Technically I had been to Nairobi before our last trip last month, so I replied yes when people there asked. But then I told them it was when I was two years old and they laughed about how that didn’t count – partly because I can’t remember a thing from that time and partly because the city has changed so much. Back in 1982, the population of the city was around 900,000 but today it is over 3 million, and possibly up nearer 4 million during the day as people come into the city to work.

I was in Nairobi with colleagues Bruce Malamud and Faith Taylor on an initial research trip for our work on the physical dimensions of hazards in urban areas of Africa. During a meeting on the trip at Mzuzu University near another of our study sites – Karonga in Malawi – someone asked why we were focusing on hazards in urban areas particularly. The answer is partly because of the growth exemplified by Nairobi; Africa is urbanising rapidly and estimates are that 56% of the population of African will be urban by the middle of the century.