1. Department of Geography and Program in Applied Mathematical and Computational Sciences, 316 Jessup Hall, The University of Iowa, Iowa City, IA 52242, U.S.A.
2. Department of Geography, 316 Jessup Hall, The University of Iowa, Iowa City, IA 52242, U.S.A.
3. Department of Statistics and Actuarial Science, MacLean Hall, The University of Iowa, Iowa City, IA 52242, U.S.A.