Adaptability Of The CI And SPEI Indexes Over The Middle And Lower Reaches Of Yangtze River Basin

Due to the deficiencies of the CI for monitoring the droughts and floods in the middle and lower reach of Yangtze River(YZR), the improved CI index was designed, by using a simple water balance model to weight the daily precipitation in the standardized precipitation index and optimizing the relative moisture index. Using the 1964 to 2013 of 164 stations meteorological observational data in YZR, the applicability of the improved CI index and SPEI index in region of YZR was assessed. The results show that:(1) the improved CI index with more reasonable physical meaning could reflect the start and end time, and processes in strength of droughts more accurately, especially the rapid shift between drought and flood in YZR.(2) The multi-time scales CI indexes are significantly positively correlated to SPEI indexes with the correlation coefficient of more than 0.8, which indicating that the multi-time scales CI indexes have a better assessment for the droughts in YZR. Compare to the SPEI, the monthly CI index has a better applicability in Jiangsu and Anhui provinces in all year, and in Hunan, Jiangxi and Hubei provinces from October to April.(3) The three-monthly and six-monthly CI indexes have better applicability in the area of Jianghuai. In the Jiangnan and Yanjiang regions the three-monthly and six-monthly CI indexes have better effect in the period of raining seaon, and in the drought monitoring the three-monthly and six-monthly CI indexes exsit too wet problems in the period of less raining seaon. With the time scales longer the problems reduced. The 12-monthly CI index has a good application in the whole region.In YZR drought has its remarkable characteristic, the improved CI index has brought a good prospect for the drought analysis, monitoring, forecast and warning in YZR. The results of adaptability give good guidelines in the drought monitoring and assement.