The Modification And Application Of Palmer Drought Severity Index In Middle And Lower Reaches Of Yangtze River Area

Drought is one of major agricultural meteorological disasters that occurs frequently and affects a wide area in China. Recently drought has an increasing trend in the south of China, Yangtze River region is a developed region as well as one of China’s major grain production bases, but droughts and floods caused huge economic losses. Therefore, accurate assessment of drought is necessary.Drought causes complex, in order to objectively assess and study drought events, it is required to develop or select the appropriate drought index. Palmer Drought Severity Index (PDSI) based on water balance principle is meaningful in physics. It could not only indicate the drought severity degree, but also when the drought would occur. But PDSI has strong spatial discontinuity. The Paper based on several early modified Palmer Drought Severity Models of China existing in the Yangtze River region’s problems, The conventional surface observations precipitation and temperature data of 90 stations were used as basic data (1961-2013) and the methods of choosing stations, calculating the potential evapotranspiration and available water capacity of the soil(AWC),correcting for K have been modified to establish the Palmer Drought Severity Index in middle and lower reaches of Yangtze River, with this modified index we have calculated the monthly drought index for 90 stations in the middle and lower reaches of Yangtze River area, we compare with the situation of drought and waterlog recorded in documents and analyze the characteristics of the drought.and detect the droughts,The main conclusions can be summarized as follows:1. It is found that the farther modified Palmer Drought Severity Model is distributed substantially between-4 to+4, according with the Palmer index dryness & wetness grade. It can reflect the severity of meteorological drought comparatively and be consistent with the actual onset time, duration time, the severity of droughts and floods and regions where droughts and floods occur, it is sensitive to droughts and floods.2. For drought assessment related to different scales, we calculate the Self-Calibrating Palmer Drought Severity Index in Yangtze River area, the study finds that the different scales of the SC-Palmer are more accurate evaluation of the results and they can well reflect the drought trend and be more accurately describe the facts besides that the monthly scale SC-Palmer droughts and floods has a low sensitivity.3. By analyzing the characteristics of the Yangtze River region drought, we find that:area of light drought occurs quite different depending on the month in the Yangtze River region and the higher frequency regions of light drought occurrence are in north of Hubei, the south of Hunan, the central and north of Jiangxi; Drought occurs mostly in summer and autumn and extreme drought occurs often in autumn; Drought often happens in west and north of Anhui, north of Zhejiang and northwest of Hunan in summer and autumn, extreme drought mostly happens in Fuyang. Ningguo, Hengyang, Chenzhou. Cixi, Dinghai and Badong in autumn.There are marked seasonal and interannual variation of drought, and decadal variation is obvious in Summer (from June to August). Summer PDSI index linear trend points that the drought in the Yangtze River region is weakened, and the PDSI index abrupt change occurs in the late 1960s, from 1960s to the 1970s is drought period, It becomes wet trend until the early 2000s and dry trend in the nearly 10 years. The seasonal drought index mainly have 2a,3-4a,8-10a of periodic oscillations in middle and lower reaches of Yangtze River area.4. Based on the modified Palmer Drought Severity Model, we use the precipitation, temperature and evaporation scroll to calculate daily PDSI index, the results show that daily PDSI index can accurately reflect drought trends and patterns, it can detect the occurrence, development and end of the drought and sensitivity is lower than CI.