Hydrological Changes to Climate Wetting in a Wetland‐Dominated Agricultural Watershed

Understanding the partition of input flux like precipitation into output fluxes (evapotranspiration ( ET ) and streamflow ( Q )) is important to understand the hydrological responses under a changing climate in the Northern Great Plain (NGP). Devils Lake basin (DLB) in NGP has been experiencing a pronounced deluge period with intermittent dry phases since 1990. This study introduces a novel analysis of storage dynamics, scenario‐based modelling, and flux diagnostics, offering new insights into the process‐based hydrology of DLB. The study investigates two adjacent watersheds at DLB—Edmore at Edmore and Edmore at Webster coulee, differing in wetland density, land use and topographic relief. Precipitation ( P ) is partitioned into vertical losses [ V —evapotranspiration and sublimation components] and streamflow ( Q ), represented by the ratios V / P and Q / P . Strong inverse relationships between vertical flux ratio ( V/P) and horizontal flux ( Q/P) were observed, where V/P responded non‐linearly to atmospheric moisture, while soil moisture and precipitation timing contributed to considerable. The comparison of V/P and Q/P ratios highlights a strong climate dependency in water‐loss partitioning, with ET dominating in dry years and runoff efficiency increasing under wet conditions. Snowmelt was the dominant driver of hydrologic connectivity, with years of high snow water equivalent ( SWE ) and snow‐covered days corresponding to larger spring contributing areas and elevated Q/P ratios. The contributing area changed with precipitation regime, reflecting fill‐spill thresholds in depressional storage. Results reveal a clockwise hysteresis relationship, indicating rapid streamflow response followed by delayed contributing area expansion, a behaviour driven by depression storage, fill‐spill thresholds and wetland connectivity. For DLB where wetlands and low‐relief topography promote strong storage control, lake expansion is primarily contingent upon threshold‐driven connectivity and lagged hydrological response to climatic forcing.