Flood exposure in Rotterdam’s unembanked areas from 1970 to 2150: sensitivities to urban development, sea level rise and adaptation

Abstract. Uncertainties in the rate of sea level rise, coupled with ongoing urban expansion, create challenges for city planners in designing flood risk adaptation strategies. This study analyzes flood exposure rates in Rotterdam's unembanked areas from 1970 to 2150. We modeled flood hazards for 10–1000 year return periods under both low (RCP2.6) and high (RCP8.5) emission scenarios, while assessing exposure using historic and planned urban development data. Without adaptation measures, flood exposure in Rotterdam’s unembanked areas is projected to increase. For 10-year flood events under RCP8.5, exposure rates are expected to increase 7-fold by 2150 compared to 2020. For RCP2.6, a 3-fold increase is projected, reflecting uncertainties in long-term sea level rise. A retrospective analysis reveals an improvement in flood exposure: exposure levels observed in 2020 were approximately half those observed in 1996, due to construction of the Maeslant storm surge barrier. Temporal variations in exposure rates are attributed to three factors: urban development, sea level rise, and the construction of the Maeslant barrier. Exposure rates are primarily influenced by the Maeslant barrier, followed by sea level rise and urban development. Understanding the interplay of these three factors is crucial for urban planning and flood risk management in delta cities.