Geoscience Reference
In-Depth Information
Storms and floods
Storms and floods are major natural hazards. Over the last decade they have been respons-
ible for three-quarters of the global insured losses, and over half the fatalities and economic
loses from natural catastrophes. It is, therefore, essential we know what is likely to happen
in the future. There is evidence that the temperate regions, particularly in the Northern
Hemisphere, have become more stormy over the last 50 years. In particular the climate
models suggest that the proportion of rainfall occurring as heavy rainfall has and will con-
tinue to increase, as will the year-to-year variability. This will increase the frequency and
magnitude of flooding events.
Two-fifths of the world's population lives under the monsoon belt, which brings life-giving
rains. Monsoons are driven by the temperature contrast between continents and oceans. For
example, moisture-laden surface air blows from the Indian Ocean to the Asian continent
and from the Atlantic Ocean into West Africa during Northern Hemisphere summers, when
the land masses become much warmer than the adjacent ocean. In winter, the continents be-
come colder than the adjacent oceans and high pressure develops at the surface, causing
surface winds to blow towards the ocean. Climate models indicate an increase in the
strength of the summer monsoons as a result of global warming over the next 100 years.
There are three reasons to support why this should occur: (1) global warming will cause
temperatures on continents to rise higher than those of the ocean in summer and this is the
primary driving force of the monsoon system; (2) decreased snow cover in Tibet, which is
to be expected in a warmer world, will increase this temperature difference between land
and sea, increasing the strength of the Asian summer; (3) a warmer climate means the air
can hold more water vapour, so the monsoon winds will be able to carry more moisture.
For the Asian summer monsoon, this could mean an increase of 10-20 per cent in average
rainfall, with an inter-annual variability of 25-100 per cent and a dramatic increase in the
number of days with heavy rain. The most worrying model finding is the predicted increase
in rain variability between years, which could double, making it very difficult to predict
how much rainfall will occur each year—essential knowledge for farmers.
One of the more contentious areas of climate change science is the study and predictions of
future tropical cyclones, or hurricanes as they are better known. Professors Kerry Emanuel
(Massachusetts Institute of Technology) and Peter Webster (Georgia Institute of Techno-
logy in Atlanta) and colleagues using different methods have demonstrated that the number
and intensity of hurricanes have increased over the last three decades in the North Atlantic
and Western Pacific Oceans. This is because the number and intensity of hurricanes are dir-
