Heat drives Pakistani migration

Shahdadpur, Sanghar district, Pakistan: Residents collecting their belongings on a higher ground outside village during floods. Though they may be displaced temporarily, Valerie Mueller from the International Food Policy Research Institute (IFPRI) in Washington DC and her team find high temperatures are more likely to drive permanent migration. Image credit: Oxfam International

Shahdadpur, Sanghar district, Pakistan: Residents collecting their belongings on a higher ground outside village during floods. Though they may be displaced temporarily, Valerie Mueller from the International Food Policy Research Institute (IFPRI) in Washington DC and her team find high temperatures are more likely to drive permanent migration. Image credit: Oxfam International

Excessive rainfall rarely drives Pakistanis to permanently leave their villages, even when it causes hardship like the flooding that hit around a fifth of the country in 2010. Yet they do consistently move in response to extreme temperatures, Valerie Mueller from the International Food Policy Research Institute (IFPRI) in Washington DC and her colleagues have found. She says the finding is a first stage in establishing if, how, and why people’s choices are affected by climate and climate change. “This is a useful step in order to be able to predict migration flows and inform local governments how might they better prepare in terms of the delivery of resources and investing in infrastructure given the occurrence of extreme weather events,” she told me.

There are few efforts collecting information about who has migrated and why over long periods of time, especially in areas where extreme weather occurs. But IFPRI has a long history of evaluating questions linked to food security in countries across the world, including Pakistan. From 1986-1991 its Pakistan Rural Household Survey questioned 800 households about how they lived and farmed, and it has tracked those households ever since. “Local collaborators found the original households in 2001 and 2012 and asked the head of household or an otherwise knowledgeable person what happened to each household member who resided with them in 1991,” Valerie said. “Our study is one of the first to quantify long-term migration patterns over a long period of time.”

The follow-ups recorded the long-term movements and fortunes of 4,428 people from 583 households. The researchers combined these answers with temperature and rainfall data in one ‘logit’ and one ‘multinomial logit’ model designed to let them measure the odds that people moved. “The first model allows us to answer: What are the odds of a person moving out of the household in response to extreme temperature or rainfall?” Valerie explained. “The second model allows us to distinguish moves by location and allows us to answer the following questions: What are the odds of a person moving out of the household but within the village in response to extreme temperature or rainfall? What are the odds of a person moving out of the household but out of the village in response to extreme temperature or rainfall?”

Farms and finances dry up

Migration and climate trends from 1991-2012, with migration in blue, rainfall in red, and temperature in purple. Migration rates are percentages of total population, where 0.01 would be 1%. Climate trends are shown as a seasonal average divided by the average for all years. So, if a year was exactly average its value would be 1, higher than average and the value is above 1, lower than average and it is below 1. Image copyright Nature Climate Change, used with permission.

Migration and climate trends from 1991-2012, with migration in blue, rainfall in red, and temperature in purple. Migration rates are percentages of total population, where 0.01 would be 1%. Climate trends are shown as a seasonal average divided by the average for all years. So, if a year was exactly average its value would be 1, higher than average and the value is above 1, lower than average and it is below 1. Image copyright Nature Climate Change, used with permission.

The results, published in Nature Climate Change on Sunday, consistently show that men and women consistently migrate the most in response to extreme temperatures. Men in particular leave villages during temperature extremes in the wheat-growing season, from November-April, and are eleven times more likely to do so in extreme temperatures than cooler periods. Valerie’s team find no robust effect of rainfall or flooding alone on movement, although men are slightly more likely to migrate when temperature is also high.

Their findings also point to one possible way that heat forces this move. Historically, when average temperatures for the wheat growing season from November-April are in the highest quarter of the all-time record, over a third of farming income is wiped out. Non-farm income in extreme heat also falls by about a sixth, but high rainfall increases all sources of income substantially. That’s likely partly because people have ways to cope with flooding, and partly because the study looks at annual, not seasonal, income, Valerie suggested. “Flooding can be good for the soil and productivity over the long-term,” she pointed out. “If we would have focused on seasonal income trends, we might have found short-term losses.” Overall, though both landowners and non-landowners are driven to move by heat, the financial driver seems strongest for the land- and asset-poor.

This echoes a study Valerie did of Bangladesh, published in 2012. “There, flooding does not encourage long-term migration, but drought-related crop failure does,” she noted. And that insight could help ensure the best use of the approximately $4.6 billion donated per year in emergency relief for natural disasters. “Perhaps, with increases in climate change, we might want to divert funds towards encouraging the adoption of heat-resistant varieties, and the production and dissemination of better weather forecasting data and weather insurance packages,” Valerie said. “We also need to think more carefully about perfecting the climate-induced migration predictions in the wake of climate change. We need to expand the scope of geographic coverage as well as improve the data used in these analyses. Estimating the predicted population shifts from climate-induced migration will be important in local government planning from the provision of local public services to its effects on employment.”

Number of migrants from the original 1991 Pakistan Rural Household Survey. The map only shows some migrants because, although Valerie's team know know whether all migrants moved within the village or beyond, they may not know the specific districts they moved to. International migrants are also not shown. Image copyright Nature Climate Change, used with permission.

Number of migrants from the original 1991 Pakistan Rural Household Survey. The map only shows some migrants because, although Valerie’s team know whether all migrants moved within their village or beyond, they may not know the specific districts they moved to. International migrants are also not shown. Image copyright Nature Climate Change, used with permission.

Journal references:

V. Mueller, C. Gray and K. Kosec (2014). Heat stress increases long-term human migration in rural Pakistan Nature Climate Change DOI: 10.1038/NCLIMATE2103
Clark L. Gray and Valerie Mueller (2012). Natural disasters and population mobility in Bangladesh Proceedings of the National Academy of Sciences of the USA DOI: 10.1073/pnas.1115944109

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7 Responses to “Heat drives Pakistani migration”

  1. Jim in IA Says:

    Interesting and important study.

    I would appreciate some elaboration on the chart at the left. I am not seeing the cause-effect relationship between temperature and migration. What am I missing?

    • andyextance Says:

      Ooh, crikey, that’s a question! I’ll have to see if my mind-reading antennae are working…

      The scale doesn’t help see much variation in migration (the blue line at the bottom). There are two clear spikes, and you can see the biggest one tallies with a step in the purple temperature line. The other one seems to coincide with a dip, so I agree, it’s not easy to see.

      Obviously there’s a whole load of statistical modelling in this work, so in one sense that’s what you’re missing. Nevertheless, yours is an important question, as there are problems around how statistics are used in research and whether they actually show what they say they do. I’d expect a simple graph to be a good sanity check. Unfortunately I don’t have the statistical skils to grapple with your question in detail. I’ll ask Valerie if she wants to weigh in.

    • andyextance Says:

      Valerie is getting ready to fly to Uganda but sent through a short answer: “These are trends. There are other things affecting migration in a given year not captured in the graph but controlled for in the model. Some migration peaks correspond with high temperatures and others might correspond with variables not presented in the graph. For this reason, it’s a visual guide only.”

  2. Andy Hurley Says:

    My family moved from Scotland to Jersey 50 years ago, because it was too bloody cold, , is this relevant?
    So people on the shore migrate to higher ground , when there are floods and as things settle move back again because the shore is where people want to be.
    Lots of houses around Vesuvius as well. People just never learn.


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