Assessing sensitivity of reference evapotranspiration to changes in climatic variables : A case study of Akola, India

Accurate estimation of crop water requirement is essential for irrigation scheduling, and future planning and management of water resources under changing climate scenarios. In the present study, an attempt has been made to study the sensitivity of reference evapotranspiration (ETo) to changes in different climatic variables, and effect of temperature change and elevated CO2 on ETo at Akola. The FAO - 56 Penman-Monteith equation has been used to estimate ETo using the meteorological data (1970-2008) of Dr. Panjabrao Deshmukh Krishi Vidyapeeth (PDKV), Akola. The sensitivity of ETo was studied in terms of changes in temperature, solar radiation, wind speed and vapour pressure deficit. Each of the climatic variables was varied from -25% to 25% at an interval of 5%, and only one climate variable was modified at a time. The combined effect of temperature change and elevated CO2 was studied by varying the changes in temperature from 1 degrees C to 5 degrees C and the CO2 levels from 330 ppm to 660 ppm. Simulation results showed that the mean temperature (T-mean) influenced the annual ETo the most followed by vapour pressure deficit (VPD), solar radiation (Rs) and wind speed (U-2). Changes in T-min, T-max, and T-mean affected ETo most during monsoon (June to September), winter (January, February), post-monsoon (October to December) seasons, respectively. Simulation of the combined effect of temperature change and elevated CO2 concentrations indicated that the effect of 4.0 degrees C rise in temperature is offset by increase in CO2 levels up to 660 ppm. Thus, the effect of rising temperature is moderated by the increasing CO2 concentrations, and the crop water demand may not rise significantly under the climate change scenarios.