The effect of urban form on Curve Number (CN) use in rainfall-runoff modelling is explored in an arid wadi watershed in Oman. The standard hydrologic CN used in the Soil Conservation Service method may not be appropriate to use in urbanized arid wadi regions since the land-use characteristics are different than those for which the CN method was developed for. In this paper a new method is described to develop regional CN for arid wadi regions. The modified CN are then used to predict peak-flow and time-to-peak in a wadi watershed and are compared to results from the standard CN method. The regional values produce higher peak-flow (an increase of 19% or 7.4 m3/s, on average) with shorter time-to-peak (a decrease of 16% or 86 minutes, on average), mimicking the flash-floods seen in the region. In addition, the regional CN were used to model the change in hydrology caused by urbanization.
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