STUDY ON THE FREQUENCY AND PRINCIPLE OF FLOOD CATASTROPHE IN THE CHANGJIANG DELTA AND ITS NEIGHBORING REGIONS IN THE LAST 2000 YEARS

Documented materials, especially those about flooding catastrophe, are abundant comprehensive and well-preserved, which makes possible the systematical collection of materials about historical document about climate evolution in Changjiang (Yangtze) Delta region and its neighboring areas. We make good use of the exceptional information to discuss the genesis and principle of flooding in this region. Analysis shows that the main flooding periods in the studied region in the last 2000 years were the Western Jin Dynasty, Eastern Jin Dynasty, Northern and Southern Dynasties, Southern Song Dynasty, Yuan Dynasty, Ming Dynasty and Qing Dynasty. The periods with flooding peak values were the 4th century, 5th century, 7th century, 9th century, early 12th century, early 14th century, mid-15th century, and early 18th century A.D. Possibility of reappearance of flooding peak value in the early 21st century will be great, and the hazard prevention and the hazard reduction will be still hard.

A 249-Year Record of Floods at Appleby in Westmorland, UK

An analysis of nearly 250 years of flood records on the river Eden at Appleby-in-Westmorland has enabled a flood frequency relationship to be established. The most severe floods were in the late 18th and early 19th century. With such a long history of flooding, some remedial measures would have been expected but the local people have, to some extent, adapted to the flood hazard by means of temporary and permanent flood proofing methods such as a cemented board across a doorway and removable flood boards. These measures were overwhelmed during the 2015 flood, as were the flood gates installed by the Environment Agency in 1998. A higher level of protection from floods at Appleby is called for.

Human-environmental interaction with extreme hydrological events and climate change scenarios as background

Climate change significantly impacts the lives of all people.Global change is composed of multiple factors that affect the population differently,having a very significant impact in the Mediterranean area.Human beings,through their actions,try to mitigate this impact and thus generate a more resilient society.Extreme hydro-logical events are affected by this climate change,with torrential rainfall events and severe droughts becoming frequent.Understanding these trends will allow us to better adapt to future conditions.This study aims to analyse catastrophic floods and severe droughts from paleo studies to studies that focus on future projections.For this purpose,a search for information has been carried out through other studies over the last five years to have a current perspective of this situation.Studies point to changes in the dynamics of floods and droughts,not only worsening the extremes but also affecting the average values of the records of each.In addition,the studies point out that anthropic action is accelerating the changes,with human beings and their capacity to adapt being infe-rior to the velocity of this global change.It is necessary to generate a paradigm shift in terms of global production by trying to adapt to future extreme flood and drought hazards.

Influence and mechanism of solar radiation intensity on the interdecadal variability of strong Meiyu events during historical periods

Most recent studies on Meiyu over the middle and lower reaches of the Yangtze River(MLRYR)have focused on its interannual variability or the mechanism of certain abnormal events.The influence and physical mechanism of solar radiation intensity on the interdecadal frequency of strong Meiyu events over the MLRYR during historical periods were investigated using reconstructed precipitation data,reconstructed solar radiation data,and model simulation data.First,according to the solar radiation intensity,the Ming and Qing Dynasties(1470-1850)were divided into three periods of strong solar radiation and three periods of weak solar radiation.It was found that during the periods of strong solar radiation,the frequency of strong Meiyu events was significantly higher than that during the periods of weak solar radiation in the reconstructed precipitation data and model simulations.Mechanism analyses show that during the periods of strong solar radiation,the Western Pacific Subtropical High(WPSH)is stronger,and the blocking highs over the middle-high-latitudes are also stronger,which is conducive to the continuous convergence of the southward cold air and the northward warm and humid air flow at the MLRYR.Therefore,a circulation spatial pattern conducive to the occurrence of strong Meiyu events is then induced.The probability distributions of precipitation also show that,during periods of strong solar radiation,changes in circulation patterns cause the probability distribution of precipitation to shift significantly to the right,increasing the probability of strong Meiyu events occurring on the right side of the probability distribution.