Development of a tropical geographic unit hydrograph in the Luquillo Mountains of eastern Puerto Rico

Abstract

Synthetic unit hydrographs (SUHs) are useful numeric models developed to predict empirical unit hydrograph parameters as a function of watershed characteristics. These statistical equations usually relate peak flow and timing to watershed characteristics. Once produced, a SUH estimates a storm hydrograph at the outlet of a watershed for a given excess precipitation amount. A sub class of SUHs is the Geographic Unit Hydrographs (GUH), which is informed by the geographic properties of basins (i.e. average slope, average land use, annual precipitation). Recent GUH models use geographic information systems (GIS) allow scientist and engineers to model the flow path and velocity to calculate the runoff response of that basin. This Tropical Geographic Unit Hydrograph (tGUH) model is developed for a specific tropical island environment, and includes an analytical methodology to derive required empirical coefficients directly from observed geographic characteristics, which in turn can provide a more consistent runoff estimate between users. Additionally, with the tGUH described here, unit hydrograph parameters are found to be sensitive to non-stationary parameters including land use (attributable to anthropogenic change) and annual precipitation change (attributable to climate change).