Cold air outlet model KLAM 21

The cold air outflow model KLAM_21 (KLAM_21) is a two-dimensional, mathematical-physical simulation model developed by the German Weather Service (DWD) for the calculation of cold air flows in orographically structured terrain for questions of location , city and regional planning .

Brief description of the model

The model simulates the development of cold air flows and the accumulation of cold air in a freely selectable, rectangular area of ​​investigation. In doing so, obstacles protruding from the terrain (e.g. individual buildings, dams, noise barriers) can be modeled, which the cold air will only overcome when it has reached a corresponding height. The interaction of these influencing factors determines the emergence, flow and accumulation of cold air. In contrast to highly simplified models that are based on a "static" analysis of the relief and land use, KLAM_21 can reproduce cold air movements in their dynamics and temporal development across the board. The result is the areal distribution of the cold air height and its mean flow velocity or the volume flows at any point in time of the simulation. The comparison of actual and planning states is visualized with difference maps or temporal animations of the cold air level, the flow velocity or the volume flows.

Evaluation by the LANUV NRW

The State Office for Nature, Environment and Consumer Protection in North Rhine-Westphalia (LANUV NRW) also used KLAM_21 as a basis for creating the climate atlas planning maps for cold air outflows. For the calculation of the cold air flows throughout North Rhine-Westphalia, the model area covered over 72,000 km². The input data was based on a digital model for the elevation of the terrain and land use data (Corine data) derived from satellite data in a grid of 200 m. The LANUV NRW rated the model as follows:

"Overall, comparisons with measurements have shown that KLAM_21 generally delivers very good results, but the model also has its limits. When interpreting the results, it should be noted that a grid width of 200 m is quite rough. In order to be able to correctly resolve the effect of a terrain structure, at least three to four grid points are necessary, which means that, for example, the conditions in a valley that is less than 800 m wide can only be reproduced to a limited extent by the simulations In reality, a downward wind blows across the valley axis near the ground, while there is a downward wind up in the valley. Since KLAM_21 is a two-dimensional model that considers the entire cold air as a uniform layer, such a simulation in the model is not possible very small-scale patterns cannot be reproduced and in narrow valleys or sharp bends it can happen that the flow velocity t is underestimated and unrealistic cold air jams occur. On the other hand, due to the coarse resolution, long slopes become too "smooth", since smaller elevations and depressions are not reproduced or only to a limited extent. As a result, the flow velocity is presumably overestimated, especially on the slopes of the low mountain ranges facing the lowlands. Both in the model and in reality, e.g. For example, strong inflows from side valleys and limited outflow in the main valley mean that the cold air has to flow up the valley or overflows the heights that border the valley. This is also evident in the simulations for North Rhine-Westphalia, e.g. B. in the Ruhr valley or the Wuppertal to observe. Due to the limited resolution and the two-dimensionality of the model, this is an indication that such phenomena can occur at these points. Whether this is also the case in reality, however, must in individual cases, e.g. B. on the basis of measurements and / or more detailed modeling, can be checked. Despite the above-mentioned limitations in the small-scale interpretation of the maps, the results of the KLAM_21 calculations provide a good starting point for assessing cold air outflows e.g. B. in the context of regional planning. "

Concrete application using the example of the city of Aachen

The city of Aachen is to be cited as a current example for the application of the cold air discharge model KLAM_21. As far as can be seen, when a new land use plan is drawn up, for the first time in a major German city, climate protection issues will be systematically taken into account in accordance with the 2011 climate protection amendment to the Building Code; In 2013/2014, the Institute of Geography at RWTH Aachen University , Climatology Working Group, Prof. Dr. C. Schneider and Dr. Gunnar Ketzler, together with the Department of Environment of the City of Aachen, created a Climate Impact Adaptation Concept (KFK), which u. a. includes a city-wide climate report from 2000 as well as earlier investigations about the local cold air flow conditions.

In addition, in addition to numerous meteorological measurements, extensive model calculations have also been carried out with the aid of the KLAM_21 cold air model. A configuration was developed so that results that matched existing measurement data were achieved; the model output was prepared in such a way that the results could be processed in a meaningful planning manner based on VDI guideline 3787, sheet 1, environmental meteorology - climate and air hygiene maps for cities and regions. With these supplementary investigations by RWTH Aachen University, the fundamental findings on the formation of cold air at night and its effectiveness in the Aachen valley basin, which is particularly polluted in terms of climatic and air hygiene, could be further deepened and a map base that could be used over a wide area was developed.

In the additional model run with the KLAM_21, fictitious additional development in the scope of the current FNP test areas was assumed for 2030. This prognostic study was able to prove that future development of the relevant cold air generation and runoff areas would be accompanied by significantly reduced night-time cooling in some areas; The cartographic representation of the changes in 2030 compared to 2010 makes it clear that a decrease in nighttime cooling with values ​​of over 1.0 ° C would occur, especially on the southern and western outskirts of the city center and on the edge of the Burtscheid core area ( Beverau ).

literature

• SIEVERS, U., 2005: The cold air discharge model KLAM_21. Theoretical basics, application and handling of the PC model: DWD report Volume 227 ( abstract ).

Footnotes

1. ↑ DWD website on Klam_21
2. ↑ Information sheet of the DWD on the cold air discharge model KLAM_21 , DWD PDF file
3. ↑ Climate Atlas NRW - Cold Air Drains - Map Interpretation ( Memento of the original from July 29, 2017 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. 
4. ↑ G. Ketzler et al. a .: Aachen climate change adaptation concept: Implementation of results of urban climatological research in an FNP list
5. ↑ VDI guideline 3787
6. ↑ Aachen Climate Impact Adaptation Concept (AKA) , Geographical Institute of RWTH Aachen University
7. ↑ Submission to the Aachen Environment Committee on June 28, 2016