Interannual variability of evapotranspiration and energy exchange over an annual grassland in California

Ryu, Youngryel; Baldocchi, Dennis; Ma, Siyan; Hehn, Ted

doi:10.1029/2007jd009263

Cited by 189 publications

(147 citation statements)

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“…In a study on global ET linkages to MAT and precipitation during the 1982-2008 period, Jung et al (2010) declared that precipitation dominated inter-annual ET behavior in northern China, but in southern China ET was mainly temperature limited. ET in the semi-arid and arid northern areas of China was limited by the supply of soil moisture, which is significantly affected by precipitation, the key constraining factor of ET here (Ryu et al, 2008;Wang and Dickinson, 2012). Using daily meteorological data and gauging station data, Zhang et al (2011b) indicated that precipitation was the major determinant of ET in the YeRB.…”

Section: Linkage Of Et To Climate Factorsmentioning

confidence: 99%

Evapotranspiration and water yield over China's landmass from 2000 to 2010

Liu

Zhou

et al. 2013

Hydrol. Earth Syst. Sci.

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Abstract. Terrestrial carbon and water cycles are interactively linked at various spatial and temporal scales. Evapotranspiration (ET) plays a key role in the terrestrial water cycle, altering carbon sequestration of terrestrial ecosystems. The study of ET and its response to climate and vegetation changes is critical in China because water availability is a limiting factor for the functioning of terrestrial ecosystems in vast arid and semiarid regions. To constrain uncertainties in ET estimation, the process-based Boreal Ecosystem Productivity Simulator (BEPS) model was employed in conjunction with a newly developed leaf area index (LAI) data set, MODIS land cover, meteorological, and soil data to simulate daily ET and water yield at a spatial resolution of 500 m over China for the period from 2000 to 2010. The spatial and temporal variations of ET and water yield were analyzed. The influences of climatic factors (temperature and precipitation) and vegetation (land cover types and LAI) on these variations were assessed.Validations against ET measured at five ChinaFLUX sites showed that the BEPS model was able to simulate daily and annual ET well at site scales. Simulated annual ET exhibited a distinguishable southeast to northwest decreasing gradient, corresponding to climate conditions and vegetation types. It increased with the increase of LAI in 74 % of China's landmass and was positively correlated with temperature in most areas of southwest, south, east, and central China. The correlation between annual ET and precipitation was positive in the arid and semiarid areas of northwest and north China, but negative in the Tibetan Plateau and humid southeast China. The national annual ET varied from 345.5 mm in 2001 to 387.8 mm in 2005, with an average of 369.8 mm during the study period. The overall rate of increase, 1.7 mm yr −1 (R 2 = 0.18, p = 0.19), was mainly driven by the increase of total ET in forests. During 2006During -2009 and LAI decreased widely and consequently caused a detectable decrease in national total ET. Annual ET increased over 62.2 % of China's landmass, especially in the cropland areas of the southern Haihe River basin, most of the Huaihe River basin, and the southeastern Yangtze River basin. It decreased in parts of northeast, north, northwest, south China, especially in eastern Qinghai-Tibetan Plateau, the south of Yunnan Province, and Hainan Province. Reduction in precipitation and increase in ET caused vast regions in China, especially the regions south of Yangtze River, to experience significant decreases in water yield, while some sporadically distributed areas experienced increases in water yield. This study shows that the terrestrial water cycles in China's terrestrial ecosystems appear to have been intensified by recent climatic variability and human induced vegetation changes.

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Section: Linkage Of Et To Climate Factorsmentioning

confidence: 99%

Evapotranspiration and water yield over China's landmass from 2000 to 2010

Liu

Zhou

et al. 2013

Hydrol. Earth Syst. Sci.

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“…[16] In this example, we apply the method to the Vaira Ranch data set of the Ameriflux network [Ryu et al, 2008] where measured evaporation flux data is available for verification. The site is located in California (N38.4067/ W120.9507, elevation 129m).…”

Section: Example Of Methodologymentioning

confidence: 99%

“…[5] Below we demonstrate the method at the Vaira Ranch Ameriflux site [Ryu et al, 2008] using field measured atmospheric forcing and remotely sensed soil moisture (AMSR-E derived LPRM [Owe et al, 2008] product) and Leaf Area Index (MODIS level 4 product available through the USGS Land Processes Distributed Active Archive Center). To keep the parameter estimation manageable for large scale applica-1 tions, we start with default soil and vegetation parameters sets and then further refine key parameters within these sets.…”

Section: Introductionmentioning

confidence: 99%

An alternate and robust approach to calibration for the estimation of land surface model parameters based on remotely sensed observations

Salvucci

Entekhabi

2011

Geophys. Res. Lett.

