Declines in an Aridland River's Base Flow Due to Increasing Air Temperature: Implications for Springs Ecosystems

Considerable attention has been paid to perennial aridland rivers due to their disproportionate importance both ecologically and socially within aridlands. The Verde River Basin (VRB) is a large aridland watershed in central-northern Arizona. The river is subject to variable surface flow inputs, but its baseflow is sourced from springs. We investigated trends in increasing summer temperature and reduced June baseflow beginning in 1990 and continuing through the present. We discuss the potential impacts on the 965 reported springs in the watershed. Springs of the VRB support a wide array of flora and fauna. Early summer dry-season flows are almost entirely derived from springs making the aquatic species of the VRB almost entirely springs-dependent. VRB baseflow was increasing prior to 1990, with a change in trend that coincides with a change in air temperature. Declining snowpack and infiltration, coupled with warming temperatures since 1990 have reduced baseflow basin-wide through reduced groundwater supply, with likely impacts to springs ecosystems, especially springs fed by “younger” groundwater that is most vulnerable to reduction in aquifer recharge. The empirical results of this study indicate a trend of warming temperature correlated to diminishing groundwater dependent resources; supporting recent hydrological and climate projections for the American Southwest.