Trend analysis of evapotranspiration over India: Observed from long-term satellite measurements

Abstract

Owing to the lack of consistent spatial time series data on actual evapotranspiration (ET), very few studies have been conducted on the long-term trend and variability in ET at a national scale over the Indian subcontinent. The present study uses biome specific ET data derived from NOAA satellite’s advanced very high resolution radiometer to investigate the trends and variability in ET over India from 1983 to 2006. Trend analysis using the non-parametric Mann–Kendall test showed that the domain average ET decreased during the period at a rate of 0.22 mm year−1. A strong decreasing trend (m = −1.75 mm year−1, F =17.41, P<0.01) was observed in forest regions. Seasonal analyses indicated a decreasing trend during southwest summer monsoon (m = −0.320 mm season−1 year−1) and post-monsoon period (m = −0.188 mm season−1 year−1). In contrast, an increasing trend was observed during northeast winter monsoon (m =0.156 mm season−1 year−1) and pre-monsoon (m = 0.068 mm season−1 year−1) periods. Despite an overall net decline in the country, a considerable increase (>4mm year−1) was observed over arid and semi-arid regions. Grid level correlation with various climatic parameters exhibited a strong positive correlation (r>0.5) of ET with soil moisture and precipitation over semi-arid and arid regions, whereas a negative correlation (r