Spatial distribution of imperviousness and the space-time variability of rainfall, runoff generation, and routing

We study the relationship between the spatial distribution of imperviousness and the space-time variability of rainfall, runoff generation, and hydrologic response. For this study we follow an analytical framework that is able to represent space-time variability and use it to determine relationships for quantities commonly used in hydrology, for example, the amount of rainfall excess, the total runoff from a storm, the runoff ratio of developed land use to undeveloped land use, and the mean time and variance of the runoff time. The relationships are derived such that the space-time variability of rainfall, runoff, and the hydrologic response, and their relative importance, can be identified and compared. In addition, the method allows the separation of pervious and impervious contributions to runoff and the estimation of their relative influence on the hydrologic response. We illustrate the estimation of the relationships from available data and apply them to two cases. In the first case, the space-time variability of rainfall and its interaction with impervious cover is investigated. In the second case, we examine the impacts of the imperviousness pattern on runoff relationships. We find that the imperviousness and rainfall pattern can interact to either increase or decrease the average amount of rainfall excess. We also find that the influence of pervious and impervious contributions on the response can depend on the form of the overall imperviousness pattern. The proposed framework can be a useful tool for identifying the importance of different space-time hydrologic components in mixed pervious-impervious landscapes.