Research On Precipitation Concentration Degree And Drought And Flood Of Summer And Annual

It is necessary to research the precipitation concentration degree, because the precipitation concentration degree is closely related to the severe drought and flood. The most visable tool is the PCD, which can be an uantitative characterization to research the intra-seasonal heterogeneity of the precipitation in time and space.However, it may not be able to exactly reflect the precipitation concentration degree under certain conditions. So based on the theory of information entropy,we propose a new method Q to research the precipitation concentration degree. The Q values between 0-1, the larger value means that the precipitation is concentrated and the less value means the contrary. When the Q is close to 1, it is possible to lead to flooding or drought, regardless of the more or less precipitation. But when the Q is close to 0, the precipitation is very average, then the probability of disaster is relative low.During the calculation of the new method Q, the daily precipitation is turned into the contribution rate of precipitation, thereby eliminates the effects of the total amount of precipitation. In fact, the total precipitation is an important factor to the severe disaster.so a new flood and drought index W has been proposed for characterization of drought and flood by combining Q with precipitation intensity INT. The larger value means that the probability of disaster is relative large.In order to research the drought and flood, the onset, duration and intensity of drought and flood, and require droughts be monitored at a daily to weekly scale. However, previous tools cannot monitor drought and flood well at short timescale. The weighted average of precipitation (WAP) do not require a timescale, can provide the drought and flood extent of each day, and can monitor drought and flood at scales from daily to weekly, monthly, and any longer scale, and is really "flexible and versatile for all timescales". The standardized WAP (SWAP) can also work rather well in monitoring the flood, and can provide the details of the drought and flood,such as when the drought emerged over the region, how long it maintained there.Based on the daily precipitation data from 553 stations in China during 1961-2010, the intra-seasonal heterogeneity of the precipitation in summer and annual over China were analyzed, the precipitation concentration degree, flood and drought of the middle and lower reaches of the Yangtze River were also researched, besides the standardized WAP (SWAP) is used to monitor the severe drought and flood of 1994 and 1999 over China, by using precipitation concentration degree(PCD), the new method Q, the flood and drought index W and the standardized WAP. we obtain the following conclusions:(1) The precipitation is relatively concentrated in the most of northwest China, dispersed in southwest and the middle of northwest China. The precipitation is integrally not concentrated in east,while is relatively concentrated in the middle and lower reaches of the Yellow River. The precipitation trends to disperse in the western Xinjiang and Tibet、the middle of northwest China and the southeast coast. The precipitation trends to be more concentrated in north China and the most of northeast by the method Q, while PCD is on the contrary.(2) The average value of the flood and drought index W in summer is 1.06, W in west China is so small that the probability of the floods is relatively low, the value of W in the reaches of Yellow River, middle and lower reaches of the Yangtze River and south China is so large that the probability of the floods is relatively high. Flood or drought is more frequent in part of Tibet and Qinghai Province、Yangtze River and Yellow River while the interannual variation of W is relatively small. In most part of China, W trends to be more concentrated. In addition, the index W has significant 2-3 and 7-8 years periodical oscillation.(3) The precipitation is relatively concentrated in the west of the middle and lower reaches of the Yangtze River, and dispersed in the southeast, when in summer, the precipitation is relatively concentrated in the north of the middle and lower reaches of the Yangtze River, especially the Anhui and Jiangsu province. Winter or summer, the precipitation trends to disperse in most parts of country. The value of W in the reaches of Anhui, north of Jiangsu and Hubei is so large that the probability of the floods is relatively high, while the value of W is low in Yangtze River Delta. In most part of China, W trends to be more dispersed. In addition, the probability of flood is more likely.(4) The standardized WAP (SWAP) can also work rather well in monitoring the flood, and can provide the details of the drought and flood,such as when the drought emerged over the regionIn summer of 1994, originally there is no obvious drought or flood in Jianghuai river, flood in south of the Yangtze river, and drought in north China and northeast China. In July, drought occurred in Jianghuai river, rainfall and flood decayed in north China and south China. In August, the obvious feature that "north and south flood, Yangtze-Huaihe river basin drought" occurred, and maintain until mid to late August.The obvious feature that "north drought, south flood" in summer of 1999 began to show gradually in July. Bounded by the Yangtze river, the severe drought occured over north China and northeast China, the severe flood occured over Jianghuai and south China. Then the extent of drought and flood changed to varying degrees. In late August, the future is most obvious. In mid September, the extent began to diminish, and disappeared until October.