Abstract: By taking account of the climatic characteristics in different regions, in this study the comentropy method was used to obtain the zonal precipitation at two intrinsic scales, i.e. the homogeneous state intrinsic scale and variational state intrinsic scale, and a new meteorological drought index named MSPI was developed. The mutual information method was used to divide the drought ranks based on set of critical points for MSPI series at all 2 211 stations in China and get the standards of different drought and flood ranks, because this set of critical points was optimal when the mutual information between the MSPI series and the rank order reached their maximum. The MSPI series was divided into 9 ranks, i. e. the “extremely severe drought, severe drought, moderate drought, slight drought, normal situation, slight rainy, moderate rainy, severe rainy and extremely severe rainy”. On which the percentages of monthly days and stations at different drought ranks were calculated, the spatial distribution of the ratio of days at moderate, severe and extremely severe drought ranks at all the stations in different seasons during the period from 1981 to 2010 was analyzed, and the anomaly percentages of precipitation for  alleviating drought were estimated. The occurrence, development, duration and alleviation of severe meteorological drought in the middle and lower reaches of the Changjiang River in 2011 were discussed, and a case study on moderate or more severe drought events in Shanxi Province during the period from 1981 to 2010 was carried out based on MSPI so as to examine the capability of MSPI in monitoring meteorological drought. The result shows that MSPI can be used to monitor meteorological drought at different ranks, and it can also be used to perfectly develop the meteorological drought process.  

Key words: standardized precipitation index, precipitation, comentropy, intrinsic scale, drought index, drought classification