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1.
Sensitivity studies on the calculation of the radiation balance of urban surfaces: I. Shortwave radiation 总被引：1，自引：0，他引：1
A rigorous model is developed to calculate the shortwave radiation incident on building surfaces, based on radiation enclosure theory. When compared with field measurements, the model predictions are found to be associated with errors of approximately 10 W m–2, with underestimations of 5–10 W m–2 being caused on some walls by neglect of specular reflections. The effects of various simplifying assumptions are tested. The assumption of isotropic sky radiation and the neglect of multiple reflections are found to lead to errors of 15 W m–2 or less; the neglect of horizon obstructions and the use of albedos taken from the literature instead of measured values can result in errors of 50 W m–2 or more. Although these magnitudes of errors are site-specific, it is concluded that the use of simplifications in the modelling of shortwave radiation incident on urban surfaces must be approached with care. 相似文献
2.
Abstract Second generation land surface schemes are the subject of much development activity among atmospheric modellers. This work is aimed at, among other things, improving the representation of the soil water balance in order to simulate, more properly, exchanges with the atmosphere and to permit the use of model output to generate streamflow for model validation. The Canadian development program is centred on CLASS, the Canadian Land Surface Scheme, developed at Environment Canada. This paper focuses on the improvement of hydrology in CLASS. This was accomplished by designing a two‐way interface to WATFLOOD, a distributed hydrologic model developed at the University of Waterloo. The two models share many features, which facilitated the coupling procedure. The interface retains the three‐layer vertical moisture budget representation in CLASS but adds three horizontal runoff possibilities. Runoff from the surface water follows Manning's equation for overland flow. Interflow is generated from the near‐surface soil layer using a parametrization of Richard's equation and base flow is produced by Darcian flow from the bottom of layer 3. An approximation of the internal topography of grid elements is used to supply horizontal gradients for the runoff components. Tests are in progress in four Canadian study areas. Initial results are presented for the summer of 1993 for the Saugeen River in southwestern Ontario. The new scheme produces realistic hydrographs, whereas the old scheme did not. Bare ground evaporation is reduced by about 17% as a consequence of reduced water availability in layer 1. Evapotranspiration is not affected because the rooting depth extends into layer 3, in which soil moisture does not change appreciably with the new scheme. These results suggest that the new scheme improves the representation of streamflow in WATFLOOD/CLASS and of the soil moisture budget in CLASS. Work is in progress to validate this result over basins, such as the BOREAS study watersheds, where both runoff and evapotranspiration measurements are available. 相似文献
3.
Abstract This study reports on testing of the peatland version of the Canadian Land Surface Scheme (CLASS) for simulating the energy balance of subarctic open woodland terrain. Model results are compared against several years of measured data from a site near Churchill, Manitoba. In contrast to most forest environments, the floor of the open forest plays a large role in total ecosystem energy exchange. This behaviour presents a significant challenge for land surface models like CLASS and their simplified treatment of vegetation canopies. Simulations of summer energy balance for seven years encompassing a wide range of meteorological conditions produced consistent results. Root mean square errors for sensible and latent heat fluxes fell between 11 and 28 W m?2. CLASS consistently underestimated slightly the daily latent heat flux and overestimated the sensible heat flux, average mean bias errors being ‐7.6 and 9.1 W m?2, respectively. The soil heat flux was less well represented. In general, CLASS was able to capture the diurnal and seasonal behaviour of the measured fluxes under a range of conditions with reasonable accuracy. In a full year simulation, CLASS reproduced the annual variations in energy balance with some discrepancies associated with snow accumulation and ablation periods. The model performance was sensitive to both snow density and specification of the surface cover. Recommendations for improving the model for subarctic woodlands and terrain types with similar features are discussed. 相似文献
4.
