Extreme heat events can pose substantial health risks. Such events are often exacerbated in large cities where the urban heat island effect can significantly raise temperatures during both the day and night. Ottawa’s Hot Weather Response Plan seeks to address these issues. However, such a plan must be carefully evaluated to ensure it is delivering on the protections that it promises. There are multiple ways in which a hot weather response plan can be evaluated. Process evaluations analyze the performance of key alert, response and communications mechanisms and activities (e.g. sending of alerts, outreach to key service providers of vulnerable populations, and the dissemination of heat-health messages that underpin the Heat Alert and Response System in a community). Outcome evaluations gauge whether the Heat Alert Response System has actually resulted in a reduction in morbidity and/or mortality over time. These kinds of analysis need to be conducted on a frequent basis, as the conditions that affect the success of a hot weather response plan can change over time. The demographics and locations of vulnerable groups may shift, a city might embrace an aggressive tree planting campaign that changes the locations of greatest heat stress, carbon mitigation programs may alter the projected long-term effects of climate change, and many other potential factors all affect such a plan’s effectiveness.
In 2011, the City of Ottawa, Ontario, undertook a workshop evaluating the effectiveness of their Hot Weather Response Plan. Since the early 2000’s, Ottawa has been working on improving their resilience to extreme heat events and making continual improvement over the years. However, a city is not a static system; nor is the climate. As time goes by, demographics shift and urban form changes. This alters the distribution of vulnerable groups across the city and the conditions that can exacerbate or mitigate the negative health effects of extreme heat. Additionally, the projections for anticipated extreme heat events in the future are dependent on climate projections are both being refined by improved understanding and modified by anticipated political, economic, technological, and other factors. As such, it is important to conduct regular evolutions of the heat response system and to consider changes in these or other factors that might necessitate changes to the system. The 2011 evaluation revealed five key characteristics that would affect the efficacy of the program in the near future.