Preprints
https://doi.org/10.5194/egusphere-2025-245
https://doi.org/10.5194/egusphere-2025-245
17 Feb 2025
 | 17 Feb 2025

Characterizing precipitation and soil moisture drydowns in Finland using SMAP satellite data

Kerttu Kouki and Andreas Colliander

Abstract. Precipitation (P) and soil moisture (SM) are critical components of the global water, energy, and biogeochemical cycles, yet their patterns and interrelations in the Arctic are poorly understood. Due to the sparse in situ measurement network, satellites are the only way to observe P and SM in high-latitude regions. This study uses NASA’s SMAP satellite to analyze the relationship between SM and P, assess the feasibility of estimating P from SM, and examine SM drydown patterns in Finland from April to September over 2018–2019. The analysis reveals a notable spatial and temporal variability in SM, with a weaker correlation between P and SM in spring due to snowmelt and a stronger relationship in summer and fall. Water bodies complicate the SM retrieval causing the SM retrievals to saturate. Using the SM2RAIN algorithm, we estimated P from SM data. The algorithm shows promising results, detecting the area of rainfall accurately in most cases but estimating the intensity of the rainfall is more challenging, particularly for light and very heavy rain. We analyzed SM drydown patterns by fitting an exponential model to each SM drydown period, from which we estimated the exponential decay time scale (τ) and the lower bound of SM (SMmin). τ does not show much spatial or temporal variability. The distribution of τ is positively skewed, with a mode of 1.6 days and a median of 4.0 days, consistent with other studies. The distribution of SMmin is also positively skewed, with a mode of 0.14 m3 m-3 and a median of 0.17 m3 m-3. SMmin exhibits another lower peak at 0.02 m3 m-3, the lower limit of SMAP SM retrievals, possibly causing an artifact in the results. SMmin shows spatial variability, with the lower bound being slightly higher near water bodies but also showing a more prominent peak at 0.02 m3 m-3. Grid cells with dense vegetation and low vegetation agree better with each other, indicating that water bodies particularly affect and complicate SM retrieval. The promising results suggest that the method could be applied across the entire Arctic region.

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Journal article(s) based on this preprint

30 Sep 2025
Characterizing precipitation and soil moisture drydowns in Finland using SMAP satellite data
Kerttu Kouki and Andreas Colliander
Hydrol. Earth Syst. Sci., 29, 4791–4810, https://doi.org/10.5194/hess-29-4791-2025,https://doi.org/10.5194/hess-29-4791-2025, 2025
Short summary
Kerttu Kouki and Andreas Colliander

Interactive discussion

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2025-245', Anonymous Referee #1, 18 Mar 2025
    • AC1: 'Reply on RC1', Kerttu Kouki, 24 Apr 2025
  • RC2: 'Comment on egusphere-2025-245', Anonymous Referee #2, 18 Mar 2025
    • AC2: 'Reply on RC2', Kerttu Kouki, 24 Apr 2025
  • RC3: 'Comment on egusphere-2025-245', Preet Lal, 18 Mar 2025
    • AC3: 'Reply on RC3', Kerttu Kouki, 24 Apr 2025

Interactive discussion

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2025-245', Anonymous Referee #1, 18 Mar 2025
    • AC1: 'Reply on RC1', Kerttu Kouki, 24 Apr 2025
  • RC2: 'Comment on egusphere-2025-245', Anonymous Referee #2, 18 Mar 2025
    • AC2: 'Reply on RC2', Kerttu Kouki, 24 Apr 2025
  • RC3: 'Comment on egusphere-2025-245', Preet Lal, 18 Mar 2025
    • AC3: 'Reply on RC3', Kerttu Kouki, 24 Apr 2025

Peer review completion

AR: Author's response | RR: Referee report | ED: Editor decision | EF: Editorial file upload
ED: Reconsider after major revisions (further review by editor and referees) (01 May 2025) by Efrat Morin
AR by Kerttu Kouki on behalf of the Authors (26 May 2025)  Author's response   Author's tracked changes   Manuscript 
ED: Referee Nomination & Report Request started (04 Jun 2025) by Efrat Morin
RR by Anonymous Referee #3 (06 Jun 2025)
RR by Anonymous Referee #1 (06 Jul 2025)
ED: Publish subject to minor revisions (review by editor) (06 Jul 2025) by Efrat Morin
AR by Kerttu Kouki on behalf of the Authors (07 Aug 2025)  Author's response   Author's tracked changes   Manuscript 
ED: Publish as is (14 Aug 2025) by Efrat Morin
AR by Kerttu Kouki on behalf of the Authors (18 Aug 2025)

Journal article(s) based on this preprint

30 Sep 2025
Characterizing precipitation and soil moisture drydowns in Finland using SMAP satellite data
Kerttu Kouki and Andreas Colliander
Hydrol. Earth Syst. Sci., 29, 4791–4810, https://doi.org/10.5194/hess-29-4791-2025,https://doi.org/10.5194/hess-29-4791-2025, 2025
Short summary
Kerttu Kouki and Andreas Colliander

Data sets

SMAP Enhanced L3 Radiometer Global and Polar Grid Daily 9 km EASE-Grid Soil Moisture, Version 6 P. E. O'Neill et al. https://doi.org/10.5067/4DQ54OUIJ9DL

Finnish Meteorological Institute Open Data Finnish Meteorological Institute https://en.ilmatieteenlaitos.fi/open-data

The Sodankylä in situ soil moisture observation network J. Ikonen et al. https://doi.org/10.5194/gi-5-95-2016

Hydrological data measured in Lompolonjängänoja (LJO) catchment J.-P. Nousu et al. https://doi.org/10.5281/zenodo.10820563

SMEAR Värriö and Hyytiälä SmartSMEAR https://smear.avaa.csc.fi/

Kerttu Kouki and Andreas Colliander

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Short summary
Precipitation (P) and soil moisture (SM) are critical components of the climate system but poorly understood in the Arctic. Using NASA's SMAP satellite, we analyzed SM and P patterns in Finland. SM and P correlate strongly in summer and fall but weakly in spring due to snowmelt. While the area of P can be estimated from SM, estimating its intensity is more challenging. Water bodies complicate SM retrieval. The promising results suggest this method could be applied across the Arctic.
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