Program for the Augmentation of Rainfall in Coahulia

Overview

In 1996, concern by representatives of the Mexican State of Coahuila and Altos Hornos de México (AHMSA) regarding regional pressures on water resources, particularly during drought conditions in northern México, led to the development of a scientific program to evaluate the viability of increasing rainfall through cloud seeding techniques. Consequently, the Program for the Augmentation of Rainfall in Coahuila (PARC) was proposed as a four–year program consisting of a randomized seeding experiment, physical studies, and collaboration with and training of Mexican scientists and students.

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The overall objective of PARC was to develop, test, implement, and transfer the technology of hygroscopic seeding in Coahuila. The first step in achieving this broad objective was to characterize the development of convection and precipitation in central Coahuila, and compare them to storm characteristics in other regions where cloud seeding has been successfully evaluated. In particular, the measurements taken during the first–year field project (PARC–96) were compared with those taken in South Africa, where seeding with newly developed hygroscopic flares has met with some success. While there were general differences in storm structure and lifetime, microphysical characteristics, cloud initiation, and storm size were similar enough to warrant tests of hygroscopic seeding in Coahuila as practiced in the South African experiments.

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During the summers of 1997 and 1998, the field project focused on a randomized seeding experiment as well as continuing to collect meteorological data for further evaluation of the randomized experiment and other physical studies. Over the course of two years, a total of 94 valid cases were collected: 43 seeded cases and 51 non–seeded cases. The results provide an indication of a positive effect of seeding, in terms of precipitation flux, rain mass above 6 km, rain area, lifetimes of the storms, the integrated area of precipitation, and the total precipitation. These results are very similar to those found in the South African experiment (Mather et al., 1997). This fact is encouraging, especially because the timing as well as the magnitude of the seeding effects corresponds well to the South African results. It is important to note that the number of cases (94 cases) is still marginal for any statistical analysis. The South African experiment consisted of approximately 150 cases. The PARC program was planned for four years and the fourth year would probably have provided a sufficient number of cases. However, due to funding problems the fourth year of the experiment could not be completed. Therefore, caution should be exercised in interpreting the results as unambiguous proof of success.

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In order to transfer the knowledge and technology associated with hygroscopic cloud seeding, PARC was organized to create training opportunities for graduate students, their professors, and other scientists both within Coahuila and throughout México. A number of students (or asistentes) were trained in field operations over the three years of PARC, with a few of them continuing their formal education in meteorology or computer sciences. Other significant interactions with the Mexican scientific community included joint precipitation studies with hydrologists from the Instituto Mexicano de Tecnologia del Agua and the Servicio Meteorologico Nacional, cooperative data exchanges with the regional office of the Comision Nacional del Agua (CNA–Saltillo), and collaborations with agrometeorologists at the local university and with the faculty of the Centro de Ciencias de la Atmosfera program at the Universidad Nacional Autonoma de México in Mexico City. This project is complete.

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