WEATHER MODIFICATION (aka CLOUD SEEDING)(aka CLOUD SEEDING)

WEATHER MODIFICATION IN TEXAS – A BRIEF HISTORY

• Cloud seeding has occurred in various locations in the state off and on since the 1950s

• Texas Weather Modification Act was enacted in 1967 by the Legislature and is now codified as Chapter 301 of the Texas Agricultural Code, regulated and administered by the TDLRadministered by the TDLR

• Longest operational program in the state began in 1971 in the Colorado River Municipal Water District and ran for over 30 years

• Statistical evaluation of CRMWD’s program indicated 20-30% increase during the growing season in addition to downwind effects

WEATHER MODIFICATION IN TEXAS – A BRIEF HISTORY

• HIPLEX experiment 1975-1980 was cut short due to federal funding cutbacks and focused on collection, processing and analysis of meteorological data in order to understand cloud systems in west Texas

• Southwest Cooperative Program (SWCP) in San Angelo and Big Spring areas 1985-1990 conducted Angelo and Big Spring areas 1985-1990 conducted randomized cloud seeding operations to test efficacy of dynamic cloud seeding concept

• Results of SWCP showed cloud cell duration increased of 36%, area increase of 43%, and rain volume by 130% when compared to non-seeded cells. Corresponding rainfall increases of 25-42% were found in the target area.

WEATHER MODIFICATION IN TEXAS – A BRIEF HISTORY

• Texas Exercise in Augmenting Rainfall through Cloud Seeding (TEXARC) based out of San Angelo 1994-1996 took place when federal funding became available to the state. Randomized seeding took place during this experiment as well

• Positive results were found when the seeded and • Positive results were found when the seeded and non-seeded clouds were followed and compared

WEATHER MODIFICATION IN TEXAS – 1990s TO NOW

• West Texas Weather Modification Association – 1996

• South Texas Weather Modification Association – 1997

• High Plains UWCD Program – 1997-2002

• Edwards Aquifer Authority Program – 1998*

• Texas Border Weather Modification Assocation – 1998-• Texas Border Weather Modification Assocation – 1998-2002

• Southwest Texas Rain Enhancement Association – 1999

• North Plains GCD Program – 2000-2005

• Panhandle GCD Program – 2000

• West-Central Texas WMA – 2001-2004

• SOAR – 2002

• Trans-Pecos Weather Modification Association – 2003

WHY HAVE A WEATHER MODIFICATION PROGRAM?

• Water conservation – think long-term:• Replenishing reservoirs, aquifers, lakes, river flows

• Cannot just do this during a drought, wx mod is NOT a drought-buster

• Help reduce agricultural consumption of surface • Help reduce agricultural consumption of surface and ground water while increasing agricultural production with timely precipitation

• Even dryland farmers need grass, full tanks

• Increase vegetation (grass, food for wildlife)

• Better chance for economic stability• Money spent stays local

DOES THE COST JUSTIFY THE PROGRAM?

• For each of the programs in the state, the yearly budget ranges between $200k and $300k per year, or about 4 cents per acre of target area.

• Programs are self-sufficient; that is, they own their own equipment and personnel so costs are their own equipment and personnel so costs are lower than using an outside contractor

HOW VALUABLE IS ONE INCH OF RAIN?

• High Plains UWCD looked at effect of an inch of rain on crop production in their area

• Used 50% reduced crop yields compared to 3-5 year average to account for rainfall not always occurring in timely manner

• Cotton, grain sorghum, corn, wheat

• Total increase in crop production as a result of one inch of rainfall was over $81 million for the entire area

HOW VALUABLE IS ONE INCH OF RAIN?

• Benefit-cost analysis of West-Central TX Wx Mod Program

• Looked at value of a 5% increase in precipitation (about an inch for this part of Texas)

• One inch of rainfall over land would reduce irrigation • One inch of rainfall over land would reduce irrigation pumping by 6.5%

• Benefits to agricultural production would be over $7 million

• Economic stability & growth in region would be over $3.5 million

• Cost to run program would be $290k

THE METHOD EXPLAINED…

HOW IS CLOUD SEEDING CONDUCTED?

• Two plane-based methods: base seeding; top seeding.

• Texas programs conduct base-seeding.• Plane flies near cloud base searching for updraft (≥

300 ft/min), at which point pilot will ignite flares containing silver iodide and/or calcium chloride (salt) into the updraft. Silver iodide is good for clouds with few natural glaciogenic nuclei but plenty (salt) into the updraft. Silver iodide is good for clouds with few natural glaciogenic nuclei but plenty of supercooled water droplets. Calcium chloride is good for clouds which are primarily warm but cloud droplet growth is slow

HOW DOES AgI SEEDING WORK?

• Once in the cold region of the developing cloud, particles go to work: Ice crystals begin to grow at the expense of supercooled water droplets within the updraft

• Ice growth releases latent heat, which strengthens the updraftstrengthens the updraft

• Updraft ingests more moist air which can provide more available water/nuclei and may also increase cloud height and area

• Snowflakes/ice crystals grow through accretion/aggregation, and eventually become too heavy to be supported by cloud updraft and fall through the cloud.

• Snowflakes become rain drops when they fall into warm air and melt

HOW DOES HYGROSCOPIC SEEDING WORK?

Texas Weather Modification Association Analysis

Operational Day and Cloud Targets Acre-Feet Increases Precip Increases

Year

Op

Days Clouds Small Large Type B Small Large Type B Total

Inches

Increased

Seasonal

Precip

Percent

Increase

*2002* 237 897 599 135 107 288,559 1,259,671 636,584 2,184,814 0.42 - 25

*2003* 274 933 609 141 183 276,880 1,094,181 1,455,353 2,826,414 - - -

2004 229 447 189 131 127 119,086 2,378,250 2,083,996 4,581,332 1.98 19.74 10.16

2005 184 494 219 146 111 129,272 2,288,140 1,087,064 3,504,476 1.18 11.97 10.12005 129,272 2,288,140 1,087,064 3,504,476 1.18 11.97 10.1

2006 218 551 298 116 131 253,240 957,891 211,540 3,322,671 1.89 13.82 15.8

2007 110 228 75 75 78 64,927 1,845,304 1,335,193 3,254,424 1.77 20.87 9.2

2008 124 233 119 59 55 131,279 1,760,470 463,850 2,355,599 1.13 13.28 9.3

2009 163 466 218 126 117 170,545 2,264,139 1,331,414 3,766,098 1.42 11.92 11.5

2010 166 399 193 79 127 144,472 2,520,772 2,095,298 4,760,542 1.65 15.46 11.2

2011 124 288 154 58 72 110,387 1,159,767 540,750 1,810,904 0.6 3.69 17

Total 1318 3106 1465 790 818 1,123,208 15,174,733 9,149,105 27,356,046 11.62 110.75 11.7825

Avg 164.75 388.25 183.125 98.75 102.25 140,401 1,896,842 1,143,638 3,419,506 1.4525 13.84375 11.7825

June 6, 2011

Karnes, Wilson counties

JUNE 6, 2011

• Weak disturbance over eastern Texas aided in convective development that evolved westward toward eastern target area

• 160P launched around 2255 UTC (5:55pm CDT)• Several clouds were seeded in Karnes and Wilson

counties• A total of 19 flares (494g AgI) were used for • A total of 19 flares (494g AgI) were used for

seeding• Three clouds that were seeded in Wilson County

merged to form one larger storm that slowly moved southwestward

• Rainfall amounts ranged from 0.25” to over 2” in Wilson County north of Floresville

QUESTIONS?QUESTIONS?