EVALUATION OF AN OPERATIONAL WINTER CLOUD SEEDING PROGRAM, SANTA BARBARA AND SOUTHERN SAN LUIS OBISPO COUNTIES

Transcription

1 EVALUATION OF AN OPERATIONAL WINTER CLOUD SEEDING PROGRAM, SANTA BARBARA AND SOUTHERN SAN LUIS OBISPO COUNTIES DON A. GRIFFITH and DAVID P. YORTY NORTH AMERICAN WEATHER CONSULTANTS (NAWC) SANDY, UTAH WMA ANNUAL CONFERENCE APRIL 23-25, 2014 RENO NEVADA

2 GEOGRAPHICAL LOCATION OF SANTA BARBARA COUNTY

3 PREVIOUS WEATHER MODIFICATION RESEARCH PROJECTS, SANTA BARBARA COUNTY, CALIFORNIA SANTA BARBARA I, RANDOMIZED GROUND BASED SILVER IODIDE SEEDING, POSITIVE EFFECTS BUT NOT STATISTICALLY SIGNIFICANT SANTA BARBARA II, (Griffith, et al, 2005, WMA Journal of Weather Modification Vol. # 37) PHASE I, RANDOMIZED GROUND BASED SILVER IODIDE SEEDING OF CONVECTION BANDS, POSITIVE EFFECTS, SOME STATISTICALLY SIGNIFICANT PHASE II, RANDOMIZED AIRBORNE SEEDING OF CONVECTION BANDS, POSITIVE EFFECTS, SOME STATISTICALLY SIGNIFICANT

4 SANTA BARBARA II, SEEDING LOCATIONS AND PRECIPITATION GAGE LOCATIONS

5 EXAMPLE OF THE PASSAGE OF A CONVECTION BAND THROUGH SANTA BARBARA COUNTY

6 SEED/NO-SEED RATIOS OF CONVECTION BAND PRECIPITATION, PHASE I, GROUND SEEDING

7 SEED/NO-SEED RATIOS OF CONVECTION BAND PRECIPITATION, PHASE II, AIRBORNE SEEDING

8 PERCENTAGE OF WINTER PRECIPITATION ASSOCIATED WITH CONVECTION BANDS

9 SUBSEQUENT OPERATIONAL CLOUD SEEDING PROGRAM Due to drought conditions experienced in the early 1980 s, an operational cloud seeding program was developed by the Santa Barbara County Water Agency beginning in WY This program has continued to the present with only a couple of years not seeded due to burn areas in or near the intended target areas. North American Weather Consultants (NAWC) has been the primary contractor selected to perform this work. Atmospherics, Inc. and Weather Modification Inc. (WMI) have also been selected to perform some of this work. NAWC s cloud seeding design for the performance of this work has focused on adopting seeding modes and procedures used during the conduct of Santa Barbara II, Phases I and II: Seeding convection bands using both ground based and airborne seeding modes.

10 TARGET AREAS

11 GROUND BASED FLARE SITE

12 FLARE BURNING INSIDE SPARK ARRESTOR

13 CESSNA 340 SEEDING AIRCRAFT

14 EVALUATIONS? Evaluations of this program are difficult. A non-randomized, operational program Target/control evaluations questionable due to the lack of upwind control sites. Cloud seeding activities conducted intermittently back into the early 1950 s. This means that not seeded precipitation data, from which target/control regression equations could be developed, is limited after the 1950 s. Stable long-term records dating back to the 1930 s and 1940 s (not seeded periods) are quite limited in number. Discussions with Santa Barbara County Water Agency personnel in the fall of 2013 highlighted the desirability of performing some type of evaluation of all the previous operational seeded seasons. NAWC offered to explore the possibility of developing an historical target/control evaluation recognizing the potential problems in identifying suitable controls.

