Effect of Iand use Changes on Potential Evapotranspiration(Case study: Saqqez catchment)

The phenomenon of evapotranspiration causes water and moisture losses from water, soil and vegetation levels. Due to the small amount of atmospheric precipitation and water resource constraints in Iran, it is important to calculate it through a suitable method. The present research attempts to evaluate the Reference crop evapotranspiration (ETo) and investigate its relationship with land use. Also long-term land use changes was considered its effects on evapotranspiration changes in the Saqqez catchment. In this study, the long-term mean values of temperature, humidity, sunshine and wind speed data at seven meteorological stations and evaporation pan data of Saqez station were used to determine the appropriate ETo estimation method. TM, ETM and Landsat 8 satellite data and ENVI and GIS techniques were used to extract land use classes during the years 1992-2013. The results of the research indicate that the best method for this region as the cold and moderate climate was FAO radiation and Blaney-Criddle with R2 = 0.89 and Nash –Sutcliffe = 0.86 and R2 = 0.94 and Nash –Sutcliffe = 0.92 in Bijar and Sanandaj station respectively. The results of land use changes indicate that the main changes in land use related to the reduction of area in the rangelands and the increase of area in urban areas, water coverage, agricultural land and garden lands. Also, the results of correlation between evapotranspiration and land use indicate that the highest correlation (0.96) was obtained on agricultural lands and the least correlation (0.38) was observed in the surface area of the rivers.