再分析资料在三峡库区气候效应研究中的应用

Applications of Reanalysis Data in the Study of Climate Effect over the Three Gorges Reservoir Area

收集CRU、ERA-Interim和JRA-55这3种再分析资料,根据三峡库区33个气象站点1991～2016年的气温和降水观测资料,通过时序分析、相关分析、偏差百分比等多种方法对再分析资料在三峡库区的准确性、适用性进行评估,并根据评估结果选取再分析资料,以趋势分析、集合经验模态分解等方法对三峡水库蓄水前后的气候变化特征进行研究。结果表明:无论是时间序列还是空间分布,3种再分析资料对于气温的再现均好于降水,但对各季节的气温都有所低估,冬季与站点观测相差最大; ERA-Interim极大高估了三峡库区的整体降水,同时ERA-Interim和JRA-55对冬季降水有较大低估,偏差百分比在-40%左右;综合来看,CRU再分析资料在三峡库区的可靠性最高。蓄水后三峡库区的整体气温变化均由蓄水前的显著上升趋势转变为略微下降,年降水及春季、夏季降水无明显变化,秋季降水则在蓄水后呈明显的上升趋势,冬季降水在蓄水后有明显下降;蓄水后库尾长江以北的重庆、北碚等地升温幅度要高于邻近地区,蓄水前后降水的空间变化则具有明显的季节性和局地性; EEMD结果表明三峡库区气温和降水均存在2～3a、5a和7～8a左右的准周期变化,且三峡库区近年的年平均气温变化较为平缓,未来降水可能出现增多趋势。

In this study,three reanalysis products（ i. e. CRU,ERA-Interim and JRA-55） are evaluated using in situ measurements at 33 weather stations over the Three Gorges reservoir area for 1991-2006. The measurement variables include monthly air temperature and precipitation at all stations. Some approaches,including timing analysis,correlation analysis and percentage deviation,are utilized to quantify the relative performance of reanalysis data with respect to each variable. The results show that the monthly temperature from all reanalysis data are overall in better agreement with in situ observations compared with the precipitation.However,three types of data all underestimate the temperatures in each season,and the significant differences are seen in winter. As for precipitation,ERA-Interim data largely overestimate the overall precipitation in the Three Gorges reservoir area, and in winter, both ERA-Interim data and JRA-55 data show a marked underestimation of precipitation,with a deviation of about-40%. On the whole,at monthly scale,CRU is superior to others in air temperature and precipitation for the Three Gorges reservoir area. Based on the result,CRU was selected to analyze the characteristics of climate changes in the Three Gorges Reservoir before and after the impoundment by using trend analysis and ensemble empirical model decomposition（ EEMD） After the impoundment,the significantly rising trend of the temperature in the Three Gorges reservoir area turns to a slight downtrend. No obvious changes are found in spring,summer and annual averaged precipitation. However,affected by the impoundment,autumn precipitation has notably increased and winter precipitation decreased.Moreover,strength of warming to the north of the Yangtze River like Chongqing and Beibei is greater than their adjacent regions. Impacts of impoundment on the spatial distribution of precipitation changes are not identical in different regions and seasons. In addition,the EEMD results indicates that quasi-periodic variations with about 2 to 3 years,5 years and 7 to 8 years in both temperature and precipitation in the Three Gorges reservoir area. It also shows that the annual averaged temperature in this area undergoes slow trend in recent years,but may increase more obviously in future.