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Open AccessArticle

Seasonal and Diurnal Variations in the Priestley–Taylor Coefficient for a Large Ephemeral Lake

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Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, Nanjing 210008, China
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Key Laboratory of Watershed Geographic Sciences, Chinese Academy of Sciences, Nanjing 210008, China
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School of Earth Science and Engineering, Hohai University, Nanjing 210098, China
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Hydrological Bureau of Jingdezhen City, Jingdezhen 333003, China
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Hydrological Bureau of Poyang Lake, Jiujiang 332800, China
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Author to whom correspondence should be addressed.
Water 2020, 12(3), 849; https://doi.org/10.3390/w12030849 (registering DOI)
Received: 27 January 2020 / Revised: 6 March 2020 / Accepted: 10 March 2020 / Published: 17 March 2020
(This article belongs to the Section Hydrology)
The Priestley–Taylor equation (PTE) is widely used with its sole parameter (α) set as 1.26 for estimating the evapotranspiration (ET) of water bodies. However, variations in α may be large for ephemeral lakes. Poyang Lake, which is the largest freshwater lake in China, is water-covered and wetland-covered during its high-water and low-water periods, respectively, over a year. This paper examines the seasonal and diurnal variations in α using eddy covariance observation data for Poyang Lake. The results show that α = 1.26 is overall feasible for both periods at daily and subdaily scales. No obvious seasonal trend was observed, although the standard deviation in α for the wetland was larger than that for the water surface. The mean bias in evaporation estimations using the PTE was less than 5 W·m−2 during both periods, and the root mean square errors were much smaller than the average evaporation measurements at daily scale. U-shaped diurnal patterns of α were found during both periods, due partly to the negative correlation between α and the available energy (A). Compared to the vapor pressure deficit (VPD), wind speed (u) exerts a larger contribution to these variations. In addition, u is positively correlated with α during both periods, however, VPD was positively and negatively correlated with α during the high-water and low-water periods, respectively. Subdaily α exhibited contrasting clusters in the (u, VPD) plane under the same available energy ranges. Our study highlights the seasonal and diurnal course of α and suggests the careful use of PTE at subdaily scales. View Full-Text
Keywords: Priestley–Taylor coefficient; seasonal and diurnal variations; changing surface conditions Priestley–Taylor coefficient; seasonal and diurnal variations; changing surface conditions
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MDPI and ACS Style

Gan, G.; Liu, Y.; Pan, X.; Zhao, X.; Li, M.; Wang, S. Seasonal and Diurnal Variations in the Priestley–Taylor Coefficient for a Large Ephemeral Lake. Water 2020, 12, 849.

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