University of Oulu

Riihimäki, H., Kemppinen, J., Kopecký, M., & Luoto, M. (2021). Topographic Wetness Index as a proxy for soil moisture: The importance of flow-routing algorithm and grid resolution. Water Resources Research, 57, e2021WR029871.

Topographic wetness index as a proxy for soil moisture : the importance of flow-routing algorithm and grid resolution

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Author: Riihimäki, H.1; Kemppinen, J.2; Kopecký, M.3,4;
Organizations: 1Department of Geosciences and Geography, University of Helsinki, Helsinki, Finland
2Geography Research Unit, University of Oulu, Oulu, Finland
3Institute of Botany of the Czech Academy of Sciences, Průhonice, Czech Republic
4Faculty of Forestry and Wood Sciences, Czech University of Life Sciences Prague, Prague, Czech Republic
Format: article
Version: published version
Access: open
Online Access: PDF Full Text (PDF, 11.7 MB)
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Language: English
Published: American Geophysical Union, 2021
Publish Date: 2022-04-11


The Topographic Wetness Index (TWI) is a commonly used proxy for soil moisture. The predictive capability of TWI is influenced by the flow-routing algorithm and the resolution of the Digital Elevation Model (DEM) that TWI is derived from. Here, we examine the predictive capability of TWI using 11 flow-routing algorithms at DEM resolutions 1–30 m. We analyze the relationship between TWI and field-quantified soil moisture using statistical modeling methods and 5,200 study plots with over 46 000 soil moisture measurements. In addition, we test the sensitivity of the flow-routing algorithms against vertical height errors in DEM at different resolutions. The results reveal that the overall predictive capability of TWI was modest. The highest r² (23.7%) was reached using a multiple-flow-direction algorithm at 2 m resolution. In addition, the test of sensitivity against height errors revealed that the multiple-flow-direction algorithms were also more robust against DEM errors than single-flow-direction algorithms. The results provide field-evidence indicating that at its best TWI is a modest proxy for soil moisture and its predictive capability is influenced by the flow-routing algorithm and DEM resolution. Thus, we encourage careful evaluation of algorithms and resolutions when using TWI as a proxy for soil moisture.

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Series: Water resources research
ISSN: 0043-1397
ISSN-E: 1944-7973
ISSN-L: 0043-1397
Volume: 57
Issue: 10
Article number: e2021WR029871
DOI: 10.1029/2021WR029871
Type of Publication: A1 Journal article – refereed
Field of Science: 1171 Geosciences
Funding: H. Riihimäki and J. Kemppinen were funded by the Doctoral Programme in Geosciences at the University of Helsinki. J. Kemppinen was also funded by the Arctic Interactions at the University of Oulu and Academy of Finland (project 318930, Profi 4). M. Kopecký was funded by the Czech Academy of Sciences (project RVO 67985939). The field research was funded by the Academy of Finland (project 286950).
Academy of Finland Grant Number: 318930
Detailed Information: 318930 (Academy of Finland Funding decision)
Copyright information: © 2021. American Geophysical Union.