By Lord Julian Hunt and Professor Johnny Chan.(*) - The devastation wrought by super-storm Sandy (253 deaths in the Americas and over 50 billion dollars in economic damage and disruption), is prompting renewed thinking about climate change and national security.
Several leading US politicians, including Representative Henry Waxman, have called for congressional hearings on this issue, while a recent US National Research Council Report commissioned by US military and intelligence agencies asserts that climate change is accelerating and will cause increasing numbers of disruptive events.
Within this broad-ranging debate, one particular issue that has grown in salience, post-Sandy, is whether climate change means storms will be more intense. The balance of risks is that they will, with the biggest threat from increased flooding caused by sea-level rises as well as increase in rainfall intensity and rainfall rate.
This has key implications for all of us, especially Government and insurers as they assess and plan for volatile weather. It is thus a key topic that will be discussed at the annual United Nations Climate Change Summit, which opened in Qatar on November 26 and concludes December 6.
The World Meteorological Organisation, which is part of the United Nations, has a committee, of which one of us (Chan) is a member that looks at the relationship between climate change and tropical cyclones. It has noted that projections indicate that global warming will cause globally-averaged intensity of tropical cyclones to shift towards stronger storms, with intensity increases of up to 11% by 2100. Increases of the order of 20% in rainfall rates within 100 kilometres of the storm centre are also projected.
As occurred with Sandy, a crucial issue is that rainfall will likely increase when cyclones hit land. Studies have found that frequency of heavy rain events as well as the rainfall intensity (amount of rain per unit of time) has increased. This has led to higher occurrence of severe flooding.
Incidences of flooding are likely to increase due to global warming because of increased moisture in the atmosphere. Moreover, because of sea-level rise caused by global warming, flooding due to storm surge associated with cyclones will exacerbate.
The sea-level rise factor is especially important because coastal communities have risen sharply in recent decades. In the case of Sandy, most damage was caused by flooding with the exception of weak structures near the shoreline destroyed by strong winds.
As the Sandy episode revealed, there has been tremendous advances in our understanding of the physics that drive cyclones. Computer forecasting now does a great job in predicting areas where a cyclone will likely hit (24 hour average error in location is less than 130km).
However, there has been much less success in predicting the maximum winds of cyclones. Moreover, little attention has been paid to forecasts of cyclone sizes (horizontal extent of damaging winds). Such predictions are important for issuing wind and storm surge warnings.
Forecasting models also have considerable difficulty predicting amounts of rain that can fall in particular locations. In many cases, unanticipated copious amounts of rain have led to disastrous consequences.
Based on the very best scientific assessments about storms of the future, insurance companies should intensify their focus on evaluation of flood risks of any asset to be insured given their huge stake in any losses. Meanwhile, government disaster preparedness agencies must urgently re-evaluate flood mitigation plans.
As in the Netherlands, where Delft University has led much ground-breaking work, this should include assessment of dykes and sea walls as the first line of defence against storm surge, drainage systems within cities, not only for roadsides but for subways and tunnels (witness the flooding in New York’s subways), reinforcement of dangerous slopes, and establishment of warning systems for flash flooding in mountainous regions etc. Moreover, increased public sector support is needed for research to improve weather monitoring systems and computer forecasting.
In addition, because significant numbers of high rise buildings are being built in coastal cities that are subject to cyclones, more research is needed about ‘high rise’ turbulence (for instance instrument towers have been constructed on China’s south coast to measure this). Such data will enable engineers to improve safety of such structures, while providing invaluable insight on the energy transfer of the ocean to cyclone winds.
(*)Lord Hunt is Visiting Professor at Delft University and former Director-General of the UK Meteorological Office. Johnny Chan is a Chair Professor at City University of Hong Kong and Chair of the World Meterological Organisation’s Tropical Cyclone Panel