1961～2013年中国蒸发皿蒸发量时空分布特征及其影响因素

分析了1961～2013年中国1302个台站的蒸发皿蒸发量（Pan Evaporation，PE）的时空分布特征并探讨了影响PE变化的主要气候因子。结果表明:站点平均PE在全年和四季都呈明显下降趋势，且在1978年发生了突变。PE在华北平原、新疆、广东、广西及海南等地呈现出显著的下降趋势，而在福建、浙江和贵州等地为显著上升的趋势。用年平均PE距平场经验正交函数做经验正交函数（EOF）分解得到:在第一模态（EOF1）中，1981年时间系数由负转正，EOF1的空间模态与PE的变化有较好的一致性；第二模态（EOF2）中PE距平呈南北反向分布，2002年以后PE在北方减小，在南方增大。通过计算PE与近地面5个气象因子（降水、气温、风速、湿度、日照时数）的偏相关系数后发现:除了降水外，其余4个因子都和PE有很好的相关性。风速与PE为显著正相关，且相关系数最大的区域与EOF1中PE变率最大的区域吻合；相对湿度与PE为显著负相关；PE与气温的相关系数都为正值，且相关系数最大的区域对应于PE显著增加的地区，而与日照时数的相关系数在除春季以外的其他季节都大于0.6。进一步分析发现，风速和日照时数与PE的关系受两个气象因子的线性趋势影响较大，以此推断出PE的下降趋势应该很大程度是受风速和日照时数减小的影响。此外，干旱发生时，PE明显偏大，降水、气温、湿度和日照时数的变化也都对PE增大有明显的贡献，PE对干旱有很好的指示作用。

Temporal and Spatial Distribution Characteristics and Influencing Factors of Pan Evaporation in China from 1961 to 2013

Based on pan evaporation (PE) observations at 1302 weather stations in China for 1961-2013, in this paper, we present our analysis of the temporal and spatial characteristics and their impact on the climate factors of PE. The results indicate that both the annual and seasonal mean PE values from all stations show a significant downward trend, with an abrupt change occurring in 1978. The stations with a significant downward PE trend are mainly located in the North China Plain, Xinjiang, Guangdong, Guangxi, and Hainan provinces, whereas PE shows a significantly increasing trend in Fujian, Zhejiang, and Guizhou provinces. We performed empirical orthogonal function (EOF) analyses of the annual PE anomalies. For the first mode (EOF1), the time coefficient changes from positive to negative in 1981, and the variation of the EOF1 spatial pattern is similar as that of PE magnitude. The EOF2 mode presents opposite patterns in South and North China and after 2002, the PE decreased in North China, but increased in South China. Additionally, we calculated the partial correlation coefficients between PE and five climate elements, including precipitation, temperature, surface wind speed, relative humidity, and sunshine duration. The results show that except for precipitation, the other four variables are very well correlated with PE. The correlation between wind speed and PE is significantly positive, and the regions with the highest correlation are consistent with those with the largest EOF1 variability. The correlation between humidity and PE is significantly negative. The correlation between temperature and PE are positive overall, with the largest values appearing in areas where PE increases. The correlation coefficients between the sunshine duration and PE are greater than 0.6 in three seasons but not in spring. Moreover, we found that the linear trends of both wind speed and sunshine duration greatly impact their relationships with PE. Thus, we conclude that a decreasing trend in PE is largely because of decreasing wind speed and sunshine duration. Furthermore, when drought occurs, PE increases significantly, and the changes in precipitation, temperature, relative humidity, and sunshine duration also significantly contribute to the increases in PE. As such, PE could be a good indicator of drought.