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[1] Atmospheric models include land surface parameterizations of heat and moisture fluxes. Most parameterizations derive from early models of layered soil and vegetation canopy that account for liquid, vapor and heat diffusion, radiation processes, and surface turbulence. The number of parameters in these models ranges roughly from 10 to 50. Some parameters are known to vary over a small range and/or not significantly impact predictions. Others are highly influential (e.g., Leaf Area Index), but are currently well estimated from satellite data. Many parameters, however, are highly influential, vary over a large dynamic range, cannot be estimated from satellite data, and cannot be readily upscaled from in-situ measurements. For such parameters (e.g., maximum stomatal conductance and soil hydraulic conductivity), values are assigned based on look-up tables sorted by land cover and soil texture. Here we present a method for estimating these parameters by minimizing a measure of nonstationarity of model-predicted moisture state variable tendencies. This method has advantages over calibration: 1) it does not require flux data (e.g., evapotranspiration); and 2) the tendency terms are evaluated at the model grid and thus yield parameters that are effective for that scale. The method is demonstrated with the Noah Land Surface Model, using remotely-sensed soil moisture, at a site in California. Preliminary results indicate that the method is robust and performs better than both: 1) calibration to soil moisture observations, which can lead to large, compensating errors in drainage and evaporation; and 2) minimizing the sum of squares of innovations of soil moisture updates. Citation: Salvucci, G. D., and D. Entekhabi (2011), An alternate and robust approach to calibration for the estimation of land surface model parameters based on remotely sensed observations, Geophys. Res. Lett., 38, L16404,

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“…The PAR albedo is related to plant greenness and scales negatively with leaf area index, implying that it can capture the phenological events and canopy structure [32] . The spikes in the flux data were removed [33] , then small gaps were filled using linear interpolation, while large gaps were filled using the gap-filling methodology presented by ref.…”

Section: Measurementmentioning

confidence: 99%

Modeling the crop transpiration using an optimality-based approach

Lei

Yang

Schymanski

et al. 2008

Sci. China Ser. E-Technol. Sci.

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Evapotranspiration constitutes more than 80% of the long-term water balance in Northern China. In this area, crop transpiration due to large areas of agriculture and irrigation is responsible for the majority of evapotranspiration. A model for crop transpiration is therefore essential for estimating the agricultural water consumption and understanding its feedback to the environment. However, most existing hydrological models usually calculate transpiration by relying on parameter calibration against local observations, and do not take into account crop feedback to the ambient environment. This study presents an optimality-based ecohydrology model that couples an ecological hypothesis, the photosynthetic process, stomatal movement, water balance, root water uptake and crop senescence, with the aim of predicting crop characteristics, CO 2 assimilation and water balance based only on given meteorological data. Field experiments were conducted in the Weishan Irrigation District of Northern China to evaluate performance of the model. Agreement between simulation and measurement was achieved for CO 2 assimilation, evapotranspiration and soil moisture content. The vegetation optimality was proven valid for crops and the model was applicable for both C 3 and C 4 plants. Due to the simple scheme of the optimality-based approach as well as its capability for modeling dynamic interactions between crops and the water cycle without prior vegetation information, this methodology is potentially useful to couple with the distributed hydrological model for application at the watershed scale.crop transpiration, CO 2 assimilation, optimality, feedback, ecohydrological model

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Interannual variability of evapotranspiration and energy exchange over an annual grassland in California

Cited by 189 publications

References 134 publications

Evapotranspiration and water yield over China's landmass from 2000 to 2010

Evapotranspiration and water yield over China's landmass from 2000 to 2010

An alternate and robust approach to calibration for the estimation of land surface model parameters based on remotely sensed observations

Modeling the crop transpiration using an optimality-based approach

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