Research On The Definition Of Drought And Flood Abrupt Alternating Based On Complex Disaster Factors

This thesis proposes the definition and screening criteria of drought and flood abrupt alternating events which is suit for rice and dry crop,respectively.It also gives a definition of standard of droughts,floods and abrupt alternating,which are the characteristic element of drought and flood abrupt alternating,and it takes soil water potential as a index to ensure the selection criteria of abrupt alternating interval time.The paper chooses wudagou region to do rice case study and jingzhou area to research dry crop definition.The main conclusions are as follows:(1)The definitionof drought and flood abrupt alternating events of rice and dry crop,it contain not only the influence of precipitation factor,but also factors such as soil moisture content,underground water level,area waterlogging condition and so on.The definition is different as well when crop species are different.(2)In the case study of wudagou region,there are 6 drought and flood abrupt alternating events in 55 years,droughts turning to floods events occurs 2 times,floods turning to droughts events are 4 times.in jingzhou area,there are 6 drought and flood abrupt alternating events in 58 years,five times are droughts turning to floods events,floods turning to droughts events are only one time.(3)Different kinds of drought and flood abrupt alternating index are suit for different condition.The paper screened and analyzed four kinds of drought and flood abrupt alternating event definition,the result shows that SDFAI index had a short time series,but it can not judge whether they were droughts turning to floods events or floods turning to droughts events.LDFAI index can pick out both droughts turning to floods events and flood abrupt alternating events,but can not describe the starting and ending time of drought and flood abrupt alternating events.Precipitation anomaly index is able to provide the beginning and ending time of drought period and wet period,but it is only fit to research large scale watershed.The Palmer drought model can not only screen out droughts turning to floods events and floods turning to droughts events,but alse give the specific process of the extreme events.But unfortunately,the model had a low screening criteria about droughts and floods events,therefore it picked out events which did not belong to ture drought and flood abrupt alternating events.The new definition based on actual agricultural condition can not only describe the starting and ending time of drought and flood abrupt alternating events,but also show the particular change progress of soil moisture content and soil water potential.The only fly in the ointment is that the definition can only be used in small scale region.