Xu Liang Eric F. Wood Dennis P. Lettenmaier Dag Lohmann Aaron Boone Sam Chang Fei Chen Yongjiu Dai Carl Desborough Robert E. Dickinson Qingyun Duan Michael Ek Yeugeniy M. Gusev Florence Habets Parviz Irannejad Randy Koster Kenneth E. Mitchell Olga N. Nasonova Joel Noilhan John Schaake Adam Schlosser Yaping Shao Andrey B. Shmakin Diana Verseghy Kirsten Warrach Peter Wetzel Yongkang Xue Zong-Liang Yang Qing-cun Zeng 《Global and Planetary Change》1998,19(1-4)
The energy components of sixteen Soil-Vegetation Atmospheric Transfer (SVAT) schemes were analyzed and intercompared using 10 years of surface meteorological and radiative forcing data from the Red-Arkansas River basin in the Southern Great Plains of the United States. Comparisons of simulated surface energy fluxes among models showed that the net radiation and surface temperature generally had the best agreement among the schemes. On an average (annual and monthly) basis, the estimated latent heat fluxes agreed (to within approximate estimation errors) with the latent heat fluxes derived from a radiosonde-based atmospheric budget method for slightly more than half of the schemes. The sensible heat fluxes had larger differences among the schemes than did the latent heat fluxes, and the model-simulated ground heat fluxes had large variations among the schemes. The spatial patterns of the model-computed net radiation and surface temperature were generally similar among the schemes, and appear reasonable and consistent with observations of related variables, such as surface air temperature. The spatial mean patterns of latent and sensible heat fluxes were less similar than for net radiation, and the spatial patterns of the ground heat flux vary greatly among the 16 schemes. Generally, there is less similarity among the models in the temporal (interannual) variability of surface fluxes and temperature than there is in the mean fields, even for schemes with similar mean fields. 相似文献
5.
A. J. Pitman A. Henderson-Sellers C. E. Desborough Z.-L. Yang F. Abramopoulos A. Boone R. E. Dickinson N. Gedney R. Koster E. Kowalczyk D. Lettenmaier X. Liang J.-F. Mahfouf J. Noilhan J. Polcher W. Qu A. Robock C. Rosenzweig C. A. Schlosser A. B. Shmakin J. Smith M. Suarez D. Verseghy P. Wetzel E. Wood Y. Xue 《Climate Dynamics》1999,15(9):673-684
Using atmospheric forcing data generated from a general circulation climate model, sixteen land surface schemes participating
in the Project for the Intercomparison of Land-surface Parametrization Schemes (PILPS) were run off-line to equilibrium using
forcing data from a GCM representative of a tropical forest and a mid-latitude grassland grid point. The values for each land
surface parameter (roughness length, minimum stomatal resistance, soil depth etc.) were provided. Results were quality controlled
and analyzed, focusing on the scatter simulated amongst the models. There were large differences in how the models’ partitioned
available energy between sensible and latent heat. Annually averaged, simulations for the tropical forest ranged by 79 1 3;W m-2 for the sensible heat flux and 80 W m-2 for the latent heat flux. For the grassland, simulations ranged by 34 W m-2 for the sensible heat flux and 27 W m-2 for the latent heat flux. Similarly large differences were found for simulated runoff and soil moisture and at the monthly
time scale. The models’ simulation of annually averaged effective radiative temperature varied with a range, between all the
models, of 1.4 K for tropical forest and 2.2 K for the grassland. The simulation of latent and sensible heat fluxes by a standard
‘bucket’ models was anomalous although this could be corrected by an additional resistance term. These results imply that
the current land surface models do not agree on the land surface climate when the atmospheric forcing and surface parameters
are prescribed. The nature of the experimental design, it being offline and with artificial forcing, generally precludes judgements
concerning the relative quality of any specific model. Although these results were produced de-coupled from a host model,
they do cast doubt on the reliability of land surface schemes. It is therefore a priority to resolve the disparity in the
simulations, understand the reasons behind the scatter and to determine whether this lack of agreement in de-coupled tests
is reproduced in coupled experiments.
Received: 15 October 1997 / Accepted: 22 April 1999 相似文献
6.
