A first assessment of the effect of storm climate trends and uncertainties on Dutch levee design

For the safety assessment and design of levees in the Netherlands probabilistic tools are used, which account for both statistical and model uncertainties in the determination of hydraulic loads. However, climate change induced uncertainties in extreme wind climate or storminess are not yet accounted for. This paper presents a first assessment of the effect of uncertainties in storminess on Dutch levee design. An expert panel was consulted to define a range of plausible trends and uncertainties in extreme wind climate. Three scenarios were defined with variations of the current wind climate, including changes in wind speed high percentiles and in wind direction. For the defined scenarios probabilistic computations were carried out to determine the effect of the wind statistics variations on the water level, wave loads, and required levee height along the Dutch lakes and coast. In the case of an increase in wind percentiles (mean + 5%, standard deviation 12%), the required levee height increases significantly: up to 1.5–4 m along the Dutch coast and up to 1–2 m along the Dutch lakes. Given the large impact of the considered changes, it is first recommended to carry out a more robust assessment of the uncertainties in future storm climate and to measure and monitor evolution of future wind speeds.