In Our Changing World, Microclimates Matter
Have you ever driven around in the late fall or early spring and seen the dewy fog that flows through the low places at night? The mechanism behind this is warm humid air rising from the earth. As the air rises, it cools to the dew point or near to it. This humidity or condensate allows us to see these variations in temperature in the landscape. However, that same flow of warm air rising and cool air sinking is constantly around us whether we can see it or not.
What is a Microclimate?
When you talk about climate, you’re referring to a very large region of land, where borders don’t really matter. A desert climate, temperate climate, or coastal climate cover large swaths of land where broadly, the weather conditions follow roughly the same pattern over years.
Microclimates, however, are smaller areas within that region where the conditions vary slightly. Think of things like the lee of a mountain which gets all the rain as humid air has to travel over it, and then the other side remains dry. The invisible movements of air affect the patterns of weather around obstacles in the landscape.
We see it in the vultures, riding hot rising winds above quarries, or following our pavement’s updraft. We see the footprint of our paved cities in the air above us. Heat rising from all that concrete creates a static bubble of hot air as high as it can go, which cold fronts crash into.
If the cold front is weak, or if there’s not much momentum behind it, you’ll watch as the front fails to breach the warm dome and the storms flow around us. You’ll see the most violent damage on the far side of the dome, as the bifurcated flow reconnects and there’s turbulence. Second worst is the initial contact crash point.
All this to tell you that the landscape has a climate of its own. Elevation, orientation to prevailing winds, sun, and storms, and any protection of structures or plants around us change the effects of the local climate in subtle ways.
Let’s Go Smaller – Our Garden
When I moved into my current home, I didn’t plant a single thing in the ground until I had a full year just seeing what spots were super hot or how the angle of the sun changed over the year. Even 5 years in, I’m still learning the heartbeat of this hill. A plot a mile away if it’s in a low valley can have markedly different experience in chill hours.
Why Climate Change Sucks for Gardens
We’re getting warmer winters with short sharp spikes of bitter cold below freezing. Neither are helpful for those critical hours of good REM sleep dormancy that our trees need to produce at their best. USDA climate zones were just updated in 2023 and the whole map had to be updated with the change in dormancy schedules from the last 30 years of reported data.
We’re trying to predict the impossible.
Here’s $20. Bet how many chill hours we’re going to get at this precise geographic location over the next 10-15 years. Are you going to go with historical odds without the last 20 years of data and bet on 800 – 1000 hours? What if you look at the trend over the past 20 years? Perhaps you should go with the median, which is the middle number in a set of values arranged from smallest to largest? Or are you going to follow the trend of the past 10 or so years?
