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viii I I I I I I I I I I I I I I I I I I I 3. Scientific analysis and evaluation. - A number of physical studies have been conducted as part of Programme AI Ohait. Some of these have concentrated on understanding seeding opportunities in Morocco. Physical studies with measurements taken inside precipitating storms of the High Atlas indicate that conditions which are favorable to seeding occur frequently and extend over large areas. Analyses of supercooled clouds observed in 1985 by the University of North Dakota cloud physics aircraft indicated that supercooled liquid water occurred often, with concentrations ranging from 0.2 to 0.7 g/m3 in the absence of natural ice at temperatures of -5 to -12 oC. These conditions are considered favorable for cloud seeding and, to some degree, more so than those found in the Sierra Nevada of California, where ice occurred more frequently. Cloud physics data collected after 1987 with the instrumented King Air have confirmed the earlier estimates of frequency and areal extent of regions of opportunity for seeding. Radar, satellite, and numerical modeling studies are being conducted to better define the frequency of favorable opportunities and the areal extent of seedable conditions detected in the cloud physics analyses. Statistical analysis of historical target and control streamflow data indicated that at least 6 years with cloud treatment are necessary to provide a 50-percent probability of detecting a to-percent increase in streamflow. However, only 1.5 years of seeded results are available for evaluation, as a result of the elimination for analysis purposes of the first 2.5 seasons of seeding due to the low initial cloud seeding efficiency (less than 15 percent) and unavailability of control streamflow for the 1988-89 season. With only a 1.5-year treated sample available, which represents about one-fourth of the required data, it was decided not to analyze any seeded results because they could be misleading. Even when the 1988-89 results become available, at least 4 more years of efficient cloud seeding are required for the statistical evaluation. 4. Increased awareness or weather modification as a water resources management option. - Hydrologic and economic studies were designed to assess the economic feasibility of cloud seeding programs in Morocco. These studies were conducted by Moroccan water resources agencies working with Reclamation hydrologic and economic experts and DMN scientists to develop objective methods for the evaluation of hydrologic impacts on the Moroccan economy. Through close cooperation and collaboration, the water resources management institutions in Morocco eventually became aware of Programme AI Ohait and its potential for impacts on their operations. American experts presented special seminars and workshops to the Moroccan water resources experts and Programme AI Ohait staff. Such meetings increased interest in weather modification as an additional tool in water resources management. Preliminary results of conducted studies provided additional credence to its feasibility for that purpose. Hydrologic studies produced some interesting results. Numerical river simulation models that included the hydroelectric generating characteristics of powerplants and irrigation and domestic water diversions within the Oued Oum Er Rbia basin were used to simulate the effects of additional water from November to July of the period 1940 to 1985. The additional water represented the effects of 5- and to-percent increases in monthly- streamflow due to seeding. The Administration de Hydraulique (Hydraulique) river model that was employed gave results indicating significant increases of 46 and 89 gigawatt hours (OWh) above the normal annual average hydroelectric power generation for the 5-and 10-percent streamflow increases, respectively. The National Electrical Organization (ONE) river model produced