Global estimates of the land–atmosphere water flux based on monthly AVHRR and ISLSCP-II data, validated at 16 FLUXNET sites

Fisher, Joshua B.; Tu, Kevin; Baldocchi, Dennis

doi:10.1016/j.rse.2007.06.025

Cited by 886 publications

(1,021 citation statements)

References 106 publications

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“…The Priestley-Taylor model for PET uses a single parameter, α, to account for adiabatic component of latent heat transfer 29 . While α may vary as a function of meteorological conditions 30 , a standard α value of 1.26 has been applied successfully at large scales 35 . Priestley-Taylor PET is given by the equation:…”

Section: Methodsmentioning

confidence: 99%

Water balance creates a threshold in soil pH at the global scale

Slessarev

Lin

Bingham

et al. 2016

Nature

420

255

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Soil pH regulates the capacity of soils to store and supply nutrients, and thus contributes substantially to controlling productivity in terrestrial ecosystems 1 . However, soil pH is not an independent regulator of soil fertility-rather, it is ultimately controlled by environmental forcing. In particular, small changes in water balance cause a steep transition from alkaline to acid soils across natural climate gradients 2,3 . Although the processes governing this threshold in soil pH are well understood, the threshold has not been quantified at the global scale, where the influence of climate may be confounded by the effects of topography and mineralogy. Here we evaluate the global relationship between water balance and soil pH by extracting a spatially random sample (n = 20,000) from an extensive compilation of 60,291 soil pH measurements. We show that there is an abrupt transition from alkaline to acid soil pH that occurs at the point where mean annual precipitation begins to exceed mean annual potential evapotranspiration. We evaluate deviations from this global pattern, showing that they may result from seasonality, climate history, erosion and mineralogy. These results demonstrate that climate creates a nonlinear pattern in soil solution chemistry at the global scale; they also reveal conditions under which soils maintain pH out of equilibrium with modern climate.Climate controls many aspects of soil chemistry, affecting soil pH (ref. 4). Alkaline soils are known to be common in arid climates, while acid soils are known to be common in humid climates 1 . Surprisingly, however, the global-scale mechanisms governing this pattern remain broadly defined, and untested by direct observation. What are the dominant chemical equilibria that constrain soil pH? What aspect of climate defines the transition between alkaline and acid soils, and is the transition linear? The answers to these questions are fundamental to understanding soil development and surface geochemistry at the global scale. Furthermore, achieving this understanding may prove essential for representing soils in models of the terrestrial biosphere, given that soil pH controls many aspects of soil fertility 5,6 . Here we illustrate that simple geochemical and hydrological concepts can be used to build a mechanistic understanding of soil pH at the global scale.Interpretations of acid-titration experiments indicate that the soil pH is typically most strongly buffered by equilibrium with two secondary minerals: calcite (CaCO 3 ), or gibbsite (Al(OH) 3 ) 7,8 Fig. 1).Local studies of climate gradients have shown that the relative importance of these two buffers is determined by leaching, which removes Ca 2+ from the soil 2,3,8,9 . In climates where evaporative demand exceeds precipitation, leaching rates are low, and dissolved Ca 2+ accumulates as CaCO 3 -buffering soil pH near 8.2 (ref. 4). Conversely, in climates where precipitation exceeds evaporative demand, water leaches through the soil, removing Ca 2+ and allowing accumulation of relatively immobile...

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Section: Methodsmentioning

confidence: 99%

Water balance creates a threshold in soil pH at the global scale

Slessarev

Lin

Bingham

et al. 2016

Nature

420

255

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“…However, in previous applications (Fisher et al 2008), most modeling research considered ET into three compositions. Besides canopy transpiration (T), the evaporation are split into two sources, soil evaporation (Es) and interception evaporation (I):…”

Section: Flux Measurementsmentioning

confidence: 99%

“…Managing land use change is an important way for humans to mitigate the effects of and adapt to ongoing climate change. Land use change may significantly affect ecosystem WUE by changing ecosystem carbon and water budgets (Fisher et al 2008) and consequently have impact on regional and global climates. There has been limited research on land use pattern effects on grassland ecosystem WUE (Brümmer et al 2012).…”

Section: Introductionmentioning

confidence: 99%

“…Though various controlling factors of WUE have been widely discussed in previous studies (Fisher et al 2008;Xu et al 2013), consensus lacked the conclusions on critical factors and regulation trends (Lauenroth et al 2000;Li et al 2008). The divergences might mainly be attributed to different calculation methods and scales of research (Lauenroth et al 2000).…”

Section: Introductionmentioning

confidence: 99%

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Comparison of evapotranspiration components and water-use efficiency among different land use patterns of temperate steppe in the Northern China pastoral-farming ecotone

