Assessment of Climate Change Impacts on Reference Evapotranspiration and Simulation of Daily Weather Data Using SIMETAW

In this study, a SIMulation of EvapoTranspiration of Applied Water (SIMETAW) model was evaluated using monthly climatic data of four stations in Iran, namely Bushehr, Tabriz, Zahedan, and Mashhad, to investigate the effects of climate change on reference evapotranspiration (ETo). SIMETAW generates daily weather data from monthly values applicable in climate change studies. HadCM3 (Hadley Centre Coupled Model ver.3) outputs were statistically downscaled to project future variables. Maximum, minimum, and dew point temperature, precipitation, and wind speed were downscaled under two emission scenarios (A2 and B2) and two future periods (2020-2050 and 2050-2080) to simulate ETo. Calculated ETo values were compared with those simulated by SIMETAW in the base period (1961-2000). Results showed that, except for daily wind speed, the model accurately generated daily temperature variables and monthly precipitation. Furthermore, ETo is expected to increase in most months. Values of ETo at Bushehr Station are projected to increase from 164.7 to 181.2mm/month in 2050-2080, under the B2 scenario. The corresponding values are 125.4 to 137.5, 182.7 to 197.5, and 118.3 to 128.8mm/month for Tabriz, Zahedan, and Mashhad, respectively.