Monthly Archives: January 2016

Just How Unlucky Was Britain to Suffer Desmond, Eva, and Frank in a Single December?

Usually, it’s natural disasters occurring elsewhere in the world that make headlines in Britain, not the other way around. But you’d have to have been hiding under a rock to have missed the devastation wrought by flooding in the U.K. last month, thanks to the triple-whammy of storms Desmond, Eva, and Frank. Initial analysis from the Association of British Insurers suggests that the damage done could run to the region of £1.3bn.

But just how unlucky was the suffer not just one, or two, but three big storms in one December, and for these three storms to interact in such a way as to produce the chaos that followed?

First it’s worth pointing out that floods in the U.K. are—as is usually the case elsewhere—subject to important seasonal variation (see chart below). The winter months bring the highest number of events, and December does in fact come out (slightly) on top, especially for flooding events of the sort seen last month, which tend to follow heavy rainfall leading to soil saturation (November 2015 received about twice the average climatological rainfall for November in the U.K.).

Source: RMS

The reason this matters is that, when soil is sodden following an extended period of heavy rains, further rains can more easily run off the surface, exacerbating the risk of pluvial flooding. The water will then follow natural and artificial drains until it reaches the closest river network, in which it can accumulate, potentially triggering river or “fluvial” flooding. The runaway effect of the masses of water can also cause what is known as ground-water flooding. This cumulative phenomenon means that—as we saw in December—flooding can persist for a significant amount of time, leading to several flood events in close succession.

A flood CAT model that properly captures these sorts of interactions between rainfall events and hydrological systems will allow not just for an assessment of the likelihood of a single severe event, but also a better understanding of the compounding factors that can lead to the sort of flooding seen in the U.K. last month. And based on our latest RMS pan-Europe flood model, the chances of having three rainstorms lead to major inland flooding over a single December are far from negligible.

Source: RMS Europe Flood Model

The chart above shows the probability of one, two, three, and four flood events for the month of December. What it means is that, on average, every second December in the U.K. has at least one flood event, and every third December has only one flood event. Around every eight years there are two flood events, and a cluster of three flood events happens once every quarter-century.

Now, this does not mean that flooding on the scale just witnessed happens on average every 25 years—just that this is the average period for seeing three flood events in one December. Even if it did, it wouldn’t mean that the U.K. can rest on its laurels until 2041… this is just a statistical average. It is quite possible for clusters to hit several years in a row—a so-called “flood-rich period”.

This gets to the real nub of the issue. The question of how often this sort of flooding takes place in the U.K. is almost by-the-by. The point is that it isn’t rare as hen’s teeth, and so the U.K. needs to be prepared. And what was most shocking about December wasn’t the flooding itself, so much as the sheer lack of resilience on display. A media storm has understandably been whipped up regarding the level of investment into flood walls and so on, but protective infrastructure is only part of the equation. What is needed is not just flood walls (which can actually be counterproductive on their own), but a wider culture of resilience. This includes things such as flood warning systems, regular evacuation drills, citizens having personal plans in place (such as being ready to move furniture to upper levels in the case of an alert) and, critically, the ability to respond and recover should the defences fail and the worst happen (which is always a possibility). The U.K. is the world’s sixth richest country—it has the resources to cope with flood events of this magnitude… whether they happen every five, ten or 25 years.

Can Flood Walls Reduce Resilience?

In early December 2015 Storm Desmond hit, bringing an “atmospheric river” to the northwest of England with its headwaters snaking back to the Caribbean. It broke the U.K.’s 24 hour rainfall record, with 341.1mm of rain recorded in Cumbria.

Just three weeks later, while a great anticyclone remained locked in place over central Europe and the atmospheric flows had only shifted south by 150km, Storm Eva arrived. The English counties of Lancashire and Yorkshire were drenched during December 26th, and the media was once more overwhelmed with flood scenes—streets of Victorian-era houses inundated by 30-40cm of slow-moving water.

Journalists soon turned their attention to the failure of flood protections in the affected regions. In one interview in Carlisle, a beleaguered Environment Agency representative commended their defenses for not having failed—even when they had been overtopped. If the defenses had failed, maybe the water would not have ponded for so long.

 The call for “resilience”?

The call has gone out worldwide for improved “resilience” against disasters. As outlined by the UN Secretary General’s Climate Resilience Initiative, resilience is defined as the ability to “Anticipate, Absorb and Reshape” or “A2R”.

How did the U.K.’s flood defenses match up to these criteria in December? Well, as for the two “A”s in A2R, the residents of Carlisle did not anticipate any danger, thanks to the £38 million spent on flood defenses since the last time Carlisle had a “1 in 200 year” flood in January 2005 (which hit 1,900 properties). And the only thing the houses of Carlisle were absorbing on the first weekend in December was the flood water seeping deep into their plaster, electricals, and furnishings. As for “reshaping”, beyond the political recriminations, now is the time for some serious thinking about what constitutes resilience in the face of floods.

A flood wall is not the same as resilience. Resilience is about the capacity to recover quickly from difficulties, to bounce back from adversity. Organizations such as the UK’s Environment Agency may be good at building flood defenses, but not so proficient at cultivating resilience.

A flood wall can certainly be part of a culture of resilience—but only when accompanied by regular evacuation drills, a flood warning system, and recognition that despite the flood wall, people still live in a flood zone. Because flood walls effectively remove the lesser more frequent floods, the small risk reminders go away.

A growing reliance on the protection provided by flood walls may even cause people to stop believing that they live in a flood plain at all, and think that the risk has gone to zero, whether this is in New Orleans, Central London or Carlisle.

Even when protected by a flood wall, residents of river flood plains should be incentivized, through grants and reduced insurance rates, to make their houses resistant to water: tiling walls and floors and raising electrical fittings. They should have plans in place—such as being ready to carry their furniture to an upper floor in the event of an alert—as one day, in all probability, their houses will flood.

Given the U.K.’s recent experience we should be asking are people becoming more resilient about their flood risks? It sometimes seems that the more we build flood walls, the less resilient we become.