Observed Landscape Responsiveness to Climate Forcing

Abstract

Climate variability and change shift environmental conditions on global land surfaces, creating uncertainties in predicting hydrologic flows, crop yields, and land carbon uptake. Land surfaces can present varying degrees of inertia to atmospheric forcing variability (e.g., precipitation). This study asks: are regions with the most variable environmental forcing necessarily the regions with the largest land surface variability? Specifically, it seeks to determine why land surfaces show varying responsiveness to environmental forcing. The degree to which and the mechanisms for how landscapes modulate the forcing are evaluated using a decade‐long satellite observation record of Africa's diverse climates. Surface responsiveness is quantified using intra‐seasonal energy flux variability, based on the observed diurnal temperature amplitude. We map the responsiveness and analyze the underlying mechanisms over intra‐seasonal timescales (especially interstorms). We show that, at a location, land surface responsiveness is dependent on the soil moisture distribution and the nonlinear relationship between energy fluxes and soil moisture. Land surfaces with greater responsiveness to climate are those with soil moisture distributions that span the threshold between evaporation regimes and spend most of their time in the water‐limited regime. Consequently, surface responsiveness mechanisms drive land surface variability beyond high climatic variability. Since we find these results to hold from intra‐seasonal to interannual timescales, we expect that these responsive regions will be most vulnerable to long‐term shifts in climate forcing. The quantification of these phenomena and determination of their geographic distributions based on observations can help assess land surface models used to evaluate hydrologic consequences of climate change.

Tropical surface temperature response to vegetation cover changes and the role of drylands

“…The results at seasonal timescales do agree that net vegetal cooling effects decrease in water‐limited locations (Figure S6 ), but stronger cooling effects are found at sub‐annual timescales (Figures S5 and S6 ). Evaluating seasonal timescales of these effects thus may be overestimating net vegetal cooling feedbacks given that FVC and d (LST)/ dt seasonal cycles carry spurious relationships between variables that may inflate the strength of their relationship (Feldman et al, 2022 ; Tuttle & Salvucci, 2017 ). There is less confidence in interactions at intra‐seasonal timescales because the FVC intra‐seasonal variability has a reduced signal, occupying less than 5% of the power spectrum, which likely approaches the variability of instrument noise (Figure S6 ).…”

“…For example, recent work found biases in model reanalysis diurnal temperature behavior and its interactions with vegetation compared to in‐situ measurements (Panwar & Kleidon, 2022 ). For these reasons, diurnal temperature observations have been previously used to establish surface energy balance interactions with vegetation and the atmosphere, though for different research questions (Dai et al, 1999 ; Feldman et al, 2022 , 2019 ; Panwar et al, 2020 ; Panwar & Kleidon, 2022 ).…”

Preferential Hydrologic States and Tipping Characteristics of Global Surface Soil Moisture

“…As soil hydrologic states and the dynamic shift of SM therewithin are intrinsically linked to climatic perturbations and dynamic vegetation stress, tipping characteristics of SM can be important indicator of ecosystem sensitivity to climate change. Recent studies have used the fraction of time spent by θ RS in the water-limited regime as a measure of SM responsiveness to atmospheric forcing (Feldman et al, 2019(Feldman et al, , 2022. However, a comprehensive assessment of the tipping characteristics of θ RS , their controls, and ecohydrological implications at a global scale remains largely unavailable.…”

Uncertainty in projected critical soil moisture values in CMIP6 affects the interpretation of a more moisture-limited world

“…Coupling between soil moisture (SM) and evaporation, quantified by surface latent heat fluxes (LE), controls the exchange of water and energy across the interface between land and atmosphere (Entekhabi et al 1996 (Dirmeyer et al 2000;Feldman et al 2022). This is called the energy-limited regime.…”