Using High-resolution Radar Rainfall Products to Improve City-scale
Flood Models for Urban Resilience
Abstract
Assessing the extent and impact of past extreme weather events within
cities can help identify vulnerabilities, map potential solutions, and
prevent future calamities. Modern urban environments are particularly
vulnerable to hydrological extremes due to high population densities,
expansive impermeable surfaces, more intense precipitation extremes, and
infrastructure designed for a now obsolete climate. Intense rainfall in
urban environments can lead to impacts ranging from nuisance flooding to
overloading of sewage and drainage systems to neighborhood inundation.
In the flood-prone city of Chicago, storm waters are contained in a
network of tunnels and reservoirs until treated and released to the
waterways. Management decisions for a 600 km^2 metropolitan area are
made based on precipitation data collected at just 9 gauge sites. Here,
we combine high-resolution radar-derived precipitation data with
urban-scale hydrological models to improve our understanding of water
flow, advance stormwater management practices, and potentially mitigate
flood risks. Proximity of the NEXRAD system to Chicago allows us to
improve the spatial resolution of rainfall estimates to 500m, which will
be used to produce neighborhood-scale rainfall hindcasts. Different
dual-polarimetric radar-rainfall retrieval methods, e.g., rainfall from
reflectivity, attenuation, specific differential phase, and differential
reflectivity will be examined to determine the most accurate
representation of rainfall estimates. This suite of rainfall estimates
will be used to derive catchment-level precipitation, and serve as input
in a coupled hydrological-hydraulic MetroFlow model. To verify the
utility of our radar precipitation data, we examine an April 2013 event
that delivered a record-breaking 7 inches of rain in 2 days in some
areas. We compare our highly-resolved precipitation-driven hydrological
model predictions with those made using the 9 gauge stations. This
research is conducted under the premise that hydrological extremes are
expected to be exacerbated by climate change. Understanding drivers of
urban flooding using high-resolution precipitation data and models can
be used to improve resiliency-focused infrastructure design in Chicago
neighborhoods.