Study On Precipitation Characteristics And Its Relationship With The Flood In The Yangtze River Catchment

Yangtze River Catchment has always been one of the most serious flood disaster areas.Precipitation as the most important factor of flood and its spatio-temporal variation and its influence on flood has been academic concern. Yangtze River Catchment has a vast, economically developed and densely populated, has always been a high flood prone areas. Under the backgound of Global climate change and the frequency of extreme weather events, research on the relationship between precipitation and flooding in the Yangtze River Catchment, to develop appropriate flood control departments to provice a scientific basis for decision-making.Using the daily precipitation data of 178 meteorological stations form 1961-2010 in the Yangtze River Catchment, the spatio-temporal variation of precipitation and rainstorm for last 50 years in the Yangtze River Catchment were analyed with Cycle analysis,mutation test, trend analysis and other methods. Using the monthly runoff data of Yichang and Datong hydrological station and the monthly precipitation data of their control catchment from 1961-1989 in Yangtze River Catchment, the response relationship between with precipitation and runoff in the Yangtze River Catchment were analyed.The results show that:(1)Ina normal years, the precipitation is the most in the Yangtze River Catchment in June and July. But the precipitation center is located in Dongting Lake and Poyang Lake River Catchment in June, and the precipitation center moved to the upper reaches of the Yangtze River Catchment in July. It is because of this natural disaster prevention mechanism of the Yangtze River Catchment thathad the summer precipitations just staggered in time and space. In the recent 50 years the increase of summer precipitation inYangtze River Catchment,especiallythe summer precipitationanormaly more events occur frequently after 1979, has increased probability of floods in the Yangtze River Catchment, and even the whole Catchment.(2)In a normal years,there are high annual precipitation,low precipitation concentr-ation degree(PCD) and early precipitation concentration period(PCP) in the eastern region of the Yangtze River Catchment, but the western region is the opposite.In more annual precipitation of the year,PCP has atendency to lag and PCD has atendency to increase in center region of Yangtze River Catchment.PCP in the west and the east also presents a trend of earlier and later accordingly, which increases the chance of upstream and downstream flood encounter. Since 1979annual precipitationmutation increases in the Yangtze River Catchment,which, to some extent, has increased the probability of the whole Catchment flood.(3)More of annual rainstrom is largely caused by heavy precipitation of more than one times in the Yangtze River Catchment.Heavy precipitation in the Yangtze River Catchment focuses in June and July.Rainstrom appeared in the middle and lower reaches of the Yangtze River Catchmentis a little earlier than the upsteram. and in the middle reaches of the Yangtze River region rainstrom concentratein June and July. It’sa time when the average intensity of the storm is the largest.That theabnormal of the rainstorm in June and July cancause the whole Catchment flood easily.(4) Precipitation is the main and the most direct factor for the forming of runoff in the Yangtze River Catchment. Summer total rainfall and total runoff has the highest correlation, The increasing trendof summer rainfall will lead to the increaseof runoff.Dueto "accumulation effects" and "linkage effect" in the Yangtze River Catchment,so that flood in downstream areais not only by their influence, but also affected by its upstream flood.