The Historic Flood Map is a GIS layer showing the maximum extent of individual Recorded Flood Outlines from river, the sea and groundwater springs that meet a set criteria. It shows areas of land that have previously been subject to flooding in England. This excludes flooding from surface water, except in areas where it is impossible to determine whether the source is fluvial or surface water but the dominant source is fluvial.

The majority of records began in 1946 when predecessor bodies to the Environment Agency started collecting detailed information about flooding incidents, although we hold limited details about flooding incidents prior to this date.

If an area is not covered by the Historic Flood Map it does not mean that the area has never flooded, only that we do not currently have records of flooding in this area that meet the criteria for inclusion. It is also possible that the pattern of flooding in this area has changed and that this area would now flood or not flood under different circumstances. Outlines that don’t meet this criteria are stored in the Recorded Flood Outlines dataset.

The Historic Flood Map takes into account the presence of defences, structures, and other infrastructure where they existed at the time of flooding. It will include flood extents that may have been affected by overtopping, breaches or blockages.

Flooding is shown to the land and does not necessarily indicate that properties were flooded internally.

Collection of flood and inundation maps over Queensland at various scales 1893-1974, these show flood levels and probable inundation areas at various flood heights. A number of the map series include key maps.

Note: Each CSV in this series includes basic metadata about each map in the series and a URL to access a high resolution scan of each map.

Groundwater is the water that soaks into the ground from rain and can be stored beneath the ground. Groundwater floods occur when the water stored beneath the ground rises above the land surface. The Historic Groundwater Flood Map shows the observed peak flood extents caused by groundwater in Ireland. This map was made using satellite images (Copernicus Programme Sentinel-1), field data, aerial photos, as well as flood records from the past. Most of the data was collected during the flood events of winter 2015 / 2016, as in most areas this data showed the largest floods on record.This map is to the scale 1:20,000. This means it should be viewed at that scale. When printed at that scale 1cm on the map relates to a distance of 200m.The map is a vector dataset. Vector data portray the world using points, lines, and polygons (area). The floods are shown as polygons. Each polygon has info about the type of flood, the data source, and the area of the flood.The flood extents were calculated using data and techniques with various precision levels, and as such, it may not show the true historic peak flood extents.The Winter 2015/2016 Surface Water Flooding map shows fluvial (rivers) and pluvial (rain) floods, excluding urban areas, during the winter 2015/2016 flood event, and was developed as a by-product of the historic groundwater flood map.This map is to the scale 1:20,000. This means it should be viewed at that scale. When printed at that scale 1cm on the map relates to a distance of 200m.The map is a vector dataset. The floods are shown as polygons. Each polygon has info about the type of flood, the data source, and the area of the flood.The flood extents were made using remote sensing images (Copernicus Programme Sentinel-1), which covered any site in Ireland every 4-6 days. As such, it may not show the true peak flood extents.The Synthetic Aperture Radar (SAR) Seasonal Flood Maps shows observed peak flood extents which took place between Autumn 2015 and Summer 2021. The maps were made using Synthetic Aperture Radar (SAR) images from the Copernicus Programme Sentinel-1 satellites. SAR systems emit radar pulses and record the return signal at the satellite. Flat surfaces such as water return a low signal. Based on this low signal, SAR imagery can be classified into non-flooded and flooded (i.e. flat) pixels.Flood extents were created using Python 2.7 algorithms developed by Geological Survey Ireland. They were refined using a series of post processing filters. Please read the lineage for more information.The flood maps shows flood extents which have been observed to occur. A lack of flooding in any part of the map only implies that a flood was not observed. It does not imply that a flood cannot occur in that location at present or in the future.This flood extent are to the scale 1:20,000. This means they should be viewed at that scale. When printed at that scale 1cm on the maps relates to a distance of 200m.They are vector datasets. Vector data portray the world using points, lines, and polygons (areas). The flood extents are shown as polygons. Each polygon has information on the confidence of the flood extent (high, medium or low), a flood id and a unique id.The Groundwater Flooding High Probability map shows the expected flood extent of groundwater flooding in limestone regions for annual exceedance probabilities (AEP’s) of 10%, which correspond with a return period of every 10 years. The map was created using groundwater levels measured in the field, satellite images and hydrological models.This map is to the scale 1:20,000. This means it should be viewed at that scale. When printed at that scale 1cm on the map relates to a distance of 200m.The map is a vector dataset. The floods are shown as polygons. Each polygon has info on the data source, and the area of the flood.The flood extents were calculated using remote sensing data and hydrological modelling techniques with various precision levels. As such, it should be used with caution.The Groundwater Flooding Medium Probability map shows the expected flood extent of groundwater flooding in limestone regions for annual exceedance probabilities (AEP’s) of 1%, which correspond with a return period of every 100 years. The map was created using groundwater levels measured in the field, satellite images and hydrological models.This map is to the scale 1:20,000. This means it should be viewed at that scale. When printed at that scale 1cm on the map relates to a distance of 200m.The map is a vector dataset. The floods are shown as polygons. Each polygon has info on the data source, and the area of the flood.The flood extents were calculated using remote sensing data and hydrological modelling techniques with various precision levels. As such, it should be used with caution.The Groundwater Flooding Low Probability map shows the expected flood extent of groundwater flooding in limestone regions for annual exceedance probabilities (AEP’s) of 0.1%, which correspond with a return period of every 1000 years.The map was created using groundwater levels measured in the field, satellite images and hydrological models.This map is to the scale 1:20,000. This means it should be viewed at that scale. When printed at that scale 1cm on the map relates to a distance of 200m.The map is a vector dataset. Vector data portray the world using points, lines, and polygons (area). The floods are shown as polygons. Each polygon has info on the data source, and the area of the flood.The flood extents were calculated using remote sensing data and hydrological modelling techniques with various precision levels. As such, it should be used with caution.

