1. Research Assistant Professor, Dept. of Civil and Environmental Engineering, Univ. of Massachusetts Amherst, 130 Natural Resources Rd., Amherst, MA 01002 (corresponding author).
2. Deputy Division Director, International Food Policy Research Institute, 2033 K St. NW, Washington, DC 20006.
3. Associate Professor, Dept. of Civil and Environmental Engineering, Univ. of Massachusetts Amherst, 130 Natural Resources Rd., Amherst, MA 01002.
4. Research Fellow, International Food Policy Research Institute, 2033 K St. NW, Washington, DC 20006.