Issue 596: A new analysis suggests that while generally effective, flood and drought risk management strategies are usually not designed to cope with unprecedented events – which may increase with climate change.

Previous analysis looking at global trends from 1980-2010 suggests that adaptation efforts have led to decreasing vulnerability to the human and economic effects of floods and droughts1. For example, infrastructure such as flood defences, reservoirs and water supply management, as well as public-awareness raising and warning systems, have all contributed to this. However, loss of life, economic disruption and other impacts can still be significant – and are increasing due to extreme weather events in some parts of the world. This will be exacerbated by climate change – in Europe, for example, the economic damage caused by drought is projected to triple with a temperature increase of 2 °C2.

There is a lack of empirical data on the drivers behind these impacts, note researchers in a new study that aims to offer insights to inform future policy. Theyanalysed data on 45 pairs of events (26 floods and 19 droughts) that occurred in the same area, on average about 16 years apart. They looked at differences in the extent of the impacts caused by the floods or droughts, and whether this was related to the level of hazard, exposure, vulnerability or management.

Impacts may be quantified in terms of direct (e.g. fatalities), indirect (e.g. tourism disruption) and intangible (e.g. cultural heritage impacts) effects, say the researchers. They are dependent on three drivers: hazard (e.g. level of rainfall), exposure (e.g. population) and vulnerability (e.g. level of awareness prior to event) – which may be partly addressed by management actions.

The researchers acknowledge that there were only a few cases where only one driver changed in the later event, so it is difficult to draw conclusions about the contribution of each individual factor to impacts. Nevertheless, the analysis highlights the effect of management actions. In most cases (71%), management improved, indicating that societies had learned from previous events. The majority of pairs also exhibited a decrease in vulnerability, linked to this improvement.

Most pairs with lower impacts in subsequent events also showed a decrease or no change in hazard. For the two paired events for which the only driver that changed was a small increase in hazard, the impacts did not alter. In one of these cases, good irrigation infrastructure and increased water retention capacity led to Poland experiencing similar impacts from a drought in 2015 compared with a less severe drought nine years earlier, for example.

A pair of droughts in Central Europe also show how decreasing vulnerability also reduces impacts. A 2003 drought raised public awareness of water management and triggered improvements in institutional planning – for example, the European Commission provided technical guidance for drought management plans3. When drought hit in 2015, many reservoirs were kept filled until the beginning of summer, alleviating water shortages, and in some cities (e.g. Bratislava and Bucharest) water was supplied from tanks. Economic impacts of the 2015 drought were estimated at €2.2 billion, compared to €17.1 billion in 2003, despite the later event being larger in extent.

Kreibich, H., Van Loon, A.F., Schröter, K., Ward, P.J., Mazzoleni, M., Sairam, N., Abeshu, G.W., Agafonova, S., AghaKouchak, A., Aksoy, H., Alvarez-Garreton, C., et al. (2022) The challenge of unprecedented floods and droughts in risk management. Nature, 608 (7921): 80–86. Available from: https://www.nature.com/articles/s41586-022-04917-5

“Science for Environment Policy”: European Commission DG Environment News Alert Service, edited by the Science Communication Unit, The University of the West of England, Bristol.

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