HydroSocialExtremes - Understanding the interplay of water and society

More than 100 million people per year are affected by hydrological extremes, i.e. floods and droughts. Fatalities and economic losses caused by hydrological extremes have dramatically increased in many regions of the world over the past decades (UN-ISDR, 2016), and there is serious concern about future risk, given the potentially negative impact of climatic and socio-economic changes (Hallegatte et al., 2013; Aerts et al., 2014; IPCC, 2014; Kundzewicz et al., 2017). Moreover, this risk is not equally distributed throughout society as humans have significantly altered the hydrological regime and some population groups have more resources than others to prevent, mitigate, or recover from extreme events (Masozera et al., 2007). To develop appropriate policies and measures reducing the undesirable impacts of hydrological extremes, it is essential to understand where, how and why risk changes over time, and assess short- and long-term effects of alternative strategies.

While societies shape hydrological extremes, hydrological extremes in turn shape societies. Following the impact of floods or droughts, humans respond and adapt through a combination of spontaneous processes and deliberate strategies that can lead to e.g. changing social contracts (Adger et al., 2013). Four dynamics (i.e. adaptation effect, levee paradox, water supply-demand cycle, and sequence effect) can emerge from the interplay of hydrological extremes and society (Di Baldassarre et al., 2015; 2017; 2018). They have been described by different scholars for various test sites. Yet, the causal mechanisms explaining their emergence are still poorly understood. Also, it is still unclear whether they are exceptional cases or generic patterns, and whether they occur under identifiable circumstances.