[pccgrads] Brian Henn - PhD Final Exam "Combining indirect observations and models to resolve spatiotemporal patterns of precipitation in complex terrain"--Tue Dec 1 at 9:30

UW PCC uwpcc at uw.edu
Tue Nov 24 16:09:34 PST 2015

Brian Henn - PhD Final Examination

Tuesday, December 1, 2015

9:30 AM

Allen Library South, Ground Floor, Room Green A

Supervisory Committee Chair: Jessica Lundquist

Title: Combining indirect observations and models to resolve spatiotemporal
patterns of precipitation in complex terrain

Mountain precipitation in the Western United States is critical for the
water resources of the region, but resolving patterns of precipitation in
complex terrain is challenging due to lack of observations, measurement
error and high spatial variability. As a result, precipitation datasets
contain uncertainty and biases over these areas, which has many scientific
and operational implications. This dissertation develops approaches for
improving resolution of precipitation patterns over complex terrain by using
indirect observations and models, focusing on the Sierra Nevada mountain
range of California. A methodology is developed for inferring water-year
total, basin-mean precipitation given daily streamflow observations, using
lumped hydrologic models and Bayesian model calibration. Under this
approach, patterns of precipitation can be inferred from streamflow, both in
terms of spatial and year-to-year variability. The research also shows that
when snow observations are included with streamflow in the inference,
uncertainty in inferred precipitation is reduced by up to half as compared
to using streamflow alone. To resolve patterns of precipitation over the
Sierra Nevada, streamflow observations from 56 gauges in relatively
unimpaired basins are used to infer precipitation over 1950-2010. Inferred
precipitation is compared to precipitation gauge-based gridded data, showing
that significant differences exist between the mean spatial patterns of
precipitation over the range. In particular, inferred precipitation suggests
that gridded products underestimate precipitation for higher-elevation
basins whose aspect faces prevailing winds. Better agreement is found in
lower-elevation and leeward basins. These findings suggest that
methodologies for developing precipitation datasets should consider related
hydrologic observations, in addition to precipitation gauge observations, in
order to better resolve patterns of precipitation in complex terrain.

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