Research press release


Nature Climate Change

The heat is on for migration



今回、Valerie Muellerたちは、1991~2012年にパキスタン農村部の583世帯の4,428人の長期的移動を調べ、異常気温(通常、11月から4月)を経験すると、村から移動するという一貫した傾向が見られるが、異常降雨があっても、それに応じた動きが非常に少ないことを明らかにした。そして、Muellerたちは、村から移動するという決定が、猛暑の時期の収入減によって影響される可能性があると考えている。現に、Muellerたちは、異常高温になると、農業所得が大きく損なわれ、3分の1以上が失われるという計算結果を示している。農業以外の所得も熱ストレスによって減少するが、農業所得ほど大きくなかった(16%減)。これに対して、降水量が多いと、全ての収入源が大きく増えることも指摘されている。


Climate-related heat stress, not high rainfall, flooding or moisture, has increased long-term human migration in rural Pakistan over the past 20 years. This finding, published in Nature Climate Change, provides the first quantitative evidence of how long-term migration decisions in Pakistan are affected by weather extremes.

Pakistan is known to be vulnerable to climate change and subsequently, involuntary displacement within its population is common. Efforts have been made to try to counteract this, but the country’s social protection strategies and international relief efforts have been most responsive to flood victims.

Valerie Mueller and colleagues examine the long-term migration of 4,428 individuals from 583 households in rural Pakistan between 1991 and 2012 and find that individuals consistently move out of villages in response to extreme temperatures (usually from November to April), but very little movement is observed in response to excessive rainfall. They suggest that people’s decision to move may be influenced by a fall in income during times of extreme heat. Indeed, the team calculate that agricultural income suffers greatly when temperatures are extremely high, wiping out over a third of farming income. Non-farm income also experiences losses from heat stress, but to a lesser extent (16%). They note, however, that high rainfall increases all sources of income substantially.

Based on these findings, the authors propose that relief efforts should be shifted to help improve individuals’ ability to adapt and prepare for extreme temperature conditions. They also suggest that continuing work that expands knowledge of what motivates migration is important for designing appropriate policies that respond to natural disasters, migration and displacement.

doi: 10.1038/nclimate2103


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