Sensitivity of Reference Evapotranspiration to Glob al Warming in the Caspian Region, North of Iran

Abstract

The goal of this study was to estimate the sensitiv ity of reference evapotranspiration ( ET 0 ) to changes in meteorological parameters in the Ca spian region. Long-term meteorological data (1961-2008) were obtained from three synoptic meteorological stations. The region was primarily classified into three climatic zones, based on De Martonne climate classification. The Penman–Monteit h equation was applied to calculate the ET 0 and the sensitivity of ET 0 was studied in terms of changes in air temperature, solar radiation, wind speed and vapor pressure with in a possible range of ±20% from the normal long-term meteorological parameters. The res ults indicated that the Caspian region could be classified into the three climatic classes: Mediterranean, humid, and extremely humid. During the last half century, mete orological parameters and, in particular, temperature of the Caspian region has c hanged dramatically and the ET 0 has increased as a result of climate change. The study suggests that an increase in temperature by 20% (approximately 3.3 ºC) will result in ET 0 demand increase by 16%. Changes in vapor pressure (20% ) represented the highest inverse effect on annual ET 0 throughout the Caspian region (-19% in the Mediterranean, and -30% in other climates). The Mediterranean and extremely humid climates of t he Caspian region showed an increase of 2 and 5% of the total ET 0 , respectively, in response to 20% change in the wind speed. It is quite essential for managers to take i nto consideration the expected change in evapotranspiration owing to global warming while pl anning for development of artificial and natural ecosystems in the Caspian region. Keywords : Climate change, Meteorological parameters, Penman -Monteith.