Integrating Flood and Heat Risks in AlexRenew's Climate Resilience Plan

LEARNING OBJECTIVE
This paper presents an overview of the methods to assess the risk of climate hazards on operations and personnel at AlexRenew, a mid-size wastewater treatment facility in Alexandria, Virginia. AlexRenew's exposure to climate hazards was assessed through site visits, system inspection, data analysis, and flood and thermal modeling. This paper details the methodology used to assess and apply a scoring rubric for probability, impact, and risk of climate hazards on utility operations and personnel. The results of the study provide a method for prioritizing action based on asset risk, including proposed mitigation measures and future design criteria for risk reduction.

INTRODUCTION
AlexRenew, the wastewater treatment authority for Alexandria and parts of Fairfax County, Virginia, has initiated a Climate Resilience Study to understand risks and develop strategies to enhance the resilience of its facilities to climate change impacts. AlexRenew's system includes the water resources reclamation facility (WRRF), interceptors, pump stations, a tunnel system, overflow structures, and administrative spaces. The authority is aware of the growing threats of climate-related hazards and is seeking a robust method for prioritizing systems for protection. The paper includes visualization tools used to analyze and communicate climate-related risks and impacts that inform AlexRenew's climate resilience strategy.

METHODOLOGY
The authors assessed the most acute climate change risks to AlexRenew based on its location, geography, and operations (process shown on Figure 1). Models were developed to assess current and projected risks from flooding, thermal stress, extreme weather events, and other climate variables using SSP5-8.5 greenhouse gas emission scenarios for future conditions projected to 2045, 2075, and 2085.

The vulnerability assessment involved determining the level of exposure and sensitivity of AlexRenew's 5,800+ assets to flooding and heat, distributed across the service area (Figure 2). The authors identified the locations and elevations of potential flood entry to buildings and underground galleries such as doorways, louvers, and stairways, and conducted site visits to categorize, locate, and document assets' elevation and evaluate heat exposure (Figures 3 and 4). Indoor and outdoor thermal modeling was conducted to evaluate future cooling needs and identify heat exposure for assets as well as personnel (Figure 5). A variety of thermal metrics were employed to measure how long and when thermal stress levels exceeded safety thresholds for equipment and personnel. Findings from the Universal Thermal Climate Index (UTCI) model demonstrate a rise in heat stress levels, along with an increase in discomfort hours (Figures 6). Flood modeling was conducted for interior, riverine and coastal flood scenarios (Figures 7 and 8). Sensitivity was based on whether a particular asset would be expected to be inoperable due to exposure to a particular climate hazard. Based on the model results, about 3,500 assets were eliminated from the risk assessment due to low exposure or sensitivity to climate hazards. The risk assessment evaluated and scored remaining assets to determine the probability of a climate hazard causing equipment failure and the resulting impacts to plant operations. Probability scores consider the relative likelihood of current and projected future climate events (Figure 9). Impact scores, which represent the severity of consequence to AlexRenew's operations, were assigned to each system in a manner consistent with the organization's existing methodology to assess assets' risk. The authors determined total risk scores for each asset by multiplying probability and impact scores together. Asset-level probability, impact, and risk scores were then averaged to provide results at the system and facility levels. These scores can be used to prioritize actions to increase resilience. This methodology mirrors the one used to develop the asset management system risk registry, allowing AlexRenew to integrate climate risk scores into its existing risk registry.

RESULTS
The risk assessment results were used to create a prioritized list of assets and systems most at risk of flooding or extreme heat (Figures 10 and 11). The 1,236 assets located in connected underground galleries are most at risk for flooding. As such, implementing flood mitigation measures at entryways is a simple strategy that can improve flood resilience for many critical assets. At-risk systems outside of the galleries require different climate mitigation measures depending on their locations, characteristics, and criticality (Figure 12). The heat risk analysis pinpointed electrical systems and regions with high risk of overheating, which could negatively affect onsite personnel (Figure 13). Personnel were interviewed to determine which facilities were most utilized by staff, which helped identify assets to prioritize for heat mitigation strategies.

AlexRenew will use the results of the Climate Resilience Study to prioritize capital investments and operating procedures to reduce climate risk. Conceptual mitigation strategies are being developed for assets found to be most at risk. A visualization tool is also being developed to illustrate flooding and thermal risk for all facilities.

The results of the Climate Resilience Study are being discussed with facility managers and will be finalized by March 2025.