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Abstract

Hydroclimatic extremes, including floods and droughts, have become increasingly frequent and intense worldwide, leading to severe environmental and socio-economic consequences. However, assessing these events in isolation without considering their interactions can underestimate their compounding risks. This study aims to provide a thorough understanding of the changing risks of dry and wet transitions in North America, by using multiple hydroclimate variables to identify these extremes and their transitions. To achieve this, the study merges dry-wet spell indices, estimated by precipitation, soil moisture, and runoff simulations, into an integrated indicator, and applies an ensemble pooling approach to enhance the sample size for index estimation, which enables projecting the characteristics more robustly. The research also investigates nonstationary hydrological swings between flood and drought based on streamflow data. The analyses are conducted using a suite of downscaled CMIP5 GCM simulations, that are used to drive the Variable Infiltration Capacity hydrologic model, and multiple large ensembles for global warming levels of 1.5°C-4°C. Results indicate that hydroclimatic whiplash in North America is expected to become more frequent and intensified in a warmer climate. The study highlights the urgent need for effective adaptation strategies that address the compounded risks associated with hydroclimatic whiplash events, which are projected to increase in frequency, intensity, and duration in a warming climate. Specifically, the importance of developing and implementing adaptive water management strategies, such as constructing resilient infrastructure and adopting effective water conservation practices, is underscored.