KNMI Climate Scenarios
Current KNMI'06 scenarios for precipitation
01-09-2008
Future worldwide
Climate models calculate an increase in total annual precipitation for the temperate regions and a decrease in the subtropics. However, the calculations vary considerably among themselves. For southern Europe nearly all climate models calculate a decrease in summer precipitation and an increased chance for drought. For northern Europe the change in precipitation is less consistent. For Europe as a whole, an increased chance of prolonged heavy precipitation and short intense showers is calculated (Figure 9).
Figure 9 Illustration of the typical change in spatial precipitation patterns in the W+ scenario for summers around 2050 compared to 1990. The maps are constructed using results of the KNMI regional climate model RACMO2. At left the change in average summer precipitation, and at right the change of the intense showers (daily precipitation sum exceeded once every 10 years). The average precipitation is decreasing almost everywhere, whereas the precipitation amount in heavy showers is increasing.
Future in the Netherlands
In the G and W scenarios (those without significant change in air circulation patterns) precipitation increases both in summer and winter with approximately 3% per degree global temperature increase. In the G+ and W+ scenarios (those with significant change in air circulation
patterns) precipitation increases more in winter (about +7% per degree C) and decreases in summer (about -10% per degree C; Figure 10 and Table 1). The decrease in summer precipitation can be
attributed mainly to the decrease in the number of rainy days.
In all scenarios, the average precipitation amounts on extremely wet summer days increase due to the occurrence of heavier rain showers (largest increase in the W scenario). In winter the relative increase of the extreme 10-day precipitation amounts is approximately the same as
the increase of the average precipitation amount, for all 4 scenarios.
Figure 10 Precipitation in the Netherlands (average of 13 stations) between 1906 and 2005, and the four climate scenarios for 2050 (coloured points). The thick black line represents the 30-year moving average of the observations. The thick coloured and dashed lines connect each climate scenario with the baseline year 1990. The grey band represents the year-to-year variation, derived from the observations.
