Perspectives on climate change, mountain hydrology, and water resources in the Oregon Cascades, USA

From both social and environmental perspectives, water is the
main connection between highland and lowland processes in
mountain watersheds: Water flows downhill while human
impacts flow uphill. For example, in the Oregon Cascades
mountain range, geology, vegetation, and climate influence the
hydrologic connections within watersheds. Geology determines
which watersheds are surface runoff-dominated and which are
groundwater-dominated. In this Mediterranean climate with dry
summers, surface runoff watersheds will consistently
experience near-zero late summer discharge, so declining
snowpacks will have little effect on low flows. This contrasts
with groundwater-dominated watersheds, where a shift from
snow to rain or a decline in precipitation will reduce recharge,
thereby reducing late summer groundwater contributions to
streamflow. Earlier snowmelt causes forests to transpire
earlier, resulting in decreased springtime streamflow. Reduced
snowpacks lead to soil moisture stress, making forests more
vulnerable to extensive wildfires and affecting the lifespan and
composition of forests. Monitoring and quantifying these
complex linkages and feedbacks require appropriate
measurement networks. Sampling strategies often use
watershed typology to identify where measurements should be
focused. Such an approach should include not only established
watershed classification parameters such as topology and
geology but also interannual climate variability and land cover.
As concerns of water scarcity and vulnerability move to the
forefront, our watershed classifications should be extended to
include ecosystem and social–ecological parameters. An
integrated and agent-based modeling scheme called Envision
has been developed to simulate alternative future landscapes
at the watershed scale. Using fully coupled models of
hydrology, ecosystems, and socioeconomics, decision-makers
can simulate the effects of policy decisions in conjunction with
other climate forcing, land use change, and economic
disturbances. To understand the combined impacts of climate
change and humans on water in mountain watersheds,
researchers must develop integrated monitoring and modeling
systems that explicitly include connections across eco-hydrologic
and social-ecological systems.

Keywords: Mountain hydrology; water scarcity; vulnerability;
snow; climate change; watershed classification; eco-hydrology;
social–ecological system; agent-based modeling;
USA.