Climate change impacts on spatial-temporal variations of reference evapotranspiration in Iran

Global warming due to greenhouse effect is expected to cause major changes in climate of some regions. The change of climate is likely to have a profound effect on hydrological cycle. Evapotranspiration (ET, as the major component of hydrological cycle, will affect crop water requirement and future planning and management of water resources. This study was conducted to investigate climate change impacts on spatiotemporal pattern of reference evapotranspiration (ETo) in Iran. To this purpose, using Hargreaves and Samani -formula and monthly meteorological data at 20 meteorological stations, ETo was calculated for the historical period. ETo was calculated for two future periods (2015-2045 and 2070-20799) from the outputs of 15 AOGCM models under three emission scenarios (A2, A1B, and B2). The spatial distribution of ETo was interpreted by Inverse Distance Weighted Interpolation method. Results showed that Scenarios A2 and A1B predict the same increase in annual mean ETo in both the future periods (5% and 15% for the first and the second future period, respectively), however in scenario B1, the amount of increase in ETo in the first and the second future periods were determined as 3% and 9.4 %, respectively. Spatial variation of annual ETo showed that the increase in ETo in future periods will be decreased by moving from the Persian Gulf regions toward the Northern regions.