Identifying Regime Shifts in the Arkansas River Near Larned, Kansas

Abstract

Characterizing the drivers of flow in non-perennial streams is increasingly important for understanding the effects of variable flow regimes on local communities and ecosystems. Regime shift theory has been used to explain changes in other hydrologic systems, but the theory as it applies to non-perennial streams has yet to be fully explored. Here, we use the Arkansas River basin near Larned, Kansas, to determine whether changes between flow and no-flow conditions can be described using a regime shift framework. We combined hydrological, meteorological, and ecological time series data to test for the presence of statistical hints commonly associated with regime shifting systems and used a sequential t-test analysis of regime shifts (STARS) algorithm to test for regime shifts in the time series of weekly and monthly no-flow days. Although flow data exhibited hints such as critical slowing down and asymmetry of flow rates, evidence for increased variance and autocorrelation was weak. STARS identified at least five shifts between dry (predominantly no-flow conditions), intermediate (alternating flowing and no-flow conditions), and wet (predominantly flowing conditions) regimes in the river between 1998 and 2021. The intermediate regime appears to be a transitory phase between the stable wet and dry regimes observed at Larned. Regime shifts at the site are likely driven by a complex interaction between climate, pumping, and stream-aquifer interactions.