Flood website: Indication of
forecasts have certain accuracy, of course. No forecast can be exact given
the uncertainties in location and in the parameters that are needed as
inputs. Furthermore, the hydrological and hydrodynamic models that are used
for the MRC flood forecast are by definition a simplified representation of
the real world. Given these considerations, and the fact that rainfall
predictions are notoriously uncertain, it is unrealistic to expect 100%
accuracy. Still, it is very useful to have an idea of the errors.
easily be understood that the accuracy is higher if the rainfall forecast
and the other daily input parameters (primarily water levels to determine
river flow) are more certain.
This means that forecasts that look further
ahead depend on forecasts that are less certain. Also, the impact of a given
river flow at an upstream station becomes less significant the further it
travels downstream, because (uncertain) river flows of tributaries join the
mainstream. Finally, if we move upstream, we have less upstream river
monitoring stations, adding to the uncertainty. Overall measurement and
other errors should be considered too.
The conclusion is that the MRC Mekong
Flood Forecast is in general more accurate for downstream locations, while
it becomes less accurate if we look further ahead.
discussion of uncertainties may give the impression that the forecast is not
very useful. Still, the forecasts are actually rather accurate, considering.
However, the final judge of the usefulness is the user. If the user demands
10 cm accuracy with 5 days lead time the RFMMC nor anyone else can help him
for most of the stations; if the user needs to know if the water level is
going to reach the flood level within three days with an uncertainty of 25
to 50 cm the product is useful in all but 5 of the forecast locations.
Typically, a user of flood forecast information will also accept a larger
margin of error more upstream because the maximum rise rate of the Mekong is
indication of the accuracy is given in the figure on this page. The graph
uses the mean absolute error of the MRC Mekong Flood Forecasting System,
based on the 2008 data and the configuration for the 2009 flood season.
actual flood forecast these values are further adjusted by the
Forecaster-In-Charge using knowledge of bias and system behavior, and of
weather patterns and specifics of the input data. This usually improves the
future the performance of the MRC Mekong FFS will be measured against a set
of performance indicators that is established by combining international
standards and the specific circumstances in the Mekong River Basin.
note that the flood levels used in the flood forecast are determined by the
member states. The definition of flood level is thus depending on national
standards; usually it indicates the level where the local or national
authorities need to take urgent measures to prevent significant damage.
Alarm stage is defined by the MRC as the level where flood stage is
predicted within the next three days. Alarm level is defined by the member
states and is mentioned as reference.