Presenter
Prof. Yangwen Jia
Co-author(s)
Prof. Cunwen Niu, Dr. Cunfeng Hao, Dr. Junkai Du, Prof. Jiajia Liu
Organisation
State Key Laboratory of Simulation and Regulation of Water Cycle in River Basin, China Institute of Water Resources and Hydropower Research (IWHR)
Sub-theme
3. Building Resilience for Disaster Prevention and Mitigation
Topic
3-5. Monitoring and early warning of water-related disasters
Body
Disasters caused by flash floods in medium and small watersheds are dominant (over 70%) in the flood disasters in China. However, simulation and forecast accuracy of flash floods is still not high, and early warning is quite difficult. One of key scientific issues behind the problem is the impact mechanism of soil moisture re-distribution on runoff generation in hillslopes. Specifically speaking, the rainfall-runoff generation from hillslope top to hillslope waist to hillslope toe is not a simple "infiltration-excess runoff generation" mode or "saturation-excess runoff generation" mode, but is a compound runoff generation mode caused by two-dimensional soil water movement under the control of many factors like terrain, soil and vegetation etc. However, the most of current hydrological and flash flood models use one-dimensional vertical conceptual models, such as rainfall-infiltration model or water storage capacity curve, thus cannot scientifically depict the compound runoff generation mechanism, quantitatively depict the terrain effect in hillslopes and accurately calculate the scale and process of mountain torrents due to the comprehensive impact of underlying surface and meteorological factors. In addition, distributed hydrological model technology and data fusion technology of multi-source such as remote sensing and ground observation need to be used jointly to extend the foresight period of hydrological and flash flood forecast and early warning. Aiming at the key scientific issue of impact mechanism of soil moisture re-distribution on runoff generation in hillslopes, a typical small watershed in Sichuan province is selected to carry out the observation and analysis of rainfall-runoff-soil moisture-evapotranspiration in hillslopes, to quantitively depict the soil moisture re-distribution effects to hillslope runoff-generation due to the roles of topography and soil-vegetation changes. Based on the multi-layer Green-Ampt infiltration model and two-dimensional saturated soil water simulation, the mode of variable source area and compound runoff-generation in hillslopes are studied, a distributed flash flood model is developed and validated in the case study watershed, and the quantitative factors and early warning thresholds of flash flood under the combined influence of climate and landform are put forward. This study may form a basic support for simulation and early warning of flash flood based on "scientific mechanism - mode cognition - model tool - comprehensive thresholds".