The American West, basin by basin

Our American West scope includes the western contiguous states and western Great Plains. River basins and aquifers cross state lines and overlap this region; their boundaries, climate, and demands differ. Each assessment should identify its actual basin and service area before comparing results.

Snowpack, river flow, reservoir operations, and groundwater should be assessed together. Groundwater discharge sustains streams through dry periods, including in the Upper Colorado River Basin. Reservoir storage alone cannot describe the reliability of the wider system.

A 2016 USGS synthesis of eight representative western aquifers found different recharge responses across locations and pathways. Reduced snowpack can affect mountain recharge; projected responses in southern aquifers were generally less favorable than in northern aquifers. These findings support basin-specific analysis, not one forecast for the entire West.

Use the regional view to connect risks, then evaluate supply and interventions at the basin and community scale. These are planning priorities, not a ranking of depletion or a newly calculated regional forecast.

• Colorado River Basin: connect mountain snowpack, reservoir deliveries, pumping, and groundwater discharge to streams.
• California: evaluate Central Valley storage and subsidence alongside local recharge; distinguish coastal salinity and water-quality constraints.
• Great Basin and Southwest: assess basin-specific pumping, mountain-front and channel recharge, springs, and environmental water needs.
• Pacific Northwest and Idaho: examine groundwater levels alongside snow-fed rivers, irrigation withdrawals, and seasonal supply.
• Western Great Plains: separate local High Plains well conditions and recharge pathways instead of applying one aquifer-wide exhaustion date.

Establish a seasonal baseline before testing interventions. Coordinate surface-water and groundwater use through conjunctive management, with operating rules tied to local monitoring.

• Compare snowpack, precipitation, streamflow, reservoir storage, and well levels.
• Track demand, pumping, recharge, and groundwater contributions to rivers.
• Compare demand reduction, reuse, recharge, storage operations, and additional supplies by dependable local benefit, cost, and environmental effects.