This hosted feature layer has been published in RI State Plane Feet NAD 83.Statewide flood hazard areas compiled from county-based Digital Flood Insurance Rate Map (DFIRM) databases for Rhode Island. The Digital Flood Insurance Rate Map (DFIRM) Database depicts flood risk information and supporting data used to develop the risk data. The primary risk classifications used are the 1-percent-annual-chance flood event, the 0.2-percent-annual-chance flood event, and areas of minimal flood risk. TheDFIRM Database is derived from Flood Insurance Studies (FISs), previously published Flood Insurance Rate Maps (FIRMs), flood hazard analyses performed in support of the FISs and FIRMs, and new mapping data, where available. The FISs and FIRMs are published by the Federal Emergency Management Agency (FEMA), and in this case redistributed by the Rhode Island Geographic Information System (RIGIS) at the request of the Rhode Island Emergency Management Agency.This dataset provides the user with information on the flood risk hazard zones throughout the state of Rhode Island. Note: the above summary is a slightly modified version adapted from source metadata records provided by FEMA. To provide the user with information on the statewide flood risk based on information provided by the Federal Emergency Management Agency (FEMA) in the DFIRM databases created specifically for the five counties of Rhode Island (Bristol, Kent, Newport, Providence, and Washington). This dataset provides information on the likelihood that a flood may occur at a given location in the state. The files and information used to create this dataset were originally provided to the Rhode Island Emergency Management Agency (RIEMA) by FEMA.This information was in the form of DFIRM databases for each of the five RI counties. This information was then redistributed by RIGIS at the request of RIEMA. The information provided by this data is only a subset of the information available in the original DFIRM databases located on the RIGIS website. For a specific county's complete DFIRM database, please visit the RIGIS website and download the appropriate DFIRM database. This metadata record is specific to this dataset and only contains information relevant to this dataset as provided by FEMA the original DFIRM metadata records. These can be found and referenced in the /DOCUMENT folder that is downloaded as part of a DFIRM package for a specific Rhode Island county. Another valuable source of documentation is FEMA's "Guidelines and Specifications for Flood Hazard Mapping Partners". It is currently available online at https://www.fema.gov/guidelines-and-standards-flood-risk-analysis-and-mapping. The Guide offers a tremendous amount of information regarding how DFIRM data are created, and detailed information about the individual files that constitute a DFIRM database.

