CHARM is the hydrological modeling component in WATFLOOD. CHARM is supported by a number of pre and post processors in the data management system. CHARM was designed for distributed modelling using remotely sensed data, particularly from remotely sensed land cover maps and weather radar. To efficiently interface with such data, WATFLOOD/CHARM uses gridded modelling system, usually aligned with the local UTM system or lat-long coordinates with variable areas. It can therefore easily accommodate any georeferenced imagery, be connected to a GIS for input and output, and can be setup for any appropriate resolution.

Data Requirements

Compared to other hydrological modelling systems, WATFLOOD can be considered as a data intensive system. The initial development stages of the system (1972-75) coincided with the advent of remotely sensed data to provide land cover and meteorological data. It was immediately apparent that such data could enhance hydrological modelling but the models that existed at the time could not be easily adapted to take advantage of the high spatial and temporal resolution. From the onset, WATFLOOD was designed to incorporate the remotely sensed data in an efficient manner. This led to the gridded format of all data used by WATFLOOD, including discretization of the watershed itself. Thus in WATFLOOD, each "sub watershed" or grid cell is more-or-less the same size. Exceptions occur along basin and sub- basin boundaries to ensure drainage areas at streamflow gauges are preserved.