This article is devoted to the use of a mathematical model of a flood runoff for calculating rainfall runoff hydrographs from small catchments of the northwest coast of the Black Sea. The described model was tested and applied for the following catchments located in various geographical conditions, with various amounts of initial data: experimental catchments in Zacarpathian, the northwest of the Black Sea region – Ukraine and the Republic of Moldova, small catchments of the northern part of Vietnam, etc. This work was carried out on the basis of Moldavian Water-Balance Station databases. The development of a complex approach to a mathematical simulation of the formation of the processes of rain floods from small catchments is also given further investigation in this article. A brief description of the structure of a flood runoff spatial model from small catchments then provided. As well as this, the advantages of using radiolocation measurement of rainfall in the mathematical modeling of the formation of a flood runoff are shown. The results of construction runoff hydrographs confirm the possibility of applying this spatial model with the use of radar information. The optimization of model parameters was made with the data of 123 floods. The values of the quality criterion S/σ turned out not to exceed the value 0.8 in 81% of the considered cases of floods.