Spatial and temporal variation of monthly rainfall nonuniformity of the upper Yangtze basin

Apportionment entropy, defined by Shannon´s information entropy theory, was applied to analyze the monthly rainfall nonuniformity of the upper Yangtze basin within a year. The spatial variability analysis indicates that the intra-annual monthly apportionment of rainfall is relatively even in Wu sub-basin, while rainfall is relatively aggregate in the lower Jinsha sub-basin and the middle Jialing sub-basin. In temporal domain, the Mann-Kendall method was applied to analyze the change trend of the intra-annual nonuniformity. For 17 meteorological stations, the intra-annual monthly apportionment of rainfall trended to evenness, while that trended to aggregate for only 2 meteorological stations. For the other 29 meteorological stations, no significant change trend of the intra-annual monthly rainfall nonuniformity was observed.