1. Visiting Assistant Professor, Dept. of Civil Engineering, Univ. of Qom, Qom, Iran.
2. Associate Professor, Dept. of Irrigation and Reclamation, Faculty of Agricultural Engineering and Technology, College of Agriculture and Natural Resources, Univ. of Tehran, Karaj, Tehran, Iran.
3. Professor, Dept. of Geography, Univ. of California, Santa Barbara, CA 93106-4060 (corresponding author).
4. Distinguished Professor Emeritus, Dept. of Land, Air and Water Resources, Dept. of Civil and Environmental Engineering, and Dept. of Biological and Agricultural Engineering, Univ. of California, 139 Veihmeyer Hall, Davis, CA 95616-8628.