Abstract
Abstract. Soil water content (θ) influences the climate system by controlling the fraction of incoming solar and longwave energy that is converted into evapotranspiration (ET). Therefore, investigating the coupling strength between θ and ET is important for the study of land surface–atmosphere interactions. Physical models are commonly tasked with representing the coupling between θ and ET; however, few studies have evaluated the accuracy of model-based estimates of θ ∕ ET coupling (especially at multiple soil depths). To address this issue, we use in situ AmeriFlux observations to evaluate θ ∕ ET coupling strength estimates acquired from multiple land surface models (LSMs) and an ET retrieval algorithm – the Global Land Evaporation Amsterdam Model (GLEAM). For maximum robustness, coupling strength is represented using the sampled normalized mutual information (NMI) between θ estimates acquired at various vertical depths and surface evaporation flux expressed as a fraction of potential evapotranspiration (fPET, the ratio of ET to potential ET). Results indicate that LSMs and GLEAM are generally in agreement with AmeriFlux measurements in that surface soil water content (θs) contains slightly more NMI with fPET than vertically integrated soil water content (θv). Overall, LSMs and GLEAM adequately capture variations in NMI between fPET and θ estimates acquired at various vertical depths. However, GLEAM significantly overestimates the NMI between θ and ET, and the relative contribution of θs to total ET. This bias appears attributable to differences in GLEAM's ET estimation scheme relative to the other two LSMs considered here (i.e., the Noah model with multi-parameterization options and the Catchment Land Surface Model, CLSM). These results provide insight into improved LSM model structure and parameter optimization for land surface–atmosphere coupling analyses.
Highlights
Soil water content (θ ) modulates water and energy feedbacks between the land surface and the lower atmosphere by determining the fraction of incoming solar energy that is converted into evapotranspiration (ET; Seneviratne et al, 2010, 2013)
The Level 2 (L2) AmeriFlux latent heat flux (LE) and H flux observations are based on high-frequency eddy covariance measurements processed into half-hourly averages by individual AmeriFlux investigators
Simulations are acquired from the Noah model with multiparameterization options (NOAHMP) (Niu et al, 2011) and Catchment Land Surface Model (CLSM) (Koster et al, 2000) land surface models (LSMs) embedded within the NASA Land Information System (LIS, Kumar et al, 2006) and the Global Land Evaporation Amsterdam Model (GLEAM) ET retrieval algorithm (Miralles et al, 2011)
Summary
Soil water content (θ ) modulates water and energy feedbacks between the land surface and the lower atmosphere by determining the fraction of incoming solar energy that is converted into evapotranspiration (ET; Seneviratne et al, 2010, 2013). Nearing et al (2018) used information theory metrics (transfer entropy, in particular) to measure the strength of direct couplings between different surface variables, including soil water content, and surface energy fluxes at short timescales in several LSMs. non-parametric mutual information measures are generally more appropriate. MI values are normalized by entropy in the corresponding ET time series to remove the effect of inter-site variations to generate estimates of normalized mutual information (NMI) between θ and ET Both surface (roughly 0–10 cm) soil water content (θs) and vertically integrated (0–40 cm) soil water content (θv) are considered to capture the impact of depth on NMI results. AmeriFluxbased NMI results are compared with analogous NMI results obtained from LSM-based and GLEAM-based θ and ET time series
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
