Cool Boulder initiative is a good start, but not nearly enough
The planet is warming, and urban areas are warming faster than the average, thanks to heat-absorbing pavement and buildings. In response, the Cool Boulder initiative aims to reduce temperatures in the city by increasing tree cover. This is a welcome step. Trees are the gift that keeps on giving: They sequester carbon. They provide shade. They beautify. They moderate our fierce winds. They buffer rainfall, reducing stormwater surges. Yay, trees!
Unfortunately, the Cool Boulder initiative tries to do both too much and too little. It tries to do too much because it wraps endeavors that aren’t directly connected to urban warming — pollinator protection and regenerative agriculture — in with expanding tree canopies. These are both great goals, but mitigating the heatisland effect is a big enough task that it shouldn’t be bundled with other efforts, no matter how admirable.
On the other hand, Cool Boulder does too little, because just adding trees is not enough to cool the city. We also need to look at how changes to our built environment — especially roofs, pavement, and buildings — can reduce local warming.
First, consider roofs. Reflective roofing is a win-win: It keeps the surrounding area cooler, and it also reduces the cooling load on the building itself. My wife and I recently had our roof replaced, and we chose a qualifying cool roof color, which cost no more than any other color. It looks good, and it reduces heat buildup in our attic. Boulder should require that all new or replacement roofs meet a cool-roof standard.
In many places dark, heatretaining pavement is the primary cause of the urban heatisland effect. Phoenix, ground zero for urban warming, has been experimenting with whitepainted asphalt, but this is just white lipstick on a suburban-sprawl pig. Boulder, while surely better than Phoenix in this regard, still has many surface parking lots and overlywide streets. This is one of many reasons
to reduce or eliminate our parking mandates. Less parking means less dark pavement and more space for greenery, housing or other more productive uses.
When opportunity presents itself, such as when a street is being reconstructed, we should also consider narrowing existing streets. Many of our streets, especially local ones, were built too wide. Narrowing them and using the reclaimed space for landscape plantings would have many benefits: calming traffic and improving safety, reducing stormwater runoff, and making walking more pleasant, as well as moderating summer heat.
Street rain gardens are a way to get some of the benefits of street-narrowing at much less expense. They are small areas, less than the size of one parking space, that have been “depaved”, filled with permeable gravel and plantings (including trees), and designed so street stormwater can flow into them. They add cooling greenery and can make pedestrian crossings safer while absorbing rain and using it to recharge groundwater aquifers.
We should also be thinking harder about how to build in a hotter world. Several of our land use code provisions are designed to maximize buildings’ (and their occupants’) exposure to sun.
For instance, the site review criteria that regulate larger projects require “protect buildings from shading by other buildings.” As the climate warms, our regulations should recognize that access to shade will become more important. And whether it’s heating or cooling season, sharing walls is the most effective way to reduce energy loss.
Urban heating is not just a matter of discomfort. It’s an issue of equity. In Boulder, exclusionary zoning restricts many leafy areas like Mapleton Hill and University Hill to those wealthy enough to buy a detached house. People of lesser means, if they can live in the city at all, are pushed to parts of town with wide streets, big parking lots, and few mature trees — areas that will suffer the greatest heat-island effects.