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2.6.b Effects of additional rainfall on crops and forage The responses of crops and forage to increased rain- fall were investigated in a field investigation at Miles City and with crop yield models. At Miles City, plots of native grasses were irrigated to simulate various possible cloud seeding effects. The effects on forage yield, insect populations, and so on were monitored very closely over several seasons to detect not only the short term but the cumulative effects. A detailed account of the results is given in section 5. The crop yield studies were carried out in several States, often by teams of specialists from the respec- tive State's colleges of agriculture. Crop yield models employed ranged from regression equations relating yield of a given crop for a given site to the monthly values of the relevant agrometeorological factors to complex daily crop yield models that could only be run on a computer. All of the crop yield models predicted that increases in crop yields, gen- erally in the range of 1 to 15 percent. would be obtained if cloud seeding could increase rainfall by 10 to 15 percent. Translation of such effects into economic impacts is not simple. Possible changes in farming practices (e.g., varieties of wheat planted) that would evolve if rainfall really were increased by 10 percent cannot be anticipated exactly. However, there is no doubt that the economic impacts would be important. amounting to hundreds of millions of dollars per year in the High Plains Region. Texas stud- ies indicate that in addition to the direct benefits of additional rainfall, the increases of precipitation would reduce pumping and irrigation costs and thereby contribute to a substantial savings of energy (Kengla. 1 979). 2.6.c Other environmental effects Studies of the ecological impacts of HIPLEX were carried out as part of the effort toward preparation of an EIS (Environmental Impact Statement) covering Project Skywater in general. Skywater Conference IX was held at Vail. Colorado, in November 1976, to consider both the effects of seeding agents and the effects of increased precipitation. The EIS was filed in October 1977. The EIS referred to several laboratory studies that indicated that Agl would not have serious impacts on living organisms. For example, fish kept in tanks heavily dosed with Agl did not show any detectable reaction to it. Furthermore, the traces of silver from cloud seeding are overwhelmed by the amounts already present in the soil, in water, and in living tissues. Dry ice sublimes away to gaseous CO2, so its environmental impact is completely negligible. It was concluded therefore that the seeding agents used on Project Skywater, including HIPLEX, posed no direct threat. The effects of increased precipitation from seeding summer showers are likely to be small and the Skywater EIS reflects that. Nevertheless. increases in summer rainfall would have to have some impact. including slight shifts in the distributions of plant and animal species. As annual rainfall increases from west to east almost everywhere in the High Plains at the rate of about 25 mm every 50 km (1 in every 30 mil, the long-term change due to a 10-percent increase in summer rainfall would be like that observed in traveling about 50 to 80 km (30 to 50 mil eastward across the Plains. However, the establishment of a new equilibrium would take decades. The short-term impacts would consist mainly in increased production of all existing crops and native plants. Additional discussion of short-term impacts is given at various places in later sections. 3. ACCOMPLISHMENTS OF TEXAS H IPLEX 3.1 Introduction The primary goals of the Texas HIPLEX research effort were to understand natural processes leading to rainfall in west Texas in order to develop a sound cloud seeding hypothesis and to conduct agroeco- nomic studies to estimate the potential benefit-to- cost ratio for weather modification. Specific objectives included: (a) collection and analysis of rainfall, radar echo, cloud physics, mesoscale rawin- sonde, and satellite data to provide .a base of infor- mation required to design a precipitation management program; (b) development of physical hypotheses relating cloud seeding to enhanced rain- fall; and development of social-economic baselines of information for implementation of an areawide experiment. Figure 3.1 shows the Texas HIPLEX field site map and observation networks in 1979 and 1980. Texas HIPLEX was managed by the Texas DWR (De- partment of Water Resouces) under a Cooperative Agreement with the Bureau. Eight !~roups partici- pated directly in Texas field operations. and three other Federal agencies (NSF (National Science Foun- dation), NASA (National Aeronautics and Space Administration), and NOAA (National Oceanic and Atmospheric Administration)) coope,rated through equipment loans, other personnel support. and provi- sion of data services. Table 3.1 lists thl3 major partici- pants and their principal contributions to the program. The history of the Texas HIPLEX has been sketched as part of the history of the total HIPLEX program in section 2. An overview of Texas HIPLEX 11