Benchmark products for land evapotranspiration:  LandFlux-EVAL multi-data set synthesis

Mueller, Brigitte; Hirschi, Martin; Jiménez, Carlos; Ciais, Philippe; Dirmeyer, Paul A.; Dolman, A. J.; Fisher, Joshua B.; Jung, Martin; Ludwig, Fulco; Maignan, Fabienne; Miralles, Diego G.; McCabe, Matthew F.; Reichstein, Markus; Sheffield, Justin; Wang, Kaicun; Wood, Eric F.; Zhang, Yongqiang; Seneviratne, Sonia I.

doi:10.5194/hess-17-3707-2013

Cited by 332 publications

(348 citation statements)

References 51 publications

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“…29). We also explored the relationship between soil pH and the difference of MAP and AET, which we represented using the mean of the diagnostic data included in the LandFlux-EVAL synthesis 18 . By definition, MAP minus AET cannot take negative values, but approaches zero where PET > MAP 10 .…”

Section: Methodsmentioning

confidence: 99%

“…If we predict that leaching drives an immediate transition between CaCO 3 and Al(OH) 3 equilibria where MAP minus PET = 0, the predictions explain 42% (interquartile range 42%-45%) of the observed variation in pH (here 'variation' means the median absolute difference from the median; see Methods). The threshold pattern is robust, appearing when MAP is balanced with an ensemble estimate of actual evapotranspiration rates 18 , or with simpler models of PET driven by different environmental data sets (Extended Data Fig. 3).…”

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confidence: 99%

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

Slessarev

Lin

Bingham

et al. 2016

Nature

391

252

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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%

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confidence: 99%

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

Slessarev

Lin

Bingham

et al. 2016

Nature

391

252

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“…The five global ET products included a MODIS ET product (MOD16) (Mu et al, 2011), a merged ET synthesis product (MUE13) (Mueller et al, 2013), a normalized differential vegetation index (NDVI)-based ET product (ZHA10) , a product based on a machine-learning algorithm (i.e., model tree ensemble) (JUN11) (Jung et al, 2011), and a product based on water balance approach (ZEN14) (Zeng et al, 2014). Their brief information was summarized in Table 2.…”

Section: The Published Global Et Productsmentioning

confidence: 99%

Spatial variation in annual actual evapotranspiration of terrestrial ecosystems in China: Results from eddy covariance measurements

Zheng

Wang

et al. 2016

J. Geogr. Sci.

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Abstract:Understanding the spatial variation in annual actual evapotranspiration (AET) and its influencing factors is crucial for a better understanding of hydrological processes and water resources management. By synthesizing ecosystem-level observations of eddy-covariance flux sites in China (a total of 61 sites), we constructed the most complete AET dataset in China up to now. Based on this dataset, we quantified the statistic characteristics of AET and water budgets (defined as the ratio of AET to annual mean precipitation (MAP), AET/MAP) of terrestrial ecosystems in China. Results showed that AET differed significantly among both different vegetation types and climate types in China, with overall mean AET of 534.7±232.8 mm yr -1 . AET/MAP also differed significantly among different climate types, but there were no distinct differences in AET/MAP values across vegetation types, with mean AET/MAP of 0.82±0.28 for non-irrigated ecosystems. We further investigated how the main climatic factors and vegetation attributes control the spatial variation in AET. Our findings revealed that the spatial variation of AET in China was closely correlated with the geographical patterns of climate and vegetation, in which the effects of total annual net radiation (R n ), MAP and mean annual air temperature (MAT) were dominant. Thus, we proposed an empirical equation to describe the spatial patterns of AET in China, which could explain about 84% of the spatial variation in AET of terrestrial ecosystems in China. Based on the constructed dataset, we also evaluated the uncertainties of five published global evapotranspiration products in simulating 1392 Journal of Geographical Sciences site-specific AET in China. Results showed that large biases in site-specific AET values existed for all five global evapotranspiration products, which indicated that it is necessary to involve more observation data of China in their parameterization or validation, while our AET dataset would provide a data source for it.

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“…Despite the recent initiatives dedicated to exploring these evaporation data sets -LandFlux-EVAL in particular Mueller et al (2011Mueller et al ( , 2013 -the relative merits of each model on the global scale remain largely unexplored. To date, the lack of inter-model consistency in the choice of forcing data has hampered the attribution of the observed skill of each evaporation data set to differences in the models.…”

Section: Introductionmentioning

confidence: 99%

The WACMOS-ET project – Part 2: Evaluation of global terrestrial evaporation data sets

Miralles

Jiménez²,

Jung

et al. 2016

Hydrol. Earth Syst. Sci.

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Abstract. The WAter Cycle Multi-mission Observation Strategy -EvapoTranspiration (WACMOS-ET) project aims to advance the development of land evaporation estimates on global and regional scales. Its main objective is the derivation, validation, and intercomparison of a group of existing evaporation retrieval algorithms driven by a common forcing data set. Three commonly used process-based evaporation methodologies are evaluated: the PenmanMonteith algorithm behind the official Moderate Resolution Imaging Spectroradiometer (MODIS) evaporation product (PM-MOD), the Global Land Evaporation Amsterdam Model (GLEAM), and the Priestley-Taylor Jet Propulsion Laboratory model (PT-JPL). The resulting global spatiotemporal variability of evaporation, the closure of regional water budgets, and the discrete estimation of land evaporation components or sources (i.e. transpiration, interception loss, and direct soil evaporation) are investigated using river discharge data, independent global evaporation data sets and results from previous studies. In a companion article (Part 1), Michel et al. (2016) inspect the performance of these three models at local scales using measurements from eddy-covariance towers and include in the assessment the Surface Energy Balance System (SEBS) model. In agreement with Part 1, our results indicate that the Priestley and Taylor products (PT-JPL and GLEAM) perform best overall for most ecosystems and climate regimes. While all three evaporation products adequately represent the expected average geographical patterns and seasonality, there is a tendency in PM-MOD to underestimate the flux in the tropics and subtropics. Overall, results from GLEAM and PT-JPL appear more realistic when compared to surface water balances from 837 globally distributed catchments and to separate evaporation estimates from ERAInterim and the model tree ensemble (MTE). Nonetheless, all products show large dissimilarities during conditions of water stress and drought and deficiencies in the way evaporation is partitioned into its different components. This observed inter-product variability, even when common forcing is used, suggests that caution is necessary in applying a single data set for large-scale studies in isolation. A general finding that different models perform better under different conditions highlights the potential for considering biome-or climatespecific composites of models. Nevertheless, the generation of a multi-product ensemble, with weighting based on validation analyses and uncertainty assessments, is proposed as the Published by Copernicus Publications on behalf of the European Geosciences Union. D. G. Miralles et al.: The WACMOS-ET project -Part 2best way forward in our long-term goal to develop a robust observational benchmark data set of continental evaporation.

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Benchmark products for land evapotranspiration: LandFlux-EVAL multi-data set synthesis

Cited by 332 publications

References 51 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

Spatial variation in annual actual evapotranspiration of terrestrial ecosystems in China: Results from eddy covariance measurements

The WACMOS-ET project – Part 2: Evaluation of global terrestrial evaporation data sets

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