Recent Trends in Extreme Weather

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5.1.1.d

For many regions in the mid- and high-latitudes, mainly in the Northern Hemisphere, heavy and extreme precipitation events have increased by 2 to 4 percent in the last 50 years. Parts of Africa and Asia have suffered increases in both the frequency and intensity of drought in recent decades.

Figure 1 Linear trends (% / decade) of heavy precipitation (above the 90th percentile) and total precipitation during the rainy season over various regions of the globe. Seasons for each region usually span at least 50 years.

Source: Climate Change 2001: Working Group I: The Scientific Basis Section 2.7.2.2

There have been regional increases in hurricanes in the North Pacific and parts of North America and Europe. In the Southern Hemisphere the reverse is true: research shows a decrease in hurricanes since the 1970s.

Table 1 compares observed changes in extreme weather with projected changes in this century.

Table 1. Estimates of confidence in observed and projected changes in extreme weather and climate events. Likely means 66-90% chance and very likely means 90-99% chance

CHART NEEDED —  3 Columns, 9 rows

Source: IPCC Climate Change 2001 Synthesis Report p. 211

Questions:
Refer to Figure 1.

1. How are the changes in heavy precipitation measured? What is the time period for these measurements? What is the difference between the black and gray bars?
2. Identify regions with the largest changes in heavy precipitation.
3. State whether they represent positive or negative changes in heavy precipitation.
4. Explain in your own words what these changes mean.Look at the eastern USSR. What do you notice about the changes in mean total precipitation with the changes in mean heavy precipitation? Explain how this can be true.

Refer to Table 1.

6. How does the level of confidence change between present observed changes and future projections?

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