Main Street in downtown Ellicott City, Maryland has experienced two "thousand-year" flash floods in under two years. The extreme historical improbability of each event occurring singly, let alone in such short succession, belies changes in Maryland's natural environment. While increased storm intensity due to greenhouse warming has long been a prediction of climate scientists, the vulnerability of Ellicott City is aggravated by the intensity of human land use in its watershed, particularly the effect of man-made impervious surfaces on its ability to moderate extreme rainfall. In an interview published by WTOP (

GEOG professor Joseph Sexton quoted a pair of studies conducted through the UMD Global Land Cover Facility ( (Sexton et al. 2010, Song et al. 2016), saying that " the Washington, D.C. - Baltimore metro area put on 94 square miles of pavement between 1984 and 2010. ...That's an area the size of Baltimore". Funded by the Maryland Sea Grant program and NASA Earth and Space Science Fellowship, the studies were led and conducted by Sexton, GEOG graduate students Xiaopeng Song and Praveen Noojipady, and Professor Matthew Baker at the University of Maryland, Baltimore County. The studies are published in the journal Remote Sensing of Environment, and the data products are posted for open access at the Global Land Cover Facility (






Flood waters ravaged Main Street in Ellicott City on May 27, 2018. (Courtesy Twitter user Max Robinson/@DieRobinsonDie)