1. a Department of Geography , University of North Texas , Denton , Texas , 76203 , USA
2. b US Environmental Protection Agency, Western Ecology Division , Corvallis , Oregon , 97333 , USA
3. c School of Civil and Environmental Engineering , Georgia Institute of Technology , Atlanta , Georgia , 30332 , USA
4. d School of Earth and Atmospheric Sciences , Georgia Institute of Technology , Atlanta , Geogia , 30332 , USA