Using Machine Learning with Partial Dependence Analysis to Investigate
Land-Atmosphere Coupling
Abstract
Soil moisture influences near-surface air temperature by partitioning
downwelling radiation into latent and sensible heat fluxes, through
which dry soils generally lead to higher temperatures. The strength of
this coupled soil moisture-temperature (SM-T) relationship is not
spatially uniform, and numerous methods have been developed to assess
SM-T coupling strength across the globe. These previous methods tend to
involve either idealized climate-model experiments or linear statistical
methods which cannot fully capture nonlinear SM-T coupling. In this
study, we propose a nonlinear machine learning-based approach for
analyzing SM-T coupling, and apply this method to various mid-latitude
regions using historical reanalysis datasets. We first train
convolutional neural networks (CNNs) to predict near-surface temperature
given daily soil moisture (SM) and geopotential height fields. We then
use partial dependence analysis to isolate the average sensitivity of
each CNN’s temperature prediction to the soil moisture input, yielding
nonlinear SM-T relationships. We find that daily temperature predictions
are insensitive to small changes in local SM anomalies during extreme
dry and wet SM conditions. However, during moderate SM conditions,
temperature predictions are highly sensitive to the local SM anomaly.
This nonlinear behavior is consistent with previous studies that
indicate the presence of three seasonal SM regimes (wet, dry, and
transitional), though our SM-T relationships suggest that these SM
regimes also have relevance at daily timescales. Although this study
focuses specifically on local SM-T coupling, our machine learning-based
method can be extended to investigate other complex coupled interactions
within the climate system using both observed and model-derived
datasets.