In these cases, the portion of groundwater recharge derived from snowmelt is typically significantly higher than the portion of average annual precipitation that falls as snow. Isotopic studies in western mountains show that 50 to 90% of recharge is from snowmelt. Because large and intense infiltrations of water are required to break through the region's thick unsaturated zones, and because snowpacks store and then release precipitation from several storms at once, snowmelt provides more recharge than does rain. Mountains are generally wetter and cooler than adjacent basins, so groundwater in the West is derived mainly from mountain precipitation.
As a result, changes in groundwater recharge could cause major changes in streamflow, affecting the quantity of flow, the chemical quality of the flow, and the timing of seasonal flow events. Groundwater is also an important contributor to surface-water resources: groundwater inflows make significant contributions to western streamflow, sustaining flows during long dry seasons and contributing significant fractions even during intense rainfall and snowmelt episodes. In addition to accounting for a significant portion of human consumption, groundwater sustains many wetlands ecosystems. more Groundwater is an important resource in the West. In addition to accounting for a significant por. Groundwater is an important resource in the West.
Given ground water's crucial role in western water, potential impacts of warming on recharge deserve more attention than they have received to date, preferably from a long-term monitoring system incorporating multidisciplinary observations. Declines in recharge triggered by warming could seriously impact ground-water supplies and surface-water resources to which ground water contributes. All these factors can play a role in affecting groundwater recharge, and none are well understood or predicted at present. Changes in temperature will bring concomitant changes in water temperatures, and thus in streambed conductance and leakance changes in dominant vegetation may also occur.
#Earman river plus
However, if the water that is not recharged in the mountains is mostly evapotranspired from the mountain soils, the overall recharge (mountain plus basin) may decline. Although recharge that supplies mountain groundwater may decline, much of this unrecharged water may run off onto fans and basins, increasing recharge beyond the mountains. Declines in mountain recharge triggered by loss of snowpack would have immediate impacts on mountain water resources, including low flows and stream temperatures, and may also have serious impacts on long-term ground-water supplies in surrounding basins. If so, mountain-block recharge also may also decline, as recharge areas shrink and snow available for melt generation dwindles. Snowline elevations are expected to rise, reducing snow-covered areas in western mountains, and decreasing the amount of snow in areas where snowpacks remain.
Current projections of future climate suggest that these trends will continue. Warming temperatures have already caused declines in Western snowpacks and earlier flows in melt-fed streams.
Because snowpacks store and then release precipitation from several storms at once, snowmelt contributes disproportionately more recharge than does rain. Large infiltrations of water are required to break through the region's thick unsaturated zones. Because mountains are generally cooler and wetter than adjacent basins, groundwater in the West is derived mostly from mountain precipitation. In addition, groundwater is a major contributor to surface-water resources, sustaining baseflows throughout the year, and contributes important fractions of streamflows even during high-flow periods following rainfall and snowmelt. more Groundwater is a vital resource in the western USA, accounting for over a quarter of total supplies and irrigation uses. Groundwater is a vital resource in the western USA, accounting for over a quarter of total suppli.
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