Flood and drought analysis shows that impact-reduction strategies are effective – but fail in unprecedented events

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. They analysed 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.

Most pairs where the impacts increased also showed a larger hazard and exposure. For example, a 2015 flood in Corigliano-Rossano City, Calabria, Italy, was far more severe than a similar event in 2000; and in 2015 exposure was higher as the flood occurred in August – the peak tourist season.

In an era of increasingly extreme weather events, however, the researchers note that management actions that reduce vulnerability are not always sufficient. For example, despite actions to help the city of Malmö, Sweden, cope with heavy rainfall, an exceptional flood in 2014 overwhelmed the sewage system, causing €66 million worth of damage. Having suffered a severe flood a few years previously, the city was somewhat prepared, but this level of damage was ten times worse than caused by the previous flood.

The study also found that management actions could significantly reduce impacts of flooding, but not particularly the effects of droughts. This may be because drought measures that alleviate impacts in one sector may exacerbate them in another – for example agricultural irrigation may reduce drinking water supply. Actions may also have unintended consequences. For instance, improved levees (embankments) may encourage building on floodplains, increasing potential exposure in extreme circumstances.

The research highlights that although non-structural measures – such as land-use planning and precautionary measures – can mitigate infrastructure failure, there will always be a residual risk. Although flood risk management plans, under the Floods Directive, may prompt actions that reduce risk, actions are usually implemented after the need for them is highlighted by major floods and droughts. The researchers posit that policy should focus on improving preparedness for exceptional events, which are increasing in likelihood, and learn lessons from success stories, such as effective preparedness and emergency management, transnational collaboration and investment in structural and non-structural measures.

Footnotes:

1. Formetta, G. and Feyen, L. (2019) Empirical evidence of declining global vulnerability to climate-related hazards. Global Environmental Change, 57: 101920.
2. See: European Commission, Joint Research Centre (2020); Cammalleri, C., Naumann, G., Mentaschi, L., et al., Global warming and drought impacts in the EU: JRC PESETA IV project: Task 7, Publications Office. Available from: https://data.europa.eu/doi/10.2760/597045
3. European Commission (2007) Drought Management Plan Report. Available from: https://ec.europa.eu/environment/water/quantity/pdf/dmp_report.pdf

Source:

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

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“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.

Notes on content:

The contents and views included in Science for Environment Policy are based on independent, peer reviewed research and do not necessarily reflect the position of the European Commission. Please note that this article is a summary of only one study. Other studies may come to other conclusions.