2. WHAT ARE THE METHODS OF FLOOD
FORECASTING?
• Flood forecasting can be done using various methodologies, which can be
broadly categorized into physically-based models, data-driven models, or a
combination of both. The choice of the most suitable approach depends on
factors such as data availability, catchment characteristics, and desired
prediction accuracy.
3. SEASONAL FORECASTS ALERT OF A HEIGHTENED CHANCE
OF FLOODING IN THE COMING MONTHS
• The BoM regularly issues forecasts of rainfall and temperature for the coming
three months(external link). The prospect of a wet season would lead to an
increased chance of flooding, so forecasting seasonal rainfall can help alert us
of flood risk.
4. FORECASTING RIVER LEVELS AND FLOOD EXTENT IS
COMPLEX
• Flood forecasters rely heavily on real-time data about rainfall and river water
levels as well as rainfall forecasts. A network of rain gauges (sometimes
combined with radar images) are used to monitor rain that has fallen on the
catchment. Water levels (i.e. River height) at stream gauging stations along
the river are also measured. The forecasters then use hydrological computer
models to work out how much rainfall will run off different parts of the
catchment, how long it will take for runoff to reach the river, how long that
water will take to travel from upstream to downstream, and how water from
different tributaries converges in the river network.
5. WEATHER FORECASTS PROVIDE ADVANCE WARNING
OF A FLOOD
• Reliable forecasts of weather, in particular rainfall, can allow advance warning
and forecasting of floods. Weather forecasts for the next one to seven days
rely on increasingly accurate computer models of the atmosphere and
ocean/atmosphere interactions. Dramatic improvements in the data available
to such models (from satellite observations) and in computing power have
contributed to this increased accuracy.
6. FLOOD RECURRENCE INTERVAL
• Recurrence Interval: usually
measured in years. It is the average
interval between floods of a particular
size. Therefore, on average, a 100-year
flood will occur at regular intervals of
100 years. This means that a 100-year
flood size could not occur two years in
a row! It means that the chance of a
100-year flood occurring in any year is
1 in 100.
7. FLOOD FREQUENCY CURVE
A Flood Frequency Curve plots discharge, or in some
cases stage, against recurrence interval.
Recurrence intervals constructed from data obtained by
the gaging stations are used by planners in “floodplain
zoning”.
By understanding the size of floods in a given period of
time, the planners can estimate those parts of the
floodplain that are likely to be flooded, say, every 50 or
100 years. Zoning of parks, recreation areas, homes,
businesses, hospitals, etc., can then be made
accordingly.
