Technical Reports Document Library

2007 marked the sixth year of operations for the Edwards Aquifer Authority (EAA) by the Southwest Texas Rain Enhancement Association (SWTREA). The project this year was business as usual, with seeding taking place in Uvalde County from May until October. There was caveat this year. An extremely wet pattern emerged over the Aquifer target area early in the spring. Even before operations began in the EAA target area, saturated soils and full rivers were the case. As the summer continued, even wetter conditions continued over the area, with a total of almost 5 weeks were seeding was not conducted due to river flooding and saturated soil.

Seeding in the Authority target area of Uvalde County saw a total of flights seven for the 2007 operational year compared to twenty flights in 2006. As seen above, there were more missions in 2006 than 2007, due mostly to the fact that flooding suspension criteria was [sic] put into place for the most active part of the operational season. Also, another reason that clouds were not seeded was due to the fact that clouds this year in particular were more tropical in nature and warm rain processes were occurring. When clouds are more tropical in nature, they lack natural ice which is required for the activation of the seeding agent. For the most part, seeding was not conducted at all during July and September across the EAA target area, which is normally the two months in which cloud seeding operations are at their peak. The Aquifer this year saw record rainfall totals during the summer, usually when Aquifer levels are at their lowest and water restrictions are in place. Additionally since summer temperatures were so mild this year, overall water usage was down.

In addition to normal weather modification activities in the Edwards Aquifer Authority (EAA) target area, 2007 was the first year of a three year randomized seeding experiment. The randomized seeding experiment was also being conducted by the EAA’s other weather modification contractor, the South Texas Weather Modification Association (SWTMA). The objective of randomized seeding operations for the Edwards Aquifer Authority will be to selected clouds that meet the criteria for suitable seeding candidates. This will be seeding at random and from that point measurements and observations will be taken to determine if seeding had had an effect on the cloud. The experiment will be double blind so that ground operations staff will not know which clouds are seeded and which are not seeded due to bias that may occur. In other words they will be unaware of the seeding decision.

Since 2007 was an unusual year, in terms of how much rainfall fell and suspension of operations, only a very small sample size was acquired. Data was collected from roughly a total of five to six flights between the two projects and will be analyzed per the randomized criteria.

Randomized procedures will involve a black box that inside will contain envelopes that contain a card. The card will either be denoted “SEED” or “NO SEED”. A box is placed in the office for both projects, STWMA and SWTREA. Each of the aircraft that will be participating in the experiment will also have a box place in the aircraft. Once the pilot has declared a “case” based on the criteria listed above, both the meteorologist and the pilot open then first envelope in the box. The  meteorologist will then tell the pilot the word on the card, who then will determine whether to seed or not to seed …

The pilot, under any circumstances, will not tell the meteorologist whether the decision is to seed or not seed, and the pilot and meteorologist will not communicate on issues related to the apparent effect of seeding or no noticeable effect. Any other normal conversation regarding safety of the pilot, aircraft, or any type of air traffic communication should be talked about as normal.

At the conclusion of the 2007 operational season for the EAA target area, September 30th, a radar evaluation was completed for the program. The findings are presented and discussed towards the end of this report. The flight logs for the 2007 seeding season are on the following page.