Parched and drenched – we can expect both in the Northwest

March 15, 2017
By Sonia A. Hall

The snow-covered landscape, the Columbia River, and the pine forests covered with signs of the recent ice storm provided the backdrop for the Climate Impacts to Water Conference, hosted by Washington State University Extension. University of Idaho climate scientist John Abatzoglou gave a plenary talk, titled Parched and Drenched: Future Climate and Water Resources in the Pacific Northwest (check out the recording here).

What I really liked about Abatzoglou’s presentation was that he focused on one key number, and then got into the weeds of what it means and why it’s important to us. That key number in this case was the fact that the Northwest has seen an increase in average temperatures of 1°C (that’s almost 2°F, if you prefer Fahrenheit), which has mostly occurred in the last 50 years. Is this an important change, and should we care? Yes, because this past temperature increase has already led to more rain and less snow, a reduced winter snowpack, and spring runoff coming earlier in the year, leaving us drier in the summer.

But even more important is what this tells us about the future. Climate change projections give us a pretty good picture of what to expect. And that picture tells us that continuing this trend—and you can expect another 1 to 2°C increase (say around 5°F) by the middle of the 21st century—could mean that the wet gets wetter (drenched, actually), and the dry gets drier, and for longer (parched).

Droughts in the Northwest have historically lasted one or two years, while they have lasted longer in other regions, like California. The Palmer Drought Severity Index is a measure of dryness, and values under -2 (shown with the red line) represent moderate drought. Graphs obtained from NOAA National Centers for Environmental information, Climate at a Glance: U.S. Time Series, Palmer Drought Severity Index (PDSI), published February 2017, retrieved on February 9, 2017 (http://www.ncdc.noaa.gov/cag/).

 

Let’s start with “parched.” In the Northwest, we are relatively lucky in that, historically, droughts have lasted one or two years, no more (think of how different it’s been in California over the last 5 years). So farmers, ranchers, irrigators and others are pretty good at rolling with those dry-spell punches, and coming back to business as usual in quick order. According to Abatzoglou, another 1°C or more increase in average temperature could make droughts—like the one we saw in 2015, for example—three times more likely to occur. So you could still roll with those punches, but you’ll have much less time to recover compared to what you have now.

And that’s not all. The climate models that Abatzoglou and others work with are projecting longer, multi-year droughts for the Northwest’s future. That’s a whole new ball game. What you need to do to survive and come back from a three- or five-year drought may well not be the same as gets you through just one bad season. The return on investing in high-efficiency irrigation systems may look very different. Building up soil organic matter to maintain more moisture in the soil—which can take decades to do—may also have a different return. Using all your water for perennial crops, when you may have big dips in water availability in the future, may not be as good of an investment. These are the things that climate research like Abatzoglou’s should have us thinking about, evaluating, testing, and sharing with others in the agricultural and research community in the Northwest.

Droughts and floods in our future. Left: tomato plants in drought-stricken California, watered with an underground micro irrigation system (photo by Phil Hogan/USDA under CC BY 2.0). Right: flooding of the Chehalis River, Washington, in January 2009 (photo by Washington Department of Transportation under CC BY-NC-ND 2.0).

Now that I’ve brought on the parching doom and gloom, let me move on to drenching. When you look at projections of precipitation for the region, annual precipitation is not expected to change very much. And the direction of change is uncertain: some models project increases in precipitation, and others project decreases. But in the same way that warming of 1°C on average is hard to really understand, annual precipitation does not tell us that much. What I took away from Abatzoglou’s presentation, though, is that climate models are in closer agreement in projecting that the intensity of precipitation—that is, how big the storms will be—will increase. They are also projecting that the “atmospheric rivers” that drive big storms on the west side will become more frequent. So the Northwest will get bigger storms, and more often, whether it all adds up to more rainfall overall or not.

These are serious impacts. But they should not be thought of as paralyzingly serious. We’ve seen the impacts of big storms. Where and what to farm or grow, how much native habitat to keep by the rivers (habitats where flooding is a natural process), water management and water storage projects, flood preparedness, response to flooding… All these are aspects that, individually or collectively, we can make different choices on. What climate information—and the oh-so-valuable interpretation of what it all means—can give us is a heads up on what’s coming. It can allow us to make informed choices now, that will ensure Northwest agricultural producers, and the communities that they support, can prepare for future drenching and parching, and be ready to roll with the new punches, and come out on top.

 

This article is also posted on the Agriculture Climate Network blog

Filed under Climate Change

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