Flooding and the interannual variability of hydrologic quantities in the Missouri River basin

The six mainstem reservoirs in the Missouri River basin (MRB) are managed mainly to prevent flooding from snowmelt and heavy rainfall, a goal for which the interannual variabilities of precipitation ((Figure presented.)), evapotranspiration ((Figure presented.)), and surface air temperature ((Figure presented.)) are vitally important. We tested the hypothesis that under the expected higher variability owing to global climate change, the months with the highest contributions to the interannual variability of (Figure presented.), (Figure presented.), and (Figure presented.) in the MRB will remain unchanged and quantified likely temporal trends in these quantities. Using high-resolution, downscaled Coupled Model Intercomparison Project Phase 5 multi-model ensemble data sets, we compared the multi-year ratio of monthly and annual interannual variability and temporal trends in (Figure presented.), (Figure presented.), and (Figure presented.) during 2011–2020 with three future decades. Results showed that the 6 months with the highest interannual variability in (Figure presented.) and (Figure presented.) (April–September) are the same in all four decades. However, for (Figure presented.), only 4 months (December–March) retain their status as highly variable throughout the four decades; September and October variability is exceeded by the variability in other months. This implies that, compared to (Figure presented.) and (Figure presented.), the cyclical change in the probabilities of (Figure presented.) in the MRB is less stable under future global climate change. This finding can be used to consider the need to alter existing strategies for reservoir release while minimizing the likelihood of aggravating flooding below the reservoirs.