Fan

et al. 2015

Int J Biometeorol

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Water-use efficiency (WUE), which links carbon and water cycles, is an important indicator of assessing the interactions between ecosystems and regional climate. Using chamber methods with and without plant removal treatments, we investigated WUE and evapotranspiration (ET) components in three ecosystems with different land-use types in Northern China pastoral-farming ecotone. In comparison, ET of the ecosystems with grazing exclusion and cultivating was 6.7 and 13.4 % higher than that of the ecosystem with free grazing. The difference in ET was primarily due to the different magnitudes of soil water evaporation (E) rather than canopy transpiration (T). Canopy WUE (WUEc, i.e., the ratio of gross primary productivity to T) at the grazing excluded and cultivated sites was 17 and 36 % higher than that at the grazing site. Ecosystem WUE (WUEnep, i.e., the ratio of net ecosystem productivity to ET) at the cultivated site was 34 and 28 % lower in comparison with grazed and grazing excluded stepped, respectively. The varied leaf area index (LAI) of different land uses was correlated with microclimate and ecosystem vapor/carbon exchange. The LAI changing with land uses should be the primary regulation of grassland WUE. These findings facilitate the mechanistic understanding of carbon-water relationships at canopy and ecosystem levels and projection of the effects of land-use change on regional climate and productivity.

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“…3); and (ii) the BouchetMorton (BM) approach (4)(5)(6)(7)(8), which, in effect, uses the deviation of atmospheric temperature and humidity from equilibrium conditions to estimate the deviation of E from the equilibrium E rate. The first approach applies to conditions of unlimited moisture supply at the surface (i.e., a wet surface due to moist soil or open water), whereas the latter applies to the more challenging prediction of E from water-limited surfaces.…”

mentioning

confidence: 99%

Emergent relation between surface vapor conductance and relative humidity profiles yields evaporation rates from weather data

Salvucci

Gentine

2013

Proc. Natl. Acad. Sci. U.S.A.

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The ability to predict terrestrial evapotranspiration (E) is limited by the complexity of rate-limiting pathways as water moves through the soil, vegetation (roots, xylem, stomata), canopy air space, and the atmospheric boundary layer. The impossibility of specifying the numerous parameters required to model this process in full spatial detail has necessitated spatially upscaled models that depend on effective parameters such as the surface vapor conductance (C surf ). C surf accounts for the biophysical and hydrological effects on diffusion through the soil and vegetation substrate. This approach, however, requires either site-specific calibration of C surf to measured E, or further parameterization based on metrics such as leaf area, senescence state, stomatal conductance, soil texture, soil moisture, and water table depth. Here, we show that this key, rate-limiting, parameter can be estimated from an emergent relationship between the diurnal cycle of the relative humidity profile and E. The relation is that the vertical variance of the relative humidity profile is less than would occur for increased or decreased evaporation rates, suggesting that land-atmosphere feedback processes minimize this variance. It is found to hold over a wide range of climate conditions (arid-humid) and limiting factors (soil moisture, leaf area, energy). With this relation, estimates of E and C surf can be obtained globally from widely available meteorological measurements, many of which have been archived since the early 1900s. In conjunction with precipitation and stream flow, long-term E estimates provide insights and empirical constraints on projected accelerations of the hydrologic cycle.canopy conductance | moisture stress | hydroclimatology I n the simplest terms, evapotranspiration (E) is controlled by the gradient of humidity near the land surface. At the surface, humidity depends strongly on temperature, which itself reflects a balance of radiative heating and cooling, conversion to latent heat, canopy and soil heating, and the turbulent transport of sensible heat into the atmosphere. For a given radiative forcing, the key parameter controlling the relative strength of the turbulent sensible and latent heat fluxes (and thus the magnitude of evapotranspiration) in most land surface models is the surface vapor conductance (C surf ) (in meters per second). The surface vapor conductance accounts for the biophysical (e.g., vegetation structure, leaf area, senescence state, stomatal conductance) and hydrological (e.g., soil texture, soil moisture, water table) status of the land surface.The turbulent fluxes of heat and moisture, however, in turn modify the humidity and temperature of the surface layer, and thus the gradients that drive the fluxes themselves. Given this tight coupling of the surface and boundary layer, one can anticipate statistically meaningful relations to emerge between E and the screen height humidity and temperature, independent of the surface conditions (and thus independent of site-specific model paramete...

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Global estimates of the land–atmosphere water flux based on monthly AVHRR and ISLSCP-II data, validated at 16 FLUXNET sites

Cited by 886 publications

References 106 publications

Water balance creates a threshold in soil pH at the global scale

Water balance creates a threshold in soil pH at the global scale

Comparison of evapotranspiration components and water-use efficiency among different land use patterns of temperate steppe in the Northern China pastoral-farming ecotone

Emergent relation between surface vapor conductance and relative humidity profiles yields evaporation rates from weather data

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