Research On The Method Of Determining Drought Warning Water Level In Hongze Lake Wetland

Extreme hydrometeorological events have always been a major problem that plagues mankind.In recent years,they have shown a trend of frequent occurrence,which has seriously threatened human production,life and economic and social development.Since the 21 st century,due to rising global temperatures and the influence of monsoons,drought events have occurred frequently in the Hongze Lake area.As the most important water source in northern Jiangsu and the dense junction of migratory birds migrating from north to south across the country,its impact under drought events is related to The quality of the water environment and the survival of plants and animals in the surrounding area.This study selects the Hongze Lake wetland as the research objective,and proposes a method for determining the optimal pattern of the lake wetland based on the habitat needs of migratory birds,considering the value of ecological services and water shortage,and on this basis,determines the appropriate water level for the survival of migratory birds.Based on the TM/ETM+/OLI remote sensing data of the long-sequence Landsat satellite from1984 to 2017,using the pixel binary model,trend line analysis,statistical analysis and normalized difference water index to study the dynamic change characteristics of the vegetation cover of the Hongze Lake wetland,construct The four seasons of Hongze Lake's vegetation coverage-water body area-water level relationship model determines the appropriate water level of wetland vegetation in seasons,and comprehensively restricts water levels such as navigation and water supply,and conducts research on the determination method of Hongze Lake wetland drought warning water level.The research methods and main results are as follows:(1)From 1984 to 2017,the overall vegetation coverage of Hongze Lake Wetland showed a slight downward trend,with a change rate of-0.07%.The vegetation coverage of Hongze Lake Wetland was mainly degraded,with a degraded area of approximately668.8km2.Significant degradation(72.9%)accounts for the largest proportion.The vegetation coverage-water area-water level relationship model was constructed for the four periods of Hongze Lake from 1984 to 2017.According to the three relationship models,the most suitable water levels for the four seasons are 12.31 m in spring,12.90 m in summer,12.12 m in autumn and 12.24 in winter m.(2)The lake wetland is ideally divided into lakes and swamps,the inner circle is the lake area,and the outer circle is the swamp.Based on the principle of maximum ecological service value and minimum water shortage in the Hongze Lake lake and marsh system,combined with the habitat requirements of key protected migratory birds,the suitable water level for summer migratory birds is determined to be 11-13 m,and the suitable water level for winter migratory birds is 10.8-12.24 m.(3)On the basis of the suitable water level of wetland vegetation and the suitable water level of migratory birds,combined with the water demand of Hongze Lake wetland such as shipping and water supply,the four seasons of Hongze Lake Wetland I,II,and III drought warning water levels were determined as spring(March-May)11.72 m,12.09 m and 12.43m;Summer(June-August)11.5m,11.68 and 12.08m;Autumn(September-November)11.5m,11.85 m and 12.48m;Winter(December-February))11.5m,12.19 and 12.52 m.