Risk Profiles of Impactful and Extreme Hydrological Events for Alpine Reservoirs

Climate change impacts in the Swiss Alps have been seen through changes in the hydrologic regime. These include glacier mass loss, shifts in peak snowmelt and changes in seasonal precipitation type and timing (e.g., more rain-on-snow events in winter). In addition, it is expected that global warming will lead to more intense extreme rainfall events in the Alps in the future. Combined, all of these changes pose a challenge to planning, management and optimization for hydropower producers operating in the Alpine region. In particular, because the impacts are not expected to be felt homogeneously across the region, it is difficult to ascertain how the risks will differ between individual reservoirs without more localized assessment. This study focuses on the use of statistical tools that are specifically adapted for application to small datasets (such as the extended generalized pareto distribution), in order to calculate return periods of extreme precipitation and high reservoir inflow events for individual Alpine reservoirs. In addition, we show how the return periods of persistent low inflow periods (droughts), which have the potential for significant negative impacts on hydropower production, are determined using extreme value theory. The result is effectively a risk profile comprised of return periods for both extreme high precipitation/inflow and impactful low precipitation/inflow events that can be used by researchers and practitioners alike to further understanding of local climate change risks to individual reservoirs.