WMOD00383

• Title: Simulation of Winter Precipitation in Western Mountain Watersheds with a Local-Scale Model
• Date: 11/1/1992
• Weather Modification - Doc Type: Report

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Presented at the 28th Annual Conference & Symposium of the
Amerioan Water Resources Assooiation in Reno, Nov~)er, 1992

SIMULATION OF WINTER PRECIPITA'I~ION IN WESTERN MOUNTAIN
WATERSHEDS WITH A LO~~-SCALE MODEL

J. G. MEDINA1

ABSTRACT: A LSPM (local-scale orographic precipitation model) was
adapted and applied to the Gunnison River watershed of western Colorado.
The modeling is a key component of Reclamation's (Bureau of Reclamation)
GCCRP (Global Climate Change Response Program) aimed at identifying
potential impacts of global climate change on western river basins and
developing strategies to deal with the impacts. The model is two-
dimensional, steady-state, and multilayer. The grid spacing employed is
either 10 or 5 km. Twice-daily local atmospheric soundings, and four-
times-daily RSM (regional-scale model; here, the National Center for
Atmqspheric Research's MM4 model) gen~~rated souridings, supplied the
required inputs of vertical profiles of temperature, relative humidity,
and winds. The RSM generated soundings were of interest because a
nesting of GCM (general circulation model), RSM, and LSPMs is a major
component of the GCCRP. The LSPM output,s included precipitation at all
grid points and specified gauge locations; and watershed integrated
volume precipitation. Model estimate comparisons with higher-elevation
daily precipitation data were performed for wet (1982-83) and dry (1988-
89) winters. Results indicate the model should be able to produce
realistic local-scale precipitation p:I~ofiles that may occur from a
dOubled-C02 altered climate simulated by a nesting of a RSM and a GCM.
Additionally, the model has potential t,o serve as an operational tool
for river managers.
KEY TERMS: model, precipitation, GCCRP, watershed, local-scale, nested

INTRODUCTION

Reclamation operates numerous water storage facilities and
hydroelectric dams located in the West. The prospects of global climate
changes over the next few decades have, led to increased interest in
climate modeling to study and estimclte the potential impacts of
augmented greenhouse gases on the fut:ure climate in western river
basins. Modeling offers a consistent and perhaps the most comprehensive
approach, in applying physical principlefJ for simulating future climate.

A vital component of climate modeling is atmospheric modeling. A
product of the latter is precipitation estimates that can then be
employed to develop new, or improve existing, scenarios of the impacts
on precipitation caused by anticipated effects of climate change.
Because Reclamation's interests are at the watershed level, atmospheric
modeling must address precipitation at that resolution to best serve
needs. Because existing GCMs (general circulation model) yield

lMeteorologist, u.S. Department of the Interior, Bureau of Reclamation,
P. O. Box 25007, Code 0-3720, Denver, CO 80225.

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