Most people affected by Nepal quake have returned home: study

Most of the people who had left their homes after the devastating earthquake that hit Nepal in April this year have now returned, according to researchers who tracked mobile phone data to monitor the movement of those affected by the quake.
The Nepal earthquake that killed over 9,000 people and injured more than 23,000 was followed by about 300 aftershocks. An estimated 500,000 buildings were destroyed or severely damaged.
Researchers from the University of Southampton in UK used mobile phone data to monitor the movement of people affected by the earthquake and help with the continuing relief effort in Nepal.

Just a week after the disaster took place, the team began daily monitoring of anonymised phone data to track the displacement of populations in the affected areas.
Five months on, they are continuing to supply accurate, up-to-date reports to the United Nations.
"Although we have used mobile phone data before to measure population movements, this is the first time we have used the method in an ongoing 'live' situation," said Andy Tatem, Professor of Geography at University of Southampton.

"By watching how the population moves on a daily basis, we have been able to help directly with aid efforts and the rebuilding of infrastructures," said Tatem.

Every time a person uses a mobile it sends information to a receiving tower and gives an approximate location of where they are.
When this information is repeated multiple times, over millions of users, a detailed picture can be extracted of population density, movement and how it changes over time in a given area.
In Nepal, the researchers linked up with the country's largest mobile phone operator to analyse anonymised data from 12 million mobiles across the country.
By comparing information on the movement of these phones after the quake, with population distributions and movements before it hit, the team has established trends of where people are moving to and from. The work to monitor this continues.

Two weeks after the quake, the researchers' data showed that an estimated extra 500,000 people had left Kathmandu Valley (taking into account normal patterns of movement).
Most went to the surrounding districts and the Terai areas in the south and southeast of Nepal - something which had previously been completely unknown.
On a wider scale, across the country an estimated 1.8 million people left their home district.
Latest analysis shows that of those people who left their homes soon after the disaster, most have now returned - with approximately four to 14 per cent still remaining elsewhere.
Return rates have varied across districts of Nepal, with those from Kathmandu Valley the slowest to return. Kathmandu city centre has seen the largest inflow of population.