2007) Multisatellite Precipitation Analysis (TMPA) and ground-based gauge stations to examine spatial variability in warm-season rainfall events around Oklahoma City (OKC), Oklahoma, as a function of prevailing wind and urban land cover. The study uses 9 yr (1998–2006) of warm-season (June–September) mean daily rainfall accumulation obtained from both the Tropical Rainfall Measuring Mission (TRMM) ( Kummerow et al. This research takes a unique approach to examine urbanization and rainfall modification. Such uncertainties highlight the need for more observational and modeling research in this area ( Dabberdt et al. He noted that the urban effects being sought usually cannot be distinguished from other influences, such as local topography and temporal changes in the relative frequencies of different synoptic weather types. Lowry (1998) discussed several potential problems with methods and inferences used in many historical studies of urban-induced precipitation. 2005) are beginning to shed light on the possible role of giant cloud condensation nuclei (CCN) (enhancement) and smaller CCN (suppression). Recent studies ( van dan Heever and Cotton 2007 Rosenfeld et al. Smaller cloud droplet size distributions and suppressed rainfall have been shown to occur because of increased aerosol concentrations from anthropogenic sources over and downwind of urban areas ( Rosenfeld 1999, 2000 Borys et al. (2006) found decreased cumulative rainfall around Beijing, China. (2007) suggested that urbanization in the Pearl River Delta of China has reduced local precipitation because of changes in surface hydrology. 2008) providing evidence that convection and precipitation can be enhanced or initiated by urban regions, the debate over the role of urban environments on precipitation is ongoing. Areas 25–75 km downwind of the city center and within a 125° sector will typically experience the greatest increase in rainfall due to the urban region.ĭespite recent results ( Shepherd 2005 Mote et al. ![]() (2002) showing the region of highest rainfall increases due to urban effects is shown in Fig. An idealized diagram based on Shepherd et al. Increases in precipitation due to urban effects are typically observed at distances between 30 and 75 km from the city center ( Landsberg 1970 Sanderson and Gorski 1978 Bornstein and Lin 2000 Shepherd et al. 2007) highlighted the growing body of research linking urban-related processes and regional precipitation. The urban heat island (UHI) is well studied ( Oke 1982), and the Intergovernmental Panel on Climate Change report ( Trenberth et al. “Urban footprints” spread well beyond the immediate vicinity of cities, affecting local- to global-scale atmospheric composition, surface energetics, water and carbon cycle processes, and ecosystem development. In 2008, more than one-half of the world’s population lived in urban areas, and this fraction could balloon to 81% by 2030 ( UNFPA 2007). Overall, the study establishes a prototype method for utilizing satellite-based rainfall estimates to examine rainfall modification by urbanization on global scales and in parts of the world that are not well instrumented with rain gauge or radar networks. It was also quantitatively confirmed, using a relatively new concentration factor analysis, that prevailing wind–rainfall yields were consistent with the overall framework of an urban rainfall effect. ![]() TRMM products slightly underestimate the precipitation recorded by gauges, but the correlation R improves dramatically when the analysis is restricted to mean daily rainfall estimates from OKC urban grid cells containing multiple gauge stations ( R 2 = 0.878). ![]() ![]() The study also established that satellite precipitation estimates capture spatial rainfall variability as well as traditional ground-based resources do. Climatological sounding and reanalysis data revealed that, on average, the NNE area of OKC was the climatologically downwind region, confirming that precipitation modification by the urban environment may be more dominant than agricultural/topographic influences on weakly forced days. Results from both satellite and gauge-based analyses revealed that the north-northeastern (NNE) regions of the metropolitan OKC area were statistically wetter than other regions. It was hypothesized that with warm-season rainfall variability, under weakly forced conditions, a rainfall anomaly would be present in climatological downwind areas of OKC. This study used 9 yr (1998–2006) of warm-season (June–September) mean daily cumulative rainfall data from both the Tropical Rainfall Measuring Mission (TRMM) Multisatellite Precipitation Analysis and rain gauge stations to examine spatial variability in warm-season rainfall events around Oklahoma City (OKC).
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