LONDON (Thomson Reuters Foundation) - Extreme rainfall and floods regularly force large numbers of people to leave their destroyed or damaged homes in vulnerable countries like Pakistan. But how long do they stay away?
Take the 2010 monsoon floods in the South Asian nation, for example: some 20 million people were affected, with 14 million temporarily relocated and 200,000 taking shelter in aid camps. Crops to the tune of $1 billion were destroyed.
Headline figures like this create the impression that many are on the move. But recently published research suggests the longer-term impact of too much wet weather is less than that of too much hot weather.
A study that tracked around 4,400 individuals from nearly 600 households between 1991 and 2012 showed that flooding — a climate shock associated with big aid responses — had modest to insignificant impacts on migration. Heat stress, on the other hand - which attracts relatively little relief — increased the long-term migration of men to look for work elsewhere, mainly because it cut income from farming and other sources.
Unusually high temperatures reduce people's wellbeing because they harm agricultural yields, according to the research published in the journal Nature Climate Change. For example, when heat stress caused wheat to mature early in Pakistan in 2010, yields dropped by 13 percent.
"However, Pakistan's social protection programmes and international relief efforts have been far more responsive to flood victims than heat stress victims, as in other parts of the developing world," the study said.
The researchers deliberately took a longer-term view than most studies, since academic work looking at the causes of migration tends to focus on data covering just a few years, they said.
In the Pakistan study, a household member was considered a migrant in any particular year if he or she was permanently not present in that year for reasons other than death. The heads of households in a 1991 survey were re-surveyed in 2001 and 2012 to track the movement of original household members from 1991, both inside and outside villages.
The study found that rainfall had no robust effect on the mobility of men or women. Men were slightly more likely to move out of the village in response to higher rainfall, but only when the temperature was also sufficiently high. Flooding was found to have no effect on out-of-village moves and in fact caused a modest decline in the within-village migration of men and women.
But men consistently moved out of the village in response to extreme temperatures in the rabi growing season, which begins in late October and runs through to April-May. Rabi crops include wheat, tobacco, rapeseed, barley and mustard.
The risk of a man moving out of the village was 11 times higher when the village was exposed to temperatures at the top end of the scale, the study found.
MIGRATION AS ADAPTATION
The researchers also looked at the influence of weather on income. Extremely hot temperatures wiped out over a third of farming income and 16 percent of non-farm income. High rainfall, conversely, was found to increase all sources of income substantially.
"This analysis suggests one possible reason why heat stress drives migration, whereas extreme rainfall does not,” the study said.
Looking at differences in wealth, the researchers found those most likely to migrate were people with the least land and assets. "It seems that for the poor, the migration benefits following heat stress outweigh the moving costs, spurring migration of all forms," they wrote.
They concluded that their work has broader relevance for development strategies in Pakistan. They suggested that flood relief programmes may "potentially crowd out private coping mechanisms" like migration, particularly for the poor and risk-averse who live in flood-prone areas.
To promote sustainable development, policies are needed that promote adaptation to weather-related risks for farmers and rural businesses, they argued. Those might include investment in heat-resistant crop varieties, producing and disseminating better weather forecasts, weather insurance, and encouraging the kind of migration that boosts incomes and welfare.
"Addressing weather-related displacement will require policies that both enhance resilience to climate shocks and lower barriers to welfare-enhancing population movements," the study said.
Its findings tally with research published in 2012 by CARE International and the U.N. University, in which modelling showed that migration from vulnerable households in Tanzania could double over the next 25 years under the most extreme drying scenario.