Controls on watershed flashiness across the continental US

Abstract

Hydrograph flashiness is a commonly used and valuable measure of hydrologic behavior, calculated directly from streamflow measurements. There is limited understanding of how and why flashiness varies at continental scales and within different hydroclimatic regions, which can aid in predicting regional responses to an accelerating water cycle. We addressed this knowledge gap by calculating a widely used metric of flashiness, the Richards-Baker Flashiness index (RBI), for 1144 watersheds across the continental US for a ten year period, using daily streamflow from USGS gages. While regional studies have suggested that flashiness is organized by watershed size, we show that flashiness is poorly organized by drainage area at continental scales. Moreover, relationship strengths and directions with drainage area varied by hydroclimatic regions. Using a regionally based random forest analysis, we show that empirical relationships between watershed characteristics and flashiness are diverse, emphasizing that drivers of flashiness are likely related to regional or smaller scale features that encapsulate relationships between climate, human impacts, and the subsurface.