Valeri Goldberg

Wind fields in heterogeneous conifer canopies: parameterisation of momentum absorption using high-resolution 3D vegetation scans

Applications of flow models to tall plant canopies are limited, amongst other factors, by the lack of detailed information on vegetation structure. A method is presented to record 3D vegetation structure and make this information applicable to the derivation of turbulence parameters suitable for flow models. The relationship between wind speed, drag coefficient (CD) and plant area density (PAD) was experimentally investigated in a mixed conifer forest in the lower part of the Eastern Ore Mountains. Essential information was gathered by collecting multi-level high-frequency wind velocity measurements and a dense 3D representation of the forest was obtained from terrestrial laser scanner data. Wind speed dependence or streamlining was observed for most of the wind directions. Edge effects, i.e. the influence of the here not regarded pressure gradient and the advective terms of the momentum equation, are assumed to cause this heterogeneity. Contrary to the hypothetic shelter effect, which would reduce the drag on sheltered plant parts, the calculated profiles of drag coefficients revealed an increasing CD with PAD (i.e. a dependence on canopy and plant structure).

GIS‐based regionalisation of radiation, temperature and coupling measures in complex terrain for low mountain ranges

In low mountain-range areas with complex topography, climate elements show a high variability caused by manifold interactions between relief and land use. The lack of continuous measurements demands concepts for the transfer of regional climatic information to smaller scales. In this study, a radiation model and a coupled vegetation atmosphere model using GIS were combined to estimate radiation balances, temperature and evapotranspiration as well as coupling and feedback mechanisms between vegetation and atmosphere of small-scale heterogeneous areas. In the system HIRGIS, these approaches were parameterised with the output of the vegetation-boundary layer model HIRVAC and transferred in a GIS (ArcView) environment to consider topographic influences including sky view factors as well as the influence of different land uses (e.g. pasture and forest) especially on net radiation. Depending on the horizontal resolution of the digital elevation data, it is feasible to model area-related meteorological surface data without any interpolation methods and associated loss of precision. The results are applicable to water budget modelling, forest management, alternative energy supply or downscaling of satellite information. To illustrate the results, the area of the Tharandter Wald near Dresden as well as the Sperrgraben watershed in the Bavarian Alps were selected. The results clearly show the combined effects of topography and land use. The differences of solar irradiance on a clear spring morning between slopes oriented east–west and south–east in the Tharandter Wald reach up to 800 W/m2. The daily sum of evapotranspiration on a steep, south-facing spruce-covered surface in the Sperrgraben watershed is two times higher than the evapotranspiration on a north-facing grass surface. Model results match data collected at the ‘Anchor Station Tharandter Wald’ and from the Sperrgraben watershed for the periods under investigation. Copyright

Upgrading the coupled vegetation boundary layer model HIRVAC by new soil water and interception modules

The coupled atmospheric boundary layer model HIRVAC (High Resolution Vegetation Atmosphere Coupler) combines a 1.5 dimensional planetary boundary layer model (developed at the Humboldt University Berlin) and the mechanistic photosynthesis module PSN6 (University of Bayreuth) as well as a soil water module. This multi layer model includes a vertically structured vegetation and covers a range from 0-2 km height. The model layers are coupled via the turbulent exchange using a K-approach. Recent work aimed to include several new modules to enable model calculations for realistic conditions. Therefore rainfall and a multi layer interception and a soil water module were included. Further the light extinction through the canopy was upgraded by including sunfleck dynamics for calculating a more realistic radiation distribution within and below canopy. The upgraded model version was run for the Anchor Station in Tharandt where various measurements for comparison with model results are available. The obtained results demonstrate that periods of several days can be modelled successfully. A good model performance was found for both, soil water and interception. The modelled energy fluxes finally confirm the reliability of the overall model performance.

Application of a radiation model for small-scale complex terrain in a GIS environment

To calculate the radiation balance of small-scale heterogeneous terrain well known approaches were combined with the vegetation-boundary layer model HIRVAC (HIgh Resolution Vegetation Atmosphere Coupler). These modified approaches were transferred in a GIS (ArcView) environment to consider both topographic influences (terrain geometry, sky view factor) and the influence of different land uses (e.g. pasture and forest) on radiation components. The GIS application is based on the digital elevation model of the Saxonian land surveying office (SLVA) with a resolution of 25 meters and on the land use classification from the Institute of Cartography of the Technical University Dresden. The model was applied to the Eastern Ore Mountains (Saxony/Germany). To illustrate the results the area of the Tharandter Wald near Dresden was selected. The results show that the influences of topography and land use on radiation balance are equally important on a terrain with complex land surface patterns and a strong domination of small-scale topography. The shortwave insolation on a clear Spring day is, e.g., over areas with northern aspect up to 10 times lower than over southward orientated areas. The spruce areas in the forest are characterised by 2 times higher daily sums of net radiation than the adjacent clearcuts. The model results are in adequate agreement with measurements of the Anchor Station Tharandter Wald for the investigated period. The results can be applied for water budget modelling, forest management and for downscaling of satellite information.