Improving the complementary methods to estimate evapotranspiration under diverse climatic and physical conditions

Abstract

Abstract. Reliable estimation of evapotranspiration (ET) is important for the purpose of water resources planning and management. Complementary methods, including complementary relationship areal evapotranspiration (CRAE), advection aridity (AA) and Granger and Gray (GG), have been used to estimate ET because these methods are simple and practical in estimating regional ET using meteorological data only. However, prior studies have found limitations in these methods especially in contrasting climates. This study aims to develop a calibration-free universal method using the complementary relationships to compute regional ET in contrasting climatic and physical conditions with meteorological data only. The proposed methodology consists of a systematic sensitivity analysis using the existing complementary methods. This work used 34 global FLUXNET sites where eddy covariance (EC) fluxes of ET are available for validation. A total of 33 alternative model variations from the original complementary methods were proposed. Further analysis using statistical methods and simplified climatic class definitions produced one distinctly improved GG-modelbased alternative. The proposed model produced a singlestep ET formulation with results equal to or better than the recent studies using data-intensive, classical methods. Average root mean square error (RMSE), mean absolute bias (BIAS) and R 2 (coefficient of determination) across 34 global sites were 20.57 mm month −1 , 10.55 mm month −1 and 0.64, respectively. The proposed model showed a step forward toward predicting ET in large river basins with limited data and requiring no calibration.

Evaluating the complementary relationship for estimating evapotranspiration using the multi-site data across north China

“…However no similar observations were found for the GG model (Han et al, 2011;Xu and Chen, 2005). Recently, Anayah and Kaluarachchi (2014) reported that the GG model was the most attractive when compared to the CRAE and AA models across 34 global sites. In our prior evaluation studies, the performance of the GG model was quite satisfactory among five commonly used ET models (see details in Supplement 1).…”

“…Thus, its applicability over a wide range of land types and climatic conditions need to be further investigated (Long and Singh, 2010). Secondly, the GG model has mostly been used on a specific timescale, namely monthly (Xu and Singh, 2005;Anayah and Kaluarachchi, 2014), daily (Han et al, 2011) and subdiurnal (Crago and Crowley, 2005). However, systematic comparisons of its performances on different timescales are relatively sparse and its dependence on timescales is not fully understood (Crago and Qualls, 2013).…”

Historical Drought Assessment Over the Contiguous United States Using the Generalized Complementary Principle of Evapotranspiration

“…The complementary principle, first proposed by Bouchet (1963), has provided a convenience for estimating terrestrial ET from meteorological observations only (e.g., Anayah & Kaluarachchi, 2014;Granger & Gray, 1989;Han & Tian, 2018;Kahler & Brutsaert, 2006;Morton, 1983;Szilagyi et al, 2017). This framework includes three ET definitions, namely, the actual ET (ET a ), the wet environment ET (ET w ), and the potential ET (ET p ).…”

A new drought index that considers the joint effects of climate and land surface change

“…Estimating in equation is key to calculate SWI. There are several methods for estimating , such as remote sensing [ Mu et al ., ] and Bouchet hypothesis (AA or GG model) [ Anayah and Kaluarachchi , ]. Here we use the Budyko framework [ Budyko , ; Wang and Tang , ; Zhou et al ., ], one of the most widely used equations, as follows [ Choudhury , ]: where represents the joint effects of climate and land surface [ Berghuijs and Woods , ].…”