Here comes the rain again

Today, I am documenting a year’s worth of temperature and precipitation data from our place so that I can try to make better decisions about what I will or will not grow. Our climate in western Oregon seems to be becoming hotter and drier in summer and more chaotic in winter. Now that things are no longer “normal”, what can I expect in terms of temperature and precipitation each year?

As an aside, it was odd writing this post while sitting indoors listening to rain pour down on the skylights during a very wet spring break. The juxtaposition is perfect: planning for drought during a rainstorm.

We are often 5°F cooler in the foothills of the Coastal Mountains (~500 feet) than in Corvallis (~235 feet) and my impression is that we also get more rain and snow. Here is our daily weather log from 2022 (dates are in 30 day increments).

Our lowest temperature was 21°F, which occurred twice: once on February 24th and once again on December 17th. The highest temperature was 103°F on June 26th, exactly 1 year after the 2021 record breaking heatwave from June 26th-28th when we reached 117°F (here).

Recall that 2022 was supposed to be a wetter year than average for the PNW because of La Niña, which tends to give us colder, wetter winters. Last year, we had a total of 47.5 inches of precipitation at our place, occurring mainly from January through June 19th, and then from October 31st through the end of December. Almost a tenth of that 2022’s total fell on a single day on November 6th (4.4 inches). Our total for the year was 7.85 inches more than that from the Hyslop station in Corvallis (39.7 inches), supporting my impression that we get more rain in the foothills than down in the Willamette Valley. Even so, our summer was relatively hot (by my standards – I prefer temperatures in the 70s) and very dry from July through October. That’s about 4 months without much precipitation at all. Fortunately, we didn’t have many nearby wildfires to contend with. There was about one week where the air was smoky and the skies had a slight orange tinge, then the winds shifted and blew it away. Might be interesting to track smoke this year to see how many days we typically get.

I remember being concerned about drought during the dry stretch in January and February. Weather scientists were saying that we were behind on rainfall and that much of the state was still in drought.  I also remember that Paul Bonine over at Xera Plants said not to worry, that this was normal, and that the rains would return in March. And, they did.

Now, let’s assess the data another way and take a look at our monthly averages.

I thought it was interesting that the average difference between the minimum and maximum temperature in summer was about 15-20°F and about 5-10°F during the rest of the year. And, although the heatwaves tend to occur in June, that month is still on average about 10°F cooler than July and August, our hottest months. November and December were by far our wettest months, bringing in 41% (19.4 inches) of our yearly precipitation. July through October were the driest months, with only 4% (1.75 inches) of our our yearly total.

Curious, I wanted to see how our 2022 precipitation total compared to the 30 year average. Taking a look at precipitation maps from the Prism Climate Group and the USDA Northwest Climate Hub, I see that our place typically gets 60-70 inches of precipitation per year. So, even though 47.55 inches sounded like a lot, we actually had about 10-20 inches less than would be predicted based on the last 30 years.

PRISM map of precipitation for Oregon
Map by Janelle Christensen posted at USDA Northwest Climate Hub

This is borne out by the current drought monitor conditions for the state as shown by the National Integrated Drought Information System. We’ve now had La Niña for three winters in a row. Yet, despite that, much of the state is abnormally dry (like at our house) or under moderate to exceptional drought conditions. As Paul Bonine said over on his blog at Xera Plants, “La Nina being La Nina, but drier“.

Recently, we’ve switched to El Niño, which means that things are going to get much hotter and drier around here… and back to the constant threat of wildfire and smoke. Scary.

Reddish-orange smoke filled skies on September 8, 2020 in the foothills of the Coastal Mountains, Oregon
Smoke filled skies on September 8, 2020

So, even in a wetter and colder year than normal, it looks like I can expect at least 3 to 4 months without precipitation. That’s a long time for plants to go without water and explains why my row of arborvitae started dying when I didn’t water them last year. My goal is to get by with as little irrigation as possible while still having a beautiful garden and conserving most of our water for household use. I’ve not been very successful at selecting plants that look good after extended periods of drought and my garden tends to look bedraggled, wilted, and burnt by August. No wonder I dislike summer compared to the other three seasons. It’s depressing to see everything looking so pathetic. I want plants that will survive wet clay in winter, heat and drought in summer, and still look good. Is that too much to ask? Slowly, I’ve been transitioning to more drought adapted plants.

Sadly, this means that my row of arborvitae needs to go. I removed four of the worst ones on 3/31/2023. They had been doing so well with supplemental irrigation, but the moment I stopped, they started dying. It still makes me mad that I didn’t water them sooner and more often last year. I mistakenly assumed they were established and by the time I noticed the scales were turning brown, it was too late. Although not terribly interesting by most gardeners’ standards, they served a purpose to screen us from the road. I chose arborvitae based on their narrow growth form, which left me more room for gardening, and because there was an older, more established arborvitae hedge nearby that hasn’t needed watering at all. Now, I need to find drought tolerant replacements, most of which are going to be bulkier, wider growing plants. Italian cypress, although narrow, are not reliably hardy here. 