PLEASE NOTE: This dataset has been retired. It has been superseded by https://environment.data.gov.uk/dataset/04532375-a198-476e-985e-0579a0a11b47.The Flood Map for Planning (Rivers and Sea) includes several layers of information. This dataset covers Flood Zone 2 and should not be used without Flood Zone 3. It is our best estimate of the areas of land at risk of flooding, when the presence of flood defences are ignored and covers land between Zone 3 and the extent of the flooding from rivers or the sea with a 1 in 1000 (0.1%) chance of flooding each year. This dataset also includes those areas defined in Flood Zone 3.This dataset is designed to support flood risk assessments in line with Planning Practice Guidance ; and raise awareness of the likelihood of flooding to encourage people living and working in areas prone to flooding to find out more and take appropriate action.The information provided is largely based on modelled data and is therefore indicative rather than specific. Locations may also be at risk from other sources of flooding, such as high groundwater levels, overland run off from heavy rain, or failure of infrastructure such as sewers and storm drains.The information indicates the flood risk to areas of land and is not sufficiently detailed to show whether an individual property is at risk of flooding, therefore properties may not always face the same chance of flooding as the areas that surround them. This is because we do not hold details about properties and their floor levels. Information on flood depth, speed or volume of flow is not included.NOTE: We have paused quarterly updates of this dataset. Please visit the “Pause to Updates of Flood Risk Maps” announcement on our support pages for further information. We will provide notifications on the Flood Map for Planning website to indicate where we have new flood risk information. Other data related to the Flood Map for Planning will continue to be updated, including data relating to flood history, flood defences, and water storage areas.

Flood maps calculated from space-borne remote sensing Synthetic Aperture Radar (SAR) VV backscatter data during the extreme hydro-meteorological events occurred along the Panaro River . Sentinel 1/TerraSarX SAR data has been processed by a method combining thresholding and segmentation (CThS method). The main idea of CThS is to find some samples which are definitely seeds of the flood water areas. In doing so, a statistical measure of randomness, i.e. entropy filtering, is applied to characterize the texture of the input image. It tries to find locally some pixels, which contain the entropy values of the 3-by-3 neighborhood around the corresponding pixel in the input image. What the local filtering identifies is areas with a significant difference with the surrounding areas. These areas could contain different ground targets, which have the same signature as water. Then histogram thresholding is performed. The histogram of all pixels extracted by filtering is reasonably bimodal so that a suitable threshold value can be determined by fitting a curve to the histogram to separate water and non-water pixels. Having separated water seed points, an active contour segmentation method is used to delineate the full flood extent. The dataset contains flood maps for the dates: 12 and 13 December 2017 and water maps on 20 January 2014 and 8 December 2020. You are not authorized to view this dataset. You may email the responsible party OPERANDUM to request access. Flood maps of historical flood events (Panaro)

The Flood Map for Planning (Rivers and Sea) includes several layers of information. This dataset covers Flood Zone 3. It is our best estimate of the areas of land at risk of flooding, when the presence of flood defences are ignored and covers land with a 1 in 100 (1%) or greater chance of flooding each year from Rivers; or with a 1 in 200 (0.5%) or greater chance of flooding each year from the Sea.This dataset is designed to support flood risk assessments in line with Planning Practice Guidance; and raise awareness of the likelihood of flooding to encourage people living and working in areas prone to flooding to find out more and take appropriate action.The information provided is largely based on modelled data and is therefore indicative rather than specific.Locations may also be at risk from other sources of flooding, such as high groundwater levels, overland run off from heavy rain, or failure of infrastructure such as sewers and storm drains.The information indicates the flood risk to areas of land and is not sufficiently detailed to show whether an individual property is at risk of flooding, therefore properties may not always face the same chance of flooding as the areas that surround them. This is because we do not hold details about properties and their floor levels.Information on flood depth, speed or volume of flow is not included.NOTE: We have paused quarterly updates of this dataset. Please visit the “Pause to Updates of Flood Risk Maps” announcement on our support pages for further information. We will provide notifications on the Flood Map for Planning website to indicate where we have new flood risk information. Other data related to the Flood Map for Planning will continue to be updated, including data relating to flood history, flood defences, and water storage areas.

