{ "snippet": "Identification of flash flood-prone areas that may warrant outdoor warning sirens.", "summary": "Identification of flash flood-prone areas that may warrant outdoor warning sirens.", "extent": [ [ -106.629781538787, 25.8376806033772 ], [ -93.5081972018394, 35.9843632988272 ] ], "accessInformation": "Texas Water Development Board", "thumbnail": "thumbnail/thumbnail.png", "maxScale": 1.7976931348623157E+308, "typeKeywords": [ "ArcGIS", "ArcGIS Server", "Data", "Map Service", "Service" ], "description": "

Following the severe flash flooding in Central Texas in July of 2025, the 89th Texas Legislature passed Senate Bill 3, establishing requirements for outdoor warning sirens in designated flash flood-prone areas within the 30 counties included in the disaster declaration, and Senate Bill 5, providing funding through a state-administered grant program to assist local governments with the cost of installing outdoor warning sirens required under SB3.<\/span><\/p>

The Texas Water Development Board developed the Flash Flood Risk Areas (FFRA) map viewer to support community officials with identifying where sirens may be warranted within their communities. This document describes the data included in the map and how to interpret the Flash Flood Risk Areas map. <\/span><\/p>

In support of developing the FFRA mapping data, a hazard called Flash Flood Hazard Index (FFHI) was developed. FFHI provides a quantitative measure of the likelihood of flash flood occurrence. This index combines terrain, geomorphic, hydrologic, land cover, and meteorological factors into a single score to quantify flash flood potential. A threshold for FFHI was estimated based on literature review and sensitivity analyses. It was determined that a value greater than 0.525 may pose moderate to high hazard to people outdoors. A provisional FFRA was identified by combining areas above the FFHI and locations where people outdoors may be exposed to flooding in a 0.2 percent annual chance flood.<\/span><\/p>

The provisional FFRA map is a conservative estimate intended to encourage local jurisdictions to incorporate site-specific data, field observations, historical experience, and community knowledge to further refine siren placement within the identified FFRA. Absence from the mapped FFRA map should not be interpreted as absence of risk. Results are dependent on the quality, resolution, and recency of available datasets, and are generalized at a 1 kilometer scale. Final decisions to determine FFRAs require input from local officials and emergency managers with local knowledge, field observations, and site-specific considerations to request revisions to the map. Once input is received and FFRAs are finalized communities must install, maintain, and operate sirens that comply with TWC ยง16.502 (c, f, h, & j).<\/span><\/p>

For more information, please refer to Technical Memorandum: Identification of Flash Flood-Prone Areas that warrant Outdoor Warning Sirens, specifically sections 6-7 and Appendix E.<\/span><\/p><\/div><\/div><\/div>", "licenseInfo": "

Disclaimer<\/span><\/p>

This product is a screening\u2011level assessment intended to identify areas that may be susceptible to flash flooding and where outdoor warning sirens may be warranted. It is based on a regional\u2011scale analysis of physical watershed characteristics, available exposure data, and historical information, and does not predict the occurrence, timing, or severity of flash flooding during any specific storm event. This product should not be used as a predictive or forecasting tool related to flooding. The mapped areas primarily reflect riverine and channel\u2011adjacent flash flood susceptibility and may not capture all forms of localized or pluvial flooding, including flooding away from mapped streams or floodplains. Absence from the mapped areas should not be interpreted as absence of risk. Results are dependent on the quality, resolution, and recency of available datasets, and are generalized at a 1\u2011kilometer scale. Therefore, they are not intended for site\u2011specific or parcel\u2011level determinations. This product should not be used for regulatory determinations. Identification of areas that may warrant sirens does not ensure siren audibility or effectiveness under all conditions, nor does it replace the need for local knowledge, additional warning methods, or professional judgment. Final decisions regarding outdoor warning siren placement should incorporate local review, field verification, and community\u2011specific considerations.<\/span><\/p>

Data in the Provisional Flash Flood Risk Areas Map represents the best information available to the TWDB at the time. The information is not represented in real-time and should not be considered as exact conditions in your area. The TWDB provides information via this website as a public service. Neither the State of Texas nor the TWDB assumes any legal liability or responsibility or makes any guarantees or warranties as to the accuracy, completeness, or suitability of the information for any particular purpose.<\/span><\/p>

Please contact flood_sirens_program@twdb.texas.gov for any questions.<\/span><\/p><\/div><\/div>

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