Individual morphometric characteristics of river basins significantly impact their activity; they affect the flow rate of water, water accumulation in the river basin, water runoff time and other attributes that affect their intensity during flash floods and hydrological droughts. The aim of the paper is to express the risk and impact of flash floods in the Topla River basin (Slovakia) and its sub-basins with regard to the morphometric characteristics of the area. The studied locality, especially the spring of the Topla river, belongs to the area with an existing, potentially significant flood risk threatening not only important localities but also the population. The objective is to support the territories with flood mitigation measures by assessing the basin morphometric factors and classifying such areas into high, medium and low-risk categories of flash floods. The model situation is developed in the ArcGIS program, where the selected important morphological characteristics are assigned to all sub-basins for the Topla river together with its assessment. For each characteristic, the level of risk affecting the flash flood is determined. An important part of this study is developing a river basin susceptibility scale to flood activity in terms of morphometric characteristics obtained from available literature, empirical relationships and human experiences. The result of the sensitivity risk map of the upper part of the Topla river basin is to show where adverse impacts on people and the surrounding environment are expected after flash floods hit (or in the event of hydrological droughts).