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Soil moisture top 20 cm
Name: | soil_moisture top 20 cm | Abbreviation: | sm | Unit: | kg m-3 |
Definition | The volumetric soil moisture on the top 20cm of the soil layer. |
Validity | Daily averaged |
Comment | Computed from instantaneous values at 00. 06, 12 and 18Z To interprete soil moisture and to compare different models the Soil Wetness Index (SWI) is used:
SWI = (soil_moisture - wilting_point) / (field_capacity - wilting_point).
Field capacity corresponds to the maximum value that the model can sustain without precipitation for more than a few hours. The vegetated fraction of the soil evaporates at the maximum rate for soil moisture larger than field capacity and stops evaporating below the permanent wilting point, with a continuous variation between the two extremes. All Partners are asked to provide the wilting point and the field capacity for each grid point.Computed from instantaneous values
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Parameter |
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Discipline | = 2 | Land surface products |
Parameter Category | = 0 | Vegetation/biomass |
Parameter Number | = 22 | Soil Moisture
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Level |
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Type of first fixed surface | = 106 | Specified height level above ground m |
Scale factor of first fixed surface | = 0 | |
Scaled value of first fixed surface | = 0 | 0 |
Type of second fixed surface | = 106
| Missing |
Scale factor of second fixed surface | = 1
| |
Scaled value of second fixed surface | = 2
| 0.2 metre |
Comments:
Author | Contents | |
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Jörg Urban | The ECMWF runs a uniform soil scheme, where the wilting point = 170 kg/m**3, the field capacity = 320 kg/m**3 and the saturation = 470 kg/m**3 are globaly constant. Please note, using the GRIB 2 unit the three values read wilting point = 0.17, field capacity = 0.32 and saturation = 0.47. ECMWFs has four soil layers: layer 1 from 0cm to 7cm, layer 2 from 7cm to 28cm, layer 3 from 28cm to 1m and layer 4 from 1m to 2.89m. The parameter soil moisture is then computed: sm = ( 7 * Theta_1 + 13 * Theta_2 )/20, where Theta_i are the averaged volumetric soil moistures on the i-th level. Joint Meeting of CT-MTDCF/ET-DRC, Montreal, 8-12 May 2006: accepted parameter number 22. | |