Historic Groundwater Flood Map 1:20,000 Ireland (ROI) ITM. Published by Geological Survey Ireland. Available under the license Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 (cc-by-nc-nd).Groundwater is the water that soaks into the ground from rain and can be stored beneath the ground. Groundwater floods occur when the water stored beneath the ground rises above the land surface.

The Historic Groundwater Flood Map shows the observed peak flood extents caused by groundwater in Ireland. This map was made using satellite images (Copernicus Programme Sentinel-1), field data, aerial photos, as well as flood records from the past. Most of the data was collected during the flood events of winter 2015 / 2016, as in most areas this data showed the largest floods on record.

The map is a vector dataset. Vector data portray the world using points, lines, and polygons (area). The floods are shown as polygons. Each polygon has info about the type of flood, the data source, and the area of the flood.The flood extents were calculated using data and techniques with various precision levels, and as such, it may not show the true historic peak flood extents....

Recorded Flood Outlines is a GIS layer which shows all our records of historic flooding from rivers, the sea, groundwater and surface water. Each individual Recorded Flood Outline contains a consistent list of information about the recorded flood.

Records began in 1946 when predecessor bodies to the Environment Agency started collecting detailed information about flooding incidents, although we may hold limited details about flooding incidents prior to this date.

The absence of coverage by Recorded Flood Outlines for an area does not mean that the area has never flooded, only that we do not currently have records of flooding in this area.

It is also possible that the pattern of flooding in this area has changed and that this area would now flood or not flood under different circumstances.

The Recorded Flood Outlines take into account the presence of defences, structures, and other infrastructure where they existed at the time of flooding. It includes flood extents that may have been affected by overtopping, breaches or blockages.

Any flood extents shown do not necessarily indicate that properties were flooded internally.

A companion dataset Historic Flood Map contains a subset of these Recorded Flood Outlines which satisfy a certain criteria.

This is a proof of concept web service displaying trial samples of historic flood mapping from satellite. Over the next 2 years this service will be developed into a nationwide portal displaying flooding across Australia as observed by satellite since 1987.The service shows a summary of water observed by the Landsat-5 and MODIS satellites across Australia for periods between 2000 and 2012.The first layer set displays national observed water from MODIS fvrom 2000 to 2012, as derived by Geoscience Australia using an automated flood mapping algorithm. The colouring of the display represents the frequency of observed water in a 500 x 500m grid. The higher the number, the more often water was observed by the satellites over the period. This means that floods have low values, while lakes, dams and other permanent water bodies have high values.The three additional layer sets are study areas demonstrating the water observed in each study area by the Landsat-5 satellite, as derived by Geoscience Australia using an automated flood mapping algorithm. The study areas and the observation periods are:Study Area 1, Condamine River system between Condamine and Chinchilla, Qld, observed between 2006 and 2011Study Area 2, North-west Victorian rivers between Shepparton and Kerang, observed between 2006 and 2011Study Area 3, Northern Qld rivers, near Normanton, observed between 2003 and 2011Each Study Area layer set includes a water summary displaying the frequency of observed water in 25 x 25m grids, plus individual flood extents for specific dates where flooding was observed. Similar to the national, MODIS summary, the higher the value, the more often water was observed by the satellites over the period. Limitations of the InformationThe automated flood mapping algorithm can confuse cloud shadows and snow with flood water, so some areas shown as water may be incorrect. This is a proof of concept dataset and has not been validated.

Abstract

This dataset and its metadata statement were supplied to the Bioregional Assessment Programme by a third party and are presented here as originally supplied.

