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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
|
Confidence in observed changes
(latter half of the 20th century) |
Changes in Phenomenon |
Confidence in projected changes
(during the 21st century) |
|
Likely |
Higher maximum temperatures and more hot days over nearly all land
areas |
Very likely |
|
Very likely |
Higher minimum temperatures, fewer cold days and frost days over
nearly all land areas |
Very likely |
|
Very likely |
Reduced diurnal temperature range (difference between max. and
min. temperature during a day) over most land areas |
Very likely |
|
Likely, over many areas |
Increase of heat index (need definition) over
land areas |
Very likely, over most areas |
|
Likely, over many Northern Hemisphere mid- to high latitude land areas |
More intense precipitation events |
Very likely, over most areas |
|
Likely, in a few areas |
Increased summer continental drying and associated risk of drought |
Likely, over most mid-latitude continental interiors. (Lack of consistent
projections in other areas) |
|
Not observed in the few analyses available |
Increase in tropical cyclone peak wind intensities |
Likely, over some areas |
|
Insufficient data for assessment |
Increase in tropical cyclone mean and peak precipitation intensities |
Likely, over some areas |
Source: IPCC Climate Change 2001 Synthesis Report p. 211
Questions:
Refer to Figure 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?
- Identify regions with the largest changes in heavy precipitation.
- State whether they represent positive or negative changes in heavy precipitation.
- 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.
- How does the level of confidence change between present observed changes
and future projections?
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