2025-07-09 カリフォルニア大学サンタバーバラ校 (UCSB)
<関連情報>
- https://news.ucsb.edu/2025/021947/nuanced-model-soil-moisture-illuminates-plant-behavior-and-climate-patterns
- https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2024GL111403
非線形土壌水分損失関数が明らかにする植生の水利用能への応答 Nonlinear Soil Moisture Loss Function Reveals Vegetation Responses to Water Availability
Ryoko Araki, Bryn E. Morgan, Hilary K. McMillan, Kelly K. Caylor
Geophysical Research Letters Published: 03 June 2025
DOI:https://doi.org/10.1029/2024GL111403
Abstract
Soil moisture drydown patterns encode signatures of vegetation water-use. Previous characterizations of the drydown patterns assume a static linear relationship between water-limited transpiration and available moisture. However, ecohydrological studies show that vegetation exhibits a spectrum of responses to water availability, suggesting that soil moisture loss functions may be nonlinear. To represent these dynamics, we introduce a nonlinearity parameter to the loss function. Our analysis shows that the nonlinear loss model improves the characterization of the satellite-observed soil moisture drydowns. Globally, functional responses of drydowns are dominated by convex nonlinearity, showing less ecosystem water loss in dry soils than the linear loss function predicts. We find distinct degrees of nonlinearity among different vegetation types; areas with non-woody vegetation more frequently exhibit a concave nonlinearity, the signature of aggressive water-use strategies. We propose the nonlinear loss function as a continuous and dynamic framework to represent vegetation water-use under changing water availability.
Key Points
- A novel nonlinear soil moisture loss model outperforms a linear model in describing satellite-derived soil moisture across various landscape
- Globally, the nonlinearity parameter <?XML:NAMESPACE PREFIX = “[default] http://www.w3.org/1998/Math/MathML” NS = “http://www.w3.org/1998/Math/MathML” />q greater than 1 dominates, indicating slower soil drying and conservative vegetation water-use
- The q values vary by vegetation type, with herbaceous vegetation showing a more aggressive water-use strategy
Plain Language Summary
Patterns of soil moisture decline after rainfall contain signatures of how much vegetation transpires. In this study, we modified an existing theory relating soil moisture declines and evapotranspiration by introducing a nonlinearity parameter to the relationship. We applied this novel method to global satellite soil moisture data, confirmed the performance, and showed that the results are consistent with the previous understandings of interactions between soil moisture and the surrounding environments. In particular, our model successfully captures how vegetation uses water more aggressively or conservatively under varying water availability at landscape scale. This novel method allows us to characterize vegetation water-use and their vulnerability to drought conditions at the global scale.
