1. R. R. Braham, J. Meteorol. 9, 227 (1952).
2. http://en.wikipedia.org/wiki/water-circle.
3. http://water.usgs.gov/edu/watercyrcleatmosphere.html.
4. A. Baumgartner and E. Reichel, The World Water Balance (Elsevier, Amsterdam, 1975).
5. I. A. Shiklomanov, in Water in Crisis: A Guide to the World’s Fresh Water Resources, Ed. by P. H. Gleick (Oxford Univ. Press, Oxford, 1993), p. 13.