Potential Evapotranspiration over India - An estimate of Green Water flow

Abstract

The spatial distribution of Potential Evapotranspiration (PET) is studied by selecting stations that are drawn from the Koppen Climate spectrum of India that spread the length and breadth of the country using the modified Penman potential evapotranspiration equation. Annual and seasonal PET trends are reported. Variation of mean seasonal PET for the country as whole for all the four meteorological seasons and its rate of change are graphically shown. Anomalies in the annual and seasonal PET for the epoch of 1961-1995 with reference to the base period 1931-1960 are brought out. Distribution of climatic types over India according to Koppens climate classification for the period 1951-1980 are presented along with the changes that occurred compared to earlier report. Koppen climate types are characterized in terms of PET to P ratio expressed in percentage. Significant decreasing, increasing and no trend are noticed in annual PET both in space and time. Annual PET for the country as a whole is increased in the latter half of the 20th century. The mean seasonal potential evapotranspiration to precipitation ratio is found to be increased from tropical monsoon climates to dry climate types.