Theme cards

Spatial impact - relevant areas shown in thematic maps

The city of Mainz faces a variety of challenges due to climate change. In order to better understand these challenges and develop effective measures, spatial analyses were carried out, the results of which are presented in thematic maps. These maps provide detailed insights into the effects of climate change on the city and serve as a basis for planning decisions.

The maps visualize climatic influences such as heat, drought, heavy rainfall, and flooding, as well as their consequences. A total of nine thematic maps are available. An overarching focus area map summarizes the areas that are particularly affected in order to define priority areas for action.

The thematic maps are based on expert reports and geodata available at the city, state, or federal level. To this end, the results and geodata for the various topics were processed and summarized.

Focus room map

The focus area map combines the results of all thematic maps and highlights particularly vulnerable areas. Focus areas are defined as areas that are highly likely to be affected by one or more climatic influences. Since these are focus areas, relevant stresses and climate risks may also occur outside these areas. The focus area map does not allow conclusions to be drawn about individual impacts, but serves to communicate and raise awareness and to illustrate multi-climatic stresses.

Theme map Focus area mapPDF-File6,92 MB

Heat load and green space supply during the day

On hot, windless, and cloudless days, so-called heat hotspots develop in densely built-up and sealed areas. Urban green spaces with high levels of shade and evaporation are particularly important here as cooling retreats. On average, Mainz experiences 16 to 34 hot days (>30 °C) per year, significantly more than in the cool and well-shaded forest areas in the surrounding region. By 2100, the worst-case climate scenario predicts that this number will double.

Thematic map Heat stress during the dayPDF-File8,62 MB

City climate at night after a warm summer's day

Sealed surfaces store heat and cool down more slowly at night, creating heat islands. Cool air currents from green spaces and corridors are crucial for nighttime cooling. Denser development intensifies this effect. Green spaces also play an important role at night in reducing the heat island effect. Climate change will make such stressful weather conditions with high nighttime temperatures more frequent.

Thematic map urban climate at nightPDF-File8,84 MB

Function of urban greenery in the heat

On hot days, urban green spaces with the highest possible degree of shade and evaporation rates are extremely important as cooling areas for the population. Shade provided by trees is the key factor for pleasant outdoor conditions. The map shows the extent of shade provided by tree canopies in summer throughout the city for different types of land use (green spaces, open spaces, streets, paths, private and public areas). This makes it possible to assess which areas have particularly high natural shade from trees and which areas offer less shade.

Theme map Shading by treesPDF-File16,73 MB

Heavy rain

Heavy rainfall leads to flooding, especially along watercourses and bodies of water. Topographical analysis reveals critical points and possible main flow paths. Climate change is expected to bring about changes in heavy rainfall events. Studies show that heavy rainfall events will occur more frequently and become more intense in the future. It is therefore to be expected that existing flood hotspots will expand further or be affected more frequently in the future. Flooding along the Rhine and local streams can be exacerbated by heavy rainfall events.

Heavy rain theme mapPDF-File8,35 MB

Function of urban greenery during heavy rainfall

Green spaces can be used during heavy rainfall as areas that specifically retain surface water (retention areas) and as cooling places to stay on hot days. By superimposing water depths and green spaces, it is possible to identify those areas where water already accumulates during heavy rainfall events or those that have not been affected by flooding to date.

The main flow paths also show where surface runoff water could be diverted into green spaces. Especially when a flow path runs very close to a green space, it may be useful to use the green space for temporary retention of runoff. Multifunctional use of green spaces combines flood protection with recreational value, e.g., through temporary water retention in parks.

Thematic map Function of urban greenery during heavy rainfallPDF-File12,31 MB

River floods/waters

The flood hazard maps for Mainz show areas at risk along the Rhine and local waterways. The areas at risk of flooding will only be flooded if protective structures fail (e.g., dike breach). It should be noted that only the flooding situation on the surface is shown. Floodplains, which act as natural flood areas, are particularly important. Flood events will increase in intensity and frequency as a result of climate change.

Theme map watersPDF-File2,63 MB

Groundwater

In parts of Mainz, less groundwater is already being replenished. This is due to climate change, but also to changes in land use and other anthropogenic influences such as groundwater extraction. Falling groundwater levels are jeopardizing drinking water quality and infrastructure.

Groundwater theme mapPDF-File3,56 MB

Retention and erosion in outdoor areas

In the event of heavy rainfall, soil erosion can occur, particularly from outlying areas towards settlements. At the same time, outlying areas have the potential to retain surface water in a targeted manner. These soil and terrain characteristics are overlaid in the thematic map "Retention and erosion in outlying areas."

The erosion of topsoil can lead to a deterioration in soil quality and damage to ecosystems. Increased runoff carries the risk of increased soil erosion. Eroded soil material is carried along the main flow paths into adjacent settlement areas, where it can cause damage to infrastructure and settlements.

In view of climate change, these risks are expected to increase. Changing precipitation patterns and increasing extreme events are leading to an increase in erosion risk and runoff formation.

Thematic map Retention and erosion in outdoor areasPDF-File6,82 MB

Risk of soil dryness in open and green spaces

Changing precipitation patterns and longer dry periods have far-reaching consequences and pose challenges for vegetation and biodiversity, green space management, water management, and agriculture and forestry. The risk of soil drought is assessed on the basis of usable field capacity (the amount of water that a soil can store for plant use).

Soils with an increased risk are therefore more sensitive and can provide less moisture during droughts, which can result in damage to vegetation or crop losses. Mainz records around 259 dry days (precipitation below 1 mm) per year, and the water balance is already negative today.