Scheme of aridity and drought probability / 
Kovda, V. A.
United Nations.Conference on desertification.
Nairobi :  U.N. Environmental Project, 
1977.
Explanatory note prepared by FAO, Unesco und WMO.
U.N. conference on desertification, 29 Aug-9 Sep 1977 (A/CONF. 74/31).