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i Preface Operational cloud seeding for precipitation enhancement continues worldwide even though scientific proof of its efficacy, according to the stringent “proof-of-concept” criteria set forth by Silverman (2001), is lacking. Those conducting these operational efforts have weighed the evidence and concluded that the potential benefits from precipitation augmentation in their programs outweigh the risks and costs involved. Many of the current operational cloud seeding programs are being conducted in Texas where ten cloud seeding projects were in operation in 2002 (Figure 1). The history of and the rationale for the Texas operational cloud seeding programs have been addressed by Bomar et al. (1999). Most of the individuals involved in these efforts agree with Silverman (2001) that the evaluation of seeding effectiveness in all the programs should have high priority. They understand that seeding efficacy must be demonstrated or the projects ultimately will end in disillusionment and controversy. Such demonstration is difficult, however, because of the absence of treatment randomization. They understand also that the physical effects of cloud seeding must be documented if the technology is to be viewed as credible means of enhancing the water supply. These Texas programs are merely one of many manifestations that the quantity and quality of fresh water st for human use is going to be a major issue during the 21 Century, especially in arid and semi-arid regions of the globe. Water in such areas is inherently scarce, and this shortage of water will be exacerbated by the continued migration of populations into these regions. The superposition of predicted changes in climate and the deleterious effects of pollution on cloud forming processes and rainfall onto these dry regions could result in disastrous water shortages that preclude human existence. Within the past five years most areas of the United States have faced frightening droughts only to have periods of wet weather remove the threat. The Southwestern U.S. is suffering still from major water shortages. These problems are occurring with increasing frequency and it is only a matter of time before catastrophic water shortages exact a terrible toll on human existence. The potential responses to such a prospect are many and varied. One response would be to do nothing, allowing natural processes to run their course, teaching people to live within their water means or forcing them to vacate a region. Such a program of benign neglect costs virtually nothing to implement, if one can ignore the cost in human misery. The opposite course of action would be to develop programs of water conservation and enhancement to address the water needs of a region. No one opposes conservation, and most entities concerned about water have implemented water-conservation programs. Opinions vary on cloud seeding, depending on one’s point of view. There are always people willing to invest in operational seeding, secure in their expectation that the benefits will exceed the costs involved. Willingness to invest in cloud seeding research to buttress the operational activity has varied widely from a highpoint in the late ‘60’s and ‘70’s to a prolonged low point beginning in the mid-1980’s and continuing to the present day. The need has been constant, but the willingness to address it has not. The irony in the current situation is that the time of maximum research capabilities coincides with a time of almost non-existent research funding. The tools have never been better, but the fiscal means to make use of them are non-existent. This includes multi-parameter radars, lidars, microwave radiometers, multi- spectral satellite imagery, powerful fast computers, aircraft instrumentation to measure particle sizes from fractions of a micron to millimeter sizes, state parameters and air motions, exacting navigation systems, numerical models, and atmospheric tracers. 8