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Water 2017, 9(12), 952; doi:10.3390/w9120952

Simulation of Pan Evaporation and Application to Estimate the Evaporation of Juyan Lake, Northwest China under a Hyper-Arid Climate

1,2,3
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1
Alxa Desert Eco-hydrology Experimental Research Station, Northwest Institute of Eco-Environment and Resources, Chinese Academy of Sciences, Lanzhou 730000, China
2
Key Laboratory of Eco-hydrology of Inland River Basin, Chinese Academy of Sciences, Lanzhou 730000, China
3
Gansu Hydrology and Water Resources Engineering Research Center, Lanzhou 730000, China
4
Heihe Water Resources and Ecological Protection Research Center, Lanzhou 730000, China
*
Author to whom correspondence should be addressed.
Received: 30 October 2017 / Revised: 1 December 2017 / Accepted: 5 December 2017 / Published: 7 December 2017
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Abstract

Because of its nature, lake evaporation (EL) is rarely measured directly. The most common method used is to apply a pan coefficient (Kp) to the measured pan evaporation (Ep). To reconstruct the long sequence dataset of Ep, this study firstly determined the conversion coefficients of Ep of two pans (φ20 and E601, each applied to a different range of years) measured synchronously at the nearest meteorological station during the unfrozen period through 1986 to 2001, and then Ep was estimated by the PenPan model that developed to the Class A pan and applied to quantify the EL of the Juyan Lake, located in the hyper-arid area of northwest China. There was a significantly linear relationship between the E601 and φ20 with the conversion coefficients of 0.60 and 0.61 at daily and monthly time scales, respectively. The annual Ep based on monthly conversion coefficients was estimated at 2240.5 mm and decreased by 6.5 mm per year, which was consistent with the declining wind speed (U) during the 60 years from 1957 to 2016. The Ep simulated by the PenPan model with the modified net radiation (Rn) had better performance (compared to Ep measured by E601) than the original PenPan model, which may be attributed to the overestimated Rn under the surface of E601 that was embedded in the soil rather than above the ground similar to the Class A and φ20. The measured monthly EL and Ep has a significantly linear relationship during the unfrozen period in 2014 and 2015, but the ratio of Ep to EL, i.e., Kp varied within the year, with an average of 0.79, and was logarithmically associated with U. The yearly mean EL with full lake area from 2005 to 2015 was 1638.5 mm and 1385.6 mm, calculated by the water budget and the PenPan model with the modified Rn, respectively; the latter was comparable to the surface runoff with an average of 1462.9 mm. In conclusion, the PenPan model with the modified Rn has good performance in simulating Ep of the E601, and by applying varied Kp to the model we can improve the estimates of lake evaporation. View Full-Text
Keywords: pan evaporation; pan coefficient; water budget; lake evaporation; arid area pan evaporation; pan coefficient; water budget; lake evaporation; arid area
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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MDPI and ACS Style

Yu, T.-F.; Si, J.-H.; Feng, Q.; Xi, H.-Y.; Chu, Y.-W.; Li, K. Simulation of Pan Evaporation and Application to Estimate the Evaporation of Juyan Lake, Northwest China under a Hyper-Arid Climate. Water 2017, 9, 952.

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