[en] Wide collection on the historic records of the climatic changes and flood events is performed in the Yangtze Delta. Mann-Kendall (MK) method is applied to explore the changing trends of the time series of the flood frequency and humidity during 1000-1950 and the flood discharge and the maximum high summer temperature during 1950-2002. The research results indicate that the flood magnitudes increased during the transition from the medieval warm interval into the early Little Ice Age. Fluctuating climate changes of the Little Ice Age characterised by arid climate events followed by the humid and cold climate conditions give rise to the frequent flood hazards. Low-lying terrain made the study region prone to flood hazards, storm tide and typhoon. MK analysis reveals that flood frequency during 1000-1950 is in negative trend before 1600 AD and is in positive trend during 1600-1950, but not at 95 % significance level. The humidity is in positive trend after 1300s, and during 1700-1800 this positive trend is at >95 % level. Close connections occurred between wet climatic conditions and the high flood frequency. The abrupt point of the time series of the flood discharge changes is the middle 1960s and that of the maximum summer temperature changes is at the middle 1990s, the exact abrupt point is at 1993. The flood discharge changes show a negative trend before 1990s, and a positive tendency after the 1990s; the maximum high summer temperature changes are on a negative trend before the 1990s and on positive tendency afterwards. These results indicate that the trend of flood discharge matches that of the maximum high summer temperature in the Yangtze Delta. The occurrence probability of the maximum high summer temperature will be increasing under the climatic warming scenario which will in turn increase the occurrence probability of the flood events. More active solar action epochs and the higher sea surface temperature index (SST index) of the south Pacific Ocean area that lies between 4°N~4°S and 150°W~90°W are corresponding to increased annual precipitation, flood discharge and occurrence frequency of floods in the Yangtze Delta. This is partly because the intensified solar activities and the higher SST index give rise to accelerated hydrological circulation from the ocean surface to the continent, resulting in increased precipitation and higher occurrence possibility of flood hazards on the continent.

[fr] On dispose pour le delta du Yangtze d'importants recueils de données historiques sur le climat et les inondations. On a traité avec la méthode de Mann-Kendall, les séries pour la fréquence des inondations et l'humidité de 1000 à 1950, et pour les débits de crue et les températures maximales d'été de 1950 à 2002. L'analyse montre que la fréquence des inondations a présenté une tendance négative jusqu'en 1600 et une tendance positive de 1600 à 1950. L'humidité a une tendance positive après 1300, tendance très significative de 1700 à 1800. Les débits de crue et les températures maximales ont une tendance négative avant 1990, positive ensuite.Les périodes de forte activité solaire et les plus fortes températures de la surface océanique accélèrent la circulation atmosphérique entre océan et continent, et causent une augmentation des précipitations et des risques de crues.