Abstract: Flash flood is one of the most significant natural disasters in China, particularly in mountainous area, causing heavy economic damage and casualties of life. For numerous small hilly basins that need flash flood prevention and control with limited funds, it is necessary to give a priority order or to determine which basin needs to be harnessed firstly. Flash flood risk assessment is critical to an efficient flash flood management. Among many flash flood risk evaluation methods in literatures, variable fuzzy method (VFM) was chosen in this paper. To verify the results of VFM, fuzzy clustering analysis (FCA) is also used. First, taking Licheng county with 119 small basins in China as an example, 9 indexes were identified among index system, based on disaster-breeding environment (or underlying surface conditions) of small basin in hilly region. Risk levels are divided into three grading levels such as high, medium and low. Second, VFM was introduced, and the flash flood risk grade eigenvalue (H) of each small basin was calculated. The results show that no small basin belongs to high risk level, 14 basins belong to low risk level, and the remaining 105 small basins belong to medium risk level. Third, FCA was used to verify the result of VFM. The results of two methods show that they are nearly in consistence. This paper shows that VFM is feasible for flash flood risk evaluation. Finally, the priorities for flash flood mitigation of 119 small watersheds in Licheng county are mapped out, which will provide effective help for flood disaster mitigation of small basin.
