Pan Evaporative Changes in Trans-boundary Godavari River basin, India

Abstract

Pan evaporative changes are one of the key components of water resources management of a basin under changing climate and anthropogenic-induced warming. This study was undertaken for trans-boundary Godavari River (India) to identify trends through the Mann-Kendall (MK) test after removing the effect of significant lag-1 serial correlation from the climatic time-series by pre-whitening in pan evaporation (Epan) and in the probable causative meteorological parameters responsible for evaporative climatic changes in a large basin. Further, the Pettitt’s test was applied on Epan time series for estimating the change point year of Epan to find out the effective year when the change in pattern started reflecting in the time-series. At seasonal (monthly) time scales, statistically significant decreasing trends in Epan were witnessed in pre-monsoon season (in the months of March, April and May) over all the seven sites of the Godavari basin. Four sites witnessed statistically significant increasing trends in Tmin (Tmax) in July (December) and in monsoon (post monsoon) season in the basin. Statistically significant decreasing (increasing) trends in wind speed (relative humidity) in pre-monsoon and in month of March at these seven sites support the observed decline in the evaporative demand in the basin leading to possible enhancement in the total yield of the basin. Results of stepwise regression analysis showed that wind speed followed by relative humidity was found to be two main causative parameters of the observed decline in the Epan under the warmer environments in the basin. Pettitt’s test shows year 1991-1992 to be the probable year of change in the Epan in the Godavari river basin.