The colours green, yellow, orange and red are used in reports, graphs and symbols to indicate the severity of a situation. As described in the key, these colours stand for normal, pre-alert, alert and alarm respectively. The exact description of the alarm thresholds depends on the theme and the location concerned. A flood alarm is always defined differently from a drought alarm.
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The following definition applies for high water levels:
| Status |
Description |
| Normal |
No flooding |
| Pre-alert |
Heightened vigilance, no flooding |
| Alert |
Particularly heightened vigilance, non-critical flooding possible |
| Alarm |
Maximum vigilance, critical flooding possible |
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Measured and forecasted precipitation is shown on the map using different coloured zones and symbols.
| Colour |
|
Description |
| |
|
0 - 0,5 mm |
| |
|
0,5 - 1 mm |
| |
|
1 - 10 mm |
| |
|
10 - 25 mm |
| |
|
25 - 50 mm |
| |
|
50 - 75 mm |
| |
|
Meer dan 75 mm |
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The Drought theme has two colour codes. The "low flow status" which is calculated for both navigable and unnavigable watercourses, is a hydrologic indicator based on discharge in the watercourse. The "Standardized Precipitation Index" is a purely meteorological index which only takes into account precipitation.
Low flow status
The low flow status for watercourses is calculated based on the average discharge in the last number of days to avoid fluctuations. For navigable waterways, 7 days average discharge is used, for unnavigable waterways, 14 days average discharge.
These values are being compared to percentiles.
| |
Time period for which average is calculated |
Treshold |
Assessment of tresholds |
| Waterways |
Previous 7 days |
P1, P5, P10 |
Varying daily throughout the year, based on 30 years |
| Unnavigable watercourses |
Previous 14 days |
P2, P5, P10 |
1 treshold throughout the year |
Standardized Precipitation Index
The “Standardised Precipitation Index” (SPI) indicators with accumulation periods of 1 month (SPI-1) and 3 months (SPI-3) indicate how dry or how wet the past month (SPI-1) and past three months (SPI-3) were as compared to the same period of the year over the past 30 years in Uccle. SPI-1, therefore, represents the short-term situation, whereas SPI-3 represents the longer term situation (a season). In this table, the colours are explained.
| Status |
Description |
| Extremely wet |
SPI > 2 |
| Very wet |
1,5 < SPI < 2 |
| Moderately wet |
1 < SPI < 1,5 |
| Normal |
-1 < SPI < 1 |
| Moderately dry |
-1 < SPI < -1,5 |
| Very dry |
-1,5 < SPI < -2 |
| Extremely dry |
SPI < -2 |
| No data |
No data |
| Old value |
Old value |
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