to extremes dossier on floods

8/3/2019 To Extremes Dossier on Floods

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The Science of Extremes:

Floods

Floods are caused by:

Abnormally intense, fast, long-lasting or heavy rainfall, including spring rains that meltsnow fast

Changes in the surface conditions of the earth, such as sea level riseThe number of water- related disasters has increased at global scale in recent years. (Adikar

and Yoshitani, 2009)

A warmer atmosphere will mean a more moist atmosphere. But whether climate change wi

mean more floods globally is unclear:

There is limitedto medium evidenceavailable to assess climate-driven observedchanges in the magnitude and frequency of floods at regional scalesFurthermore,there is low agreementin this evidence, and thus overall low confidenceat the globalscale regarding even the sign of these changes.

(Extreme Events report summary, 2011)

Projected precipitation and temperature changes imply possible changes in floods, althougoverall there is low confidencein projections of changes in [river] floods.

Confidence is lowdue to limited evidenceand because the causes of regional changesare complex, although there are exceptions to this statement. There is mediumconfidence(based on physical reasoning) that projected increases in heavyrainfall would contribute to increases in local flooding, in some catchments oregions. (Extreme Events report summary, 2011)

It is very likelythat mean sea level rise will contribute to upward trends in extreme coastahigh water levels in the future. Small island states are in serious trouble.

There is high confidencethat locations currently experiencing adverse impacts such ascoastal erosion and inundation will continue to do so in the future due to increasing sealevels, all other contributing factors being equal. The very likelycontribution of meansea level rise to increased extreme coastal high water levels, [along with more powerfuhurricanes] is a specific issue for tropical small island states.(Extreme Events report summary, 2011)


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There is high confidencethat changes in heat waves, glacial retreat and/or permafrost

degradation will affect high mountain phenomena such as slope instabilities, movements of

mass, and glacial lake outburst floods.

There is also high confidencethat changes in heavy precipitation will affect landslides isome regions. (Extreme Events report summary, 2011)

Snow and floods

There is abundant evidence that winter snow will melt earlier in the spring or late wintthan it has in the past. Earlier snowmelt could cause harmful floods in regions near

snow. But, in a warmer world snowfall might decrease, reducing snowpack. These

details will likely vary from region to region. (Climate Change and Water, 2008)

Sea level rise will worsen coastal flooding

A study assuming relatively moderate sea level rise by 2050 of 15 cm found that thenumber of people in the world living in zones vulnerable to coastal flooding (defined

here) would go up by 18 million people, or 26%. (See chart below.)

Were polar ice-sheets to undergotipping point melt events, even more people wouldbe exposed (fifth column.)

Poor people are more vulnerable to flood events in general than rich people.

In Maputo, Mozambique, the urban poor, for example, tend to live in commonly floodeareas because the land is either very cheap or free (this is common in urban developin

areas). Floods not only destroy their homes, but tend to spread disease and pollutants

Subsistence farmers depend on each years harvest.

Floods and cyclones can severely damage crops, for example in Nairobis informalsettlements, where flash flooding has hit people living in poorly constructed

structures alongside rivers.

Scientists predict increase in heavy precipitation in East Africa.


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A number of so-called no regrets options could help the poor either way: strengthening building

designs/rules; reducing poverty; improving city drains and sewers.

(Extreme Events report 2011 summary)

Floods nurture as well as kill

In regions like coastal Bangladesh, yearly floods bring rich silt to soil, a boon foragriculture.

Datasets to explore:

Data and maps of global flood damage from NASA

http://sedac.ciesin.columbia.edu/data/set/ndh-flood-mortality-risks-distribution

Analyzed US flood data http://www.flooddamagedata.org/national.html

European flood database http://www.crue-eranet.net/
http://www.crue-eranet.net/http://www.crue-eranet.net/

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