Abstract:

Based on the monthly reanalysis data provided by the European Center for Mediumrange Weather Forecasts (ECMWF), a comparative analysis of the climate features for the water vapor resource between the upper reach and the middle and lower reaches of the the Yangtze River was studied. In need of comparative analysis, the monthly reanalysis data provided by the National Centers for Environmental Prediction (NCEP/NCAR) was also used. The main results are as follows: from the year of 1958 to 2001, the regional average of yearly atmospheric precipitable water of the upper reach,and the middle and lower reaches of the Yangtze River had both shown a significant decreasing trend, with the reduced rate of 025 and 026 kg/(m2·10) arespectively. Under the yearly average condition, the upper reach and the middle and lower reaches of the Yangtze River both are moisture sinks, and the annual mean water vapor income is 226×105 kg/s and 124×105 kg/s respectively. For the 44 years, the yearly moisture income of the upper reaches had a significant decreased trend, with an average decreasing rate of 98×105 kg/(s·10 a);While that of the middle and lower reaches had a significant increased trend, with an average increasing rate of 115×105 kg/（s·10 a）. Among four seasons, the summer moisture budget has the most important influence on the total yearly moistuare. In the 44 years, the decrease of the moisture budget over the upper reaches had been closely related to the reduced income through its south border, and the increase over the middle and lower reaches had been main caused by the significant decreasing output through its north boundary. The changes of the water vapor resource over the Yangzte River had a close relationship with the expansions vatiation of summer moonsoon, and the expansion changes of the southerly water vapor with moon is the direct impact factor.〖