Analysis of Reference Evapotranspiration Variability and Trends in the Seonath River Basin Chhattisgarh

In this study, ETo was calculated using FAO-56 Penman Monteith method. Lag-1 autocorrelation coefficient was performed to detect the presence of serially correlation in data series. Mann-Kendall (MK) or Modified Mann Kendall (MMK) and Spearman’s rho test were applied to detect the trend in annual and monthly ETo at 8 districts over 49 years (1960–2008) in the Soenath river basin, Chhattisgarh (India). The slopes of trend lines were computed using the Theil–Sen’s slope estimator. The increasing trends in ETo were more pronounced than the decreasing trends. Annual analysis of the ETo series indicated a increasing trend in almost all the districts except Bilaspur district. The percentage change in annual ETo was maximum for Raipur (1.72%) and minimum for Bilaspur (-1.41%). On the monthly time scale increasing trends were identified in ETo data in most of the months. The significant positive trend magnitude was found for the months of September, October and November with Theil–Sen’s slope equal to 1.08, 1.15 and 1.30 mm/year. The Coefficient of Variability (CV) revealed that inter-annual variability was high in the whole river basin, with highest variability noticed for Durg district (104.31%).