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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. Plain Language Summary: Variations in rainfall and incoming sunlight amount shift land surface conditions (i.e., evaporation) and constrain our ability to predict crop yields and carbon sequestration. Nevertheless, some landscapes respond more to rainfall and sunlight variability than others. Using recent decade‐long satellite observations of surface temperature and soil moisture across Africa, we investigate whether regions with the most rainfall and sunlight variability are also those with the largest land surface variability and why. Indeed, we find that more rainfall and sunlight variability do increase the land evaporation and temperature variability. However, regions that spend time in the water‐limited evaporative regime (a drier soil state where soil moisture influences evaporation rates) have an amplified land surface response to atmospheric variability. These regions tend to be semi‐arid, but isolated humid regions also show this behavior because the water‐limited regime is defined by factors beyond mean moisture availability. While these mechanistic findings are based on daily‐to‐weekly land and atmospheric variability, we find these results also hold on longer timescales of year‐to‐year variations. As a result, these regions spending time mainly in the water‐limited regime likely have increased vulnerability to climatic changes in rainfall and sunlight amount. Key Points: Observed intraseasonal energy flux variance (from diurnal temperature amplitude) is used to quantify surface responsiveness to forcingsIntraseasonal mechanisms based on the energy flux‐soil moisture relationship and weather variability describe responsiveness patternsSpending more time in the water‐limited evaporative regime enhances surface responsiveness across intraseasonal to interannual timescales [ABSTRACT FROM AUTHOR]

Plant water content observations using microwave remote sensing measurements allow monitoring of landscape‐scale plant water stress. During soil drying following rainfall events, we use a Granger causality framework to quantify the degree to which environmental factors drive satellite‐based plant water content loss across Africa's diverse biomes. After soil drying into the water‐limited regime, satellite observations show that plants dry while solar radiation, vapor pressure deficit, and diurnal temperature amplitude increase. We find that soil drying primarily drives plant water content loss across African drylands, though with regional effects of diurnal temperature amplitude increases (found to indicate vapor pressure deficit increases here). We also detect interactions between these factors that reinforce plant drying during periods of soil moisture loss. Our results provide observational evidence across Africa that individual and interactive components of surface drying and heating can all drive plant water stress, especially during intermittent poststorm drying periods. Plain Language Summary: Plant water content represents the amount of water within the volume of vegetation canopy, and its dynamics can capture plant water stress. Since plant water content can now be monitored at large spatial scales using satellites, we use a rigorous statistical framework to quantify how the climatic factors soil water content, daily temperature range, light intensity, and atmospheric dryness individually drive plant drying across the expanse of diverse biomes across Africa. We specifically conduct our analysis on water‐limited periods about a week after rainfall events, where we show that plant water content progressively declines while soil dries and light intensity, heat, and atmospheric dryness increase. We find that plant drying after rainfall is driven by soil water loss across Africa's drier ecosystems and regionally by daily temperature range increases. Additionally, the interconnectedness of the plant, soil, and atmospheric conditions evaluated here reinforces plant drying in these ecosystems. We conclude that surface drying and heating can individually and interactively drive plant water stress at landscape scales. Key Points: Granger causality tests are used to identify environmental drivers of plant water stress based on satellite plant water contentSoil moisture loss and diurnal surface heating drive plant drying across African drylands after rainfall in the water‐limited regimeLand‐atmosphere interactions and feedbacks in the soil‐plant continuum reinforce this plant water loss during soil moisture drydowns [ABSTRACT FROM AUTHOR]

Land surface energetic partitioning between latent, sensible, and ground heat fluxes determines climate and influences the terrestrial segment of land‐atmosphere coupling. Soil moisture, among other variables, has a direct influence on this partitioning. Dry surfaces characterize a water‐limited regime where evapotranspiration and soil moisture are coupled. This coupling is subdued for wet surfaces, or an energy‐limited regime. This framework is commonly evaluated using the evaporative fraction–‐soil moisture relationship. However, this relationship is explicitly or implicitly prescribed in land surface models. These impositions, in turn, confound model‐based evaluations of energetic partitioning‐–soil moisture relationships. In this study, we use satellite‐based observations of surface temperature diurnal amplitude (directly related to available energy partitioning) and soil moisture, free of model impositions, to estimate characteristics of surface energetic partitioning–‐soil moisture relationships during 10–‐20‐day surface drying periods across Africa. We specifically estimate the spatial patterns of water‐limited energy flux sensitivity to soil moisture (m) and the soil moisture threshold separating water and energy‐limited regimes (θ*). We also assess how time evolution of other factors (e.g., solar radiation, vapor pressure deficit, surface albedo, and wind speed) can confound the energetic partitioning–‐soil moisture relationship. We find higher m in drier regions and interestingly similar spatial θ* distributions across biomes. Vapor pressure deficit and insolation increases during drying tend to increase m. Only vapor pressure deficit increases in the Sahelian grasslands systematically decrease θ*. Ultimately, soil and atmospheric moisture availability together play the largest role in land surface energy partitioning with minimal consistent influences of time evolution of other forcings. Plain Language Summary: Whether available, incoming solar energy is used for evaporating surface water, or surface heating largely depends on water availability across the landscape. Under dry conditions (water limitation), increasing soil moisture increases evaporation and surface cooling. In this regime, droughts and heatwaves can be initiated and sustained because drying is positively reinforced. Under wetter conditions (energy limitation), increasing soil moisture does not generally influence evaporation. Climate models rely on these soil moisture–evaporation relationships to describe associations between water and energy cycles and predict future climate. However, due to difficulty observing evaporation at large scales, these relationships assume different forms across climate models which contribute to divergences and uncertainty in making climate projections. We use satellite observations of soil moisture and daily temperature range (quantifying surface heating; inversely related to evaporation) to evaluate these relationships free of model impositions across Africa. Following rain events during surface drying, daily temperature range increases with greatest increases in drylands indicating strong surface influence on atmosphere. Increasing incoming sunlight and atmospheric dryness after rainfall accompany and amplify this surface heating. Regions with surface moisture strongly influencing surface heating/evaporation, such as the Sahel, are expected to have soil moisture variations that can initiate future rain and/or drought/heatwave events. Key Points: Soil moisture threshold separating water and energy‐limited evaporation regimes is estimated across diverse African biomesCoupling between moisture and energetic partitioning under water limitation is strongest in drier African biomesAnomalous vapor pressure deficit time evolution during surface drying can confound energetic partitioning–‐soil moisture relationships [ABSTRACT FROM AUTHOR]

The degree to which individual pulses of available water drive plant activity across diverse biomes and climates is not well understood. It has previously only been investigated in a few dryland locations. Here, plant water uptake following pulses of surface soil moisture, an indicator for the pulse-reserve hypothesis, is investigated across South America, Africa and Australia with satellite-based estimates of surface soil and canopy water content. Our findings show that this behaviour is widespread: occurring over half of the vegetated landscapes. We estimate spatially varying soil moisture thresholds at which plant water uptake ceases, noting dependence on soil texture and proximity to the wilting point. The soil type and biome-dependent soil moisture threshold and the plant soil water uptake patterns at the scale of Earth system models allow a unique opportunity to test and improve model parameterization of vegetation function under water limitation.