Initial CAFFG Design
| The Central America
Flash Flood Guidance (CAFFG) component is designed to accommodate the
existing global digital spatial databases for Central America and also the
real time remotely-sensed and on-site precipitation and temperature
databases. The flow chart illustrates the flow of information through the
system models from the input hydrometeorological data to the computation
of flash flood guidance. The real time rainfall data pass through a
quality control model which identifies data with impossible values and
adjusts for biases in the remotely sensed data on the basis of real time
and daily on-site raingauge information. The result of this model is a
merged hourly rainfall product, estimated as a mean areal rainfall value
over small watersheds that cover the Central America region (area: 100-300
km2). A potential ET processor uses daily temperature and
climatological information on potential evapotranspiration (ET) to provide
daily potential ET input to the soil moisture model. The soil moisture
model runs on a daily or weekly basis depending on rainfall and potential
ET data availability, and determines the real time soil moisture
conditions to allow estimation of rainfall abstractions (such as actual ET
and deep groundwater flow) and of the volume of surface runoff.
Parametric databases for this model are computed from digital spatial data
of 1-km resolution terrain (TERRAIN), streams from global databases
(STREAMS), land–use and land-cover data (LULC), and soil texture (SOILS).
Threshold runoff (definition follows) is computed on the basis of
geomorphologic theory from watershed and land characteristics. Soil
moisture deficits and threshold runoff estimates are used in the flash
flood guidance model to produce the volume of rainfall of a given duration
that is just necessary to cause flooding in the small watersheds (flash
flood guidance). Threshold runoff is defined as the volume of effective rainfall of a given duration over the watershed of a small stream that is just enough to cause bankfull flow at the watershed outlet. It provides an estimate of the potential for excessive surface runoff of the small basins under soil saturation or land-surface impervious conditions. The term “effective” is used to denote the rainfall volume that remains after evapotranspiration and deep percolation abstractions, and which appears as surface runoff through the stream network. Threshold runoff is computed through geomorphologic theory and with the use of global digital terrain elevation, soils, and land use/land cover data (1-km resolution), along with regional stream data. Given these spatial databases in CAFFG, threshold runoff is produced for small watersheds on the order of 100-300 km2. |
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Hydrometeorological time series and parametric data are used by the soil moisture and flash flood guidance models in a manner coordinated by the CAFFG Model Process Core through a two-way interaction with the system Database (DB). The DB stores all parametric, historical and real-time data. This includes geometric, hydrologic and hydraulic parameters for small watersheds of area 100-300 km2 that cover the entire area of Central America (approximately 500,000 km2). The DB stores real-time hourly rainfall data together with daily and historical hydrometeorological data. The time series of raw hydrometeorological data undergoes pre-processing to remove erroneous values and any biases that may be present in the real-time satellite rainfall product. The mean areal rainfall and daily temperature products are stored in DB in the form of mean areal values for each small watershed. Periodic archival functions are engaged through an automated extract process to create regular system archives of data and products. The CAFFG Model Process Core uses the output of the soil moisture and flash flood guidance models to develop products and to make those available to the Dissemination process. System products and messages are defined in close collaboration with system users. |
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last updated: 02/19/2003
