Disaster risks are the results of complex spatiotemporal interactions between risk components, impacts and societal response. The complexities of these interactions increase when multi‐risk events occur in vulnerable contexts characterized by ethnic conflicts, unstable governments, and high levels of poverty, resulting in impacts that are larger than anticipated. Yet, only few multi‐risk studies explore human‐environment interactions, as most studies are hazard‐focused, consider only a single‐type of multi‐risk interaction, and rarely account for spatiotemporal dynamics of risk components. Here, we developed a step‐wise, bottom‐up approach, in which a range of qualitative and semi‐quantitative methods was used iteratively to reconstruct interactions and feedback loops between risk components and impacts of consecutive drought‐to‐flood events, and explore their spatiotemporal variations. Within this approach, we conceptualize disaster risk as a set of multiple (societal and physical) events interacting and evolving across space and time. The approach was applied to the 2017–2018 humanitarian crises in Kenya and Ethiopia, where extensive flooding followed a severe drought lasting 18–24 months. The events were also accompanied by government elections, crop pest outbreaks and ethnic conflicts. Results show that (a) the highly vulnerable Kenyan and Ethiopian contexts further aggravated drought and flood impacts; (b) heavy rainfall after drought led to both an increase and decrease of the drought impacts dependent on topographic and socio‐economic conditions; (c) societal response to one hazard may influence risk components of opposite hazards. A better understanding of the human‐water interactions that characterize multi‐risk events can support the development of effective monitoring systems and response strategies.

Abstract. The relation between drought severity, as expressed through widely used drought indices, and drought impacts is complex. In particular in water-limited regions where water scarcity is prevalent, the attribution of drought impacts is difficult. This study assesses the relation between reported drought impacts, drought indices, water scarcity, and aridity across several counties in Kenya. The monthly bulletins of the National Drought Management Authority in Kenya have been used to gather drought impact data. A Random Forest (RF) model was used to explore which set of drought indices best explains drought impacts on: pasture, livestock deaths, milk production, crop losses, food insecurity, trekking distance for water, and malnutrition. The findings of this study suggest a relation between drought severity and the frequency of drought impacts, whereby the latter also showed a relation with aridity, whilst water scarcity did not. The results of the RF model reveal that drought impacts can be explained by a range of drought indices across regions with different aridity. While the findings strongly depend on the availability of drought impact data and the socio-economic circumstances within a region, this study highlights the potential of linking drought indices with text-based impact reports. In doing so, however, spatial differences in aridity and water scarcity conditions have to be taken into account.

<p>Floods and drought affect millions of people each year, but what if a riverine flood rapidly follows or occurs during a hydrological drought?</p> <p>The 2022 summer drought in Europe, for instance, was punctuated by flash floods, affecting societies, economies and the environment already impacted by the persistent drought. In the same summer, in Iran and Afghanistan, devastating riverine floods followed a severe drought, causing displacement and human losses. Although the abrupt transitions between opposite hydrological extremes can pose huge risks for societies, the processes behind and effects of drought-flood interactions remain largely unknown, as most studies address droughts and floods separately. This research provides the first global study of compound and consecutive drought-flood events, shedding light on the underlying hydrological interactions between opposite hydrological extremes.</p> <p>By analysing timeseries of hydro-meteorological and other biophysical variables for 8255 catchments globally, we reconstruct the propagation of droughts and floods through the hydrological cycle, thereby identifying and characterizing flood events that follow or compound with drought conditions. We use variable and fixed threshold-level approaches to detect extreme dry and wet conditions, and seasonality statistics to analyse the timing of riverine floods. Our results show that close succession between drought and flood occurs mainly during the transition between seasons: from winter to spring in mid-latitude areas and from dry to wet at the equator and polar regions. Although these events are rare, they have increased over time, especially in countries such as France and Germany, southern Brazil, and India. Furthermore, drought conditions often shift the flood timing, resulting in later winter floods in Europe, in the north-eastern coast of the United States and western Canada, and earlier summer floods in Central America and Northern Brazil.</p> <p>This study shows that although drought and flood events evolve from different hydrological processes and atmospheric dynamics, these hydrological extremes interact with the same hydrological system, resulting in system alterations that may modify flood dynamics.</p>

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The absolute socio-economic damage from natural hazards has been increasing in recent decades in many parts of the World (Formetta & Feyen, 2019;IFRC, 2020b; IPCC, 2021), resulting in numerous humanitarian crises. These socio-economic impacts have often been attributed to a single hazard event (e.g., drought, flood, cyclone) combined with static exposure and vulnerability conditions (Ciurean et al., 2018). In reality, these impacts are often the result of complex dynamic interactions between societal and physical drivers tightly interlinked with the