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Abstract
The present study was taken up to demonstrate an overall methodology for local calibration of simpler reference crop evapotranspiration (ET0) estimation equations relative to the physically-based, albeit more data-intensive Penman-Monteith (PM) method. Climate records for the historical period 2006-2016 of 67 stations located across 10 agro-climatic zones of Karnataka State, India, were used for this purpose. The numerical coefficients in the original forms of the simpler equations namely, Blaney-Criddle (BC), Priestley-Taylor (PT), Radiation (RAD), and Turc (TC) were treated as unknown parameters and optimized for each station using PM ET0 estimates as reference. Results of local calibration indicated significant improvement in prediction accuracies and bias reduction for all the equations with the calibrated PT equation exhibiting the best performance. Spatial maps depicting the variations in the optimal values of parameters were developed to aid the accurate estimation of monthly ET0 values in the study area using only minimal climate inputs.
Acknowledgment
The authors are grateful to the Water Resources Development Organization (WRDO), Government of Karnataka, for providing the climate dataset used in the study and to two anonymous reviewers whose critical comments improved the quality of the manuscript.
Disclosure statement
No potential conflict of interest was reported by the author(s).
Correction Statement
This article has been corrected with minor changes. These changes do not impact the academic content of the article.
Additional information
Notes on contributors
S. Niranjan
S. Niranjan is a Research Scholar in the Department of Water Resources and Ocean Engineering at the National Institute of Technology Karnataka, Surathkal. His research interests are evapotranspiration, surface-water hydrology, and remote sensing/GIS applications in hydrology.
Lakshman Nandagiri
Lakshman Nandagiri is a Professor in the Department of Water Resources and Ocean Engineering at the National Institute of Technology Karnataka, Surathkal. Over the course of his 35-year academic career, he has published more than 100 research articles in refereed journals, books, book chapters, and conference proceedings. His research interests include catchment/watershed hydrology, vadose zone process, soil moisture measurement, evapotranspiration, irrigation scheduling, remote sensing/GIS applications in hydrology, multivariate statistics, artificial neural network applications and hydrological impacts of climate change.