Climate Change Compensatory Measures – Verification of functionality of compensatory measures under climatic influenced conditions using the example of the city of Kiel | Umweltbundesamt

Model simulations for the historic climate (1950 – 2005) and projections for the future climate (2005 – 2100) were calculated with the regional climate model REMO. Climate projections for the future include the climate change scenarios RCP2.6, 4.5 and 8.5. In the first variant, the climate variables were calculated exclusively with the regional climate model REMO (RCP2.6, RCP4.5, RCP8.5), driven by the global model MPI-ESM, with a spatial resolution of 0.11 ° (~ 12.5 km ) and a time resolution of one hour. This variant had to be chosen at the beginning of the development phase of the City Modular Modules, as at that time no ensemble of regional climate projections was freely available for the selected study area.

In the second variant, regional climate projections of the EURO-CORDEX initiative were used, which were generated by "dynamic downscaling" (Jacob et al., 2014). 34 climate projections were analyzed, divided into four projections based on scenario RCP2.6, and 15 projections based on scenarios RCP4.5 and RCP8.5, respectively. The ensemble includes simulations of six different regional climate models (RCMs) powered by eight different global climate models (GCMs) and GCM implementations, respectively. The REMO simulations used in the first variant are part of the EURO CORDEX ensemble used in the second variant.

The following indices related to temperature and precipitation were used for the project:

• Long-term mean of temperature and long-term seasonal average for winter
• dewpoint
• Long-term average amount of precipitation and long-term seasonal average
• Long-term mean of wind force
• Number of summer days or summer days
• number of heat days
• Number of heavy rain events
• number of dry periods
• length of the dry periods
• Average length of the growing season
• Middle beginning of the vegetation period

A comparison of the modeling with measured values took place. The station is located in Kiel-Holtenau. A comparison of the measured and modeled temperature values shows that the observations have higher values than the statistics of the EURO CORDEX ensemble. By contrast, wind simulations show higher values for the simulations. Nevertheless, the model values are on a reasonable scale, especially since the observation data are punk information and the model results are mean area results. As sensitivity studies in the context of a GERICS product development have shown for a comparable area, two measuring stations within a grid box can well have differences of over one degree Celsius. For precipitation values, differences in daily values of 100% and more can occur due to the heterogeneous distribution of precipitation - especially in small-scale events such as heavy rainfall. For all subsequent comparisons between the result of the REMO climate projections and the ensemble results, it should be noted that the time period of the ensemble is shortened by one year.

Mean wind force, number of summer days, number of hot days, start / middle length of the growing season

• Total simulation period of the historical model simulation: 1950 - 2005
• Total simulation period for future developments: 2005 - 210
• Observation data measuring station (temperature): 01.01.2002 - 31.12.2012

Based on the data obtained for the Greater Kiel results of climatic development for the "Near Future" (2020 by 2050) under the assumption of various climate change scenarios can be formulated following future changes:

Increase in the average temperature can – especially after taking into account the robustness and significance tests of Jacob et al. (2014) - considered assured. This increases the likelihood of a higher number of summer days and hot days, although the increase is considered moderate. Seasonal precipitation tends to be expected to show slight increases, but no major changes in average values. However, precipitation will not fall evenly over the indicated periods, so locally both over-supply (flooding after a heavy rainfall) and water shortage (during dry periods, which may take longer) can occur periodically. Due to the high probability of prolongation of the vegetation period, plant-related water demand will increase. This can have a negative effect on the local water supply already under consideration of constant climatic conditions and favor the drought stress in plants.

The change signals projected within the framework of this study are relatively weak, so that rather slight climatic changes with minor effects are to be expected. Climatic changes in Schleswig-Holstein or in the investigated compensation areas of the state capital Kiel are unlikely to have a significant impact on the formation of new forests or forest development through first afforestation and the development of semi-open pastureland. Thus, it can be assumed that the development goals are achieved, so that 2050 forest areas, fen meadows, reed beds as well as sedge areas and a semi-open pasture landscape have emerged.

In contrast, the (independent) development of wetlands, such as small, still and flowing waters, fen areas and partially also alluvial meadows, may be more or less at risk. In the course of higher average temperatures and altered precipitation patterns, insufficient water columns can occur at times - especially in summer. In combination with higher nutrient concentrations (higher input and lower dilution performance), the growth of pests and pathogens as well as the weeding can be promoted, which counteracts the achievement of the objective of the compensatory measures.

Nevertheless, in order to be able to achieve these development goals, it is possible to have a positive influence on independent development through additional (care) measures.

Using the example of three measures, the climatic change was examined for its functionality. Areas affected by climate change. include the water cycle and the plant society. As an example for terrestrial water systems wetlands and ponds were chosen. Regarding the flora, the focus of this study was on First afforestation, reeds and carex reed. The subject of the study was the objectives agreed under a planning approval procedure under present and future climatic conditions (period until 2050).

Comparative measures were:

• first afforestation in Mielkendorf
• Measures from the southern city of Kiel: (semi-open pasture landscape Großer Wiesenberg), Restructuring of forest areas with biotope function ("Meimersdorf Moor"), near-natural redesign of the "Wellsau"

The measures were reviewed for their cause and purpose, initial situation, review and assessment of future target achievement. Further measures in a catalog of measures for the care and support of the development of the semi-open pasture landscape with woody structures, ponds, rivers, (carex) reed and bog.