15 POSSIBLE TARGET/CONTROL SITES Desirable site characteristics: Long historical records, stable records (e.g., no station moves), control sites in areas not significantly impacted by seeding. The following target sites were considered: Gibraltar Dam, Jameson Dam, and West Big Pine in the Upper Santa Ynez target area and Porter Ranch and Twitchell Dam in the Huasna-Alamo target area. The following control sites were considered: Paso Robles, Rancho San Julian, Santa Barbara, and Santa Cruz Island. The Santa Barbara and West Big Pine sites were eliminated from consideration (breaks in double mass plots)

16 DOUBLE MASS PLOT, WEST BIG PINE VERSUS AVERAGE OF THREE OTHER CONTROL SITES

17 PORTER RANCH SITE Unusual situation: Mr. Dennis Gibbs with the Santa Barbara County Water Agency mentioned there might be some rainfall records available from this site which is located within the Huasna-Alamo Target Area. We contacted Mr. John Porter at this ranch. He indicated that his brothers had collected daily rainfall records at this location dating back to 1950 but the records were all in hand written form. We arranged to borrow these records and Ms. Stephanie Beall digitized monthly values for this site. These records were then compared with other control sites using the double mass technique. It appeared these records were stable.

18 TARGET AND CONTROL GAGE LOCATIONS

19 REGRESSION EQUATION DEVELOPMENT The December through March period selected as the most consistently seeded period. Dec. Mar. averages were calculated for the target and control stations. Forty-four not seeded seasons were used to develop a linear regression equation relating control records from three stations with the two target stations for the Upper Santa Ynez target. The same 44 not seeded seasons were used to develop a multiple linear regression equation relating each control station individually with the average of the two Upper Santa Ynez target stations. Dec. Mar. averages were calculated for the target and control stations for a 12 season not seeded period for the Huasna-Alamo target. Linear and multiple linear equations were developed for this target. Only 12 not seeded seasons were available since the Twitchell Dam station was not established until 1963.

20 UPPER SANTA YNEZ TARGET EQUATIONS Linear: y = 1.27x , r 2 = 0.84 where y = average Dec. Mar. target precipitation, x = average Dec. Mar. control precipitation. Multiple Linear: y = (Rancho San Julian) (Paso Robles) 0.03 (Santa Cruz) ; r 2 = 0.86 where y = average Dec. Mar. target precipitation

21 HUASNA-ALAMO TARGET EQUATIONS Linear: y = 0.87x , r 2 = 0.87 where y = average Dec. Mar. target precipitation, x = average Dec. Mar. control precipitation. Multiple Linear: y = (Rancho San Julian) (Paso Robles) (Santa Cruz) ; r 2 = 0.86 where y = average Dec. Mar. target precipitation

22 UPPER SANTA YNEZ, CALCULATED AND OBSERVED DEC. MAR. PRECIPITATION, LINEAR REGRESSION

23 UPPER SANTA YNEZ, CALCULATED AND OBSERVED DEC. MAR. PRECIPITATION, MULTI-LINEAR

24 HUASNA-ALAMO, CALCULATED AND OBSERVED DEC. MAR. PRECIPITATION, LINEAR REGRESSION

25 HUASNA-ALAMO, CALCULATED AND OBSERVED DEC. MAR. PRECIPITATION, MULTI LINEAR

26 TWITCHELL DAM, DEC. MAR. PRECIPITATION LINEAR REGRESSION

27 DISCUSSION More than two precipitation gages in the two target areas and more than three control gages would have been highly desirable. More gages would provide better information on the distribution of rainfall in the target and control areas. For example, how representative are two stations considering the size and differences in topography of the two target areas? The length of record for the selected target and control gages is important. Our experience has been that longer periods (preferably > 20 seasons) of record from the historical not-seeded period lead to the development of more accurate regression equations. There were only 12 historical seasons available for analysis in the Huasna-Alamo target area. This may indicate that the Upper Santa Ynez estimated increases may be more accurate. It is encouraging that the results from the linear and multiple linear regression equations were quite similar for both target areas. The 19%-21% values are surprisingly similar to estimates of seeding potential in the Upper Santa Ynez target area contained in a NAWC report to the Santa Barbara County Flood Control and Water Conservation District and Water Agency that estimated approximately an 18% average seasonal increase at Juncal (Jameson Dam) and Gibraltar Dams (Solak, et al, 1996).

28 QUESTIONS?