An Investigation of Warm-Season Spatial Rainfall Variability in Oklahoma City: Possible Linkages to Urbanization and Prevailing Wind

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). 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. 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. 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. The study also established that satellite precipitation estimates capture spatial rainfall variability as well as traditional ground-based resources do. 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). 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. 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.