76 THE FUTURE OF ARID LANDS 
a month, whereas the summertime need for water is as high as 
6 inches a month. Only in the winter does the meager precipita- 
tion equal or exceed the reduced evapotranspiration, and a slight 
storage of moisture in the soil occurs. The moisture deficiency in 
summer ts large, being over 21 inches. No form of moisture con- 
servation would make agriculture possible here. Irrigation would 
be an absolute necessity. 
Precipitation is highly variable at Barahana, Dominican Re- 
public. It is less than 2 inches per month in the winter and again 
in July, and more than 6 inches per month in May and October. 
As a result there is a considerable deficiency of moisture during 
both the summer and winter, amounting to over 24 inches for 
the year, while there is some soil moisture recharge in spring and 
fall. 
Gaza is the only Egyptian station which has an average water 
surplus at any time of year. On account of its Mediterranean type 
of climate, the precipitation at Gaza is concentrated in the winter 
half of the year and exceeds the water need of that period by a 
considerable amount. As a result there is storage of moisture in 
the ground and a water surplus of 2.7 inches in January and 
February. However, due to the lack of summer rainfall and the 
high summer water need a moisture deficiency of over 27 inches 
occurs in summer. Thus, in spite of its more than 15 inches of 
precipitation a year, agriculture without irrigation is extremely 
hazardous because of the poor distribution of rainfall through the 
year. At Zeerust in the Union of South Africa, the march of pre- 
cipitation closely follows that of water need. In no month does 
precipitation equal need so that there is no soil moisture storage. 
However, because of the fact that precipitation and need are 
nearly parallel and fairly close, the area chronically suffers from 
hidden drought. Agriculture may be possible without supple- 
mental irrigation but would be far more successful with it. 
The values of moisture surplus and deficit have been combined 
to form a moisture index which is the basis for the division of land 
areas into moisture provinces. The use of such an index in deline- 
ating moisture regions is a well-accepted practice. The need of a 
second index, the annual potential evapotranspiration itself, to 
