Preliminary Analysis on the Relation Between the Evolution of Heavy Floods in the Yangtze River Catchment and the Climate Changes since 1840

Abstract

Based on the reliable instrumental and/or historical data, 32 heavy flood records in the Yangtze River catchment from 1840 to 2000 were selected and the relation between flood evolution and climate changes were discussed. By analysis, the authors come to following conclusion: in the 19th century cold period (since 1840) before 1910s, there were 13 heavy floods and frequency is 1. 9 times /10a; from warm period 1921 to 2000, there were 19 heavy floods and frequency is 2. 4 times /10a. During the 20th century, there were two warm phases and in the decades of peak value of preceding one (1920s - 1940s), there were 9 heavy floods and in the second warm phase (1980s and 1990s), there were 8 heavy floods. The observed record of heaviest flood occurred in the ending of preceding warm period (year 1954). The 1990s is the warmest decades in the global and China as well. Influenced mainly by south-east monsoon, the middle and lower reaches of the Yangtze River catchment have experienced their top precipitation record in recent 100 years and the frequency of rainstorm also belonged to the highest in the last 40 years with detailed data source. Perhaps the high frequency of heavy floods in 1990s (5 times/10a) either indicates the significant impact of global worming on water cycle or reflects the higher rainy decades in periodical variation of 30 - 40 years which is related to the variation of monsoon circulation. Accordingly, there are possibilities that magnitude of precipitation and frequency of heavy floods might be drop slightly in the initial stage of 21st century. As to the upper reaches of the Yangtze River catchment, influenced most by southwest monsoon, the late 19th and early 20th century had witnessed a period of more rain and frequent heavy floods, while the last half century of 20th century, with lower heavy floods frequency, belongs to lower precipitation periods. There are great needs to improve the study of climate changes in the upper reaches of the Yangtze River catchment for reasonably predicting its future tendency.