Trend analysis of meteorological parameters and reference evapotranspiration in the Caspian region

This study aims at observing the long-term trends of meteorological parameters and ET0in Caspian region, North of Iran. The long-term trends of meteorological data (1961-2008) were obtained from five synoptic meteorological stations, i.e. Gorgan, Qaem Shahr, Babolsar, Ramsar, and Anzali located throughout the Caspian region. In order to observe the trends of meteorological parameters, the region was primarily classified into five climatic zones based on De Martonne climate classification index (IA). The FAO Penman–Monteith combination equation was applied to calculate the ET0. The Caspian region was categorized in five climatic classifications as Mediterranean (Gorgan), semi-humid (Qaem­ Shahr), humid (Babolsar), very humid, type 1 (Ramsar), and very humid, type 2 (Anzali). Our results indicated that trends of air temperature were significant within the past half-decade so that it was increased (0.74ºC) during the two past decades. As well, wind speed showed significant increasing trends in all stations and increased 1.1 m.s-1 as average. The ET0 has been raised 0.4 mm.d-1 in Caspian region since 1988 and IA decreased from 39.5 to 36.8 showing the region is getting warmer and drier. Changes in meteorological parameters and ET0 will definitely affect the function of natural and artificial ecosystems. It is essential for managers to think of expected changes while planning for future development in Caspian region.