Regional planners present statewide tool to project extreme rainfall; Volusia staff told to treat outputs as planning input, not regulatory replacement

John Guadiolo, GIS director for the Central Florida Regional Planning Council, told Volusia County's Environmental and Natural Resources Advisory Committee on Feb. 5 that his office has built a planning tool to project future extreme rainfall and map flood exposure across counties in East-Central Florida.

Guadiolo said the project, funded through a $1,500,000 regional grant awarded in 2022, models a 24-hour, 100-year storm and projects how that design storm may change at two planning horizons (roughly 2040 and 2070). The work combines statewide rainfall rasters, lidar elevation, soils and land-cover inputs and locally calibrated change factors to produce flood-depth and exposure outputs for planners. "This is a planning tool... to put more resources where it's necessary based on these results," Guadiolo said during the presentation.

The project is intended as a regional planning resource: the East Central Florida Regional Planning Council leads the effort and is working with five other regional councils, university partners, the Florida Division of Emergency Management and local water-management districts. Stakeholder work has included calibration against recent hurricane events and creation of two small-area conceptual mitigation plans in priority mitigation zones. Guadiolo said the team is also building a public-facing ArcGIS web tool and a regional project list for multi-jurisdictional mitigation investments.

Committee members asked technical and policy questions. One asked whether rainfall sensors used in the modeling were newly deployed for the project or legacy stations; Guadiolo confirmed the team used legacy stations and supplemented them with change-factor methods to produce a statewide raster. Several members asked whether Volusia should adopt the project outputs to redraw local floodplains or to change the rainfall depths used for stormwater design. The panel emphasized a distinction between planning use and regulatory design values.

"I wouldn't talk about altering or defining rainfall values from the state definitions," said a committee member during debate about whether counties should set their own design rainfall; the point underlined repeated legal and defensibility concerns raised by other members and staff. Several members urged a layered approach: treat the regional projections as a planning and prioritization tool while continuing to rely on state- or federally endorsed rainfall tables and hydraulics-and-hydrology (H&H) modeling for regulatory designs.

Staff and consultants at the meeting said the modeling is already being used to flag mitigation-priority areas and to test conceptual projects; it is not a substitute for site-specific H&H studies that are required for permit-level design. Guadiolo and committee members also discussed timing: the model outputs are calibrated to change factors through the 2040 and 2070 planning horizons and the team expects to post a public-facing map and data in the near term.

The committee debated next steps for Volusia: whether to use the tool to inform county-level comp-plan policy and capital priorities, to help target FEMA mitigation grants, or to propose code changes. Committee members emphasized the tool's value for regional collaboration and for prioritizing multi-jurisdictional mitigation projects, and several asked staff to track whether NOAA or FEMA updates their official rainfall and flood datasets so local rules do not outpace state or federal standards.

The presentation and subsequent questions made two limits clear: (1) the project produces planning-grade projections intended to guide investments and regional mitigation prioritization, and (2) adopting new regulatory design values requires legal and technical review and may expose a jurisdiction to legal defense risks if not tied to an accepted state or federal data source.

Guadiolo said the team will continue to refine change factors, expand stakeholder briefings and release the web tool. Committee members asked staff to share the tool and the project's calibration documentation when the web portal goes live.

Ending: The committee accepted the presentation and directed staff to circulate the project materials and the web tool link once published, and to consider ways the county can use the outputs in planning and grant prioritization. The group did not take regulatory action at the meeting; several members and staff said any regulatory application should await further calibration and formal adoption by relevant state or federal authorities.