Nguyen Khanh Van – Institute of Geography, Vietnam Academy of Science and Technology, Hanoi;
Pham Hoang Hai – Institute of Geography, Vietnam Academy of Science and Technology, Hanoi;
Hoang Bac – Institute of Geography, Vietnam Academy of Science and Technology, Hanoi.
The characteristics of heavy and very heavy rains in the Huong River catchment and influence on their origin different weather types and topomorphological factors are considered in the paper. During 1987-2006 the Huong River catchment had 111 phases of the heavy and very heavy rains. The heavy and very heavy rains may occur from March to December, but the most of them occur in the rainy season – from September to December. There are four weather types that cause heavy rain with high frequency. Morphological characteristics of terrain of the catchment (mainstream system of mountains, degree of deep split, degree of horizontal separation, slope direction, etc.), had certain influence to the frequency of the heavy rain and they formed the centers of high rainfall there. Initially identified some areas could often have heavy rainfall due to interaction of topography with the operation of the rain-causing agents in the cold air mass - the northeast monsoon. As the result the Huong River catchment is one of the rainfall regions in Vietnam, where large floods are often happened.