Flashiness and Flooding of Two Lakes in the Upper Midwest During a Century of Urbanization and Climate Change

Abstract

Globally, ecosystem services are threatened by increasing urbanization and more variable precipitation patterns driven by climate change. However, how these drivers interact over long-time scales to affect underlying processes remains poorly understood, hindering our ability to predict their long-term consequences. Here, we use long-term data spanning nearly a century to investigate changes in hydrologic attributes for two lakes in the Upper Midwest with urbanizing watersheds. We quantified flashiness—the variability of runoff rate, volume, or stage-level of waterways—to investigate the concurrent impacts of urbanization and climate change on flashiness and flooding potential. Our results indicate that flashiness generally increased for both lakes over the period of 1916–2013, although this overall trend consists of sub-periods of increase and decrease. Increasing impervious surface area has been the stronger driver of flashiness historically; however, our results suggest that the impact of urbanization may reach a threshold, such that saturation effects would cause large magnitude precipitation events to become a relatively stronger driver of flashiness. Increasing flashiness indicates an increase in flooding potential, documented by increases in the 10- and 100-year flood threshold levels as large as 30 cm. Since flashiness is strongly related to the provisioning of multiple ecosystem services, the methodology and results presented here provide a unique approach to gain insight into how non-linear interactions between global change drivers, at multiple time scales, impact the simultaneous provision of multiple services.