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Water In Ecosystems: A Non Renewable Resource
Table VII. Recommended accuracies (uncertainty levels) expressed at the 95 per cent
confidence interval for different variables * (from WMO guide to hydrological
practices ([46])).
Variable
Recommended accuracy
Precipitation (amount and form)
3-7%
Rainfall intensity
1 mmlh
Snow depth (point)
1 cm below 20 cm or 10%
above 20 cm
Water content of snow
2.5-10%
Evaporation (point)
2-5%,0.5 mm
Wind speed
0.5 rnIs
Water level
1O-20mm
Wave height
10%
Water depth
0.1 m, 2%
Width of water surface
0.5%
Velocity of flow
2.5%
Discharge
5%
Suspended sediment concentration
10%
Suspended sediment transport
10%
Bed-load transport
25%
Water temperature
0.1-0.5 0
Dissolved oxvgen (water temperature is more than 10 0 C)_ 3%
Turbidity
5-10%
Colour
5%
pH
0.05-0.1 pH unit
Electrical conductivity
5%
Ice thickness
1.2 cm, 5%
Ice coverage
5% for 20 kg/m 3
Soil moisture
I kg/m 3 20 kg/m 3
* NOTE: When a range of accuracy levels is recommended, the lower value is applicable to
measurements under relatively good conditions and the higher value is applicable to
measurements in a difficult situation.