The Moderating Influence of Spring Climate on the Rio Grande Headwaters: A Paleo Perspective

While snowpack is the main influence on Rio Grande water year streamflow, spring hydroclimate can play a role in moderating this influence in a subset of years. Through an investigation of the relationship between winter snowpack and spring hydroclimate conditions and Rio Grande streamflow, we find low snowpack years with relatively cool, wet springs coincide with slightly above median streamflow in 18% of the years in the instrumental record (1936–2018), while the opposite conditions occur during 24% of years. Over this period, an increase in years with low snowpack/cool wet springs is evident, likely due to a significant decreasing trend in snowpack. We analyze two 15-century tree-ring reconstructions to provide long-term context for the variable relationship between snowpack and spring hydroclimate. Results suggests irregular but quasi-multidecadal periods when spring conditions may have moderated the effect of a relatively dry winter or reduced the effect of a relatively wet winter. The reconstructions also provide context for the observed trend in the increasing importance of spring conditions over the instrumental period, which appears to be related to both natural climate variability and climate change. In the Rio Grande basin, as mountain snowpack declines due to warming temperatures, spring conditions may be playing an increasingly important role for water resources, at least in the near term.