Excesses of Rain

As we were putting the finishing touches to last week’s Science in Action, the US National Weather Service was warning of Hurricane Helene’s fast approach to the Florida coast – alerting people to ‘unsurvivable’ storm surges of up to 6 metres. But the category 4 storm powered, as forecast, far past the coast and into the rugged interior of Tennessee and the Carolinas. 150 billion tonnes of rainfall are estimated to have been dumped there, with devastating consequences for the towns and villages snuggled into the deep-cut valleys of the region. Bloomberg says the event could cost $160 billion. Extreme warmth in the Gulf of Mexico helped fuel the hurricane, and within a few days Berkeley climatologist Michael Wehner had computed the fingerprint of climate change on the event. The journal Nature published this week a study estimating the true number of casualties of hurricanes like Helene – not just those registered in the immediate aftermath, deaths caused by the instant trauma, but those in the months, even years, that follow, because of the disruption to lives and infrastructure. Rachel Young of Stanford University was herself surprised by the scale of harm her calculations revealed. At least the dams held in North Carolina during Helene, although the sight of torrents of water gushing down the protective spillways at the peak was fearsome to see. A year ago, the two dams upstream of the Libyan port Derna both failed during Storm Daniel – ripping out the heart of the city and claiming at least 6000 lives. We reported what we could at the time here on Science in Action. But a World Bank study on the disaster reported back to an international dam conference in India this week a more detailed investigation – though the fractious politics of Libya put constraints on their work. Climate change was a massive part – normal monthly September rain in the area is 1.5 mm – but over 200 mm, maybe 400, fell on the hills behind Derna the night of the 10th. But it was the report of independent engineer Ahmed Chraibi that interested Science in Action – on the condition of the two dams, one just on the edge of the city, the other larger one 15 km upstream. He confirmed these had been built, in the 70s, for flood protection not to store water, but were in a shocking state long before ...