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Another examples of extreme events that may have strong impacts are so called compound events, when two or more phenomena occur at the same time. This can be a low-pressure system bringing high sea-level fluctuations on a coast where a river at the same time see a strong discharge due to strong rainfall in the preceding week. Even if the compound resulting event is extreme it is not necessary that any of these two events are extreme in itself.
Compound events can also relate to a series of repeated events that may not be extreme one at the time, but, where the long period of persistent conditions may be extreme. The warm summer in northern Europe 2018 was an example of such an extreme when repeated heat waves and high-pressure dominated summer weather without precipitation led to severe drought and the warmest summer on record in Sweden (Wilcke et al., 2021). Such events, where several extremes need to take place more or less in the right time in relation to each other, are rarer compared to the individual extremes one at the time.
Due to the rarity of compound events and limited amount of data it is difficult to evaluate how models can represent such events.
References
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