Attribution of compound flooding: The case of the subsequent hurricanes Eta and Iota in Honduras

In November 2020, during the COVID-19 pandemic, two hurricanes hit Honduras in the span of two weeks. Hurricane Eta made landfall on November 4th, causing widespread damage across Central America, and particularly in Honduras. There was heavy precipitation, with widespread riverine flooding, landslides and flashfloods. The storm tragically caused at least 74 deaths. On 17 November, while the country was still responding to the immediate impacts of Eta, Hurricane Iota made landfall. Although the track was different, heavy precipitation affected the same area where Eta had already triggered floods and landslides – further exacerbating the impacts and causing 13 additional deaths. The storms had a direct reported impact on 437,000 people and indirectly affected 4.5 million, forcing the displacement of around 937,000 individuals as homes were damaged by flooding and landslides. Humanitarian needs surged, with 2.8 million people requiring assistance. The economic damage was severe, with losses reaching $1.9 billion USD and national economic growth declining by 0.8%.

To understand the potential role of climate change in exacerbating the flooding and the amount of people and buildings exposed to it, we simulate compound flooding (maximum water extent and depth) of Eta and Iota  using a 2D hydrodynamic model (SFINCS) accounting for  local precipitation, river discharges (calculated using the hydrological model wflow) and coastal water levels derived from global datasets. The model is used to simulate the factual and counterfactual scenarios. The factual simulation is based on present-day climate, whereas for the counterfactual scenarios, the precipitation and river discharges are adjusted to remove the long-term climate trend to represent pre-industrial conditions.

In addition, we also explore qualitative counterfactuals that demonstrate the compounding impacts resulting from the antecedent drought conditions, COVID-19 responses, and chronic insecurity and violence. This exploration emphasizes that the physical hazard and impacts are often strongly mediated and/or exacerbated by complex socio-economic and socio-political drivers and dynamics and highlight the role of non-climate drivers for severe impacts.

Overall, the results highlight the need for a holistic attribution perspective to develop effective response to reduce the impacts of future compound hurricanes.