Run Analysis of Rainfall Data Affected by Urbanization

Urbanization generally increases the amount of rainfall in urban areas and/or downwind areas of urban centers. This paper investigates whether urbanization significantly changes the run properties of rainfall. Three run properties, the run-length, run-sum and run-intensities of positive (surplus) and negative (deficit) runs, of the annual and monthly rainfall are evaluated by using the theory of runs. The annual rainfall is assumed to be normally or gamma distributed, and the monthly rainfall is assumed to follow a two-state Markov chain with stationary, transition probabilities. The methology is applied to annual and monthly rainfall data at La Porte and three surrounding stations in Indiana. The results indicate that these assumptions are adequate to characterize the annual and monthly rainfall. The study demonstrates that although urbanization has inadvertently increased the rainfall amounts at La Porte in relation to its surrounding stations (the so-called La Porte anamoly) the run properties at La Porte are not significantly different from those at the surrounding stations. Further it is found that the run-intensity is a better indicator than run-length or run-sum for evaluating the effects of urbanization on rainfall.