Compound and connected natural risks in the Spanish Mediterranean coast in the face of climate change. C3RiskMed

Compound events ?

 

In a recent work, Zscheischler et al. (2020) proposed a classification of compound events in four types (also Bevacqua et al. 2021), which facilitates the analysis of the mechanisms driving the impact and thereby provides a framework for risk adaptation. 

Multivariate events

A multivariate compounding event refers to the co-occurrence of hazards from multiple climate drivers in the same geographical region. This is the most common type of event when analysing compound coastal flooding, as defined by the co-occurrence of a marine driver (usually storm surge) and a ‘terrestrial’ one such as rainfall or river flow acting at the same site (e.g. Wahl et al., 2015; Hendry et al., 2019). Due to the characteristics of coastal storms in the NW Mediterranean, waves are considered the main marine driver controlling the floodwater volume to the hinterland, since the wave-induced runup, Ru, is much larger than the magnitude of the storm surge (e.g. Mendoza and Jiménez, 2009; Mendoza et al., 2011). 

 

Spatially compound

Spatially compounding events refer to co-occurring hazards from different climate drivers at distant locations within a limited time window. From a risk management standpoint, these events are very relevant because they may overwhelm the capability of emergency-response services since these have to respond to a large number of emergency situations throughout the region at the same time. In this study, these events are defined by the co-occurrence of the two above-mentioned hazards, heavy rainfall and coastal storms, within a given time window in the study area (Spanish -peninsular- Mediterranean coast).

 

Temporarily compound

Temporally compounding events refer to a succession of hazards affecting a given geographical area, leading to, or amplifying, an impact when compared with a single hazard. The hazards can be forced by one or more drivers, and they can be of the same type (e.g. multiple heavy- precipitation events or coatsal storms) or consecutive occurrence of different hazards. 

 

Preconditioned events

Preconditioned events are those where one or more hazards can cause an impact, or lead to an amplified impact, because of a pre- existing, climate- driven condition. These drivers are not necessarily causally related, but they can be.

 

References

  • Bevacqua et al. (2021) Guidelines for Studying Diverse Types of Compound Weather and Climate Events, Earth's Future, 9, e2021EF002340, doi: 10.1029/2021EF002340.
  • Hendry et al. (2019) Assessing the characteristics and drivers of compound flooding events around the UK coast. Hydrol. Earth Syst. Sci., 23, 3117-3139 , doi: 10.5194/hess-23-3117-2019.
  • Mendoza ET, Jiménez JA. (2009) Regional vulnerability analysis of Catalan beaches to storms. Proc. ICE- Marit. Eng., 162, 127-135, doi: 10.1680/maen.2009.162.3.127.
  • Mendoza et al. (2011) A coastal storms intensity scale for the Catalan sea (NW Mediterranean), Nat. Hazards Earth Syst. Sci., 11, 2453-2462, doi: 10.5194/nhess-11-2453-2011.
  • Wahl et al. (2015) Increasing risk of compound flooding from storm surge and rainfall for major US cities, Nat. Clim. Change, 5, 1093–1097, doi: 10.1038/nclimate2736.
  • Zscheischler et al. (2020) A typology of compound weather and climate events, Nat. Rev. Earth Environ., 1, 333-347, doi: 10.1038/s43017-020-0060-z.