Local engineers, developers, and planners are encouraged to reference MAAPnext data and modeling methods as the current countywide standard for flood risk assessment, once FEMA releases preliminary data.

When performing site-specific studies, MAAPnext can be cited as the foundational model for baseline conditions, with project-level refinements documented separately. References should note that MAAPnext modeling follows the methodologies outlined in:

• Interim Guidelines and Criteria for Atlas 14 Implementation
• FEMA’s Guidance for Flood Risk Analysis and Mapping Standards.

Using MAAPnext as a reference promotes consistency in floodplain management and ensures that local analyses align with countywide data and FEMA’s national standards.

Calibration and validation are critical steps that ensure the model results accurately reflect how water behaves in the real world. MAAPnext models were calibrated using rainfall, flow, and water-surface data from past storms recorded by the Flood Warning System and other regional sources. Once calibration produced close agreement between modeled and observed conditions, validation was performed using independent storm events not included in calibration. This two-step process confirmed that model results reliably predict flooding patterns across both mapped and unmapped areas of Harris County.

MAAPnext integrates a wide range of high-quality, publicly sourced, and locally collected datasets to build the countywide flood models.

Key data inputs include:

• LiDAR Terrain Data (2018): High-resolution elevation data captured across Harris County at three-foot resolution—nine times more detailed than previous datasets. 
• Land Use and Impervious Cover (2018): Updated using recent aerial imagery to reflect current development and drainage conditions.
• Rainfall Data (NOAA Atlas 14): Incorporates the most recent rainfall frequency estimates to model realistic storm scenarios.
• Hydrologic and Hydraulic Modeling Software: Based on U.S. Army Corps of Engineers HEC-HMS and HEC-RAS systems, adapted for countywide use. 
• Streamflow and Elevation Records: Historical and real-time gage data from the Harris County Flood Warning System.

These datasets form the foundation for the hydrologic and hydraulic models that estimate flood depths, velocities, and extents for different rainfall events across the entire county.