Spatial variability of annual and monthly Potential Evapotranspiration (PET) over India

In this study, meteorological data for well distributed 140 locations in India for the period (1971-2005) have been utilized for estimation of potential evapotranspiration (PET) by Penman-Monteith equation. The highest average annual PET of 2342 mm was at Jalgaon and lowest of 921 mm at Ging. Range of average annual PET is 1421 mm. The mean annual PET averaged for all stations over India is 1547 mm with 12% contribution in winter, 34% in pre-monsoon, 35% in monsoon and 19% in post-monsoon seasons. The lowest centers with annual PET less than 1400 mm are mainly located above 30 degree N latitude. The high centers with annual PET more than 1800 mm are located in desert area and central India, with lowest values at hill stations during most of the months. The higher monthly PET values in excess of 200 mm are normally observed during pre-monsoon and monsoon over western and Central India. As the monsoon advances, the PET values over western India decrease gradually. The lower PET values are observed during winter and post-monsoon season. The lowest mean monthly PET of 82.1 mm is in December and highest mean monthly PET of 199.6 mm is in May. Mean annual and monthly PET over (2 degrees x 2 degrees) latitude/longitude grids have been developed and presented.