Persistence Explains Stream High Flow and Low Flow Signatures with Differing Relationships by Aridity and Climatic Seasonality”

Snow persistence is a globally available metric of snow cover duration that has, thus far, seen limited application to the field of 10 hydrology. This study attempts to explore the controls that snow persistence exerts on streamflow at low and high flow conditions across a diverse spectrum of climatic aridity and seasonality in the United States and Canada. We statistically analyze how snow persistence, aridity, and seasonality conditions interact to control and explain streamflow shape and flashiness at low and high flows. For low flow condition, regardless of climatic aridity and seasonality, a larger snow persistence increases baseflow, reduces low flow variability, and increases the magnitude of extreme low flow relative to average flow. Our results further show that snow 15 persistence becomes a stronger factor in controlling baseflow as well as the magnitude of extreme low flow relative to average flow, in regions with a relatively high aridity and/or with summer-dominant precipitation regimes (or in-phase seasonality). On the other hand, in catchments that are moderately wet to very arid with winter-dominant precipitation regimes (or out-of-phase seasonality), a longer snow persistence could typically lead to a more variability at high flow and a larger magnitude of extreme high flow relative to average flow. This study concludes by demonstrating the relevancy of snow persistence as a globally available 20 streamflow behaviour descriptor and by demonstrating the impacts that climate change may have on snow persistence and ultimately on streamflow behaviour at low and high flows. flows are critically required for the prediction of hydrologic response in ungauged regions, particularly under changing climatic conditions and land uses 2013; 2018). This study seeks to build a generalizable understanding of the linkages between SP and catchment hydrologic functioning by 85 enlarging the scope of analysis climatically and behaviourally to ultimately evaluate SP’s effectiveness as a parsimonious and widely available tool to inform climate change impact analyses, water management, and decision-making, in (un)gauged catchments. In doing so, we adopt a statistical inference method—which acknowledges the interactions amongst catchment climatic descriptors (predictors)—to a hydrologic context by exploring the relationships between SP and shape-based streamflow signatures across a vast gradient of seasonality and aridity in the United States and Canada. Our overarching hypothesis is that 90 there are distinct relationships between SP and shape-based streamflow signatures at different levels of climatic aridities and seasonalities. Specifically, we aim to explore: tools the persistence of snowpacks streamflow flashiness at high and low flow conditions, for use in (un)gauged catchments, streamflow data exist SP data available. parsimonious predictive tools provide water stake holders with a process- based quantitative understanding to better evaluate catchment streamflow responses and make well-informed decisions about security and environmental disturbances flood & drought) and in-phase climates compared to wet and out-of-phase climates. These results imply that SP could be used as a new catchment climatic descriptor in explaining stream low flow shape-based signatures across a vast range of climatic conditions. Furthermore, there are associations between SP and stream 305 high flow shape-based signatures (normalized Q 95 and High-FDC) in catchments with out-of-phase precipitation seasonality and moderately wet to very arid climates. These high flow results are supported by previous research that suggested that there are important links between SP and the timing and magnitude of peak flows, wherein snowmelt is a primary source of high flow generation in catchments with out-of-phase (winter-dominated) precipitation seasonality (Kampf and Lefsky, 2016). These findings have implications for developing parsimonious large-scale models to predict streamflow behaviour (particularly low flow conditions). Indeed, a simple metric of snow accumulation and melt, such as SP, can be used to improve the performance of large-sample hydrology methodologies for hydrologic knowledge generalization and extrapolation to ungauged basins. SP can be a new candidate for further discovery and advancements in the field of large-sample hydrology and predictions in ungauged basins around the world with diverse climates, land cover, topographies, and geologies, particularly in conjunction with more 315 climatic and physically based catchment variables (e.g., topographic, geologic, vegetation). catchment behaviours and climatic conditions. This study sought to expand such work towards explaining hydrograph variability (shape) in low and high flow conditions across a broad range of North American climatic regimes. Through statistical analyses, it has been shown that there are generally statistically significant associations between snow persistence and stream low flow behaviour in the form of decreasing low flow variability, sustaining catchment baseflows, and increasing stream 440 low flows relative to average flows, regardless of the magnitude of climatic aridity and precipitation seasonality. The findings also depict the associations between snow persistence and increased high flow magnitude relative to average flows, as well as increased high flow variability for catchments in moderately wet to dry climates with winter-dominated (out-of-phase) precipitation seasonalities. These findings are particularly relevant for practitioners to better understand the interplays and feedback between climatic variables and hydrology in the light of climate change in the years to come. Future work can be done to expand the range 445 of descriptors used within hydrological studies to include snow persistence as a climatic metric, and to mechanistically explore the relationships between snow accumulation, melt and hydrologic behaviour, and further develop the fundamental knowledge that supports global scale snow science and hydrology.