Climate change impacts on the temperature and magnitude of groundwater discharge from shallow, unconfined aquifers

Abstract

Cold groundwater discharge to streams and rivers can provide critical thermal refuge for threatened salmonids and other aquatic species during warm summer periods. Climate change may influence groundwater temperature and flow rates, which may in turn impact riverine ecosystems. This study evaluates the potential impact of climate change on the timing, magnitude, and temperature of groundwater discharge from small, unconfined aquifers that undergo seasonal freezing and thawing. Seven downscaled climate scenarios for 2046-2065 were utilized to drive surficial water and energy balance models (HELP3 and ForHyM2) to obtain future projections for daily ground surface temperature and groundwater recharge. These future surface conditions were then applied as boundary conditions to drive subsurface simulations of variably saturated groundwater flow and energy transport. The subsurface simulations were performed with the U.S. Geological Survey finite element model SUTRA that was recently modified to include the dynamic freeze-thaw process. The SUTRA simulations indicate a potential rise in the magnitude (up to 34%) and temperature (up to 3.6 C) of groundwater discharge to the adjacent river during the summer months due to projected increases in air temperature and precipitation. The thermal response of groundwater to climate change is shown to be strongly dependent on the aquifer dimensions. Thus, the simulations demonstrate that the thermal sensitivity of aquifers and baseflow-dominated streams to decadal climate change may be more complex than previously thought. Furthermore, the results indicate that the probability of exceeding critical temperature thresholds within groundwater-sourced thermal refugia may significantly increase under the most extreme climate scenarios.

Observed groundwater temperature response to recent climate change

“…The results of this study however contradict this assumption by indicating that shallow GWT will respond to SAT warming and that the lag time between SAT warming and the associated increase in shallow GWT can be rather short (< 5 years). Similar results were obtained by Kurylyk et al (2014a), who employed a numerical model of groundwater flow and energy transport driven by downscaled climate scenarios to demonstrate a potential damping and short lagging of future groundwater discharge temperature rise in response to air temperature changes. Given the expected warming of rivers across the globe (van Vliet et al, 2011(van Vliet et al, , 2013, researchers have rightfully proposed that cold-water fish will begin to increasingly rely on the occurrence and distribution of suitable cold-water refugia (e.g., Brewer, 2013).…”

“…Numerous studies on the impact of recent or projected climate change on the thermal regimes of surface water bodies and the associated impact for cold-water fish habitats have already been conducted (e.g., Kaushal et al, 2010;van Vliet et al, 2011van Vliet et al, , 2013Wenger et al, 2011;Isaak et al, 2012;Wu et al, 2012;Jones et al, 2014), but the thermal sensitivity of shallow aquifers to climate change is a relatively unstudied phenomenon (e.g., Brielmann et al, 2009Brielmann et al, , 2011Taylor and Stefan, 2009;Kurylyk et al, , 2014a. The thermal response of GWT to climate change is of particular interest to river temperature analysts, as the thermal regimes of base-flow-dominated streams or rivers and hydraulically connected aquifers are inextricable linked (Hayashi and Rosenberry, 2002;Tague et al, 2007;Risley et al, 2010).…”

Increasing Winter Baseflow in Response to Permafrost Thaw and Precipitation Regime Shifts in Northeastern China

“…Several studies have demonstrated that there is a positive correlation between annual rainfall and groundwater recharge (e.g., [73,74]). Thus, as demonstrated by others [18,19], the increased rainfall during the spring and summer seasons in our study watersheds likely resulted in enhanced infiltration and annual groundwater recharge that in turn sustained winter baseflow. Thus, this precipitation regime shift is another possible source for the increased winter baseflows in the study watersheds.…”

“…Thus, the surface and subsurface water are mainly sourced by the rainfall in the wet season (summer) [72], during which the groundwater is recharged from both rainfall and surface water. Although the amount of snowpack decreased due to the increased rain fraction and earlier snowmelt, the duration and extent of infiltration increased, allowing for more groundwater recharge [17], which can then sustain winter baseflows [18,19].…”

“…Godsey et al [16] found that summer baseflows decreased due to the reduction of peak snow water equivalent in California's Sierra Nevada Mountains, where baseflows are primarily sustained by groundwater recharged during snowmelt. Conversely, Jyrkama and Sykes [17] found that warmer winter air temperatures reduced the extent of ground frost and shifted the spring snowmelt event earlier in the year, allowing more water to infiltrate into the ground and thus more groundwater recharge and presumably higher baseflow [18,19]. For example, Yang et al [14] observed significant increases (25%-90%) in cold season (October to April) baseflows sourced from groundwater discharge in Siberia.…”