Recent Trends in Precipitation and Streamflow in the Rio Puerco Basin

Abstract

River systems in semiarid regions are susceptible to rapid and dramatic channel erosion and arroyo formation. Climate plays an important role in arroyo development through changes in precipitation intensity, seasonality, and variability. Here, trends in precipitation and streamflow at the annual, monthly, and daily timescales for the last 50 yr are analyzed for the Rio Puerco Basin in northwestern New Mexico, and connections with recent watershed and channel changes are examined. The increasing trend in annual precipitation in the basin is shown to be part of larger-scale climatic variability that affects the U.S. Southwest region, which is associated with climatic anomalies in the northern Pacific. Results of hydroclimatic data analyses point to a general increase in wetness in nonsummer months?an increase in the number of rainy days and in the frequency of flow days in the stream system is observed. There are substantial shifts in the distributions of both daily precipitation and streamflow. Rainfall with moderate intensity has been increasing, while the intensity of annual maximum rainfall events has remained largely unaffected. At the same time, the number of annual maximum runoff events in the basin has been steadily decreasing in the studied period. It is argued that recent watershed and arroyo changes that affect the rainfall?runoff relationship in the basin may be responsible for the decreasing trend in maximum runoff events. Field evidence of such changes in the Rio Puerco watershed and fluvial system is discussed.