| Name: | soil_moisture | Abbreviation: | sm | Unit: | kg m-3 |
| Definition | The volumetric soil moisture on the top 20cm of the soil layer. |
| Validity | instantaneous |
| Comment | To interpret 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. |
| GRIB 2 |
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Comments
| Author | Contents |
|---|---|
| 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. |