Recent trends in precipitation and streamflow in the Rio Puerco Basin

River systems in semiarid regions are susceptible to rapid and dramatic cha nnel erosion and arroyo formation. Climate plays an important role in arroy o development through changes in precipitation intensity, seasonality, and variability. Here, trends in precipitation and streamflow at the annual, mo nthly, and daily timescales for the last 50 yr are analyzed for the Rio Pue rco Basin in northwestern New Mexico, and connections with recent watershed and channel changes are examined. The increasing trend in annual precipita tion 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 a nomalies in the northern Pacific. Results of hydroclimatic data analyses po int 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 syste m is observed. There are substantial shifts in the distributions of both da ily precipitation and streamflow. Rainfall with moderate intensity has been increasing, while the intensity of annual maximum rainfall events has rema ined largely unaffected. At the same time, the number of annual maximum run off events in the basin has been steadily decreasing in the studied period. It is argued that recent watershed and arroyo changes that affect the rain fall-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.