Heejun Chang, chairman of PSU's geography department and the study's co-author, says the I-205 corridor is particularly vulnerable in winter because it sits at a lower elevation and its drainage systems can't accommodate heavy rainfall. The area is also an urban heat island—meaning it absorbs heat during the day and releases it in the evening after the sun sets. (Think of the parking lots of Mall 205, which turn to ponds in the rainy months but bake like an asphalt Sahara each summer.)