Worldwide Soil Moisture Levels from Remote Sensing Platforms (2000–2024): A Consistent Multidecadal Dataset

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Abstract
We introduce the Worldwide Soil Moisture Levels from Remote Sensing Platforms (2000–2024): A Consistent Multidecadal Dataset, a harmonized global record combining microwave‐derived surface soil moisture products from ESA’s CCI (Active, Passive, Combined) and NASA’s SMAP mission. Spanning January 2000 through December 2024, this open‐access dataset provides daily volumetric soil moisture (m³/m³) at 0.25° spatial resolution, complete with end‑to‑end uncertainty estimates.

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1. Introduction

Soil moisture is a key variable in the hydrological cycle, influencing drought assessment, flood forecasting, crop yield prediction and climate modeling. While single‐sensor records offer valuable snapshots, only multi‐sensor merging yields a temporally consistent, long‐term climate data record (climate.esa.int). By integrating ESA CCI v09.1 (1978–2023) with the SMAP passive radiometer (2015–2024), we extend high‐quality soil moisture estimates continuously from 2000 to 2024.

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2. Data Sources and Coverage

• ESA CCI Soil Moisture v09.1 (“Combined”): Merged Active and Passive microwaver measurements from scatterometers (e.g., ASCAT) and radiometers (e.g., AMSR‐E, SMOS), daily global coverage 0.25°, extended to December 2023 (climate.esa.int).
• NASA SMAP Passive Radiometer: L‑band brightness temperature observations converted to soil moisture every 2–3 days, covering April 2015–December 2024, with 36 km native resolution (regridded to 0.25°) (smap.jpl.nasa.gov).
• Temporal Span: January 2000 – December 2024 (with 2000–2014 derived solely from ESA CCI Passive, and 2015–2024 as a blended record).
• Spatial Resolution: 0.25° × 0.25° global grid (land masks applied to exclude permanent water and ice).

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3. Methodology

1. Rescaling and Merging:
   • CCI Passive and Active products are first rescaled to a common climatology using Triple Collocation Analysis; the Combined product uses seasonally‐varying merging weights (climate.esa.int).
2. Temporal Extension:
   • For 2015–2024, SMAP passive radiometer data are bias‑corrected against the CCI Combined product and blended via weighted averaging to preserve multi‑sensor consistency.
3. Quality Control:
   • Automated flagging of outliers, masked barren ground, and infilling missing pixels by spatial interpolation.
4. Uncertainty Quantification:
   • End‑to‑end uncertainties provided per grid cell per day, derived from the merged sensor error budgets (climate.esa.int).

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4. Dataset Description

Component	Period	Temporal Res.	Spatial Res.	Units
CCI Combined	2000–2023	Daily	0.25°	m³ m⁻³
SMAP Blended	2015–2024	Daily	0.25°	m³ m⁻³
Uncertainty Budget	2000–2024	Daily	0.25°	m³ m⁻³

Table 1. Overview of dataset components and resolutions.

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5. Data Access

• ESA CCI SM v09.1 FTP:
  ftp://anon-ftp.ceda.ac.uk/neodc/esacci/soil_moisture/data/v09.1/combined/daily/netcdf/ (climate.esa.int)
• SMAP Passive Radiometer (L2 & L3):
  https://nsidc.org/data/SMAP_L3_SM_P/ (smap.jpl.nasa.gov)
• Blended Product Download & Documentation:
  https://climate.example.org/soil_moisture_2000_2024/

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6. Applications

• Drought Monitoring: Enhanced detection of soil moisture deficits over agricultural regions.
• Hydrological Modeling: Initialization and validation of land‐surface schemes in climate and flood models.
• Ecosystem Studies: Assessment of vegetation water stress and carbon uptake correlations.
• Climate Change Analysis: Trends in surface drying or wetting patterns at global to regional scales.

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7. Discussion

Preliminary analysis indicates regional divergence in soil moisture trends: Europe and North America exhibit slight wetting over 2000–2024, while parts of Africa and Australia show persistent drying. SMAP integration reduces biases in tropical regions where CCI Passive alone underestimates wet extremes (climate.esa.int).

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8. Conclusion

The Worldwide Soil Moisture Levels (2000–2024) dataset delivers a unique, continuous, and uncertainty‐quantified record crucial for diverse disciplines—from climate science to food security. By harmonizing ESA CCI and SMAP observations, researchers gain a robust foundation for modeling, analysis, and policy support.

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References

1. Gruber A. et al., “New upgrade to ESA CCI Soil Moisture Dataset v09.1,” ESA Climate Office News, Jan 9 2025. (climate.esa.int)
2. Entekhabi D. et al., “Introduction to the Soil Moisture Active Passive (SMAP) mission,” JPL/NASA, 2015. (smap.jpl.nasa.gov)
3. Dorigo W. et al., “New updates enhance ESA CCI soil moisture dataset,” ESA Climate Office News, Oct 19 2023. (climate.esa.int)
4. ESA CCI Soil Moisture Project Overview, European Space Agency. (climate.esa.int)