To be honest, I am still waffling all over the place on this. Part of me wants to replace them with more arborvitae and hope that they will fare better once they are big enough (and their roots go down far enough to reliably reach the creek’s water table). But, part of me is also excited about the opportunity to grow more interesting plants. I’m thinking Grevillea ‘Neil Bell’, California bay (Umbellularia californica), maybe a silktassel bush (Garrya elliptica) or a holly-leaved cherry (Prunus illicifolia), or an evergreen oak? But, I don’t know how well those will grow together en masse and I am worried that the county pruning crew will mutilate the heck out of them at some point. I also don’t know what the browse pressure will be from the local deer population. They haven’t ever bothered the arborvitae, but I have a feeling they would sample almost anything during a drought. I’ve already planted a juniper there (Juniperus chinensis ‘Spartan’), but for some reason I don’t see a lot of junipers in western Oregon and it makes me wonder if it will be a disease prone mess?

Anyway, that’s a wrap on last year’s weather and transitioning to drought tolerant plants. Now I can start planning and comparing this years weather to last years. Fun, fun. Off to Hortlandia in Portland tonight (4/7/2023).

This Post Has 6 Comments

  1. danger garden

    Interesting! I wish I kept more detailed records about the precip here at my location. Since I’m just a couple of miles from the airport I tend to go with that official recording and figure it’s good enough. That map by Janelle Christensen posted at USDA Northwest Climate Hub is a head scratcher though. It shows the Portland area as having 50-60″ of annual precip, whereas I’ve always heard it was around 36″. As for our plants they have to deal with some crazy extremes from winter wet and cold to summer drought and heat—sorry about your arborvitae!

    1. Garden Curmudgeon

      I agree, having a station nearby should be good enough. We just don’t have a reliable station nearby. I was also very surprised by that map, but then I was thinking that a lot has changed in the 30-year interval that it covers (I was still in high school back in 1991) and it is surprisingly difficult to find reliable weather station data. Many of the 30-year averages I found online were based on the older 1981-2011 interval, which had more dry years than the 1991-2021 interval, so so that might be part of issue. The graph here for Portland really shows how variable our weather can be from year to year (https://www.climatestations.com/wp-content/uploads/2023/01/portprcp.gif). That graph is interesting to me because it shows that our dry years are clustering together more than in the past and that it would have been VERY wet, miserable experience trying to garden back in 1875-1885.

      It takes a special plant to take the extremes that we experience here in the PNW. If I was on city water, I would probably be more apt to water during the summer. Maybe it’s time to think about storing some of the winter rain, but then we would have to find some place to put a giant ugly water tank.

  2. Kris P

    Identifying the messages in weather trends can make one crazy. Until recently, I didn’t realize that El Nino and La Nina affected the PNW differently than it does Southern California. I’d learned that was the case between us and Australia but I’d wrongly assumed that the US Pacific Coast experienced that oscillation the same way we do in SoCal. To complicate matters, climate pundits now remind us that El Nino doesn’t always mean low rainfall for SoCal and La Nina doesn’t always mean rainfall will be plentiful. In addition, a UCLA climate scientist I follow (at weatherwest dot com) also mentioned another factor (probably one among many!) that impacts our rainfall totals: the MJO Oscillation (Madden-Julian Oscillation). At that point, my eyes started to cross.

    In regard to long-term trends, I’ve heard it predicted that Los Angeles’ climate will be more like that of Baja California by 2050. Luckily, all gardening involves experimentation. Succulents have gained a greater presence in my own garden over the last 10 years.

    1. Garden Curmudgeon

      I didn’t know it affected Southern California differently than the PNW either. Weather is complicated and I was hoping that tracking it myself would make it a little more personal and easier to understand. Not sure how I would feel about adjusting to a Baja California landscape. I lived in a desert for many years (the Chihuahauan desert) and when it rains, everything seems amazingly diverse and beautiful. It’s those long, hot, bleak, brown, dry stretches in between that are so painful.

  3. Anna K

    This was an interesting read! I’m not very good at keeping track of what the weather does in my area, but I do pay attention to what scientists say. Or at least what the interpreters of science say (I admit to not reading the actual reports myself), and it’s scary. I’m a heat shy Swede, and I dread the summers here. They seem to get longer and hotter with each year. Garden-wise, I’m honestly not sure how to adjust to the ever-widening fluctuations – its becoming more and more of a crap shoot. All the defoliated “reliable” broadleaf evergreens currently in my garden are a good illustration of that.

    So sorry to hear about your Arbs. I think a lot of gardeners have made similar discoveries in recent years. Lately, I’ve become interested in junipers. There is one called ‘Skyrocket’ that might work as a replacement. It’s hardy to at least Zone 5…

    1. Garden Curmudgeon

      I dread summer too, mainly because of the heat, the smoke, and how brown/dead everything gets if I don’t water it. That is a really good point about the fluctuations between extremes. We can grow a lot of plants that take heat/drought or cold/wet, but there isn’t much that thrives under both extremes within a short time period. I like the idea of Skyrocket, I will have to see if I can find any around here to try out. I miss thunderstorms and summer rains out here on the West Coast, but I know I would also end up missing a lot of things from Oregon if we ever move somewhere else.

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