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Climate Impact Multiplier - Impervious Land Cover Impervious surfaces, including building and pavement surfaces, typically absorb solar radiation faster than pervious land coverings (grass, trees). This absorbed energy is typically retained throughout the day and then released slowly during the night. Consequently, ambient temperatures near building and paved areas are higher than grasslands and forest areas. The effects of higher levels of impervious surfaces impact not only large cities, but smaller cities and towns as well. Increases in impervious cover can also dramatically increase the impact of so-called 100-year flood events. Typically, floods in areas of high impervious surfaces are short-lived, but extended flooding can stress trees, leading to leaf yellowing, defoliation, and crown dieback. If damage is severe, mortality can occur. In addition, flooding can lead to secondary attacks by insect pests and diseases. Some species are more tolerant of flooding than others. Climate Impact Multiplier - Heat Island Residents of cities and town centers are more at risk for heat-related illnesses than rural dwellers. The radiant heat trapped by impervious surfaces and buildings as well as heat generated by building mechanical systems, motorized equipment, and vehicles is known as the “Heat Island Effect” . In larger cities, heat island effects create a micro-climate throughout the metro area while occupants of smaller cities and towns can still experience higher temperatures and decreased air movement due to the effects of surrounding buildings and impervious surfaces. This heat island effect serves to increase the impact of climate change effects in developed areas of all size populations, especially those with low or intermittent tree canopy coverage. A developed area’s impervious surface characteristics, and tree canopy conditions combine to exacerbate or mitigate the community’s heat island impacts. Due to the heat island effect, developed areas are usually hotter and cool off less at night than non developed areas. Heat islands can increase health risks from extreme heat by increasing the potential maximum temperatures residents are exposed to and the length of time that they are exposed to elevated temperatures. The heat island effect can make developed areas one hardiness zone warmer than the surrounding undeveloped area, allowing some more southern species to be planted. In addition to milder winters, however, heat island effects can also make summer temperatures higher, especially near dark pavements and buildings. Thus, some native plants that are becoming marginal for the area because of increased heat could experience negative effects. 1- 4 City of Arden Hills Energy and Sustainability Sustainability in Context 4-11°F -9 to 16% With Significant Seasonal Variation 30% +48 days 30 days -47 days 287% Looking Forward By 2100, Arden Hills Can Expect: Increase in annual average temperature: Increase in annual precipitation: Increase in heavy precipitation events: Increase in Days above 95: Decrease in Days below 32: Increase in growing season: Increase in Air Conditioning Demand: As the area’s climate is projected to change (with increased heat, shortened winters, greater variability in weather and precipitation, increased storminess, annual rainfall as well as increased time frames between rain and drought conditions). The chart to the right shows the anticipated changes to Arden Hills climate by the end of this century under a the “business as usual” climate model (Sources: US Climate Resilience Assessment, University of Michigan Climate Center). With the anticipated increase in extreme heat (48 additional days above 95 degrees), and the corresponding increase in Cooling Degree Days and electricity demand in the coming decades, engaging strategies to mitigate heat impacts can have long-term health and economic benefits. There are physical characteristics which can have a multiplying or mitigating affect on the impacts of climate at both the building site as well as community-wide scale. Physical characteristics impactful at the building scale include tree canopy cover, impervious surface cover, and heat island effects.