WMOD00318

• Title: A Cooperative Project Between the Kingdom of Morocco and the United States
• Date: 9/1/1989
• Country: United States, Morocco
• Weather Modification - Doc Type: Report

11

I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I

240 millimeters at Agadir in the southwest. This is due to the protective action of the Azores high-
pressure ridge extending toward southern Morocco.

The High Atlas is the longest and most massive of the Moroccan mountain ranges. It extends
from the Bay of Agadir on the Atlantic Ocean in the southwest to about 125 kilometers south of
the Mediterranean Sea near the Moroccan/Algerian border in the northeast (fig. 2.1). With a
southwest-northeast orientation, a mean altitude of about 3000 meters above mean sea level, and
peaks extending from 3500 meters to above 4000 meters, the High Atlas constitutes an effective
barrier to the oceanic storms. Because the air flowing over Morocco during winter storms usually
comes from a westerly or northerly direction, regions southeast of the High Atlas are much drier
than places at the same latitude but located northwest of the High Atlas.

The heaviest rains tend to fall on the windward slopes of the mountains. There are three important
rainfall maxima; they are located in the Rif Mountains in northern Morocco (1600 mm annually
at Outka), the northern part of the Middle Atlas (1100 mm at Ifrane), and the central High Atlas
(around 1000 mm at the higher elevations).

The mean frequency of storms that affect Morocco during the November-April period ranges from
two to five per month; storms occur most frequently during December, February, and March.
Except for situations with cyclogenesis in the vicinity of Morocco, which can last from 5 to 7 days,
zonal and meridional storms do not exceed 2 or 3 days' duration. In general, the duration of
storms is longer in autumn and winter than in spring, when the duration may be limited to a day.

The mean number of days with precipitation per year on the northwestern side of the High Atlas
Mountains ranges from 60 to 65 in the north, 45 to 50 in the center, and 30 to 35 in the south.
The intensity of precipitation varies in time and space; its value may range from 0.5 to 15 mm/h
and, under certain conditions, may reach 30 to 40 mm/h, inducing floods.

Despite the low latitude, Moroccan mountains have frequent and important snowfalls in November
and December, and more in January and February. The freezing level in the winter in the central
High Atlas is usually around 2500 meters. During winter storms of polar origin, snow is commonly
observed down to 1000 meters elevation. The snow that falls below the 2000-meter level melts
quickly and contributes to the runoff in near real-time leaving, nevertheless, an important
proportion of the High Atlas with extended snowpack. Snow depth averages from a few centimeters
in the lower elevations to as much as 150 centimeters near the crest.

2.2.2 Choice of target and control areas. - On the basis of the apparent success of
precipitation projects in the California mountains and the results of other studies indicating the
feasibility of seeding winter orographic clouds, it was determined rather early. that the most
promising approach would be to select a demonstration area in the High Atlas Mountains.

Six major rivers drain the northwest side of the mountains and cross the semiarid agricultural zone.
These river basins contain most of the reservoirs and feed seven of the nation's nine major
irrigation districts. Discussions with GOM personnel familiar with the -country's water supply
situation led to the choice of the drainage basin of the Oued Oum Er Rbia in the central High
Atlas Mountains as the target area for the demonstration project. This basin has a series of dams,
hydroelectric generating facilities, and irrigation projects that could effectively distribute additional
water supplies generated by cloud seeding operations. The Oued Tensift basin located in the High