Global drivers of future river flood risk

Abstract

Understanding global future river flood risk is a prerequisite for the quantification of climate change impacts and planning e ective adaptation strategies 1. Existing global flood risk projections fail to integrate the combined dynamics of expected socioeconomic development and climate change. We present the first global future river flood risk projections that separate the impacts of climate change and socioeconomic development. The projections are based on an ensemble of climate model outputs 2 , socioeconomic scenarios 3 , and a state-of-the-art hydrologic river flood model combined with socioeconomic impact models 4,5. Globally, absolute damage may increase by up to a factor of 20 by the end of the century without action. Countries in Southeast Asia face a severe increase in flood risk. Although climate change contributes significantly to the increase in risk in Southeast Asia 6 , we show that it is dwarfed by the e ect of socioeconomic growth, even after normalization for gross domestic product (GDP) growth. African countries face a strong increase in risk mainly due to socioeconomic change. However, when normalized to GDP, climate change becomes by far the strongest driver. Both highand low-income countries may benefit greatly from investing in adaptation measures, for which our analysis provides a basis. Between 1980 and 2013, the global direct economic losses due to floods exceeded $1 trillion (2013 values), and more than 220,000 people lost their lives 7. Global flood damages have been increasing steeply over the past decades, so far mainly driven by steady growth in population and economic activities in flood-prone areas 8,9. Future increases in flood frequency and severity due to changes in extreme weather are expected 1,9. Such increasing trends in flood risk may have severe direct humanitarian and economic impacts and lasting long-term negative effects on economic growth 10,11. In 2015, several major international policies are being initiated or renewed that may catalyse flood risk adaptation and hence risk reduction, such as the Sustainable Development Goals, Conference of the Parties (COP) 21, and the Sendai Framework for Disaster Risk Reduction. Such efforts require global understanding of the drivers of flood risk change in the future. Past efforts to enhance this understanding have focused on the global-scale mapping of present-day flood hazard 12,13 and risk 4,5 and future changes in global flood exposure and risk 14 due to either climate change 6,15,16 or socioeconomic development 8,17. One recent study 18 combined global socioeconomic and climate change into future global flood risk projections for the first time, however, this work did not reveal regional patterns nor quantify the drivers of risk change. Furthermore, no study has so far accounted for installed and maintained flood protection standards (FPS; ref. 10).

The relationship between precipitation and insurance data for floods in a Mediterranean region (northeast Spain)

“…Between 2005 and 2014, more than 85 000 000 people were directly affected by flood events annually, and around 6000 people were killed on average each year due to floods (UNISDR, 2015). The main factors involved in flood risk analysis are the hazard, or the likelihood of a natural phenomenon causing damage, and the vulnerability, that is, the characteristics and circumstances of a community/system that make it susceptible to potential flood damage (UNISDR, 2009;Kundzewicz et al, 2014;Winsemius et al, 2015). Vulnerability can include factors such as exposure and other societal factors such as early warning systems, building capacity to cope with natural hazards and disaster recovery infrastructure (Jongman et al, 2014;Nakamura and Llasat, 2017).…”

Epistemic uncertainties and natural hazard risk assessment. 1. A review of different natural hazard areas

“…The frequency and magnitude of flood disasters is likely to increase with a warming atmosphere due to climate change and with increased exposure of a growing population (Winsemius et al, 2015), which suggests that the fractional contribution to global disaster losses is likely to increase even further. There are five aspects of flood risk assessment that involve important epistemic uncertainties.…”

Micro-sized enterprises: vulnerability to flash floods

“…A significant increase in losses due to flooding was repeatedly claimed by several scholars, including river flooding (Barredo 2007;Kreibich et al 2014;Winsemius et al 2014) and flash floods (Gaume et al 2009;Calianno et al 2013). Besides the ongoing discussion on climate change (Keiler 2013), this increase is triggered by exposure dynamics of elements at risk .…”