Geoscience Reference
In-Depth Information
FIGURE 1.1 (See color insert.) Mean.annual.precipitation.from.PRISM.(Daly.et.al..2002,.
2004,. 2008). for. the. 1971-2000. period. of. record.. Note. the. sharp. gradients. in. much. of. the.
West.
OBSERVED CLIMATE VARIABILITY AND CHANGE
IN THE WESTERN UNITED STATES
The.western.United.States.is.a.land.of.juxtapositions.and.sharp.contrasts.in.physiog-
raphy,.climate,.vegetation,.and.other.biophysical.attributes..In.addition.to.the.sharp.
contrasts.across.short.distances,.the.West.has.striking.seasonality.in.precipitation;.
in.most.of.the.West,.summer.precipitation.is.substantially.less.than.winter.precipita-
tion.. Fundamental. attributes. of. average. climate,. notably. precipitation,. can. change.
greatly. over. short. distances. (Figure  1.1),. as. can. precipitation. seasonality,. annual.
amount,.and.phase.(i.e.,.rain.vs..snow)..Properties.of.temporal.variability.can.also.
vary.over.short.distances.(Redmond.2003)..Elevation.plays.a.key.role.in.shaping.the.
patterns. of. temperature. and. precipitation. (Daly. et. al.. 2008),. and. mountain. ranges.
greatly.modify.and.sometimes.cause.their.own.weather..Mountain.time.series.of.cli-
matic.variables.can.be.very.different.from.those.in.the.adjoining.valleys..Large-scale.
“teleconnections”.with.other.parts.of.the.globe.lead.to.spatially.different.responses.
in. reaction. to. faraway. phenomena. such. as. tropical. El. Nĩo. and. La. Nĩa. events..
Examples.of.observed.variability.and.change,.and.global.processes.affecting.climate.
in.the.western.United.States.are.described.in.the.next.section.
The. fundamental. issue. is. the. following:. to. fully. understand. the. interrelation.
between. ecosystems. and. the. climate. system,. we. must. ideally. irst. understand. the.
properties.of.spatial.and.temporal.variability.(and.in.addition,.combined.spatiotem-
poral. variability). of. each. of. these. two. sets. of. systems,. across. their. characteristic.
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