Substantial Declines in Salinity Observed Across the Upper Colorado River Basin During the 20th Century, 1929–2019

Abstract

The southwestern United States (US) relies on the Colorado River to sustain its ecosystems, communities, and economies. The Colorado River provides irrigation water to nearly 4.5 million acres of land, generates over 4,200 megawatts of hydroelectric power, and supplies water to over 35 million people in the United States and 3.3 million people in Mexico each year (U.S. Bureau of Reclamation, 2012Reclamation, , 2017. Furthermore, it is estimated that the Colorado River supports over 16 million jobs, with an annual economic benefit of over $1.4 trillion (James et al., 2014).

How Will Baseflow Respond to Climate Change in the Upper Colorado River Basin?

“…This pattern suggests that the projected baseflow changes may increase dissolved solids loading to the UCRB because the baseflow declines occur in areas where baseflow contributes lower dissolved solid loads, while the baseflow increases occur in areas where baseflow contributes higher dissolved solid loads (Rumsey et al., 2017). Projected climate‐induced baseflow changes could reverse the long‐term dissolved solids decline observed in UCRB streams throughout the twentieth century (Rumsey et al., 2021).…”

Long‐Term Changes in Concentration and Yield of Riverine Dissolved Silicon From the Poles to the Tropics

“…Streamflow conditions can strongly influence annual mean concentration and flux; therefore, WRTDS generates “flow‐normalized” concentrations and load by integrating the C‐Q relationship over the observed probability distribution of stream discharge over the period of record (Choquette et al., 2019). This approach removes the effect of year‐to‐year variations in streamflow, such as high‐ or low‐streamflow conditions that are largely driven by variable weather and which can be particularly influential at the start or end of a record, to provide flow‐normalized values that show gradual change over time (Hirsch et al., 2010; Rumsey et al., 2021). See Text S1 in Supporting Information S1 for more information on the WRTDS model and flow‐normalization.…”

“…WRTDS generates this information by comparing two models, one in which the distribution of annual flows (i.e., the flow regime) is allowed to change over the period of record and the other in which it was held constant. WRTDS then estimates the portion of the overall trend explained by shifts in the flow regime alone (difference between the trends generated by the two models) versus proportion of the trend explained by changes in “watershed biogeochemical processes” (model 2; Rumsey et al., 2021). For instance, changes in concentration or yield mainly driven by changes in the flow regime (i.e., “flow regime trend”) reflect shifts in the hydrologic system, such as changes in the quantity and timing of surface or groundwater flow.…”

Over half a century record of limnology data from Lake Powell, desert southwest United States: From reservoir filling to present day (1964–2021)

“…The Lake Powell Water Quality Monitoring program formally began in 1965 and was motivated by basin-wide concern over high salinity levels in surface waters across the Colorado River Basin. Although substantial reductions in salinity have occurred across the Upper Colorado River Basin since the Salinity Control Act (Rumsey et al 2021), annual economic damages related to high salinity are still estimated at 380 million USD (U.S. Bureau of Reclamation 2017) and funding for the monitoring continues from the Salinity Control Program. Objectives of the monitoring program have evolved over time in response to emerging environmental concerns related to the Grand Canyon Protection Act and the establishment of the Glen Canyon Dam Adaptive Management Program among others.…”