Comments on ''Rainfall Modification by Major Urban Areas: Observations from Spaceborne Rain Radar on the TRMM Satellite''

During the autumn semester of the 2002/03 academic year, the authors participated in a graduate-level geographical-climatology seminar (‘‘Environmental Climatology’’) at Georgia State University. The topics included climate variation and change, mesoscale climate modification, and atmospheric pollution. Peer-reviewed climatological research was critically discussed through a geographical lens, which embodies a holistic consideration of relevant processes as well as increased attention to spatialand temporal-scale issues. Therefore, we eagerly anticipated the reading of Shepherd et al. (2002, hereinafter Shepherd et al.), because it presents recent research on our locale (i.e., Atlanta, Georgia), which on the surface appears to involve a geography-based methodology. In specific terms, Shepherd et al. examine the impacts of urbanization on precipitation totals in six regions (i.e., Atlanta; Montgomery, Alabama; Nashville, Tennessee; and San Antonio, Waco, and Dallas, Texas) during the May–September period of 1998– 2000. Shepherd et al. hypothesize that the urban heat island (UHI) is responsible for precipitation enhancement downwind of the cities, and they assess this enhancement using a spatially continuous satellite-derived lower-tropospheric rainfall-rate database within an ensemble-averaging framework. The satellite data are affiliated with the Tropical Rainfall Measuring Mission (TRMM). For the above regions, Shepherd et al. conclude that their ‘‘results validated previous groundbased and modeling studies that identified urban-induced rainfall maxima over and downwind of cities.’’ Their results show an average increase of about 28% in monthly satellite-derived rainfall rates within 30–60 km