Knowledge of Climate

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Information on climate change is available on a national scale so far. The knowledge will be available on a regional scale in the form of climate atlases. Groningen runs ahead of this by visualising three important factors for spatial functions: temperature, precipitation and sea level rise (Roggema, 2007a, DHV, 2007). Precipitation and sea level rise are discussed here. Precipitation

The possible changes in future precipitation amounts and patterns are shown in Fig. 2.14. The maps show the possible changes for Groningen and Drenthe provinces (Alterra et al. 2008) in 2050 in two KNMI '06 scenarios (KNMI, 2006) for the winter and summer period.

The main conclusions of the precipitation-analysis are:

1. In the summer period drought will most likely increase. In the 'dry' scenario of the KNMI (W+) in the eastern part of the provinces (the Peat Colonies) drought becomes a serious problem. Nowadays, water shortage in this area is already a problem. Currently, the inlet of water from the IJssel Lake solves this problem. The question for the future will be if this water is still available and if the quality of the water is good enough. The problem of water shortage and uncertainty of supply will increase in the future, due to longer dry periods in summer, which are caused by climate change. Another change in precipitation is the increased intensity of severe rain showers. This happens mostly in the summer period.

2The development of scenarios was done based on the KNMI06 scenarios. The most extreme element were taken from the different scenarios and were combined in one set of data, which is methodologically not correct.

When it rains in summer it pours. This effect is not visible in the maps, but it has a huge impact on water management and implies an increased risk of floods in urban areas;

2. According to the KNMI '06 scenarios (KNMI, 2006), autumn, winter and spring become (much) wetter. Although a dry summer will have its 'drying' effects in autumn, which leads to average dryer autumns, the total amount of precipitation in the winter period increases. This raises questions as to how the water management must be arranged. Is an increased discharge towards the sea (with accompanying increase of pump capacity) the best solution or is an increased amount of water storage preferred? Beside the primary effects of changes in precipitation, there are also secondary effects, which are driven by these changes in precipitation.

3. There is an increasing necessity to store the extra water in wet periods or pump it into the sea with heavier pumping engines;

4. In dryer periods an increasing demand for water, especially in dry areas, asks for extra supply;

5. The question may be raised if agriculture and nature are capable of withstanding and surviving the longer lasting dry periods;

6. Urban areas increasingly have to cope with the impossibility to discharge the extra water, falling in the form of severe showers in the summer period, leading to periodical floods. Sea Level Rise

The sea level will continue to rise for the next decades and most probably for the next centuries. The speed and degree of sea level rise is dependent on the pace of melting processes of land ice on Greenland and Western Antarctica. Even if the emissions of CO2 could be frozen at today's emissions level, the melting process would continue for the next decades. Therefore, adaptation to the rise of the sea level is inevitable. The maps (Fig. 2.15) show the possible impact of the rise of the sea level for Groningen, compared with current altitudes, in two scenarios (+50 and +150 cm). The maps show the maximum impact, because they were modelled with an undisturbed flooding by the sea after a dike breach. In reality several obstacles (roads, little dikes) in the landscape prevent the sea from entering the land without barriers.

The maps show an indication of what might happen in the two sea level scenarios. The images are based on altitude lines and do not take into account the real circumstances in which a breakthrough takes place, namely when the sea level is much higher than normal (spring tide) and heavy rain and wind are present. Also, the map does not show the positive effect of good maintenance of dikes in order to keep them strong, which makes a breakthrough less likely to happen. On the other hand, the impact of a much faster melting land ice, leading to possible sea level rises of 3 m (Gore, 2006) or up to 10 m (Carlson, 2006) above the current level, is not visualised in the maps either.

Based on these maps a couple of conclusions can be drawn:

1. The southern parts of the province (Peat Colonies, Westerwolde, Southern Western-quarter) and the city of Groningen are the highest parts of the province. In these areas flood risk is low. Naturally, a sea level rise of 3 m or more would place these areas at risk as well;

2. The industrial areas of Eems-harbour and Delfzijl are located at artificially constructed higher levels. These areas are relatively safe, even in a more extreme sea level rise scenario;

3. Though not visible in the maps, the salinity of agricultural land along the coast increases, due to the sea level rise, which results in increased seepage;

4. The lower and wetter parts of the province show a spatial connection between Lauwers Lake and Dollard. This connection, together with the brook system in Drenthe is potentially the most important wet ecological structure for the future. Here, nature is able to survive the longer periods of drought.

Another effect of sea level rise is the possible disappearance of parts of sandbanks in the Wadden Sea. Stive (De Boo, 2005) expects that a fast sea level rise, up to 60 cm in this century, will lead to an inability of the sedimentation process to supply the sandbanks with enough sand, which results in the drowning of the sandbanks. It is estimated that in this case 50% of the sandbanks will have disappeared within 40 years from now.

Fig. 2.15 Flooding according to altitude lines (current situation (left), 50 cm sea level rise (centre) and 150 cm (right), (Roggema, 2007a)

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