Studies On Temporal And Spatial Distribution Characteristics Of Droughts And Floods In Horqin Sandy Land In The Recent 300 Years

The global change research is one of significant scientific research topics about global environment questions. The global climatic change is a core issue, specially the climatic change process and the predictable climatic change in 10 years to 100 years scale are hot topics in the climatic change researchs.Horqin sandy land is located the monsoon climate edge, and it is typically environmental sensitive and vulnerable. The strength of the monsoon and the resulting repeatedly fluctuations of the climate conditions significantly performed in the area ancient soil layers and sand layers, inland water levels ,changes in plant pollen, droughts and floods climate changes. Using the historical literature material and the actual precipitation data,this article has minutely discussed the rules of the floods and droughts changes of the Horqin Sandy Land during the recent 300 years. Droughts/floods Index is used to determine the regional droughts/floods rank,and this article analyzed the regional droughts/floods stage,and elaborated the temporal and spatial distribution characteristics of the appearance of relatively moist time and relatively dtought time.so that we can get a view about natural environment driving factor contributions to the 20th century Horqin sandy land forming.The floods/droughts climate evolution in Horqin Sandy Land during the rencent 300 years fully reflects the mid-west China millennium and hundreds of years'climate changes.Mainly as follows:(1)The drought climate mainly appeared in the 18th century, and humid climate occupy the superiority in the 19th century; the cycle of drought/flood evolution shortened,droughts and floods transformation was frequent.(2) In Horqin sand Land climate change in the recent 300 years, there are seven flood and drought stages, that is: 1701-1713 relative flood stage; 1714-1814drought stage; 1815-1894flood stage; 1895-1908 drought stage; 1909-1966 flood stage ;1967-1984 relatively drought stage; 1985-2000 flood stage.(3) in the droughts and floods climate evolution of Horqin sandy land during the recent 300 years,big drought year appeared 19 times(frequency of 6.33%), that is,once per 16 years. Big flood year appeared 22 times (the frequency of 7.33%), that is, once per 14 years. Big floods years have the slightly larger number of emerging opportunities than big drought years. Big flood years in the mid-19th century to the end of the 20th century account for 90% of the whole big flood years.(4) According to the analysis of the recent 40 years'precipitation measured data,The drought stage lasted longer than the humid stage,and the drought is more intensive than humid.In the spatial distribution, drought and flood climate change in the west of Horqin sandy land were greater than the east.In the season distribution, changes in the spring in the east was greater than in the west, changes in the autumn in the west was greater than in the east. In particular, special autumn drought in the west was more than in the mid-east. summer drought and flood climate of Keerqinzuoyi Banner changed greatly,and drought and waterlogging appeared frequent,the normal summers were relatively few; and summer droughts and floods climate change in the Horqin district in Tongliao City is relatively small,with more normal summers.(5)The cluster analysis on droughts/floods changes in three seasons-spring, summer and autumn- revealed that frequencies of relatively moist (or relatively dry) and the special flood (or special drought frequencies) in summer in the central area is simultaneously or similar to that in spring in the west, and appearance frequencies are opposite in other seasons or in different regions in the same season.This shows that we should prevent not only flooding (or drought) disasters in the study area but also the accidental special drought(or deliberate logging).