Late May 2019 was a startlingly active period for severe convective storms (SCS) in the U.S., even after considering that May is typically one of the most active months of the year. Until about halfway through the month, the number of tornadoes being reported was around average, but after a major outbreak starting in mid-May this number shot up, bringing the year-to-date total to 1,017 tornado reports. This count is only surpassed by the extremely active years of 2008 and 2011 (Figure 1).
This year’s late May outbreak was also unusually long: by the end of Wednesday, May 29, at least eight tornadoes had been experienced each day across a record-breaking 13 consecutive days, according to preliminary data from the National Weather Service (NWS). The previous record was set in 1980, after 11 consecutive days with at least eight tornadoes.
Last weekend (April 13-14) marked the first major U.S. severe convective storm (SCS) outbreak of 2019. Drawing energy from warm, humid air brought over land from the Gulf of Mexico by a dip in the jet stream, hail, strong winds and/or tornadoes were reported in 19 states stretching from Texas to New York. There have been at least nine fatalities reported. The worst damage occurred in Texas, Louisiana, Mississippi, and Alabama, where over 150,000 homes and business lost power.
Damage surveys are ongoing, but as of April 16, there had been 22 tornadoes confirmed by the National Weather Service, including two EF-3 rated tornadoes in Texas, with estimated wind speeds of 140 miles per hour (225 kilometers per hour). Early assessments indicate that several hundred buildings have been damaged or destroyed, but the total number will unlikely be known for a few more days at least – and could be significantly higher. In the meantime, insurers will be sending out loss adjusters to try to establish the scale of the claims they are likely to incur. The final cost may not be known for several months.
But why is spring and not summer the peak season for SCS, what is the current state of SCS risk – and what has its impact been on the insurance industry over the past few years?
Christopher Allen is senior analyst – model development, working within the Event Response team at RMS, and is based in London. He joined fellow employees from RMS and RMS clients on our annual Impact Trek in Nepal during March this year. This is Chris’s account of his time in Nepal.
On Wednesday, March 21, eight somewhat-still-jetlagged RMS Impact Trekkers left the Summit Hotel in Kathmandu bound for the village of Dhunkharka, three hours’ drive southeast of the capital. We were going to see some of the retrofitting work that was being done by Build Change, a social enterprise partner of RMS that aims to build local capacity for safer construction practices. As we weaved our way through Kathmandu traffic (a chaotic affair at the best of times) we noticed several of the characteristics of the capital’s buildings that had been pointed out to us by Build Change over the past few days: soft story, three-floor brick masonry, new construction sprouting up with reinforced concrete columns, the occasional ground floor still occupied by goats or buffalo…
Climate modeling studies generally agree that anthropogenic climate change will likely cause tropical cyclones globally to be more intense on average, and that the most powerful ones will become more frequent. In response, climatologist Michael Mann (particularly well known for his so-called “hockey-stick” temperature graph) recently advocated the introduction of a sixth category to the Saffir-Simpson Hurricane Wind Scale (SSHWS), in order to better describe the very strongest storms. According to Mann, sturdier construction practices mean that Category 5 storms no longer all cause near-total destruction of human infrastructure and introducing a Category 6 would increase public awareness of the effects climate change is having on tropical cyclone strength. Mann is not the first to propose introducing a Category 6; after powerful tropical cyclones make landfall this is frequently deliberated. Before wading into this debate however, let us look at the SSHWS itself.
What is the El Niño Southern Oscillation? More conveniently known as ENSO, it is the planet’s largest source of natural climate variability on interannual time scales. ENSO describes the interaction between ocean and atmosphere in the equatorial Pacific, but the results of this interaction are global, and can last for many months. There is a good level of ENSO awareness in our industry, such as that warm phases of the oscillation (El Niño) tend to suppress Atlantic hurricane activity, and that cool phases (La Niña) tend to enhance it. But how was ENSO discovered? And how does it work?