WMOD00263 ‎(2)‎

• Applicant: CWCB
• Sponsor Name: USBR
• Project Name: Response to RFP
• Title: Numerical Simulations of Snowpack Augmentation for Drought Mitigation Studies in the Colorado Rocky Mountains
• Prepared For: USBR
• Prepared By: Joe Busto, CWCB
• Date: 8/20/2003
• Weather Modification - Doc Type: Application

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8. Offer Experience and Past Performance

8.1 CSU Team

The Principal Investigator, Dr. Cotton has over 28 years of contract and grant experience
at CSu. Likewise he has supervised the construction of RAMS and its application to
mesoscale and cloud-scale modeling for over 16 years.

1) A project similar in scope completed during the last three years:
Development of New Methodologies for Determining Extreme Rainfall

2) A description of the work is contained in the Executive Summary below:

Executive Summary

A new approach to extreme precipitation estimation has been developed using a
convective-storm-resolving mesoscale model, the Regional Atmospheric Modeling
System (RAMS). RAMS was run for six historical heavy precipitating cases over
Colorado. The storms simulated were the Aug. 31, 1976 Big Thompson Storm, the July
28, 1997 Fort Collins Storm, the July 31, 1999 Dallas Divide Storm, the Sept. 18-22,
1997 Park Range Storm, the Sept. 4-6, 1970 Southern San Juans Storm, and the July 26,
1999 Saguache Creek Storm. A total of27 simulations have been performed for these
case studies in which land surface parameters such as soil moisture are varied, model
parameters are varied, different large-scale analyses are used, and the synoptic pattern is
moved relative to the underlying terrain.

The precipitation fields from each simulation were re-mapped on a common grid to
produce composite results for PMP estimation. Maximum precipitation for a given
duration, and maximum depth-area-duration (DAD) events produced by all simulations
were mapped on the common grid. The re-mapped data were then used to compute
Hershfield parameters. The sampled Hershfield parameters were then kriged and co-
kriged back onto an estimation grid and these data were used to make PMP estimates.

The following conclusions have been drawn from the analyses of these cases.

. In each of the observed extreme precipitation cases, RAMS is able to produce one
or more heavy rain events. However, the position and timing of those events does
not always coincide with the observations. Typical spatial and timing errors are
10 to 50km and one to several hours, respectively.

. The most accurate control simulations occur with the least convective, large-scale
forced storms like the San Juan and Park Range storms. The least successful
simulations occur with the older convective events like the Big Thompson storm.
This is likely due to the coarse resolution of the initial NCEP reanalysis data used
for the older events and unavailability of good, high-resolution soil moisture data.

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