Impact of the exceptionally high flood from the Changjiang River on the aquatic chemical distributions on the Huanghai Sea and East China Sea shelves in the summer of 1998

On the basis of the field observation in the Huanghai Sea and East China Sea in the summer of 1998, a rare event of exceptionally high discharge from the Changjiang River was described and how this high discharge altered water masses as well as chemical distributions on the shelves of the Huanghai Sea and East China Sea. The maximal extending ranges of the Changjiang diluted water and the nutrients in the freshwater from the Changjiang River were recorded for the first time. It was also found that there was a closed area with high oxygen and pH values in the offshore area of the southern Huanghai Sea and the northern East China Sea, indicating that the extensive spreading of nutrients due to the high discharge led to photosynthesis of phytoplankton mostly taking place in the offshore area far from the river mouth. The presence of ＂excess nitrogen＂ in almost all the northern East China Sea and the south of the Huanghai Sea suggests that these areas are potentially phosphorus-limited rather than nitrogen-limited, manifesting more like an estuarine ecosystem rather than a common marine ecosystem.

Assessment of Flood Catastrophe Risk for Grain Production at the Provincial Scale in China Based on the BMM Method

Flood catastrophe risk assessment is imperative for the steady development of agriculture under the context of global climate change,and meanwhile,it is an urgent scientific issue need to be solved in agricultural risk assessment discipline.This paper developed the methodology of flood catastrophe risk assessment,which can be shown as the standard process of crop loss calculation,Monte Carlo simulation,the generalized extreme value distribution（GEV） fitting,and risk evaluation.Data on crop loss were collected based on hectares covered by natural disasters,hectares affected by natural disasters,and hectares destroyed by natural disasters using the standard equation.Monte Carlo simulation based on appropriate distribution was used to expand sample size to overcome the insufficiency of crop loss data.Block maxima model（BMM） approach based on the extreme value theory was for modeling the generalized extreme value distribution（GEV） of flood catastrophe loss,and then flood catastrophe risk at the provincial scale in China was calculated.The Type III Extreme distribution（Weibull） has a weighted advantage of modeling flood catastrophe risk for grain production.The impact of flood catastrophe to grain production in China was significantly serious,and high or very high risk of flood catastrophe mainly concentrates on the central and eastern regions of China.Given the scenario of suffering once-in-a-century flood disaster,for majority of the major-producing provinces,the probability of 10% reduction of grain output is more than 90%.Especially,the probabilities of more than 15% decline in grain production reach up to 99.99,99.86,99.69,and 91.60% respectively in Anhui,Jilin,Liaoning,and Heilongjiang.Flood catastrophe assessment can provide multifaceted information about flood catastrophe risk that can help to guide management of flood catastrophe.