WMOD00318 - Laserfiche WebLink

Home Browse Search

10 I I I I I I I I I I I I I I I I I I I 1. Physical evaluation. - To determine the seedability of winter clouds over mountainous areas of Morocco. 2. Statistical evaluation. - To determine the amount of additional streamflow produced as the result of cloud seeding operations. 3. Economic evaluation. - To determine the costs and benefits of the production and use of additional streamflow as the result of cloud seeding operations. 4. Application activities. - Studies and training which apply the findings and recommendations of the physical and economic evaluations to practical issues in water resources management. 2.2 Choice of Location 2.2.1 Climatology.. The choice of a location for a demonstration project depended upon a number of factors, including facilities and communications. However, climatological considerations played a key role in the selection. Morocco is located on the northwest corner of Africa and has a varied topography including coastal plains, upland plateaus, and rugged mountains. Its climate is determined by its latitude and its topography. The subtropical high-pressure zone that enc'ircles the earth around 300 N. often extends from east to west across southern or central Morocco. The Azores high-pressure area, which is part of this zone, strongly controls the weather over the northwestern part of Africa and accounts for the prevailing dryness. From November through April, the Azores high-pressure area sometimes shifts westward, which allows storms of polar origin to affect most of Morocco north of 300 N. Generally speaking, Morocco has a very dry summer, centered around July, and two wet periods in early winter (November-December) and late winter (February-March) separated by a somewhat drier January. The winter storms follow one of the two principal storm tracks, namely, west-to-east and north-to- south. The two storm tracks are associated with zonal and meridional flow, respectively. The established statistics show that the storms associated with a meridional circulation appear to be three times more frequent than those associated with a zonal circulation. In autumn the principal cause of precipitation is low-pressure areas moving into Morocco from the northwest and associated passages of cold fronts marking the leading edges of polar air masses. A cold front passage is frequently preceded by a flow of moist, tropical air from the southwest that results in widespread precipitation over the High Atlas Mountains. In the late-winter wet period (after January's typically drier weather), incursions of the Mediterranean front into Morocco from the northeast playa major role in the production of precipitation. The geographical distribution of normal annual precipitation shows clearly the effects of latitude and topography. In the coastal plains, the average annual precipitation drops from 800 millimeters at Tangier in the north to 400 millimeters at Casablanca in the central area, and finally to