trend analysis on precipitation data showed that there is a decrease trend at all station except Mahabad. Furthermore, annual ET0 data at 5% level at the same period did not show any significant increase, The Theil-Sen test results showed the highest positive slope rate at Khoy station (3.44 mm/year). In addition, the minimum and maximum of the Sen-slope rates were 4.2 and 2.88 mm/year at Khoy and Tabriz stations, respectively. The Sequential Mann-Kendall test revealed that Khoy and Tabriz stations faced a abrupt change with decreasing trend in annual precipitation data but non-significant at 5% except at Khoy station. For the PMF56-Hybrid based ET0 time series data, abrupt changes are not significant at all stations during 1976-2005.In present study, the trend analysis of precipitation and reference evapotranspiration (ET0), as the most important input and output variables of the Lake Urmia basin were investigated. The analysis was based on monthly meteorological data at five synoptic stations located in the basin consist of Urmia, Tabriz, Khoy, Saghaz, and Mahabad during 1976-2005 data period. At first step, monthly ET0 rates at each station were estimated using a newly developed model, known as PMF56-Hybrid. Then the non-parametric Mann-Kendall and the Theil-Sen slope tests were applied. In addition, the sequential Mann-Kendall test was used to detect abrupt changes in the time series. Annual trend analysis on precipitation data showed that there is a decrease trend at all station except Mahabad. Furthermore, annual ET0 data at 5% level at the same period did not show any significant increase, The Theil-Sen test results showed the highest positive slope rate at Khoy station (3.44 mm/year). In addition, the minimum and maximum of the Sen-slope rates were 4.2 and 2.88 mm/year at Khoy and Tabriz stations, respectively. The Sequential Mann-Kendall test revealed that Khoy and Tabriz stations faced a abrupt change with decreasing trend in annual precipitation data but non-significant at 5% except at Khoy station. For the PMF56-Hybrid based ET0 time series data, abrupt changes are not significant at all stations during 1976-2005.In present study, the trend analysis of precipitation and reference evapotranspiration (ET0), as the most important input and output variables of the Lake Urmia basin were investigated. The analysis was based on monthly meteorological data at five synoptic stations located in the basin consist of Urmia, Tabriz, Khoy, Saghaz, and Mahabad during 1976-2005 data period. At first step, monthly ET0 rates at each station were estimated using a newly developed model, known as PMF56-Hybrid. Then the non-parametric Mann-Kendall and the Theil-Sen slope tests were applied. In addition, the sequential Mann-Kendall test was used to detect abrupt changes in the time series. Annual trend analysis on precipitation data showed that there is a decrease trend at all station except Mahabad. Furthermore, annual ET0 data at 5% level at the same period did not show any significant increase, The Theil-Sen test results showed the highest positive slope rate at Khoy station (3.44 mm/year). In addition, the minimum and maximum of the Sen-slope rates were 4.2 and 2.88 mm/year at Khoy and Tabriz stations, respectively. The Sequential Mann-Kendall test revealed that Khoy and Tabriz stations faced a abrupt change with decreasing trend in annual precipitation data but non-significant at 5% except at Khoy station. For the PMF56-Hybrid based ET0 time series data, abrupt changes are not significant at all stations during 1976-2005.