Paradox of decreasing evaporation and evapotranspiration under increasing temperature conditions in the semi-arid tropics assumes greater importance as agriculture in these areas is more vulnerable to climate change. Trends in annual reference crop evapotranspiration (ETo) at Patancheru, Andhra Pradesh indicated a reduction of about 200 mm from 1850 mm to 1650 mm during the past 35 years. Contribution of energy balance term to the total ETo has shown an increasing trend while aerodynamic term has a decreasing trend. Wind speed has shown a strong negative trend leading to the dramatic fall of the aerodynamic term and consequently the ETo. Rate of reduction in evapotranspiration demand was about 10% for kharif (Jun-Oct) and about 14% for rabi (Nov-Feb). At Patancheru, measured temperature and solar radiation showed opposite trends and at locations where no measured solar radiation data available and if solar radiation is estimated from air temperature alone for use as an input in crop modelling, outputs under such conditions need to be interpreted with caution. Present study highlights the need for climate change impact studies at a local level in addition to those based on regional and global circulation models.
Kesava Rao, A.V.R.; Wani, S.P. Evapotranspiration paradox at a semi-arid location in India. Journal of Agrometeorology (2011) 13 (1) 3-8.