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

Abstract

Because of its nature, lake evaporation (E L ) is rarely measured directly. The most common method used is to apply a pan coefficient (K p ) to the measured pan evaporation (E p ). To reconstruct the long sequence dataset of E p , this study firstly determined the conversion coefficients of E p 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 E p was estimated by the PenPan model that developed to the Class A pan and applied to quantify the E L 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 E p 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 E p simulated by the PenPan model with the modified net radiation (R n ) had better performance (compared to E p measured by E601) than the original PenPan model, which may be attributed to the overestimated R n 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 E L and E p has a significantly linear relationship during the unfrozen period in 2014 and 2015, but the ratio of E p to E L , i.e., K p varied within the year, with an average of 0.79, and was logarithmically associated with U. The yearly mean E L 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 R n , respectively; the latter was comparable to the surface runoff with an average of 1462.9 mm. In conclusion, the PenPan model with the modified R n has good performance in simulating E p of the E601, and by applying varied K p to the model we can improve the estimates of lake evaporation.

Reservoir evaporation in a Mediterranean climate: comparing direct methods in Alqueva Reservoir, Portugal

“…Pan measurements generally overestimate evaporation from large water bodies because, in contrast to a lake, a pan receives large quantities of energy through its base and sides and thus becomes much hotter than a lake. Moreover, the surface area of the water in the pan is much smaller than that of a lake, thus allowing a greater air renewal over the free surface (Jacobs et al, 1998;Lim et al, 2013;Yu et al, 2017). The measured pan evaporation rates are generally 30 % higher than that of lake evaporation at the annual scale.…”

“…Furthermore, the equipment is quite expensive and requires continuous maintenance, which means that it is not possible to perform regular measurements. Several studies using EC measurements to evaluate reservoir evaporation have been conducted in various places worldwide (Blanken et al, 2000;Nordbo et al, 2011;Zhang and Liu, 2014;Metzger et al, 2018;Jansen and Teuling, 2020). Another technique to estimate the actual reservoir evaporation based on direct measurements is the pan evaporation method (Riley, 1966).…”

Changes in Water Surface Boundary of East Juyan Lake in Northwest China Based on Remote Sensing Data

“…Because of the water diversion for many years, the ecosystem restoration of the downstream Heihe River basin has improved significantly. However, in the context of global changing climate, water bodies of terminal lakes still face the risk of drying up [7,8]. Therefore, research on the temporal changes and spatial distribution of the East Juyan Lake surface area has important practical The research on the dynamic change of lake water areas and its influencing factors has always attracted the attention of scholars worldwide.…”

Reservoir evaporation in a Mediterranean climate: Comparing direct methods in Alqueva Reservoir, Portugal

“…Pan measurements generally overestimate evaporation from large waterbodies because, in contrast to a lake, a pan receives large quantities of energy through its base and sides, and thus becomes much hotter than a lake. Moreover, the surface area of the water in the pan is much smaller than that of a lake, thus allowing a greater air renewal over the free surface (Jacobs et al, 1998;Lim et al, 2013;Yu et al, 2017). The measured pan evaporation rates are normally 30% higher than lake evaporation at the annual scale.…”