Spatial And Temporal Variability Of Extreme Rainfall In North South Transect Of Eastern China During The Last 54 Years

In China, about 70 percent of losses of natural disasters were caused by meteorological disasters each year, such as drought, rainstorm floods, consecutive precipitation, high temperature, heat wave, sand-dust storm, typhoon, and so on. The direct economic loss caused by meteorological disasters account for 3 to 6 percent of GNP. Losses resulting from Ecological environmental disasters, which concerned with weather condition such as debris flow, forest fire, grassland fire, plant disease and insect pest, desertification, were even more incalculable. Disasters mentioned here were chiefly caused by extreme rainfall. Although the frequency is not high, they can cause serious damage. In recent years, natural disasters caused by extreme rainfall are becoming more and more. This phenomenon has attracted significant coverage from public and government. Extreme rainfall is closely related to climate change, and it has a big impact on economy and natural environment. Research on extreme rainfall has become one of the forefront of climate change science in today's world.North South Transect of Eastern China is the 15th international sample transect which set by International Geosphere-Biosphere Programme in 2000. From south to north, the transect crosses the Equatorial Monsoon Climate Zone, the indistinct wet and dry Tropical Monsoon Climate Zone, the indistinct Subtropical Monsoon Climate Zone, the humid and semi-humid Warm Temperate Monsoon Climate Zone, the semi-humid or semi-arid Temperate Monsoon Climate Zone, and the Frigid Temperate Monsoon Climate Zone of East Continent Coast, with significant thermal gradient, water-heat combinatorial gradient, and land-use-intensity gradient. This area is our important grain-producing region, and its arable land occupies a large proportion of the whole land. The transect is densely populated. The proportion of this area's total economic volume in the whole of country's has been increasing over time. The level of urbanization further accelerates the development, and the influences of human activities further strong. In this thesis, by doing research on previous meteorological events, the author wants to obtain the changing regulation of extreme rainfall in future, and then enhance the monitoring, forecasting capacity, so as to reduce the destruction of extreme rainfall events and provide scientific basic for the precaution of natural disasters and the plan of sustainable development.Based on daily rainfall datasets from 266 valid stations in North South Transect of Eastern China from 1951 to 2004, 10 indices for extreme rainfall were calculated. To get temporal variability tendency, linear tendency method was adopted. To get spatial distribution rule, Universal Kriging interpolation technology was adopted. With nonparametric statistic method, comparison was made with results obtained by using linear regression. The results indicate that the maximum number of consecutive dry days significantly increased before mid-1960s, and no obvious change has been found since then; the maximum number of consecutive wet days has always been decreasing significantly; annual count of days when daily rainfall rate>=10mm and annual count of days when daily rainfall rate>=20mm decreased significantly from early 1950s to early 1970s, increased from early 1970s to early 1980s, and decreasing trend has been found again since then; annual total rainfall when daily rainfall rate>95th percentile of 1961-1990 shows no obvious change; before mid-1990s, annual total rainfall when daily rainfall rate>99th percentile of 1961-1990 shows no obvious change too, but increasing trend has been found since then; annual maximum 1-day rainfall and annual maximum consecutive 5-day rainfall show insignificant negative trends; as to the percentage of annual total rainfall from days with daily rainfall rate>=95th percentile of 1961-1990, it decreased before mid-1970s, increased from mid-1970s to late 1980s, and decreasing trend has been observed again since then; when it comes to the percentage of annual total rainfall from days with daily rainfall rate>=99th percentile of 1961-1990, it decreased significantly before 1980s, increased from 1980s to 1990s, and little change has been found since then; the maximum number of consecutive dry days increased and the maximum number of consecutive wet days decreased in most areas during the last 54 years; annual count of days when daily rainfall rate>=10mm and annual count of days when daily rainfall rate>=20mm decreased in the eastern part of Inner Mongolia, most of Northeast China, most of the North China and part of upper reaches of Yangtze River basin, increased in other parts; annual total rainfall when daily rainfall rate>99th percentile of 1961-1990 and annual total rainfall from days with daily rainfall rate>=95th percentile of 1961-1990 shows decreasing trend in the northern part and increasing trend in the southern part; annual maximum 1-day rainfall decreased in the central part, and increased in the other parts; annual maximum consecutive 5-day rainfall show a increasing trend in most areas; the percentage of annual total rainfall from days with daily rainfall rate>=95th percentile of 1961-1990 decreased in the eastern part of Inner Mongolia, most of Northeast China, western part of North China, Shanxi and Shaanxi, increased in other parts; the percentage of annual total rainfall from days with daily rainfall rate>=99th percentile of 1961-1990 increased in most areas. Comparing the results estimated by two methods, although there is little difference in quantized interval of grade, the absolute values of trend estimated by them are basically the same, and the spatial variation rule they revealed is similar too.