Volumetric soil water content references to the volume of water reported to the volume of soil expressed as m³/m³. Volumetric soil water content is calculated using the next formula : VWC=SWI*[(1-(ρb/ρs))-θr]+θr (Mladenova et all., 2010 ) where:
-SWI is Soil Water Index
-ρb is soil bulk density
-ρs is mean density of soil particles as a constant of 2.65 g/cm³
-θr is the residual SM being calculated as the average of the minimum SM values recorded at the in situ stations, calculated as a value of 0.04 m³/m³
Soil Water Index quantifies the moisture condition at various depths in the soil(https://land.copernicus.eu/global/products/swi). Recognized up to 5cm as a Essential Climate Variable by Global Climate Observing System, soil moisture is an important parameter derived from satellite sensors, especially activate radar missions. With a 1km spatial resolution, resulted as a combination of Metop ASCAT surface soil moisture (SSM) and Sentinel 1 C-band SAR SSM products, SWI covers Europe with a daily temporal resolution. The dataset can be found at Copernicus Global Land Service (https://land.copernicus.eu/global/products/swi).
ρb is the Soil Bulk Density (SBD) which represents an indicator of soil compaction and it is calculated as the dry weight of soil divided by its volume. SBD was downloaded from Google Earth Engine catalog at 5 depth levels (0, 10, 30, 60,100 cm) and is a part of OpenLandMap project (Tomislva Hengl, 2018). Since the SWI is at the 2, 5, 10, 20, 40, 60 and 100 cm depth and the SBD is at 0, 10, 30, 60, 100 the soil bulk density was used as it follows:
-SBD at a depth 0 cm with SWI at depth 2 and 5 cm
-SBD at a depth 10 cm with SWI at 10 and 20 cm
-SBD at a depth 30 cm with SWI at 40 cm
-SBD at a depth of 60 and 100 cm with SWI at 60 and 100 cm
The decision was based on the fact that bulk density increases with soil depth and those depths were the closest one, excluding any mediation between the before and after depths.
Sources:
1. Mladenova, I.; Lakshmi, V.; Walker, J.P.; Panciera, R.; Wagner, W.; Doubkova, M. Validation of the ASAR Global Monitoring ModeSoil Moisture Product Using the NAFE’05 Data Set. IEEE Trans. Geosci. Remote Sens. 2010, 48, 2498–2508
2. Tomislav Hengl. Soil bulk density (fine earth) 10 x kg / m-cubic at 6 standard depths (0, 10, 30, 60, 100 and 200 cm) at 250 m resolution (Version v02) [Data set], 2018, Zenodo. 10.5281/zenodo.1475970
©The data is under copyright of Copernicus Programme of the European Commision. The data is downloaded through Copernicus Global Land Monitoring Service and MeteoRomania is not responsible for any errors in raw data that could affect the processing workflow.