Comparison of actual water evaporation and pan evaporation in summer over the Lake Poyang, China

Abstract

水面蒸发是湖泊水量平衡要素的重要组成部分.基于传统蒸发皿观测蒸发不能代表实际水面蒸发,而实际水面蒸发特征仍不清楚.本研究基于涡度相关系统观测的鄱阳湖水体实际水面蒸发过程,在小时和日尺度分析了水面蒸发的变化规律及其主要影响因子,并与蒸发皿蒸发进行比较.研究表明,实际水面蒸发日变化波动剧烈,变化范围在0~0.4mm/h之间.水面蒸发的日变化特征主要受风速的影响.鄱阳湖8月份日水面蒸发量与蒸发皿蒸发量在总体趋势上具有很好的一致性.8月份平均日水面蒸发速率(5.90mm/d)比蒸发皿蒸发速率(5.65mm/d)高4.6%.水面日蒸发量与蒸发皿蒸发量的比值在8月上、中、下旬平均值分别为1.24、1.00、0.92,呈现下降的趋势.鄱阳湖夏季水面日蒸发量与风速和相对湿度相关性显著,而蒸发皿蒸发与净辐射、气温、饱和水汽压差和相对湿度均呈显著相关.这是由于蒸发皿水体容积小,与湖泊相比其水体热存储能力小,因此更容易受到环境因子的影响.;Evaporation is an important factor in water balance of lakes. The evaporation pan is a traditional method to observe water evaporation, while it cannot represent actual water evaporation. So the characters of actual water evaporation are still unclear. In this study, the actual water evaporation was measured by an eddy covariance system over the Lake Poyang in August of 2013. We analyze the diurnal and monthly variations of water evaporation and its main influencing factors, and compare it with pan evaporation measured at Tangyin station. The results show that the water evaporation has strong turbulence in diurnal variations in the range of 0-0.4mm/h. The diurnal variation of water evaporation is mainly controlled by the wind speed. The daily water evaporation has similar trend with daily pan evaporation in August over the Lake Poyang. The average water evaporation in August is 5.90mm/d, which is higher than 4.6% for average pan evaporation(5.65mm/d). The ratio of water evaporation to pan evaporation in August shows decreasing trend, and the ten-day average ration was 1.24, 1.00, 0.92, respectively. The daily water evaporation in August has good relationship with wind speed and relative humidity, and pan evaporation was significantly related to net radiation, air temperature, the saturation vapor pressure deficit and relative humidity. This is due to evaporation pan has small volume and weak water heat storage capacity comparing with the lake, thus it easily affected by environmental factors.