Characterizing the flow regime of ephemeral streams in the Southwestern USA using stream-gaging data
Freshwater resources are essential to life, but at least half of the world's rivers run dry at some point in time and space. As the geographic extent of periodically dry rivers increases, it becomes increasingly important to establish the spatial and temporal variability of hydrologic conditions. This thesis reviews current understandings of intermittent rivers and ephemeral streams and discusses methods to characterize how patterns in streamflow vary through time, also known as flow regime. Four USGS stream gages were selected across New Mexico and Arizona. They were chosen on the basis that the decreased to zero at some point in the time series, there was minimal impact from human modification, and the period of record went through 2013 and exceeded 50 years. Daily streamflow values were summarized by year, then three hydrological indicators were calculated for each gage: mean annual streamflow, peak annual streamflow, and annual number of dry days. The data was then grouped into two time bins and statistics were derived to assess temporality. The results of the flow analyses indicate that streamflow conditions of intermittent fluvial systems in the Southwestern USA are highly varied through space and time. The gages exhibited unique flow regimes that were challenging to generalize, emphasizing the need to establish the variability in hydrologic conditions so that societies can be well-equipped to adapt to future changes in water-resource availability.