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.
Highlights
IntroductionOver the past several decades, serious environmental degradation has occurred in arid northwest of China, in which the most remarkable event was a vast number of inland lakes drying up and the disappearance of aquatic
Lakes are sentinels of climate change and/or human activities [1,2,3]
Based on the estimated monthly Cp (E601/φ20 = 0.61), the Ep from 1957 to 2001 measured by φ20 was converted to the E601 during the unfrozen period by multiplied by the Cp and adding the φ20 during the frozen period, and, along with the Ep measured by E601 from 2002 to 2016, the long-term
Summary
Over the past several decades, serious environmental degradation has occurred in arid northwest of China, in which the most remarkable event was a vast number of inland lakes drying up and the disappearance of aquatic. Water 2017, 9, 952 ecosystems [2,4,5,6]. In order to protect and restore these degraded ecosystems, the Ecological Water. Conveyance Project (EWCP) in the arid inland river basin was implemented by China’s government in. For the operability of management, the EWCP identified that maintaining a certain size of lake area is an important index of whether this project has succeeded or not [9]. The question is how much water evaporated from those lakes There has been considerable debate as to whether it is the waste or utilization for the limited water resource [9,10,11].
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