Study On Runoff Change In Central And Eastern China

Previous studies have shown that in the past half century,the annual runoff of major rivers of China has shown a downward trend,and in the northern China has decreased significantly.Through attribution analysis,scholars believe that the change of rainfall is the main factor affecting the change of river runoff.However,studies have also shown that the annual rainfall in China has changed little in the past half century.Therefore,more detailed data analysis is needed to reveal the reasons for the decline in river runoff.At present,there are many studies on the inter-annual rhythm of runoff,while there are few studies on the law of change during the year,and there is no systematic study on the composition of different runoff components.In order to study the distribution and variation of river runoff during the year in China's central and eastern regions,345 research watersheds with an area of 50 to 5000 square kilometers were selected in the river basins of the central and eastern China.Most of these research basins are located in the source area of rivers.avoiding large-scale water conservancy projects,we can consider its environment less affected by human activities.The data used included daily-scale runoff data from the basin outlets and daily-scale meteorological data from the National Weather Station near the river basin.Referring to the rules for the flood season of major rivers in China,the data used in the study are divided into two parts,the flood season and the non-flood season,and the spatial distribution rules of the river runoff during different periods of the year are discussed.The collected data were divided into two research periods,from 1968 to 1988 and from 2006 to 2014.The data of runoff and rainfall in the study area can be changed between two periods.The daily runoff data was divided by using Arnold's automatic baseflow segmentation method to obtain the baseflow and stormflow sequences.With reference to the research methods of runoff,the spatial distribution of baseflow and stormflow in the flood season and non-flood season are discussed separately,and the change law between the two research periods is discussed.By comparing the analysis results of the two research periods,we can obtain:(1)In the flood season,the runoff of the northern rivers and the southern rivers both decreased and the trend is significantly,while the rainfall was generally reduced,and in the dry areas the correlation between the runoff depth and the precipitation was even greater.Significantly,the changes of baseflow in the Heilongjiang River Basin,the Liaohe River Basin,the Haihe River Basin,the Yellow River Basin,and the southeastern river basins have a greater impact on runoff,and changes of the stormflow in the Huaihe River Basin,the Yangtze River Basin,and the Pearl River Basin have a greater impact on runoff.(2)In the non-flood season,the runoff of the northern rivers generally decreased,and the runoff of the rivers in the south generally increased.The precipitation in the northern river basins generally increased,and in the southern river basins the precipitation generally decreased.However,the trends of runoff and rainfall in all river basins are consistent.Comparing with the arid regions,in the humid areas the correlations between the runoff depth and the precipitation are more significant,so do the correlations between the runoff depth and the drought index.Changes in stormflow in the Heilongjiang River Basin,the Haihe River Basin,the Yellow River Basin,the Huaihe River Basin,and the Pearl River Basin have a greater impact on runoff,and runoff in the Yangtze River Basin is greatly affected by the baseflow.