New Mexico Geological Society Annual Spring Meeting — Abstracts

The Pecos River is the principal source of surface water for Eastern New Mexico and variability in its flow presents natural and economic challenges.  Projections of anthropogenic climate change show increasing temperature year round in the Pecos Valley and decreasing winter precipitation within its upper drainage area.  Through analysis of stream gage and SNOTEL data, and monthly temperature and precipitation data from New Mexico Climate Division 2, we attempt to ascertain the degree to which observed climate change in recent decades may have affected Pecos River flows.  Interannual variability of precipitation within the upper drainage basin is quite large and strongly tied to the El Nino Southern Oscillation (ENSO) and the Pacific Decadal Oscillation (PDO).  Long term time series of annual flow of the Pecos River at Pecos, NM show large interannual and decadal variations correlated to precipitation, but no significant long term change in the annual flows in the river.  However, decadal averages of melt season central timing (MSCT) are at their earliest historically recorded levels despite comparable precipitation deficits in the mid 20th century.  Melt season monthly stream flow percentages show a decline in June and an increase in the months of March and April.  Changes in streamflow timing may be an indicator that increased air temperatures due to climate change are increasing the speed of the spring snow melt that feeds the river.  Increased temperatures for the period of March through June show a significant correlation to early MSCT dates.  A linear regression model for the most recent 30 year period (1983-2012) shows reduced amounts of melt season streamflow per unit of winter precipitation when compared to the regression model for the previous 30 year period (1953-1982).  The more recent regression model lies outside the 95 percent confidence interval of the previous model and may be an indicator of increased evaporation in the region.