Meteorologists warned us of a hot, dry summer to rival the past two. Although the forecast for a hot summer might attract tourists to the coast, prolonged heat is hard on residents. It burdens our energy systems as we crank up the air conditioners and turn on fans, it taxes the parks and boulevard trees that provide shade and cooling, and it stresses our health and our medical system.
Here on the coast, where temperatures rarely stay hot for long, we usually have few opportunities to adapt to extreme heat. That鈥檚 why the heat-warning system for the south coast kicks in at 29 C, not 40 C, as it does for most other areas in sa国际传媒.
However, climate projections indicate that, by 2050, extreme heat events that now occur about once every 25 years on the south coast will occur every eight years, with summer temperatures above 24 C occurring twice as often as they do today.
Studies on deadly heat waves show mortality rises as the temperature rises. When the temperature goes up, clinics see more patients with headaches, dizziness, dehydration, and other signs of heat-related illness.
How long heat sticks around is also key, with the toll really kicking in by Day聽3.
During the 2009 heat wave in sa国际传媒, temperatures reached 40 C in some areas and stayed high over a period of eight days. A subsequent study that compared death rates during the heat wave to normal conditions found that 110 more people died that week than would be seen in an average summer week in the province.
And if nights remain hot, the impact worsens. Our bodies need to cool down at night.
People living in cities often experience greater extremes. The roads, sidewalks, buildings and other hard surfaces that shape cities absorb heat from the sun. Some is radiated back into the environment immediately, adding to surface and air temperatures. Studies have found the average air temperature in large cities is 1 C to 3 C warmer than the surrounding countryside, and can be as high as 12 C warmer in some places within a city.
For example, a thermometer placed in the shade may read 30 C, but when placed in the sun, it could rise to 37 in less than a minute. Place the thermometer on asphalt, and it may shoot up to the mid-40s.
The hard surfaces also store the heat, releasing it at night. This increases night-time temperatures.
A recent study published in Scientific Advances suggests that limiting climate change to 1.5 or 2 C 鈥� two of the scenarios outlined in the Paris Agreement on Climate Change 鈥� could save thousands of lives in U.S. cities over the next 50 years. Keeping the global average temperature increase to 1.5 C would prevent up to 2,720 heat-related deaths during a one-in-30-year heat-wave event in each of the 15聽cities studied.
Another study examined how trees dampen the heat island effect caused by city roads, roofs and parking lots. Trees shade those surfaces from the sun鈥檚 rays. They also release water into the air through their leaves 鈥� a process that cools the surrounding air.
After repeatedly sampling day and night air temperature every few metres along city streets, the researchers found that the thicker and more extensive a tree canopy over a street, the lower the daytime air temperature beneath the trees. When trees shaded more than 40 per cent of a street鈥檚 surface along an entire city block, the trees cooled the air down more than the pavement heated it.
However, the researchers found that canopy cover had less effect at night. The area鈥檚 hard surfaces still stored daytime heat and released it at night. This bumped up nighttime temperatures.
A 2017 UBC study confirms the cooling value of trees in cities. Removing all trees from around buildings can increase the buildings鈥� summer energy consumption by 15 per cent.
Taken together, this suggests that, to best mitigate city heat island effects, municipalities need to be strategic in how they plant trees. They need to maximize tree cover where it would have greatest impact. They also need to decrease impervious, heat-absorbing surfaces.
