Micro-level spatial variability and temporal trends in reference evapotranspiration (ETo) at a semi-arid tropical station

Abstract

Micro-level spatial variability and temporal trends in annual and seasonal (weeks 23-39) reference evapotranspiration (ETo) were analyzed across three locations in Hyderabad. The mean ETo was highest (1694.2 mm) at ICRISAT and lowest (1489.0 mm) at Rajendranagar. It was 1555.7 mm at Hayathnagar. The coefficient of variability (C.V.) ranged between 6.8 to 8.7 % for annual and 8.3 to 12.3 % for seasonal ETo. The non-parametric (Mann-Kendall’s ‘ô’) test showed significant decreasing trend across all three locations in Hyderabad on annual as well as on seasonal ETo basis. Parametric ‘t’ test confirmed this as it brought out that the difference in mean reference evapotranspiration during 1975-1992 and 1993-2009 were highly significant (P=0.01) on annual basis and significant (P=0.05) on seasonal basis. The ETo on an average decreased between 9-10 mm per annum on yearly basis and between 1.9 to 3.1 mm per annum on seasonal basis during the period of analysis (1975-2009) at these three locations. The trends in governing weather parameters were also analyzed. The wind speed was the major parameter that showed significant decreasing trend both on annual and seasonal basis. Sunshine hours also showed significant decreasing trend on annual basis across all locations.