Just over half of 2021 is over, and several extreme weather events have already been reported from across Africa, Asia, Europe, North America, and Oceania. Global warming has been linked to this year’s heat waves, wildfires, droughts, cold spells, destructive storms (hurricanes, typhoons, tornadoes), storm surges, and extreme rainfall leading to severe flooding, all adding to the woes of economies already devastated by Covid-19.
Beginning on 13 July, large areas of Western Europe experienced torrential rainfall, in some places heavy enough to result in flash floods, when already waterlogged soil could no longer absorb any more water. During 14-15 July, some regions received as much as 10 to 15 cm rain within 24 hours, representing as much as a month’s worth of rainfall in a day. These heavy downpours then caused rivers (such as the Ahr), reservoirs, and dams to overflow. Severe flooding resulted, with landslides and sinkholes developing in places.
The contiguous areas worst affected were in western Germany (Rhineland-Palatinate and North Rhine-Westphalia states), southern Belgium (Wallonia region), and the southern Netherlands (Limburg province), although many other parts of Western Europe did not escape flooding.
The disaster was complicated by a significant loss of life (196 people had died as of 20 July-165 in Germany and 31 in Belgium-with many others unaccounted for), considerable damage to transport links (roads, bridges, rail lines), telecommunications and electricity infrastructure, and the wholesale destruction of residential buildings. Many homes collapsed under the onslaught of fast-moving water. In other instances, people were stranded in their homes, deprived of basis amenities such as drinking water, electricity, and gas, and on occasion required evacuation by emergency rescue services.
In recent years, simulations of the weather and climate using supercomputers have improved our understanding of the physical processes that influence storm systems. Climate models have been accordingly developed that allow us to better predict future weather events. In Western Europe, a lower temperature gradient between colder air at the poles and warmer air at the equator slowed air flow in the jet stream, thereby weakening it. Slow-moving storm fronts and warmer air facilitated the absorption of moisture. Increased amounts of precipitable water in a stalled low-pressure system then led to heavy rainfall.
Advance warning of the disaster was available. The European Union’s Copernicus Emergency Management Service, guided by satellite imagery, first predicted a “high probability of flooding” as early as 9 July. By the beginning of the week commencing 12 July, the European Flood Awareness System, a component of the Copernicus EMS, had issued warnings of extreme rainfall and the risk of flooding by mid-week to the relevant authorities. But it was up to these authorities to decide how to respond to these warnings, particularly relevant in Germany, where the sixteen states have considerable autonomy. In the Netherlands, a country accustomed to water management and dealing with floods, evacuation warnings were issued on the afternoon of 14 July, no lives were lost, and all major dykes held. By contrast, in Germany, Europe’s richest economy, a reluctance to evacuate early in response to warning systems and the lack of an efficient alerting system appear to have made matters worse. Sirens were often not sounded, the national warning app was too late to respond, and there was no text messaging system to alert citizens about impending disaster.
The recent floods in Western Europe have once again drawn attention to the threat of global warming and introduced a new urgency to the process for tackling climate change. Even as efforts at reconstruction take shape, the havoc wreaked by the floods has also reminded the authorities of the need for better flood preparedness in the years to come.
Ashis Banerjee