CRMWD Engineering

  Weather Modification

Since 1971, the Colorado River Municipal Water District has been conducting a Weather Modification (precipitation enhancement) Program on convective cloud systems in West Texas. As of the 2006 season, the Program is in its 33rd year of weather modification activities.

The program objective is to increase precipitation (and therefore enhance surface water runoff) for the watershed of Lake J.B. Thomas and the E.V. Spence Reservoir. This is accomplished through aerial application of silver iodide. Meteorologist Ray Jones uses the Districtís C-band radar installation to monitor promising cumulus clouds for the type of conditions conducive to silver iodide rain enhancement. When cloud bases and tops are favorable, he directs the Districtís pilot to fly into the cloud updraft to burn silver iodide flares. A GPS transponder on the plane is also tracked on the radar for accurate communication between the pilot and meteorologist. As the silver iodide particles are swept high into the cloud by the updraft, they begin to fill the deficit of ice nuclei in the cloud, increasing the amount of freezing water vapor within the cloud as the release of latent heat of fusing (freezing of liquid particles) contributes to increasing the buoyancy of the cloud and its overall size. As the freezing particles rise and increase in size, they become heavier, finally falling to the ground as they melt into rain. This type of ice-phase cloud seeding is known as glaciogenic cloud seeding.

In addition to increasing precipitation and surface water runoff, the project has a by product of enhanced rainfall for agricultural and ranching communities in the target area. Past research showed significant cotton production increases in and down wind of the target area as compared to unseeded regions upwind.

Much of the available research data on rain enhancement in the State of Texas has been gathered by this program.  In the past, the District received some state or federal matching funds or research grants for operations or evaluation of cloud seeding operations within and beyond the Districtís target area. From those experiments, preliminary evidence showed that silver iodide seeding, when done on the proper type of cloud cells, increases rain volume significantly. This is especially true in some convective clouds and research showed that seeded clouds live longer and spread over a greater area. Clouds that are seeded tend to merge with nearby convective cloud cells to create "convective complexes" which are big rain producers in Texas. An independent study of rain enhancement programs in Texas (conducted by Arquimedez Ruiz-Columbia, results available at concluded that cloud cells seeded during the Districtís 2003 season produced 63% more precipitation than similar non-seeded clouds.

The District was granted Weather Modification Permit No. 04-1 from the Texas Department of Licensing and Regulation. The permit is valid through December 31, 2007. Weather modification licenses are granted annually, and the Districtís was renewed by the TDLR September 1, 2004. CRMWD received no matching funds or grants for 2004 weather modification activities..

The operational area includes fifteen counties within and near the Permian Basin of West Texas. Cloud seeding is conducted primarily from April 1 to November 1 each year, when convective or cumulus cloud systems are present. These types of clouds deliver most of the annual precipitation for the area.

The District has operated and maintained one of the longest running weather modification programs in the State of Texas. The positive data analyzed and documented during this year continues to support the program's validity and integrity.