Effects of fine-scaled heterogeneity in urban landscape elements on evapotranspiration and other water fluxes

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Urban landscapes are highly heterogeneous when viewed as a complex network of roads, buildings, driveways, sidewalks, and other impervious surfaces. Because of this, the amount of effective impervious area, which describes the impervious area directly connected to the storm sewer network, is a better indicator of urban hydrologic behavior than the total amount of impervious area, which does not take this heterogeneity into account. However, to date most of the work on impervious surface arrangement and connectivity has focused on how it can affect stormwater runoff and surface water flows. The effect of impervious surface arrangement on subsurface flow is not as well described, but field observations in Madison, WI demonstrate that differences in soil moisture availability at locations near impervious features and far from impervious features are significant from a root water uptake perspective. This indicates that that parcel-scale subsurface and plant water fluxes may exhibit unique responses to fine-scaled heterogeneity in impervious surface arrangement. Using ParFlow.CLM, a watershed model with variably-saturated subsurface flow and fully-integrated overland flow and land-surface processes, we examine the extent to which soil moisture, evapotranspiration, and deep drainage vary under alternate impervious surface arrangement and connectivity scenarios for a residential parcel. We show that connectivity exerts a strong control on the spatial distribution and cumulative totals of these fluxes at the lot scale.