WATER RESOURCES IN ARID REGIONS 89 
1000 
mm. 
500 
Tunis 
excluding 
the desert 
Tunis — 
py 
(o>) 
(2) 
Annual depth of 
precipitation in mm. 
150 
100 
O. Medjerda — ge 
Runoff in mm. 
O. Kebir 
(3) 
PH MNW RUD OO 
ol 
1 
_ 
C5 $0) 80 70 6) 50 40 30 20 10 5 
Frequency in % 
Figure 1. Top, frequencies of annual precipitations, Tunis and aver- 
age of § stations, raised by 200 m/m. Bottom, frequencies of annual 
runoff of two watercourses in Tunisia. 
(the desert zone excepted). This figure also gives the frequencies 
of the annual average runoff for two watercourses whose basins 
receive an average of 500 millimeters of rain per year: 
Oued Kebir, whose basin surface is 225 square kilometers, and 
Oued Medjerda, whose basin surface is 16,000 square kilo- 
meters. 
Rainfall Over Entire Country 
As indicated by the curve of Figure 1, relative to the average 
of the five stations, a deficit of rainfall at one point can be com- 
pensated by a surplus at another, and the variability of the total 
rainfall on a territory is less than in any one locality. 
