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The advection‐aridity approach to estimate actual evaporation from natural land surfaces is one of the better known implementations of Bouchet's complementary principle. Detailed measurements at 2, 12, and 32 m above the ground surface during the growing seasons of 2004–2007 allowed validation of a generalized nonlinear form of this approach above the highly variable terrain in Changwu County in the southern Loess Plateau of the Yellow River basin in China. The obtained values of the parameters were found to lie well within the ranges to be expected on physical grounds or from previous measurements by different experimental means; calibration on the basis of any one year of data allowed predictions within roughly 5% on average. Relative to the corresponding observed turbulent vapor fluxes, the evaporation rates calculated with measurements at the highest level of 32 m displayed the least scatter but only slightly less than those calculated with measurements at the lower level of 12 m; however, those based on measurements at the lowest level of 2 m displayed considerably more scatter than those derived at the two higher levels. This is consistent with the existence of a blending height at higher elevations above the ground, where the effects of surface variability tend to fade away. Good agreement is obtained between the predicted values of evaporation and values measured using the eddy covariance techniqueThe values of the four calibrated parameters are consistent with their values expected on physical groundsThe method becomes more robust with height above the surface as the blending height is approached

Arctic precipitation (PG) that occurs as rainfall (Prain) or snowfall (Psnow) depending on the prevailing climatic conditions results in seasonally specific hydrological events. Climate change can affect the PG‐ and permafrost‐originated water (Pice) regimes, resulting in change to ecohydrological processes. However, the relative influences of source waters (i.e., Prain, Psnow, and Pice) on terrestrial hydrological processes have not yet been fully established. Here, we report the development and implementation of a numerical water tracer model designed to quantify changes in the storages and fluxes of the source waters and the hydrogen and oxygen isotopic tracers associated with hydrometeorological events. The presented tracer model was used to illustrate the spatiotemporal variability of the tracers in the surface–subsurface system of a deciduous needleleaf boreal forest and to separate the contribution rates of the tracer waters to evapotranspiration (ET). Although Psnowaccounted for 22%–57% of ETand the subcomponents, the contribution rates to soil evaporation and transpiration were significant only during spring. The major source water for soil moisture was Prain, which accounted for 69.2% of ETand showed an increasing trend during 1980–2016. Additionally, Prainalso accounted for 77.2% of transpiration. Under the present conditions of warming permafrost, Picedemonstrated negligibly low impact on ET. The tracer model was shown capable of quantifying the contribution rates of tracer waters to ET, highlighting the advantages of the tracer model for a similar quantitative separation regarding future climate change. Although snowfall and rainfall are seasonally different processes, their influence on hydrological processes (i.e., evapotranspiration and river discharge) occurs mainly during the growing season. Quantification of their contributions to hydrological processes is an ongoing scientific problem in the field of Arctic hydrology. Thus, we developed a tracer model, which includes isotopic processes, to separate the contributions of snowfall, rainfall, and permafrost‐originated water to evapotranspiration and applied it to a boreal forest. The model simulation suggested that summer rainfall has the greatest impact on evapotranspiration, while water from snowfall is strongly implicated in springtime evaporation. Permafrost‐originated water is not connected directly to evapotranspiration at the study site. However, future warming climate could potentially increase the role of permafrost‐related water in ecohydrological processes. Thus, the presented water tracer model could potentially provide a quantitative assessment of the changes in the physics of water dynamics caused by climate change. Tracer model separates contributions of precipitation‐ and permafrost‐originated waters to evapotranspiration in deciduous boreal forestRainfall is the primary contributor to seasonal and interannual variability of evapotranspirationPermafrost‐originated water has negligibly low impact on evapotranspiration Tracer model separates contributions of precipitation‐ and permafrost‐originated waters to evapotranspiration in deciduous boreal forest Rainfall is the primary contributor to seasonal and interannual variability of evapotranspiration Permafrost‐originated water has negligibly low impact on evapotranspiration

Diurnal variation in the atmospheric CO2concentration and the carbon isotopic composition (Δ14C and δ13C) was measured in a forest in an urban area on 9 February 1999. The carbon isotope approach used in the present study differentiated between the quantitative contributions from anthropogenic and biogenic CO2sources in the urban atmosphere. The anthropogenic (fossil fuel) and biogenic (soil respiration) contributions was estimated, and they ranged from 1 to 16% and from 2 to 8% of the total atmospheric CO2. The diurnal variation of the anthropogenic CO2was the major cause of the total atmospheric CO2variation, while the biogenic CO2remained relatively constant throughout the day. Estimating the contribution of soil respired CO2provided the mean residence time of soil respired CO2within the forest atmosphere.

AbstractDiurnal variation in the atmospheric CO2concentration and the carbon isotopic composition (Δ14C and δ13C) was measured in a forest in an urban area on 9 February 1999. The carbon isotope approach used in the present study differentiated between the quantitative contributions from anthropogenic and biogenic CO2sources in the urban atmosphere. The anthropogenic (fossil fuel) and biogenic (soil respiration) contributions was estimated, and they ranged from 1 to 16% and from 2 to 8% of the total atmospheric CO2. The diurnal variation of the anthropogenic CO2was the major cause of the total atmospheric CO2variation, while the biogenic CO2remained relatively constant throughout the day. Estimating the contribution of soil respired CO2provided the mean residence time of soil respired CO2within the forest atmosphere.

Wind speed data in the atmospheric boundary layer (ABL) observed during two recent experiments over a wide stability range and over different experimental areas allowed an extensive test of the ABL bulk similarity equation with the similarity functions Bwpreviously proposed and calibrated with the First International Satellite Land Surface Climatology Project (ISLSCP) Field Experiment (FIFE) data set in order to obtain regional surface momentum fluxes. It was found that FIFE‐calibrated Bwfunctions produced similarly good results with the two new data sets; furthermore, one similarity function Bwbased on a simple dual‐layer ABL model which worked best with the FIFE data set was also found to perform best with the new data sets. Recalibration of the constant of this Bwfunction with all three combined data sets resulted in the same value as that calibrated with the FIFE data set.