El Niño, a Spanish term for "the Christ child", was named by South American fishermen who noticed that the global weather pattern, which happens every two to seven years, reduced the amount of fishes caught around Christmas. El Niño sees warm water, collected over several years in the western Pacific, flow back eastwards when winds that normally blow westwards weaken, or sometimes the other way round.

　　The weather effects, both good and bad, are felt in many places. Rich countries gain more from powerful Niños, on balance, than they lose. A study found that a strong Niño in 1997-98 helped America's economy grow by$15 billion, partly because of better agricultural harvests: farmers in the Midwest gained from extra rain. The total rise in agricultural incomes in rich countries is greater than the fall in poor ones.

　　But in Indonesia extremely dry forests are in flames. A multi-year drought(干旱)in south-east Brazil is becoming worse. Though heavy rains brought about by El Niño may relieve the drought in California, they are likely to cause surface flooding and other disasters.

　　The most recent powerful Niño, in 1997-98, killed around 21,000 people and caused damage worth$36 billion around the globe. But such Niños come with months of warning, and so much is known about how they happen that governments can prepare. According to the Overseas Development Institute (ODI), however, just 12% of disaster-relief funding in the past two decades has gone on reducing risks in advance, rather than recovery and rebuilding afterwards. This is despite evidence that a dollar spent on risk-reduction saves at least two on reconstruction.

Simple improvements to infrastructure(基础设施)can reduce the spread of disease. Better sewers(下水道)make it less likely that heavy rain is followed by an outbreak of the disease of bad stomach. Stronger bridges mean villages are less likely to be left without food and medicine after floods. According to a paper in 2011 by Mr Hsiang and co-authors, civil conflict is related to El Niño's harmful effects-and the poorer the country, the stronger the link. Though the relationship may not be causal, helping divided communities to prepare for disasters would at least reduce the risk