Observed Changes in Climate and Streamflow in the Upper Rio Grande Basin

Observed streamflow and climate data are used to test the hypothesis that climate change is already affecting the streamflow volume derived from snow accumulation in ways consistent with climate model-based projections of 21st century streamflow. Annual and monthly changes in streamflow volume and surface climate variables on the upper Rio Grande (URG) near its headwaters in southern Colorado are assessed for water years 1958-2015. Trends in discharge are examined together with variations in snow water equivalent and surface climate variables. Results indicate that temperatures in the basin have increased significantly primarily in the winter and spring seasons, April 1 snow water equivalent has decreased by approximately 25%, and streamflow has declined in the runoff season, but small increases in precipitation have reduced the impact of declining snowpack on streamflow. Changes in the snowpack-runoff relationship are noticeable in hydrographs of mean monthly streamflow, but most apparent in the changing ratio of precipitation (rain+snow, and snow water equivalent) to streamflow and in regression statistics. The observed changes impact our ability to predict streamflow on a seasonal basis and affect long-term water management of the Rio Grande