First Results

The climate atlas of the province of South Holland includes maps on which the climate variables are visualised. The maps with climate change data show an indicative image of climate change. The fluid lines on the maps need to be seen as rough contours, without information about regional differences. The climate scenarios of the KNMI do not include differences between regions, but the changes are assumed to be the same in the entire country. Thus, the patterns of the existing and future climate are identically.

The maps are made for current climate data and those of 2050. The W and W+ scenarios (KNMI, 2006) are used, because they represent the highest expectations of the KNMI scenarios. Apart from that, they indicate the fastest pace of changes. Thus, if climate changes less fast there is more time to implement the adaptation measures. However, the necessity to take measures stays important anyway.

Furthermore, the maps do not indicate a one to one relation between changes in primary effects and the secondary consequences. For example, it is possible that a small increase in precipitation leads to big problems, like floods, while larger increase at another location does not lead to any problem.

2.4.1.1 Temperature

The four KNMI scenarios show a rise in temperature in 2050. The winter (December-February) temperature rise varies from 0.9 to 2.3°C and the

Aantal ijsdagen per jaar (maximumtemperatuur < Û°C)

1976 - 2005

1976 - 2005

Fig. 2.5 Decrease in number of ice days (Source: Alterra et al., 2007)

temperature rise in summer (June-August) summer varies from 0.9 to 2.8°C (KNMI, 2006). Figure 2.5 shows the consequences in number of ice-days (freezing all day long) in South Holland. The chance that speedskaters still can skate in the 2050 winter has decreased.

The summers in South Holland will become warmer as well. The 2003-summer was warm and dry. In Rotterdam, the average temperature in that summer was 18.6°C, almost 2°C warmer than normal (in the period 1971-2000). In Europe a lot of deaths were counted as a result of heat stress in the same summer. On the other side a lot of people enjoyed the perfect beach weather of that time. This summer was extraordinary in the current climate, but according to the W and W+ scenarios this summer would be an average one in 2050. Figures 2.6 and 2.7 show the number of summer days (maximum temperature > 25°C) and the number of tropical days (maximum temperature > 30°C).

Aantal zomerse dagen per jaar (maximumtemperatuur >= 25°C)

1976 - 2005

1976 - 2005

Fig. 2.6 Increase of the number of summer days (Source: Alterra et al., 2007) Precipitation

Fig. 2.6 Increase of the number of summer days (Source: Alterra et al., 2007) Precipitation

According the IPCC (2007) expects a rise in average precipitation in Northern Europe and a decrease in Southern Europe. The Netherlands will have to deal with a slight average decrease of precipitation in summer and a substantial increase in winter. In the summer there is a sharp contrast between the Northern and Southern part of the country. Will the precipitation increase in the Northern part of the Netherlands, the Southern part has to face a serious decrease of precipitation. This makes the developments in summer precipitation relatively uncertain. The South Holland maps show this with a big difference between the W and W+ maps. In Fig. 2.8 the average winter precipitation increases in both scenarios while in Fig. 2.9 the W map shows an increase in summer precipitation and the W+ map shows a strong decrease. However, in both scenarios the number of intense showers increases (Fig. 2.10). For the province of South Holland this means an increasing chance at water annoyance in both the countryside as cities. The dry summers may lead in the W+ scenario to water shortages and groundwater level. If water shortages occur the drinking water

Aantal tropische dagen perjaar {maximumtemperatuur >= 30°C)

1976 - 2005

1976 - 2005

Fig. 2.7 Increase of the number of tropical days (Source: Alterra et al., 2007)

facilities are under pressure, especially when the supply from rivers decreases in dry summers. Due to low groundwater levels it becomes difficult to keep the water levels at minimal required levels necessary for minimising the effects on rottening foundation piles in the clay soils of South Holland.

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