Winter Type, Mediated by Land‐Surface Processes, Controls Seasonal Discharge Variability in Culturally Critical Ecosystems in the US 's Upper Midwest

With some of the fastest rates of winter warming in the contiguous U.S. projected in the Upper Midwest, Tribal natural resource managers in the region are concerned about milder winters' impacts on culturally important ecosystems. In particular, Manoomin (Ojibwemowin; Dakodiapi: Psiη; English: Wild Rice, Latin: Zizania palustris ), an annual aquatic grass with deep cultural significance for the Ojibwe, Dakota, and other Indigenous Peoples, is extremely vulnerable to climate change impacts. Manoomin's high sensitivity to hydrologic conditions raises urgent questions about the impacts of low snowpack winters, or snow‐droughts, on flow conditions. However, with most regional snow‐drought studies focused on mountain settings, the impacts of snowpack changes on growing‐season discharge remain uncertain in the low‐relief, humid context of the Upper Midwest. Using a framework guided by Tribal collaborators, this study examined how winter snowpack affects subsequent streamflow, the role of other winter climatic variables, and the key springtime land‐surface processes that mediate these connections. We categorised winters across watersheds in the Upper Midwest by different climatic metrics, and then compared discharge, evapotranspiration, leaf area index, and frost data for each winter category to characterise discharge behaviour and snowmelt pathways. Our results highlight winter snowpack as the main driver of springtime discharge, with total winter precipitation and thawing degrees as strong secondary controls. Due to suppressed evapotranspiration, high moisture inputs, and moderate frost, occasional cold/wet/high‐snow winters generated both uniquely strong springtime flows that may beneficially disturb Manoomin beds before germination, as well as greater recharge that may stabilise later‐season surface water levels during vulnerable stages. Warmer, wetter conditions expected with climate change fail to create comparable high springtime flow events, likely with broad, ecological consequences. Our collaborative work highlights the importance of heavy snow winters and their cross‐seasonal influence in the long storage‐time landscapes where Manoomin lives.