Rainfall, Droughts, and Floods

Rainfall, Droughts, and Floods

Rainfall, Droughts, and Floods


For many years, rain and other forms of precipitation such as snow have fallen in largely regular patterns, but science predicts that climate change will cause many changes in these patterns.

Globally, we can expect more rainfall in total. This is because as the oceans warm up more water will evaporate from them and enter the atmosphere, and also because warmer air can hold more moisture. These changes are likely to alter global patterns of how water vapor moves through the atmosphere, leading to more extreme and less predictable rainfall as global temperatures rise.

Most scientific models of rainfall predict that high latitude countries such as Canada and Russia, as well as tropical East Africa, will receive more precipitation, while the Amazon basin, Mediterranean and North Africa, Central America, the Southern Andes and parts of Australia would receive less.

Complex climate phenomena such as the South Asian and West African monsoons are proving harder to model and for many tropical and subtropical countries, scientists have less confidence in their predictions.

Extreme rainfall raises the risk of soil erosion, landslides and flooding, which can have major impacts on agriculture and infrastructure that poses serious threats to people’s security. Floods can also contaminate water supplies and make outbreaks of water-borne diseases more likely.

On the other hand, too little rainfall can lead to drought. The UK Meteorological Office has stated that while one percent of the world’s land was affected by extreme drought in 1950, this had increased to three percent 50 years later.

Droughts can devastate agriculture, killing crops and livestock and leading to reduced food supplies and famine. In very dry conditions, the risk of dangerous wildfires increases too.

If dry conditions persist for a long time, this can lead to major changes in an areas vegetation that leave areas barren and unsuitable for agriculture. A scarcity of water can also trigger conflict as different users (such as farmers and herders) compete for access to limited supplies.

Large-scale floods and droughts can trigger mass movements of people from affected areas, and such refugees face many additional health threats even when they are far from the scene of the disaster.

While droughts and floods are both naturally occurring events, many scientists expect there to be more of each as climate change takes hold. And as sea levels rise, coastal areas will face even greater risks of flooding.

Changes in the timing and intensity of precipitation will mean that countries and communities must plan for potential floods and droughts.

Tactics for reducing the risk of floods include building dams to control river flow, engineering schemes to divert waterways away from urban areas, creating reservoirs that can hold excess water during heavy rainfall, and raising the height of land alongside rivers to make them less likely to flood.

Natural vegetation such as wetlands and forests can also help to control the flow of flood waters and reduce the damage they can inflict.

Tactics for reducing the risks from drought on a household scale include rainwater harvesting — where rain that falls on rooftop is collected for storage — and water recycling, where waste water is not discarded but used to water agricultural land.

More costly options that can be implemented on a larger scale include irrigation of farmland, treatment of sewage and other waste-water to make it safe to consume. There have been significant improvements in the technology of desalination or the removal of salt from saltwater, increasing the amount of freshwater available in drought-stricken areas.

It is important for journalists to remember that an individual droughts, flood or intense rainfall event can never be proven, scientifically, to be the result of human-induced climate change. However, journalists can report events in the the context of the wider patterns that scientists predict.

With that in mind, while scientists have confidence in their projections of future rainfall patterns at a global level, any regional or national level projections should be viewed with more caution as climate models are less accurate at smaller scales. To help address this, the US National Oceanic and Atmospheric Administration has set up a Climate Attribution project to try to explain the causes of extreme events such as droughts and floods.

Beyond reporting on the immediate causes and consequences of a drought or a flood, journalists can consider many other angles such as stories that look at other aspects of water management that have a direct bearing on possible future flood or droughts.

These include reporting on how governments monitor and plan for droughts and floods, stories about transboundary water issues, and reports on how different uses of water (such as to irrigate crops for export markets) can have impacts locally.

Many countries have now developed national plans for adaptation to climate change and these can be useful documents for journalists to use. In the case of the Least Developed Countries, these plans are available online at the UNFCCC website. It is important to report on the implementation and efficacy adaptation and mitigation measures taken by governments.

The US University Corporation for Atmospheric Research has a detailed media website that includes contact details of scientists who can discuss droughts and floods with journalists. Meanwhile, Circle of Blue is a good source of story ideas.

CASE STUDY – Extreme worldwide weather in August 2010
August 2010 saw extremes of precipitation in many parts of the world. Pakistan suffered its worst ever floods, which affected 20 million people, after a period of intense rain. Heavy rainfall also hit China and caused deadly landslides.

Russia baked in a heatwave that had followed an intense drought. Crops there died, forest fires filled the air with smoke and the death rate in Moscow rose well above the average. In Africa, a cholera outbreak struck Cameroon after floods there, and millions of people in Niger continued to endure a long drought.

Many other places around the world also experienced droughts and floods. The occurrence of these event was consistent with what scientists in the Intergovernmental Panel on Climate Change stated would be likely impacts of climate change in its 2007 4th Assessment Report. But can climate change be blamed for any of them for sure?

To get an idea of the complexities involved, contrast these four articles. In the New York Times and CE Journal, reporters spoke to leading scientists who said there was unlikely to be a direct link. Meanwhile Wired magazine and a separate New York Times article quoted scientists who said a link was likely.

Writing in the Columbia Journalism Review, journalist Curtis Brainard analyses the divergent media reports and scientific viewpoints.

Adaptation to Climate Change
Climate Change and Agriculture
Water-borne Diseases
Reporting on Disasters


C2ES Drought Page
Fire Hot, Sky Blue, Australia’s Dire Drought Tests Journalists

NCA Page on Extreme Weather

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