Geoscience Reference
In-Depth Information
mean.values.for.catchments.in.North.Cascades.NP,.Glacier.NP,.Yosemite.NP,.and.
the. Snake. River. of. Colorado. were. used. to. evaluate. ecosystem. and. hydrological.
responses.
At.all.sites,.precipitation.was.more.variable.than.temperature.from.year.to.year..
Wet.and.dry.precipitation.years.ranged.30-63%.higher.to.32-51%.lower,.depending.
on. the. site,. than. the. 47-year. mean,. while. annual. mean. temperature. variation. for.
the.four.catchments.ranged.1.1-1.4°C.higher.to.0.7-1.7°C.lower.compared.with.the.
47-year. mean.. The. driest. years. and. those. with. the. lowest. snow. depths. inluenced.
ecological.and.hydrologic.responses.at.all.sites..Primary.productivity.was.stimulated.
by. warmer. temperatures. at. the. high-elevation,. low-temperature. site. in. the. Snake.
River.watershed..Productivity.at.Yosemite.NP.and.Glacier.NP.was.responsive.to.pre-
cipitation.and.declined.in.dry.years..Primary.productivity.at.North.Cascades.NP,.the.
warmest.and.wettest.of.the.four.watersheds,.was.the.least.responsive.of.the.water-
sheds.to.climatic.extremes.
Hydrologic.processes.were.proportionally.more.responsive.than.ecological.pro-
cesses. to. climatic. extremes,. and. these. responses. varied. across. watersheds.. All.
four. watersheds. showed. statistically. signiicant. increases. in. annual. stream. low.
in.extremely.wet.years.and.signiicant.decreases.in.extremely.dry.years..Between-
watershed.differences.in.the.relative.change.in.stream.low.with.change.in.precipita-
tion.should.indicate.the.extent.to.which.evapotranspiration.moderates.the.sensitivity.
of.stream.low.to.a.change.in.precipitation..North.Cascades.NP.showed.the.greatest.
inluence.of.evapotranspiration,.consistent.with.the.minimal.vegetation.responses.to.
climatic.extremes.
Stream.low.in.all.catchments.responded.strongly.to.snow.depth.extremes..The.
North.Cascades.was.least.sensitive.to.extremes,.and.Glacier.stream.low.was.most.
responsive.. While. Glacier. discharge. responded. to. both. maximum. and. minimum.
snow.depth,.Yosemite.stream.low.responded.signiicantly.to.high-snow-depth.years.
only..All.four.watersheds.had.signiicant.responses.to.high-.and.low-snow.years.in.
their. fraction. of. summer. low,. but. the. Snake. River. watershed. had. the. largest. pro-
portional.changes,.with.the.North.Cascades.watershed.having.the.smallest.changes.
Our.results.suggest.that.historically,.hydrological.and.ecological.processes.in.four.
Western.US.mountain.watersheds.have.been.more.affected.by.precipitation.extremes.
than.temperature.extremes..Temperature.is.not.unimportant.(and.was.very.important.
for. the. cold. Snake. River. catchment),. but. model. analysis. suggests. that. basin-scale.
ecohydrologic.luxes.may.be.more.sensitive.to.precipitation..The.ability.of.general.
circulation. models. to. project. precipitation. patterns. with. increased. greenhouse. gas.
concentrations. is. poor,. reducing. our. capability. to. provide. meaningful. projections.
of.future.ecohydrologic.responses..The.analysis.of.how.mountain.watersheds.have.
responded.in.the.past.is.one.way.of.adding.insight.into.the.possible.consequences.
In.addition.to.comparing.processes.across.watersheds,.RHESSys.modeling.has.
elucidated.interesting.within-watershed.patterns.in.response.to.climatic.variability.
and.change..The.response.of.forests.to.a.warmer.climate.depends.on.the.direct.effects.
of.temperature.on.ecophysiological.function.and.indirect.effects.related.to.a.range.
of.biogeophysical.processes..In.alpine.regions,.reduced.snow.accumulation.and.ear-
lier.melt.of.seasonal.snowpacks.are.expected.hydrologic.responses.to.warming..For.
forests,. this. leads. to. earlier. soil. moisture. recharge. and. increased. summer. drought.
