45年来中国蒸发皿蒸发量的变化特征及其成因

蒸发是地表热量平衡和水分平衡的组成部分，是水循环中最直接受土地利用和气候变化影响的一项。进行蒸发量变化的研究，对深入了解气候变化、探讨区域与水分循环变化规律具有十分重要的意义。文中利用中国472个气象站1957—2001年20 cm口径蒸发皿的实测资料，分析了中国小型蒸发皿蒸发量的变化趋势及其变化原因。结果表明，尽管在这45年间中国年平均气温以0.2 ℃/(10 a)的趋势递增，但是蒸发皿蒸发量总体上却以-34.12 mm/（10 a）的速度递减。蒸发皿蒸发量显著上升的地区只集中在少部分地区，如大兴安岭北部和北山地区；下降幅度最大的地区则集中在东部、西北北部和南部及西藏南部。通过对彭曼公式中能量平衡项和空气动力项的分析表明，东部蒸发皿蒸发量的下降主要是因为供蒸发的能量显著减少，而西部地区蒸发皿蒸发量的下降主要是供蒸发的动力下降所致。对各气象因子的趋势分析和相关分析表明，影响蒸发量的主要因子为风速和日照时数。

Changes in pan evaporation and its cause in China in the last 45 years.

Evaporation is an important component of the thermal balance and water budget at the earth surface and is subjected to both land use and climate change directly. The research on evaporation changes helps us comprehend climate change and probe into characteristics of regional water cycle. The observation data of 20 cm caliber evaporation pan and related meteorological elements were collected from 472 weather stations of China for 1957-2001. Statistical analysis shows that the pan evaporation in China as a whole has continuously decreased at a rate of 34.12 mm per decade, although the annual mean temperature has increased at a rate of 0.2 ℃ per decade. The regions with a significant drop in pan evaporation are East China, north part of Northwest China, South China, and south part of Tibet. Only a small part of regions with a rise in pan evaporation concentrates in Daxinganling and Beishan. Through analysis on variations of the dynamic term and energy term in Penman equation, separately, it is found that the drop of pan evaporation is mainly attributed to decreases in the energy term in East China and in the dynamic term in West China, respectively. Further investigation into tendencies of meteorological impacting factors and the correlation analysis between pan evaporation and the impacting factors tells us that sunshine duration and wind speed play the most important role in pan evaporation decrease. 