Evaluating the groundwater fluctuations with fuzzy Standardized Evapoprecipitation Index (SEPI)

In recent decades, Neyshabour basin as a semi-arid climate has faced with dramatic increasing of groundwater withdrawal. So, water demand management is important in this Basin. In this study, the effects of evapotranspiration and rainfall on groundwater fluctuations have been considered with 22 Rain gage and Evaporation gage station data during 1973-2006. The average amount of rainfall and evaporation on Plain calculated with assistance of IDW method. Results of Man-Kendall test showed the groundwater slope in the plain has a negative trend, while precipitation has no trend. Therefore, groundwater level detrended with extrapolation method to could find the correlation between cumulative evapotranspiration and rainfall with groundwater level. Standardized precipitation index and fuzzy standardized evapoprecipitation index devised for evaluating the effects of rainfall and evapotranspiration on the groundwater. Successive time series analysis shows that groundwater variations have a high Correlation with the fuzzy standardized evapoprecipitation index which is more than standardized precipitation index in different time scales.