Res 2024-045 approving the 2024 City of San Marcos Hazards Mitigation Action Plan (“HMAP”)

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SECTION 4: RISK OVERVIEW OVERVIEW OF HAZARD ANALYSIS The methodologies utilized to develop the Risk Assessment are a historical analysis and a statistical approach. Both methodologies provide an estimate of potential impact by using a common systematic framework for evaluation. Records retrieved from National Centers for Environmental Information (NCEI) and National Oceanic and Atmospheric Administration (NOAA) were reported for the City of San Marcos. Remaining records identifying the occurrence of hazard events in the planning area and the maximum recorded magnitude of each event were also evaluated. The use of geographic information system (GIS) technology to identify and assess risks for the City of San Marcos and evaluate community assets and their vulnerability to the hazards. The four general parameters that are described for each hazard in the Risk Assessment include frequency of return, approximate annualized losses, a description of general vulnerability, and a statement of the hazard's impact. Frequency of return was calculated by dividing the number of events in the recorded time period for each hazard by the overall time period that the resource database recorded events. Frequency City of San Marcos I Hazard Mitigation Action Plan Update 2024 1 Page 7 c No long-term river flooding trend has been identified in the observations, nor is such a trend projected at this point, except perhaps for the most extreme floods and areas with normally high rainfall. Urban flooding is projected to increase, both as a simple matter of urban population increase and because of the Flood projected increase of precipitation intensity, which drives flooding in fast -response drainages like those usually found in urban areas. The climate -driven trend in urban flood frequency should be similar to the climate -driven trend in extreme precipitation frequency: 30-50 percent in 2036 relative to 1950-1999 and 10-15 percent relative to 2001-2020. As the climate warms, the likelihood of winter weather decreases. Winter Weather Both extreme cold and snowfall either become less frequent or are expected to do so. Widespread snowfall events in Texas such as the one that took place in February 2021 are extremely rare. Historical trend data is unreliable. Thunderstorms (Wind, Indirect evidence supports an increase in the number of days Hail, Lightning) capable of producing severe thunderstorms and an increase in the frequency of very large hail in early springtime, but these possible trends are too uncertain to quantify. Weather and climate drivers of wildfire risk are projected to Wildfire increase the risk of wildfires throughout the state, primarily due to increased rates of drying and increased fuel load. OVERVIEW OF HAZARD ANALYSIS The methodologies utilized to develop the Risk Assessment are a historical analysis and a statistical approach. Both methodologies provide an estimate of potential impact by using a common systematic framework for evaluation. Records retrieved from National Centers for Environmental Information (NCEI) and National Oceanic and Atmospheric Administration (NOAA) were reported for the City of San Marcos. Remaining records identifying the occurrence of hazard events in the planning area and the maximum recorded magnitude of each event were also evaluated. The use of geographic information system (GIS) technology to identify and assess risks for the City of San Marcos and evaluate community assets and their vulnerability to the hazards. The four general parameters that are described for each hazard in the Risk Assessment include frequency of return, approximate annualized losses, a description of general vulnerability, and a statement of the hazard's impact. Frequency of return was calculated by dividing the number of events in the recorded time period for each hazard by the overall time period that the resource database recorded events. Frequency City of San Marcos I Hazard Mitigation Action Plan Update 2024 1 Page 7