Long Term Climate Change and Environmental Implications of Aquifer Flow Capacity in Arid Groundwater Basins

This paper reviews environmental and hydrological problems associated with long term climate change and flow capacity in arid groundwater basins. Flow capacity is defined as the maximum amount of water that a flow system can transmit. The phrase “rejected recharge” typically is applied to an aquifer at flow capacity where precipitation infiltration or other sources of potential recharge exceed the capacity of the saturated zone to accept additional recharge. Usually this results in regional saturation of the water table near land surface. The characteristics of a flow system that influence flow capacity are moisture availability, slope of the terrain, and permeability of the aquifer. Moisture is not available for flow capacity to be established in most arid aquifers. Climate change as a result of global warming or cooling may cause an arid system to reach flow capacity. Paleohydrologic evidence of flow capacity in arid aquifers is observed in the southwestern Basin and Range Province. Flow capacity was established in some of these aquifers during the pluvial periods of the late Pleistocene Epoch, when precipitation was higher. Recent concerns about global warming and climate change intensify concerns about possible effects of flow capacity on groundwater quality. Abandoned landfills and radioactive waste and other long term disposal sites could become inundated, creating a potentially threatening environmental problem. In addition, where flow capacity was achieved along basin floors several thousand years ago, basin floor salts were precipitated in phreatic playas. Playa salts may remain in soils and may not be completely leached for tens of thousands of years as climate becomes drier and as water tables fall. These salts can be long term sources of salinity enrichment in groundwater basins due to leaching. Hydrologists often focus on deeper sources of salinity in groundwater basins and should recognize historical presence of phreatic playas that may be a more prominent source of salinity.