Polygon data delineating modelled statistical flood extent with an Average Recurrence Interval (ARI) of 100 years. For historical/actual flood extents, refer to 'Historic_extent' layer. Also known as the 1 in 100 year flood layer, it is used, among other things, in the creation of 'Land Subject to Inundation' areas as used in Planning Scheme Zones. The 1 in 100 year data is not restricted. This data is part of a group of layers depicting a range of statistical ARI extents. Current layers include 5, 10, 20, 30, 50, 100, 200, 500, 1000 year intervals, each in a separate dataset. The layer called EXTENT_PMF represents areas of 'probable maximum flood' and is also part of this group. The data is statistically derived using hydrological models, historic flood extents and heights.

Purpose

Mainly used for municipal planning and risk assessment. The EXTENT_100Y_ARI layer is deemed the most appropriate to use for determining areas at risk of flooding. This layer directly inputs into the Land Subject to Inundation overlay. (LSIO)

Dataset History

Lineage: Primary

Positional Accuracy: Precision: 5m to 100m Initial data, flagged as 'modified = 20000101' varies in accuracy, and should be treated with caution, particularly at scales less than 1:25,000. Data with 'modified' values later than 20000101 are quite accurate and mostly sourced from flood studies. This data is suitable to use at township and parcel level. Reliability field provides clues to the accuracy, where a value of 1 is best and 3 is worst.

Attribute Accuracy: Attributes are verified and should be accurate. Overall reliability of the source material is indicated in RELIABILITY field, where 'HIGH' is good and 'LOW' is poor quality source information.

Logical Consistency: Attributes are consistent with other related layers e.g. flood height contours

Data Source: Flood data dates back to mid 1800s and historically has been predominantly located in DNRE Floodplain Management. Some data is located in Water Authorities.

Completeness: Floodplain Management Unit mapping conventions on definitions of flood mapping height data will be followed.

Additional Metadata: Recommend liaison with Floodplain Management Unit to clarify use of this layer

Refer to mapping reports for each major data capture effort to be kept at DNRE Floodplain Management Unit.

Dataset Citation

Victorian Department of Environment and Primary Industries (2014) Victoria - 1 in 100 Year Flood Extent. Bioregional Assessment Source Dataset. Viewed 05 October 2018, http://data.bioregionalassessments.gov.au/dataset/6e59ed35-3fde-48e3-8135-eb05263ce4aa.

Heavy rainfall occurred across Louisiana during March 8-19, 2016, as a result of a massive, slow-moving southward dip in the jet stream, which moved eastward across Mexico, then neared the Gulf Coast, funneling deep tropical moisture into parts of the Gulf States and the Mississippi River Valley. The storm caused major flooding in north-central and southeastern Louisiana. Digital flood-inundation maps for a 4.3-mile reach within the community of Monroe near Black Bayou in Ouachita Parish, LA was created by the U.S. Geological Survey (USGS) in cooperation with Federal Emergency Management Agency (FEMA) to support response and recovery operations following a March 8-19, 2016 flood event. The inundation maps depict estimates of the areal extent and depth of flooding corresponding to 4 high-water marks (HWM) identified and surveyed by the USGS following the flood event.

Flood hazard areas for the Flood Insurance Rate Map (FIRM) published by the Federal Emergency Management Agency (FEMA) within Stark County, Ohio. These flood hazard areas are part of the National Flood Hazard Layer (NFHL). Flood hazard areas in this layer were merged into single records for each class to improve web map performance and symbolization. Flood hazard areas are sometimes referred to as flood hazard zones or flood plains. They depict the floodway (areas that are frequently flood), as well as the 100 and 500-year flood plains. The FIRM is the basis for floodplain management, mitigation, and insurance activities for the National Flood Insurance Program (NFIP). Insurance applications include enforcement of the mandatory purchase requirement of the Flood Disaster Protection Act, which requires the purchase of flood insurance by the owners of properties within areas identified as having flood hazards. This layer was downloaded from https://msc.fema.gov/portal/advanceSearch in September, 2021. It was last updated and published on September14, 2018.

