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2024 Hennepin County All -Jurisdiction Hazard Mitigation Plan <br />Volume 2 — Hazard Inventory <br />referenced in other sections in this chapter, the urban warming "bias" is minimized or even non-existent. <br />Rural counties to the west have similar long-term temperature increases to Hennepin County. It is <br />therefore likely that the vast majority of the 3.1° F of average annual warming and the other seasonal <br />warming reported for Hennepin County results from human -caused climate change. <br />Applying findings from attribution studies in other areas to common hazards in Hennepin County suggests <br />the following: <br />• Climate change is likely making humid heatwaves in Minnesota more severe by increasing Heat <br />Index values by 4°-6° F over what would have been observed without a warmer global climate. <br />This also has the effect of increasing the probability of occurrence dramatically. <br />• Extremes of precipitation, including snowfall, may be 10-15% larger because of the higher water <br />content of the atmosphere due to rising global temperatures. <br />o Similarly, the damaging snows of December 13-16, 2022, to the north of the Twin Cities <br />may have had two climate changes making them more likely: 1) the increased availability <br />of moisture because of higher global temperatures, and 2) the winter warming that <br />caused the snow to be wetter, heavier, and thus more destructive. <br />• Out -of -season events that result from unusually warm conditions, like the severe weather <br />outbreak of December 15, 2021, or a record -breaking heat wave in early October of 2023, may <br />have been much more likely because of climate change, and therefore would have been <br />substantially less probable without human -caused warming. <br />• Any events of these types will become more probably with continued warming, and that <br />continued warming would make larger contributions to future events, meaning potentially <br />greater extremes of precipitation and humid heat waves in the decades ahead. <br />4.3.1.3. Spectrum of Consequences B2b <br />In Hennepin County, climate change has led to warmer conditions in general, especially during winter; <br />more precipitation, including during drought years; greater extremes of rain and snow; and more intense <br />humidity -driven heatwaves. Additionally, the seasonal ranges of heatwaves and severe weather events <br />have expanded. Even though year-to-year and multi -year variations will continue, these changes are <br />projected to continue as well, with an enhancement of some hazards as the world warms. <br />Warmer winter conditions pose some benefits for human comfort and safety but pose recreational risks <br />because of dangerous lake ice that may be unsuitable for fishing and ice skating. Natural systems <br />dependent on cold weather to keep out competitive species and predators also suffer from enhanced <br />winter warming, which can alter ecosystems and natural resources. <br />Increased rain and snow extremes mean roads and their supporting infrastructure may face increased <br />damages if they are not built to higher design standards. Heavy, wet snow, as occurred in the 2022-23 <br />winter, can damage trees, knock out power, and overwhelm some structures with snow loads. <br />Greater precipitation totals during wet years also would imply high water levels on area lakes and streams, <br />increasing chances for erosion, pollution from runoff, degraded water quality, stream bank failure, <br />landslides, and residential flooding. <br />55 <br />