ESA CCI SM RZSM Long-term Climate Data Record of Root-Zone Soil Moisture from merged multi-satellite observations

This dataset was produced with funding from the European Space Agency (ESA) Climate Change Initiative (CCI) Plus Soil Moisture Project (CCN 3 to ESRIN Contract No: 4000126684/19/I-NB "ESA CCI+ Phase 1 New R&D on CCI ECVS Soil Moisture").  Project website: https://climate.esa.int/en/projects/soil-moisture/

This dataset contains information on the Root Zone Soil Moisture (RZSM) content derived from satellite observations in the microwave domain.

The operational (ACTIVE, PASSIVE, COMBINED) ESA CCI SM products are available at https://catalogue.ceda.ac.uk/uuid/c256fcfeef24460ca6eb14bf0fe09572/ (Dorigo et al., 2017; Gruber et al., 2019; Preimesberger et al., 2021).

Soil moisture is a key variable in monitoring climate and an important component of the hydrological, carbon, and energy cycles. Satellite products ameliorate the sparsity of field measurements but are inherently limited to observing the near-surface layer, while water available in the unobserved root-zone controls critical processes like plant water uptake and evapotranspiration. A variety of approaches exist for modelling root-zone soil moisture (RZSM), including approximating it from surface layer observations through an infiltration model (Pasik et al., 2023; Wagner et al., 1999, Albergel et al., 2008).

Here, we apply the method described by Pasik et al. (2023) to the COMBINED product of ESA CCI SM v9.2 to derive RZSM and uncertainty estimates in four depth layers of the soil (0-10, 10-40, 40-100, and 0-100 cm) over the period from January 1980 to December 2024 at ~25 km spatial sampling. In situ soil moisture measurements from the International Soil Moisture Network (Dorigo et al., 2021) were used for (global) T-parameter calibration and to quantify the (structural) model error component required to propagate surface measurement uncertainties to the root-zone layers. The 0-1 m layer is a (weighted) average of the other three layers. The dataset has been validated against ERA5 reanalysis RZSM fields, with global median correlations of ~0.6 [-] and ubRMSD <0.04 m³/m³.

Filename template

The dataset provides global daily estimates for the 1980-2024 period at 0.25° (~25 km) horizontal grid resolution. Daily images are grouped by year (YYYY), each subdirectory containing one netCDF image file for a specific day (DD) and month (MM) of that year in a 2-dimensional (longitude, latitude) grid system (CRS: WGS84). The file name follows the convention:

ESACCI-SOILMOISTURE-L3S-RZSMV-COMBINED-YYYYMMDD000000-fv09.2.nc

Data Variables

Each netCDF file contains 3 coordinate variables

• lon: longitude (WGS84), [-180,180] degree W/E
• lat: latitude (WGS84), [-90,90] degree N/S
• time: float, datetime encoded as "number of days since 1970-01-01 00:00:00 UTC"

 and the following data variables

• rzsm_1: (float) Volumetric Root Zone Soil Moisture at 0-10 cm depth
• rzsm_2: (float) Volumetric Root Zone Soil Moisture at 10-40 cm depth
• rzsm_3: (float) Volumetric Root Zone Soil Moisture at 40-100 cm depth
• rzsm_1m: (float) Root Zone Soil Moisture at 0-1 m
• uncertainty_1: (float) Volumetric Root Zone Soil Moisture uncertainty at 0-10 cm depth
• uncertainty_2: (float) Volumetric Root Zone Soil Moisture uncertainty at 0-10 cm depth
• uncertainty_3: (float) Volumetric Root Zone Soil Moisture uncertainty at 0-10 cm depth

Additional information for each variable are given in the netCDF attributes.