BOARD02543

• Board Meeting Date: 3/21/2002
• Description: Flood Section - Extreme Precipitation Study Update
• Board Meetings - Doc Type: Memo

-2-

The model that will be used is the Regional Atmospheric Modeling System (RAMS) CSU under
the direction of Dr. William Cotton. The preferred procedure is to perform interactive nested grid .
simulations of the evolving large- scale or synoptic: state of the atmosphere, the corresponding
mesoscale circulations that are driven by flow over eomplex terrain and by surface heating over
the regions, and the explicit formation and evolutibn of convective storms. The procedure is
analogous to that used in the research case studies, hnd is an extension of those used daily in a
realtime forecast model. In a sense this procedute si~ulates the evolution of the "representative"
soundings and circulations at the location and time of convective storm formation. The data from
the Phase I report entitled "Colorado Extreme Storm Precipitation Data Study", May 1997, will
be used to perform simulations using the RAMS parallel processing cluster developed for this
project.

Proiect Status ,
CSU is presently in their 36th month of their proposed 30-month timetable. They were granted a
no cost extension to complete the simulation~ of historic events. They have been doing the
simulation of historical flood events that were identified in the Phase I report after spending a lot
of time calibrating the new model with the RAMS parallel cluster. They have produced six
progress reports to date and the Technical Review Group- (TRG) has met three times to review
and discuss the results with CSU. All of the progres~ reports have been reviewed by the TRG and
comments sent to Dr. Cotton. At the July 2001 m~eting, the TRG found that the progress was
very encouraging. The most significant problem identified was that the model was not able to
determine the exact storm location of historical extreme events. Dr. Cotton proposes to use a
spatial interpolation program, "Krieging", to produce a mapping over Colorado of extreme
precipitation estimates (rain plus hail). In his November 2001 report, Dr. Cotton reported that .
they have performed simulations for two additional extreme events that occurred in 1997 and
i 999 to add to the recommended list of storms.

Summary i
CSU is preparing their final report and mapping with the expectation of submitting their final
report by the end March 2002. The TRG ;will review the final report, and make
recommendations on whether or not the model can:be used for predicting extreme events. One
of the tasks that have not been completed by CSU is, to conduct hearings on the results in order to
gain credibility and acceptability of the model. FQr a complete picture of the results of their
research, you can visit their Web Page at rams,gtmotcolostate.edu/orecio-oroi/index,html.

The CWCB staffis working with the DWR staffto ~enerate a detailed presentation for the May
2002 Board meeting to update the Board on the results of this study.
.

.

Flood Protection. Water Project Planning and Fn;.ancing. Stream and Lake Protection
Water Supply Protection. C.onservation Planning

2