Relationship Between Atmospheric Water Vapor And Drought-Flood In China

In the context of global warming, drought and flooding disaster frequently occured caused serious economic damage to our country. Drought-flood conditions in one area had a direct relationship with water condition in the atmospheric, which included two aspects:water vapor content and water vapor transfer. Water vapor content in the atmospheric can also be called precipitable water. Based on precipitable water, wind and humidity data from reanalysis data, the relationship between atmospheric water vapor and drought-flood in China were researched. Firstly, by means of four reanalysis data, the relationship between precipitable water and surface vapor pressure in various latitudes and the reliability of the interdecadal characteristics of the precipitable water were validated; Secondly, based on wind and moisture from daily and monthly ERA-40 reanalysis data, the climatology and interdecadal change of vertical integrated moisture flux and diversity were analyzed in mean circulation transport, eddy transport and total transport. Finally, the anomalous vapor transportation in the past thirteen years was researched, the transportation of water vapor in southwest China from September to December in 2009 was analysised specifically. The mainly conclusions were as follows:Compared the empirical regressions between precipitable water and surface vapor pressure from the ERA-40,JRA-25, NCEP/NCAR and NCEP/DOE reanalysis data, the precipitable water were more credible at mid-latitude regions. In China area, the ERA-40 reanalysis data of precipitable water was the most reliable, and can be used as instead of sounding data. Evaluated the reliability of the interdecadal characteristics of the precipitable water from four kinds of reanalysis data, It was founded that the interdecadal change of the precipitable water from ERA-40 was the most consistent with the fact, so it was the best choice for researching the interdecadal change of moisture content of the atmosphere. In the greater part of China, the annual average of precipitable water decreased continuing during the late 1950s to the late 1980s, but it increased since the early 1990's. In south, southwest and northwest of China, the precipitable water showed the same trend as the temperature, but different in the lower and middle Yangzi valley and north of China. For the precipitable water, temperature may not prove decisive.From the view of climatological state, the zonal transport was dominant in mean circulation moisture transport, but in eddy moisture transport, the meridional transport was noticeable, the total moisture transport was consistent with the mean circulation moisture transport. There were mean circulation moisture divergence and eddy moisture convergence in the north of China, on the contrary, mean circulation moisture convergence and eddy moisture divergence in the south of China. The area of convergence and divergence in total moisture transport were similar with that in mean circulation moisture transport.After the late 1970's, accompanied with mean circulation moisture divergence and eddy moisture convergence, there existed interdecadal change of anti-cyclone form of mean circulation moisture transport and remarkable southerly eddy moisture transport in North China. In the middle and lower reaches of the Yangtze River, easterly and southerly mean circulation moisture transport and easterly eddy moisture transport turned up, which caused mean circulation moisture convergence and eddy moisture divergence. The moisture convergence in eddy and mean circulation moisture transport had the same magnitude, but smaller in value. In North China, the drought frequently increased because the total moisture diverged and the rainfall declined; in the middle and lower reaches of the Yangtze River, the flood disaster frequently increased because the total moisture converged and the rainfall enhanced. The convergence and divergence in eddy moisture transport played an important role in alleviating drought and flood.In recent decades, anticyclonic departure of mean circulation transport and southeasterly eddy transport appeared over north east and North China, which led to mean circulation moisture divergence, eddy moisture convergence and total moisture divergence. These were helpful to increase the intensity and frequency of drought in north east and North China. With the departure of west mean circulation transport and the convergence of eddy transport which from southeast and northwest, there were mean circulation moisture divergence and eddy moisture convergence in Haihe river basin. The notable eddy moisture convergence caused waterlogging in Haihe river basin.Severe drought took place in south-west region of China from September to December in 2009. The higher geopotential height existed in middle latitudes and the water vapor come from the Bay of Bengal drastically reduced. Severe drought in autumn caused of the reducing of water vapor transportation. In December, there was increased water vapor transportation in southwest China, but the low pressure located in the lake Baikal developed obviously, which make cold air shifted eastward and northward, the convergence of cold and warm air and rainfall can't happen easily. The severe drought in December was largely the result of abnormal cold air.