Abstract
Accurate estimation of reference evapotranspiration (ET0) is an essential requirement for water resource management and scheduling agricultural activities. Several empirical methods have been employed in estimating ET0 across diverse climate regimes over the past decades. In this study, the Python implementation for estimation of daily and monthly ET0 values of representative stations of ten agro-climatic zones of Karnataka from 1979 to 2014 using the standard FAO Penman-Monteith method was carried out. The assessment of temporal and spatial variability of monthly ET0 values across the various agro-climatic zones done by the various statistical measures revealed that the variation in spatial ET0 values was higher than temporal variation, indicating major difference in ET0 values was with respect to the stations rather than years under study. The nonparametric Mann-Kendall test conducted at 1% significance level on the annual ET0 values revealed a statistically significant increasing trend for all the ten stations during the study period. The trend test conducted on the climate variables like mean air temperature, wind speed, relative humidity, and solar radiation signifies their influence on the annual ET0 values. The magnitude changes in the trends detected by the Theil Sen's slope indicated that increasing values of mean temperature, solar radiation, and decreasing values of relative humidity predominantly contributed to the annual upward trend in ET0 values for the 10 stations. A trivial impact of wind speed on annual ET0 values was observed for the stations. Kalburgi and Udupi stations exhibited a positive ET0 trend with the highest and lowest annual values among ten stations.
Highlights
Evapotranspiration (ET) is a major tool in computing water balance and its requirements for plants
The trend test conducted on the climate variables like mean air temperature, wind speed, relative humidity and solar radiation signify their influence the annual ET0 values
The minimum daily ET0 values ranged between 1.59 mm/day to 4.0 mm/day between the months of July and August for all ten climatic stations which may be due to change in the season from summer to monsoon or winter characterized by decrease in temperature, wind speed and sun shine hours and higher values of relative humidity
Summary
Evapotranspiration (ET) is a major tool in computing water balance and its requirements for plants. It is responsible for inducing cloud formation by returning water vapour to the atmosphere and has a crucial role in the hydrologic cycle. Reference evapotranspiration is a significant parameter in the estimation of crop water requirement and irrigation scheduling. The crop water need or crop water requirement (ET crop) is defined as the amount of water consumed to meet the water loss through evapotranspiration That is, it is the amount of water needed by the various crops for its survival, growth and development, which mainly depends on the climate, crop type and the different growth stages of the crop. It is necessary to quantify accurate reference evapotranspiration values by considering different agro-climatic conditions for the best irrigation planning and management practices
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