Application of remote sensing technology to flood forecasting in

ungauged basin

Li Jiren Xin Jinfeng

China Institute of Water Resources and Hydropower Research

Content 1) Definition of ungauged basin and its difficulty for real-time flood forecasting 2) Input and state variables in watershed hydrological model 3) Importance of real-time flood forecasting or warning for ungauged mountainous basin 4) What can be provided by remote sensing 5) Practical examples

• Data needed for watershed precipitation-runoff model for real-time flood forecasting through traditional way:

• Input: Basin area, precipitation, discharge, water level together with relation curve between discharge and water level, evaporation, discharge released from large-and-middle scale water works

• Initial condition for state variable: soil moisture content, discharge for each sub-reach

Ungauged basin No data or lack of observed hydrological data Typical case: no observed discharge data At present, discharges released from large-and-middle scale water works become very important because a lot of reservoirs have been constructed and control a high percentage of runoff.

Difficulty for real-time flood forecasting in ungauged basin is mainly that of parameter calibration and validation. Usually the parameters are misappropriated from other hydrological similar basin with similar soil type, base rock, vegetal cover, topography, land use, catchment area and so on.

In china, more than 90% of the people died in flood is in case of flash flood occurred in mountainous area with high and earlier peak. Flood forecasting or warning is the most important, but usually these mountainous area are ungauged and small basins, with the watershed area between 20- 200 km2. the flood process lasts only several hours. Small plus ungauged, increasing the difficulty for real-time forecasting or warning in this kind of important area.

What can be provided by remote sensing for real-time forecasting in ungauged area? Input: Watershed area, Precipitation by Doppler radar Evapotranspiration DEM is used for sub-basin division, flow concentration route and slope, geomorphological unit hydrograph, characteristic reach length used for flood routing in river channel. State variables: soil moisture content

Some parameters with physical meaning can be directly determined by underlying factors such as soil and rock property, non-uniformity of topography, river length, slope.

Example: Sharp River, a branch of the Yangtze River, located in the Xianning County Watershed area: 112km2

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