Trends of Global Precipitation

During the twentieth century, the atmosphere has warmed up by around 0.6 K in global mean. This has increased the water vapor content of the atmosphere and altered general circulation patterns and the distribution of pressure systems. This is confirmed in Figure 11 . The blue areas represent regions with increased precipitation, whereas the red areas are those with decreased precipitation. In the gray-colored areas no secure precipitation trend has been proved. The overall area with increased precipitation is, as might be expected, greater than that with decreased precipitation. Regions with a mainly positive precipitation trend are, for example, large parts of Canada, Western Europe, Scandinavia, the northeastern part of Europe, eastern Siberia, a large part of South America, eastern Central Africa, and Northwest Australia. A marked negative trend is present in the African savannas north of the equator. This development with its varying regional effects is first and foremost the

Precipitation trend 1901/2000

No trend/no data Negative Positive Figure 11 Trend of the annual sum of precipitation, 1901-2000.

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Figure 12 Annual sums of precipitation, Goeteborg, Sweden.

result of altered pressure conditions and currents. Moreover, there are also areas where both positive and negative trends take place within a relatively small area, such as in the Mid-West region of the USA.

Figure 12 shows an example of precipitation increase in Scandinavia. One can see that in Goetheburg, precipitation has increased on average by around 250 mm in recent decades. This represents an increase of about 135% on the previous mean figure.

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Figure 13 Monthly mean of precipitation, Antarctic, west coast (annual sum = 674 mm), South Pole (annual sum = 111 mm).

the continent which were generated through modeling. At the South Pole itself the annual precipitation is very low, at 111 mm, and hardly varies from month to month. On the west coast of the continent the annual sum increases to 674 mm and shows a distinct seasonality with a maximum in April and a minimum in December.

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