A slow-moving area of low pressure and a high amount of atmospheric moisture produced heavy rainfall across Louisiana and southwest Mississippi in August 2016. Over 31 inches of rain was reported in Watson, 30 miles northeast of Baton Rouge, over the duration of the event. The result was major flooding that occurred in the southern portions of Louisiana and included areas surrounding Baton Rouge and Lafayette along rivers such as the Amite, Comite, Tangipahoa, Tickfaw, Vermilion, and Mermentau. The U.S. Geological Survey (USGS) Lower Mississippi-Gulf Water Science Center operates many continuous, streamflow-gaging stations in the impacted area. Peak streamflows of record were measured at 10 locations, and seven other locations experienced peak streamflows ranking in the top 5 for the duration of the period of record. In August 2016, USGS personnel made fifty streamflow measurements at 21 locations on streams in Louisiana. Many of those streamflow measurements were made for the purpose of verifying the accuracy of the stage-streamflow relation at the associated gaging station. USGS personnel also recovered and documented 590 high-water marks after the storm event by noting the location and height of the water above land surface. Many of these high water marks were used to create twelve flood-inundation maps for selected communities of Louisiana that experienced flooding in August 2016. This data release provides the actual flood-depth measurements made in selected river basins of Louisiana that were used to produce the flood-inundation maps published in the companion product (Watson and others, 2017). Reference Watson, K.M., Storm, J.B., Breaker, B.K., and Rose, C.E., 2017, Characterization of peak streamflows and flood inundation of selected areas in Louisiana from the August 2016 flood: U.S. Geological Survey Scientific Investigations Report 2017–5005, 26 p., https://doi.org/10.3133/sir20175005. First release: February 2017 Revised: April 2017 (ver. 1.1) Additionally, there is a revision history text file available on the main page that explains exactly what changed in the revision.

North Carolina Effective Flood zones: In 2000, the Federal Emergency Management Agency (FEMA) designated North Carolina a Cooperating Technical Partner State, formalizing an agreement between FEMA and the State to modernize flood maps. This partnership resulted in creation of the North Carolina Floodplain Mapping Program (NCFMP). As a CTS, the State assumed primary ownership and responsibility of the Flood Insurance Rate Maps (FIRMs) for all North Carolina communities as part of the National Flood Insurance Program (NFIP). This project includes conducting flood hazard analyses and producing updated, Digital Flood Insurance Rate Maps (DFIRMs). Floodplain management is a process that aims to achieve reduced losses due to flooding. It takes on many forms, but is realized through a series of federal, state, and local programs and regulations, in concert with industry practice, to identify flood risk, implement methods to protect man-made development from flooding, and protect the natural and beneficial functions of floodplains. FIRMs are the primary tool for state and local governments to mitigate areas of flooding. Individual county databases can be downloaded from https://fris.nc.gov Updated Jan 17th, 2025.

This shapefile (polygon feature) contains the boundary of the July 1, 2022 100-Year Storm Flood Risk Zone, one of the layers of the July 1, 2022 100-Year Storm Flood Risk Map. Areas within this boundary are highly likely to experience “deep and contiguous” flooding during a 100-year storm. A 100-year storm is a storm that has a 1% chance of occurring in a given year. “Deep and contiguous flooding” means flooding at least 6-inches deep spanning an area at least the size of an average City block. The 100-Year Storm Flood Risk Zone does not provide the exact depth of flooding at a given _location. It also does not show areas in the City that may experience shallower and/or more localized flooding in a 100-year storm. Finally, the 100-Year Storm Flood Risk Zone shows flood risk from storm runoff only. It does not consider flood risk in San Francisco from other causes such as shoreline overtopping and overland inundation from the San Francisco Bay or Pacific Ocean. In addition to the 100-Year Storm Flood Risk Zone, the 100-Year Storm Flood Risk Map shows: • “Areas not served by the Combined Sewer and Stormwater Collection System” - showing where data for rainfall driven storm runoff is not available, and where flood risk has not been analyzed. • “Historical Shoreline”, “Historical Creeks”, and “Historical Waterbodies” - historical hydrology layers to illustrate the general topography of low-lying areas in the City. The Horizontal Datum used for the GIS layers is “NAD_1983_2011_StatePlane_California_III_FIPS_0403_Ft_US.” Notes on Usage At a minimum, the 100-Year Storm Flood Risk Map is updated by the San Francisco Public Utilities Commission (SFPUC) on an annual basis on or before July 1 to account for any parcel review requests that remove properties from the Flood Zone. To confirm the latest version of the 100-Year Storm Flood Risk Map, check the SFPUC website at https://sfpuc.org/learning/emergency-preparedness/flood-maps to see if the map has been updated since the date of this shapefile or if there have been any parcel review determinations that identify parcels that are no longer part of the 100-Year Flood Risk Zone. The most recent official map, associated documentation, and list of parcels removed from the map from a parcel review process are available at https://sfpuc.org/learning/emergency-preparedness/flood-maps. Please be advised that the parcels listed are no longer considered to be within the 100-Year Flood Risk Zone as a result of the parcel review process. As of July 2022, this list is updated on an ongoing basis. Check the SFPUC website for any changes to this schedule. The boundaries of this zone align with San Francisco parcel boundaries. The user should confirm proper projection or use of the webmap at https://sfpuc.org/learning/emergency-preparedness/flood-maps to properly identify parcels within the flood zone.

