Evaluation of Climate Change Scenarios based on Two Statistical Downscaling Methods for Reference Evapotranspiration in Urmia Region

Some studies that investigate the climate change and hydrologic balance relationships utilize reference evapotranspiration to either calculate the changes in trends and magnitude of actual ET or to determine changes in atmospheric demand. Some studies utilize temperature or radiation-based empirical equation. Since many climate variables that affect ETo rates have been changing, single-variable equation for estimating the trend and magnitude of ETo should be avoided. The present and future temporal characteristics of ETo are examined in this paper. ETo are calculated during 1961-2005 by the Penman-Monteith recommended by FAO with historical weather data while ETo during 2011-2099 are downscaled from HadCM3 outputs under two emission scenarios(A2 and B2) by SDSM and under A2 by LARS-WG. Results showed that Downscaled ETo by SDSM will increasing during 2011-2099 at a Rate of 1.7 and 0.96 mmyr-1 under A2 and B2 scenario respectively. Averaged over the two emission scenarios, the projected increase of downscaled ETo by SDSM are 4.2%, 7.1% and 12.5% for the three periods 2020s, 2050s and 2080s respectively. Another model has projected 3.4%, 7.8% and 14.9% increases in ETo for these three periods respectively.