MODELING CLIMATE CHANGE WITH LANDLAB: WATERSHED RESPONSE TO INCREASING RAINFALL AND STORM FREQUENCY

Climate change increases in temperature, precipitation, and intensity of extreme weather events will generate channel and watershed altering discharges with negative impacts on infrastructure and people living in flood-vulnerable areas. Recent intense storms that have tracked through the Delaware basin in eastern Pennsylvania and western New Jersey highlight fragile parts of that watershed, particularly where the topography is steep. The storm of record for the entire Delaware watershed is Hurricane Diane (August, 1955), but increasingly, smaller, intense summer and early fall tropical storms like Ida (Sept, 2021) also cause enormous local damage due to flash-flooding on small, steep watersheds. This project aims to better understand the correlation and causation for these tropical storm generated flash floods where the precipitation rate commonly exceeds 10 cm/hr and model the resulting hydrologic and topographic changes. Here, we present a model set up for Alexauken Creek, a 40 km² watershed in Hunterdon County, NJ. We adopt a strategy using Landlab that is aimed at permitting us to track both the flood peak as well as sediment transport. The base component of our model is SPACE (Stream Power with Alluvium Conservation and Entrainment) which provides a foundation to model the movement of sediment in both a transport-limited and detachment-limited manner. Channels will be fed by a hillslope sediment flux produced by the Depth Dependent Diffuser component. Annual rainfall and storm intensity and frequency, and overland flow are provided by the Spatial Precipitation Distribution and Overland Flow components, respectively. We operate initially on a 100x100 square model grid with 10 m pixel resolution before scaling up to a 10 m resolution DEM of the Alexauken watershed. We simulate (1) current annual precipitation and storm frequency, (2) increased annual precipitation but current storm frequency, and (3) increased annual rainfall and storm frequency. Our goal is to produce a series of animations for each model run over a 100-year timescale that will show the DEM, a channel profile, a sediment flux graph, and a flood hydrograph that ultimately can be used by local planners in identifying vulnerable infrastructure and danger to life and property.