FloodScan uses satellite data to map and monitor floods daily, helping compare current flood conditions with historical averages. This dataset contains two resources: The first (hdx_floodscan_zonal_stats.xlsx) is a daily tabular dataset providing average FloodScan Standard Flood Extent Depiction (SFED) flood fraction (0-100%) per admin 1 and 2 level. Historical baseline values (SFED_BASELINE) are calculated per day-of-year from the last 10 years of historical data (non-inclusive of current year) after applying an 11 day smoothing mean window. Return Period (RP) is calculated empirically based on all historical data up to the current year (non-inclusive). The second resource (aer_floodscan_300s_SFED_90d.zip) is a zipped file containing AER FloodScan estimated daily flood fraction (0-100%) gridded data at approximately 10 km resolution (300 arcseconds equivalent to approximately 0.083 degrees) for the last 90 days. Each file represents the estimates for a single day and includes 2 bands: SFED and SFED_BASELINE. The baseline band provides users an easy way to compare current values with historical averages. The baseline is calculated per day-of-year from the last 10 years of historical data (non-inclusive of current year) after applying an 11 day temporal smoothing mean window.

Regulatory floodplains are extracted from FEMA or provided by consultants to the City. Non regulatory floodplains are provided by consultants, but their accuracy is not guaranteed.FEMA floodplains can either be amended by Letters of Map Revision (LOMR), or Physical Map Revisions (PMR). Historic data between 7/17/1978 and 5/31/2018 rely on PMRs to FIRM Panels; from 5/31/2018 onwards, FEMA exposed a web API that made tracking LOMRs much easier. This is why changes to the floodplain after this date look more "piecemeal" rather than entirely replaced. FEMA Floodplains are automatically updated by a scripted process on a monthly basis.High Hazard Zones are solely recognized by the city as areas which represent the highest risk to loss of life. More information can be found here. These zones are delineated by engineering firms on behalf of the city. They are updated manually by GIS staff.Non-Regulatory Floodplains are updated infrequently.Data: Records with Null INEFFDATEs are the current floodplains.FLOODZONEs beginning with "A" have a 1% chance of flooding (e.g. the 100 Year floodplain)FLOODZONEs equal to "X" are areas with a 0.2% chance of flooding (e.g. the 500 Year floodplain)FLOODZONEs equal to "HHZ" are the High Hazard ZonesFLOODWAYs equal to 1 are Conveyance Zones

Recorded Flood Extents shows areas that have been recorded to have flooded in the past from rivers, the sea or surface water. The records come from a number of evidence sources including Natural Resources Wales, its predecessors or other Risk Management Authorities.

It is possible that the pattern of flooding in an area may have changed and would now flood under different circumstances. In addition, the absence of a recorded flood extent does not mean that the area has never flooded, only that we do not currently have records of flooding in this area.