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Regional climate-chemistry simulations for Southern Germany (BayForUV)

It is expected that changes in temperature and cloudiness due to global climate change will also have an impact on UV and visible radiation and therefore also on photooxidant production. The effect of global climate change on air quality on a regional scale can be investigated by regional climate-chemistry simulations for present day and possible future conditions.

To investigate the potential effects of changed climate conditions on UV radiation and the photosmog situation in Southern Germany, regional simulations with the online coupled 3-dimensional meteorology-chemistry model MCCM were performed. Based on boundary conditions from a long term simulation with the global climate model ECHAM4 the regional model MCCM predicts the relevant meteorological processes as well as chemical transformations and transport of pollutants in the gas phase. Two 10 year time slices were considered, which represent the 90ths of the previous century and the 30ths of this century. In two consecutive one-way nesting steps, the global simulation (resolution T42, i.e. about 250 - 300 km, greenhouse gas scenario IS92a) was downscaled to a resolution of 60 km for Europe and 20 km for Central Europe. To our knowledge, this was the first online coupled regional climate-chemistry simulation worldwide.

As compared to the 90ths of the previous century an increase of the mean temperature in Southern Germany by about 2 degrees is simulated by the model for future climate conditions. This is accompanied by a reduction of cloud water and ice content, resulting in an enhanced global and UV radiation. Until 2030 the simulated average UV radiation during the summer months increases by about 9 mW/m2 (i.e. 6%) for the selected scenario. The highest increase with values around 15 mW/m2 was found in the western part of Southern Germany while a significantly lower increase of only 2% was simulated for the southern part of Bavaria.

   
Simulated differences between present day and future climate conditions for average values of downward solar radiation during the summer months

Simulated differences between present day and future climate conditions for the number of days with exceedance of a threshold value of 60 ppb for the 8-hourly ozone mean

Under the model assumption of unchanged anthropogenic emissions the increased income of solar radiation and the higher temperatures under future climate conditions lead in the model to an increase of near surface photooxidant concentrations in the summer months. In the case of ozone, the simulated increase of the mean daily maximum ranges between 4 µg/m3 and 10 µg/m3. As a consequence of the higher daily ozone maximum under future climate conditions, the number of days where the threshold value of 120 µg/m3 for the 8-hourly ozone mean is exceeded, increases by 3 days in northern Bavaria and by 13 days in the region near the Alps.

This investigation was funded by the Bavarian Ministry for Environment, Health, and Consumer Protection as part of the joint research project BayForUV (1999-2003).


Publications

Forkel, R. and R. Knoche (2006) Regional climate change and its impacts on photooxidant concentrations in southern Germany: Simulations with a coupled regional climate-chemistry model, J. Geophys. Res., 111, No. D12, D12302, doi:10.1029/2005JD006748 (13pp.)

Forkel, R. and R. Knoche (2007) Nested regional climate-chemistry simulations for Central Europe. Comptes Rendus Geoscience 339, 734–746, doi:10.1016/j.crte.2007.09.018

 

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Final report (in German)


Contact: Renate Forkel, Richard Knoche