Research On Precipitation Recycling Over The Mid-lower Reaches Of The Yangtze River

Over the last 100 years there has been a global warming which is not completely driven by natural forcing. By far, climate system has emerged a notable changes and variations that may impact stressed water resources and vulnerable hydrological cycle, which are worsen by human being's effect like populations increasing, improper water management. Climate change, human activities and hydrological cycle are mutual mediated and affected. One of the important effectible approaches of human being to climate is by altering the hydrological cycle. Therefore, detailed understanding of hydrological cycle can help to develop the ways of water utilization and management, thus to lessen the water-stress and, so much as mitigate climate change. The main content of this thesis is assessment and analysis of precipitation recycling and land-atmosphere interaction over mid-lower reaches of the Yangtze River under the environment of climate change, which can offer a reference to further integrated studies of local water cycle and regional climate.First of all, the precipitation recycling ratio, which describes the contribution of local evaporation to precipitation, is calculated by using the Eltahir's model and 40-year(1963-2002) NCEP/NCAR monthly reanalysis data over mid-lower reaches of the Yangtze River while its distribution and variation is analyzed. Second, according to the simulating results of RegCM2 model by using NCEP/NCAR daily reanalysis data, the effect of land surface latent heat flux on precipitation and ground air temperature over the same area during Meiyu season in 1998 is analyzed. Finally, improving on Eltahir's model, and calculating the precipitation recycling ratio over the same area during Meiyu season in 1998 by using ten-day situ data of precipitation and evaporation and NCEP/NCAR daily pressure level reanalysis data. The above study conclusions indicate as follow:1. About 24% of the precipitation in research area is attributed to local evaporation. Evaporation contribution enhances from the south to the north in research area. There is a strong intra-annual variation of average precipitation recycling ratios. And the ratios are inclinable to increase during the 40 years, which implicates theintensification of land-atmosphere interaction. It is possible due to both climate warming and land change. But the natural climate impact and human activity direct force could not be exactly distinguished.2. The second generation NCAR regional climate model(RegCM2) can reasonably reproduce the distribution and variation of precipitation and ground air temperature over mid-lower reaches of the Yangtze River during summer in 1998. The temperature simulation ability is superior to the precipitation simulation ability. The precipitation is clearly decreased while the land air temperature is appreciably increased when set ground latent heat flux transportation to atmosphere to be zero. It shows there is a considerable effect on regional precipitation and climate from ground latent heat flux and evaporation.3. With considering the derivatives of water vapor, the improved Eltahir's model can adapt to under-monthly scale assessment of precipitation recycling ratio. The average ratio is 29.4% in research area during continual heavy rainfall summer in 1998. Ten-day precipitation recycling ratios vary distinctly, which indicates the intense variation of land-atmosphere interaction.