Abstract
Abstract. The complementary principle has been widely used to estimate evaporation under different conditions. However, it remains unclear at which timescale the complementary principle performs best. In this study, evaporation estimations were conducted at 88 eddy covariance (EC) monitoring sites at multiple timescales (daily, weekly, monthly, and yearly) by using sigmoid and polynomial generalized complementary functions. The results indicate that the generalized complementary functions exhibit the highest skill in estimating evaporation at the monthly scale. The uncertainty analysis shows that this conclusion is not affected by ecosystem type or energy balance closure method. Through comparisons at multiple timescales, we found that the slight difference between the two generalized complementary functions only exists when the independent variable (x) in the functions approaches 1. The results differ for the two models at daily and weekly scales. However, such differences vanish at monthly and annual timescales, with few high x values occurring. This study demonstrates the applicability of generalized complementary functions across multiple timescales and provides a reference for choosing a suitable time step for evaporation estimations in relevant studies.
Highlights
Terrestrial evaporation (E), including soil evaporation, wet canopy evaporation, and plant transpiration, is one of the most important components in the global water cycle and energy balance (Wang and Dickinson, 2012)
Crago and Qualls (2018) evaluated the polynomial generalized complementary function (PGC) function and their rescaled complementary functions using the weekly data of seven FLUXNET sites in Australia, and the results showed that all the functions performed adequately, with a correlation coefficient between simulated E and observed E of higher than 0.9
For the 88 sites, nearly half of the sites (40) have the highest Nash–Sutcliffe efficiency (NSE) at the monthly scale, sites have the highest NSE at the daily scale, sites have the highest NSE at the weekly scale, and 23 sites have the highest NSE at the annual scale
Summary
Terrestrial evaporation (E), including soil evaporation, wet canopy evaporation, and plant transpiration, is one of the most important components in the global water cycle and energy balance (Wang and Dickinson, 2012). Meteorological studies focus on evaporation changes at hourly and daily scales; hydrological applications require evaporation data at weekly, monthly, or longer timescales (Morton, 1983); and climate change studies focus more on interannual variations. The eddy covariance, lysimeter, and scintillometer can measure evaporation at the half-hour scale, and water balance methods can observe evaporation at monthly to yearly scales (Wang and Dickinson, 2012). There are several types of methods for evaporation estimations, for example, the Budyko-type methods (Budyko, 1974; Fu, 1981), the Penman-type methods (Penman, 1948; Monteith, 1965), and the complementarytype methods (Bouchet, 1963; Brutsaert and Stricker, 1979). The Budyko-type methods perform well at annual or longer timescales, and the Penman-type methods can be applied at hourly and daily scales, while the complementary-type methods are used at multiple timescales (Crago and Crowley, 2005; Han and Tian, 2018; Ma et al, 2019) without explicit consideration of the timescale issue
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