Abstract
Pan evaporative changes are one of the key components of water resources management of a river basin under changing climate and anthropogenic-induced warming. The present study was undertaken for transboundary Godavari River basin (India) to identify the trends in pan evaporation (Epan) by non-parametric Mann–Kendall (MK) test in annual, seasonal and monthly time scales. The Pettitt test, a non-parametric test, was also used in this study to detect abrupt changes in the mean of the distribution of the Epan in the Godavari basin. Furthermore, the stepwise regression analysis was performed to find out the cause of the observed Epan changes in the basin. On seasonal (monthly) time scales, statistically significant decreasing trends in Epan were witnessed in the pre-monsoon season (in the months of March, April and May) in all the seven sites of the Godavari River basin. On the other hand, four sites witnessed statistically significant increasing trends in minimum temperature (maximum temperature) in the month of July (December) and in the monsoon (post-monsoon) season in the Godavari River basin. Statistically significant decreasing (increasing) trends in wind speed (relative humidity) in the pre-monsoon season and in the 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 Godavari River 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 Godavari River basin. Pettitt’s test shows year 1991–1992 to be the probable year of change in the Epan in the Godavari River basin.
Highlights
Evaporation, one of the main components of hydrologic cycle, which plays a vital role in agricultural and hydro-meteorological studies, water resources management and irrigation scheduling (Gundekar et al, 2008)
Evaporation is a complex process which is governed by several climatic factors, trend analysis of the pan evaporation time series shows declining trend on the contrary to the rising temperature trend which is evident from the spatial map of the evaporation and trends of the wind speed and temperature
Trends in the Epan were investigated at annual, monthly and seasonal time scales over the Godavari basin, the largest southern peninsular river basin of India, using the non-parametric Mann-Kendall test after removing the effect of significant lag-1 serial correlation from the Epan time series by using the procedure of pre-whitening
Summary
Evaporation, one of the main components of hydrologic cycle, which plays a vital role in agricultural and hydro-meteorological studies, water resources management and irrigation scheduling (Gundekar et al, 2008). Evaporation is influenced by a large number of meteorological factors, such as, air temperature, relative humidity, sunshine duration and wind speed. Shivam et al (2017) analysed the trends in rainfall events over a river basin of northeastern India and found significant rising trend in annual rainfall with increase in extreme rainfall events. Jaiswal et al (2014) conducted change detection study on climatic parameter over Raipur district of India and found significant rising trend in summer temperature with rising evaporation process attributed to increased wind speed and temperature. Godavari River is selected with the objective of studying trends in pan evaporation (Epan) through the Mann-Kendall (MK) test in annual, seasonal and monthly time scales in the current study. The stepwise regression method is used to search for the principal climatic variables associated with Epan and possibly explain the underlying mechanisms of observed pan evaporative changes in the Godavari basin
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