Characterizing Future Flood Flows for Flood Insurance Studies Active
Current methods of flood-frequency analyses for flood insurance studies assume that the statistical distribution of data from past observations will continue unchanged in the future. This is known as the assumption of stationarity. This assumption allows scientists to estimate flood magnitude and frequency based on past records and the expectation that those estimates will represent current and future conditions. However, observed trends of increases in rainfall intensity and changes in seasonal snowmelt hydrology in the northeastern United States suggest that peak-flow stationarity may no longer be an appropriate assumption. To improve the information and mapping available for decision-making throughout New England in the face of a changing climate, the U.S. Geological Survey (USGS) is developing a series of potential flood map scenarios in a pilot watershed in New England for the years 2030, 2050 and 2100.
The National Hydrologic Model (NHM) is a deterministic hydrologic model for the conterminous United States and draws on topography, land cover, soils, geology, and hydrography parameters derived from a Geographic Information System (GIS). This investigation employed a Precipitation-Runoff Modeling System (PRMS) model extracted from the NHM to evaluate the response of various combinations of climate within the pilot basin of the Housatonic River watershed in Massachusetts and Connecticut.
A historical climate dataset was used to configure and fine-tune the PRMS model focusing on the 1% Annual Exceedance Probability (AEP) flood. Based on future climate-change estimates from General Circulation Models (GCMs), systematic changes to precipitation and air temperature were applied to the input datasets which were then used to drive the PRMS model. This phase of the project has been completed. The report documenting the first phase of the project can be found at https://pubs.usgs.gov/publication/sir20235090 and the project data release can be found at https://doi.org/10.5066/P91CSH0P.
In the second phase of the project, flood-frequency estimates based on the modeling scenarios will be applied to detailed and approximate hydraulic models to establish potential Base Flood Elevations for flood mapping. Base Flood Elevations are floodwater levels that have a 1% chance of re-occurring or being exceeded during a year. These future scenario Base Flood Elevations will be mapped as a companion product to the current Base Flood Elevations for the flooding sources in the Housatonic River watershed and displayed with both an interactive online data visualization format, and the FEMA RiskMap Non-Regulatory products, to inform community members on how the floodplain boundaries and risk could change in the future.
Development of Flood Insurance Maps in New England
Current methods of flood-frequency analyses for flood insurance studies assume that the statistical distribution of data from past observations will continue unchanged in the future. This is known as the assumption of stationarity. This assumption allows scientists to estimate flood magnitude and frequency based on past records and the expectation that those estimates will represent current and future conditions. However, observed trends of increases in rainfall intensity and changes in seasonal snowmelt hydrology in the northeastern United States suggest that peak-flow stationarity may no longer be an appropriate assumption. To improve the information and mapping available for decision-making throughout New England in the face of a changing climate, the U.S. Geological Survey (USGS) is developing a series of potential flood map scenarios in a pilot watershed in New England for the years 2030, 2050 and 2100.
The National Hydrologic Model (NHM) is a deterministic hydrologic model for the conterminous United States and draws on topography, land cover, soils, geology, and hydrography parameters derived from a Geographic Information System (GIS). This investigation employed a Precipitation-Runoff Modeling System (PRMS) model extracted from the NHM to evaluate the response of various combinations of climate within the pilot basin of the Housatonic River watershed in Massachusetts and Connecticut.
A historical climate dataset was used to configure and fine-tune the PRMS model focusing on the 1% Annual Exceedance Probability (AEP) flood. Based on future climate-change estimates from General Circulation Models (GCMs), systematic changes to precipitation and air temperature were applied to the input datasets which were then used to drive the PRMS model. This phase of the project has been completed. The report documenting the first phase of the project can be found at https://pubs.usgs.gov/publication/sir20235090 and the project data release can be found at https://doi.org/10.5066/P91CSH0P.
In the second phase of the project, flood-frequency estimates based on the modeling scenarios will be applied to detailed and approximate hydraulic models to establish potential Base Flood Elevations for flood mapping. Base Flood Elevations are floodwater levels that have a 1% chance of re-occurring or being exceeded during a year. These future scenario Base Flood Elevations will be mapped as a companion product to the current Base Flood Elevations for the flooding sources in the Housatonic River watershed and displayed with both an interactive online data visualization format, and the FEMA RiskMap Non-Regulatory products, to inform community members on how the floodplain boundaries and risk could change in the future.