Cold region hydrologic changes to a wet climatic regime in the Northern Great Plain

The nature of a novel wet period beginning in the early 1990s controlled the hydrology of the northern portions of the North American Great Plains over last three decades. Such wetting with intermittent mild dry conditions influenced snow processes, streamflow generation, evapotranspiration, watershed storage and contributing areas although the hydrology of this wet period is extensively studied, aspects of the hydrology, particularly the nature of the streamflow – contributing area hysteresis relationship is little known. The temperature fluctuated during the 1990–2004 period such that there were three climate states: wetting-cooling (1990–96, CS1), wetting-warming (1997–1999, CS2) and drying-cooling (2000–2004, CS3). Here, we deploy a physically-based hydrologic model (the Cold Region Hydrologic Model, CRHM) to discern the predominant hydrological processes during each state in the Mauvais Coulee Basin (MCB) in North Dakota. Results indicate each state is characterized by distinct combinations of the lateral flux/precipitation (Q/P) and vertical flux/precipitation (V/P) ratios. The Q/P was insensitive during CS1 while it was very sensitive during CS2. In contrast, V/P was highly sensitive during CS1 and fluctuated minimally during CS2. The influence of V/P on watershed water balance was greatest during CS3. Water storage (antecedent fall soil moisture and snow water equivalent) and ET of the antecedent year control the contributing area and watershed storage states that influence the magnitude of Q generation. These dynamics are reflected in the distinct hysteresis between storage and streamflow in each of the three climate states.