|Full text PDF:||http://hdl.handle.net/11858/00-1735-0000-0028-86F0-F|
Water-induced soil erosion (WSE) is a main factor of land degradation in many parts of the world and reported as a main threat to agriculture compared to the second largest risk by wind. Some parts of Vietnam have been suffering WSE rates of over 50 t ha year−1 (t ha−1 y−1), (particularly in the North) which has negative effects on the agriculture. In addition, Vietnam is a developing country and most of the resident livelihoods are based on agriculture. However, due to a lack of information about both spatial and rates of WSE in the region, the soil erosion mitigation efforts seem to be inadequate. Furthermore, far too little attention has been paid to soil erosion modelling in the tropics in general and in the North of Vietnam in particular. In the first part of this research, surface runoff investigation and WSE evaluation were targeted employing the hydrological modelling methodology and the so-called “regionalization approach” for generating the results of calibrated watersheds to uncalibrated ones. This makes a regional scale (for the SWAT application) from watershed scale. The KINEROS2 model was also used for modelling WSE at finer event-based and watershed scale. In the results of model calibration and validation, both the SWAT and KINEROS2 presented their capabilities to generate simulated discharge matching closely to observed data. Although the mean estimated WSE rate was 4.1 t ha−1 y−1, approximately 15% of the Yen Bai province was computed at the rate of 8.5 t ha−1 y−1. Attention was given to the changes in land use/land cover (LULC) conditions (2002-2009) which have had a growth of the WSE rate from 0.2 to 3.3 t ha−1 y−1 in some areas of the province. This scenario was also found in the results of the KINEROS2 model but for the LULC conditions in 2002 and 2007.The KINEROS2 parameter sensitivity tests indicated that the model’s outputs were very sensitive to the antecedent soil moisture condition (θant) and the hydraulic conductivity (Ksat). This reveals a need of estimates θant for later applications of the model such as for flash flood (FF) prediction. Flash flooding is responsible for severe loss of life and property in lots of countries. Increases of the surface runoff not only speed up the erosive processes, but also intensify the FF risk. Many parts of Vietnam have been confronted with increasing FF consequences but the situation is much worse in northern Vietnam. Due to the fact that FF often occur in small streams and are linked to short, but heavy rains, much previous research has suggested methods to identify FF occurrences early in order to mitigate their impacts. Approaches with assembled and coupling hydrological models were used for the aim of FF prediction. The assembly of the SWAT, BEACH and KINEROS2 models filled up the hole of lacking θant and defined well the boundary conditions for the KINEROS2’s runs. The model sensitivity tests played a crucial role due to its shortening the model calibration and validation processes. To implement the latter method, the… Advisors/Committee Members: Kappas, Martin (advisor), Kappas, Martin (referee), Mitlöhner, Ralph (referee).