Climate Dynamics - Biosphere–atmosphere interactions play a very important role in modulating regional climate. To capture these bi-directional interactions, a dynamic vegetation model, the... 相似文献
7.
The model developed in Verseghy and Munro (1989) is extended to the calculation of the longwave radiation incident on building surfaces. When compared with field measurements, the average magnitude of error associated with model predictions is found to be 10 W m–2. The effects of six simplifying assumptions are investigated. The neglect of horizon obstructions is found to lead to errors of up to 60 W m–2; the assumption of wall temperatures equal to air temperatures results in errors of up to 35 W m–2. The neglect of absorption and emission by air between pairs of walls causes errors of the same magnitude as those associated with the predictions of the rigorous model itself. Of the three remaining simplifying assumptions tested (the assumption of isotrophic sky radiation, the use of published values of emissivities instead of measured values, and the blackbody surface assumption), none results om errors >5 W m–2. As in the shortware case, the errors are site-specific, but nevertheless indicate the care with which the use of simplifying assumptions must be approached. 相似文献
8.
Arman?GanjiEmail author Laxmi?Sushama Diana?Verseghy Richard?Harvey 《Theoretical and Applied Climatology》2017,127(1-2):45-59
Regional and global climate model simulated streamflows for high-latitude regions show systematic biases, particularly in the timing and magnitude of spring peak flows. Though these biases could be related to the snow water equivalent and spring temperature biases in models, a good part of these biases is due to the unaccounted effects of non-uniform infiltration capacity of the frozen ground and other related processes. In this paper, the treatment of frozen water in the Canadian Land Surface Scheme (CLASS), which is used in the Canadian regional and global climate models, is modified to include fractional permeable area, supercooled liquid water and a new formulation for hydraulic conductivity. The impact of these modifications on the regional hydrology, particularly streamflow, is assessed by comparing three simulations performed with the original and two modified versions of CLASS, driven by atmospheric forcing data from the European Centre for Medium-Range Weather Forecast (ECMWF) reanalysis (ERA-Interim) for the 1990–2001 period over a northeast Canadian domain. The two modified versions of CLASS differ in the soil hydraulic conductivity and matric potential formulations, with one version being based on formulations from a previous study and the other one is newly proposed. Results suggest statistically significant decreases in infiltration and therefore soil moisture during the snowmelt season for the simulation with the new hydraulic conductivity and matric potential formulations and fractional permeable area concept compared to the original version of CLASS, which is also reflected in the increased spring surface runoff and streamflows in this simulation with modified CLASS over most of the study domain. The simulated spring peaks and their timing in this simulation are also in better agreement to those observed. This study thus demonstrates the importance of treatment of frozen water for realistic simulation of streamflows. 相似文献
9.
10.
Modelling Carbon Dynamics of Boreal Forest Ecosystems Using the Canadian Land Surface Scheme 总被引：1，自引：1，他引：1
The ecosystem carbon (C) and nitrogen (N) simulations recently implemented in the Canadian Land Surface Scheme (CLASS) are presented. The main calculations include plant photosynthesis, autotrophic respiration, root N uptake, litterfall, plant growth, and soil heterotrophic respiration. Model experiments are made on two boreal forest ecosystems, deciduous (aspen) and conifers (black spruce). Simulated plant, soil, and ecosystem CO2 exchanges are analysed on half-hourly, daily, and annual time scales and compared with tower eddy correlation flux measurements and estimates from various authors. Modeled daily ecosystem CO2 exchange explained86% and 54%, respectively, of the observed variance of eddy correlationflux at the aspen site and at the black spruce site. Annual results show that the aspen ecosystem was simulated as a C sink in both 1994 (+164 g Cm–2) and 1996 (+142 g C m–2), and the black spruce ecosystem wassimulated as a C sink in 1994 (+39 g C m–2) and 1995 (+25 g Cm–2), but as a C source in 1996 (–27 g C m–2). 相似文献