New Mexico Geological Society Annual Spring Meeting — Abstracts

Drought conditions have impacted Rio Grande flows over the past 15 years, and have been highlighted by iconic images of low water levels in Elephant Butte Reservoir. Below average snowpack in the headwaters of the Rio Grande this spring foretell another year of low runoff. The ongoing drought has prompted the question, is this a local manifestation of global climate change, or attributable to natural variability? Given the relatively short instrumental climate records, this question can be difficult to answer. The Rio Grande gage record from the headwaters in Del Norte, Colorado, which extends to 1891, can provide part of the answer. However, to examine the range of conditions that have occurred under natural variability over longer time periods, paleoclimatic records are needed. Tree rings provide one way to investigate past hydroclimatic variability going back centuries to several millennia. A network of tree ring data has been used to develop reconstructions for the Rio Grande region including annual streamflow and monsoon precipitation. Taken together these records suggest the most severe droughts in the instrumental record have been exceeded in prior centuries. In particular, there have been episodes of dry monsoon seasons in the middle Rio Grande region of New Mexico, coupled with low flows in the Rio Grande headwaters. Although the monsoon record is limited to the last four centuries, longer tree-ring records for the San Juan Mountains suggest prolonged periods of drought occurred in the medieval period and in the second century. While these records of persistent droughts of the past may be considered analogues for future droughts, they are likely to be conservative. Recent and projected temperature trends will play an increasingly important role in exacerbating effects of droughts, including the range of drought conditions documented in the tree-ring records.