ALLAN J A . Fortunately there are substitutes for water:otherwise our hydro-political futures would be impossible [J]. Modern Economy , 1993 , 6 : 13 - 26 .
HOEKSTRA A Y , HUANG P Q . Globalization of water resources: Intenational virtual waterflows in relation to croptrade [J]. Global Environment Change , 2003 , 15 ( 1 ) : 45 - 56 .