Abstract: In order to mitigate the flooding disasters induced by severe rainfall over mountain regions,it is very important to estimate the water collection amount. However,in arid mountain regions,meteorological and hydrological stations are usually scarce and unevenly distributed,leading to difficulties in the estimation of this parameter. In such cases,a reasonable estimation of the areal rainfall is necessary and offers the initial conditions for driving hydrological models. In this paper,we studied an extreme rainfall event that occurred in Hami City,Xinjiang,China on July 31,2018 and that resulted in the break of a local dam. The northeastern part of Hami corresponds to the easternmost area of the Tianshan Mountains. This area is characterized by very hot summers and an annual mean precipitation of 43–118 mm. Due to a lack of vegetation,flooding disasters occur frequently along the hilly southern slope of this area;nevertheless,local meteorological and hydrological stations are rare. On July 31,2018,from midnight to 13：00,an extreme rainfall event occurred over northeastern Hami and led to a severe flood. This caused the break of the Sheyuegou Reservoir and,consequently,the death of many people. In this paper,the areal rainfall,water collection amount,and breaking process of the local dam were objectively evaluated. In order to obtain a reasonable estimation of the areal rainfall,three interpolation methods were applied to the meteorological station data,together with a multi-source fusion data reanalysis. Overall,the four estimation methods demonstrated correlations between 0.76–0.97;notably,the best estimation was given by the multi-source fusion data reanalysis. The estimated areal rainfall was then used to drive the FloodArea Model,obtaining the water collection amount for the upper reach of the Sheyuegou Reservoir：the values varied between 1.471×10⁷ m³ and 2.892×10⁷ m³. The water collection amount obtained by using the CMPAS areal rainfall was further compared with the results of a post-disaster investigation on the dam breaking process. The calculated hourly water collection amount and the flood peak flow were in good agreement with the results of the post-disaster investigation. In particular,the flood peak flow was 1.756 × 10³ m³·s^-1 （very similar to that derived from hydrological observations）,while the total flood charge was 2.639×10⁷ m³ （much higher that the flood control and spillway carrying capacities of the reservoir）.

Key words: heavy rain, areal rainfall, water-collecting amount, Floodarea, Hami City