Drought

Drought has become more common, especially in the tropics, since 1970. Droughts are becoming longer and more severe and are affecting a wider area. This is consistent with decreased precipitation in some areas and higher temperatures causing drying conditions. Increasing sea surface temperatures and loss of snow are direct contributors to drought. An index called the Palmer Drought Severity Index (PDSI) is used to compare the extent of local loss of surface land moisture. Figure 3-27 shows that

Global Thermal Balance

Figure 3-27 The Palmer Drought Severity Index (PSDI1) from 1900-2002 shows a tendency toward increasing drought conditions worldwide. (Source: IPCC.)

1900 1920 1940 1960 1980 2000

Figure 3-27 The Palmer Drought Severity Index (PSDI1) from 1900-2002 shows a tendency toward increasing drought conditions worldwide. (Source: IPCC.)

drought conditions overall have been increasing worldwide since 1900. Some regions, such as the southern part of South America, are not seeing drought but rather an increase in moisture. However, more areas than not are seeing drying conditions. The smooth line through the data shows a pattern of natural increases and decreases on the time scale of decades. The dominant pattern that emerges through the natural variations is a trend toward more severe drought conditions worldwide.

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