The Climate CIRCulator is a monthly newsletter covering climate science and the Northwest written by scientists and communicators.
Fire season is here. Following a very wet winter, we are in the midst of a surprisingly active fire season.
As of Monday, a total of 987,000 acres have burned in 2017 across the Northwest, encompassing the states of Washington, Oregon, Idaho, and Montana. This comes as a surprise because fire season outlooks issued just a couple months ago called for a dud of a fire season or, at the very most, an average one. The thinking was that the wet winter — one of the wettest in decades for some parts of our region — would lead to a mild summer fire season. This didn’t happen.
So what changed? How did we go from waterlogged to wilted? What explains this weather whiplash? To answer these questions, we would like to introduce you to The Northwest Climate Toolbox.
The Northwest Climate Toolbox is a suite of free online applications designed by CIRC researchers and intended to help foresters, farmers, and water managers respond to and prepare for climate variability and change. In a nutshell, the Toolbox takes in raw climatological, meteorological and hydrological information and translates them into a series of easy-to-navigate tools and interactive maps that allow users to visualize data for their location.
The Northwest Climate Toolbox currently has ten tools, or applications designed around a set of climate metrics such as temperature, precipitation, and more complex measures including the energy release component (we’ll get to that last one in a bit). These metrics are then translated into visualizations that play out in near real time — we update this data daily — so that the information is timely.
Tools in the Northwest Climate Toolbox include visualizations of short-term, seasonal forecasts (on the order of months); visualizations of historical data (going back decades); and long-term, future projections (on the order of decades out to 2100). Still more tools track how plant-growing zones are expected to shift as the climate warms and, yes, the Toolbox also tracks wildfire danger.
So what can the Northwest Climate Toolbox tell us about this year’s fire season and where earlier predictions might have gone wrong? Let’s start with the basics.
Climate, as we know, plays a crucial role in creating the right conditions for wildfires. In fact, climate plays such a reliable role in setting the stage for wildfires here in the Northwest that we even refer to a “fire season” in much the same way that we refer to the four better-known seasons.
Fire season refers to the time of the year when vegetation and soils dry and fires can start and spread. This varies from year to year, and the onset of the fire season can be delayed by abundant mountain snowpack or a cool and wet start to summer. But typically the fire season arrives in mid to late July when the Northwest settles into the hot and dry pattern of late summer. Fire season can run into September or later depending on when the fall rains arrive.
Because climate plays such a critical role in leading to wildfires, researchers have learned to ferret out and combine certain weather metrics as indicators that a potentially large wildfire season is looming on the horizon. You can think of this almost like reverse engineering fire potential from metrological metrics, such as temperature and precipitation. This is what the fire danger metric the Energy Release Component does.
The Energy Release Component effectively calculates how hot a fire could burn (the energy release part) given recent weather conditions. The Energy Release Component provides one measure of fire danger that tracks how dry the vegetation is and, therefore, how likely it is to burn given the right ignition source, say a lightning strike or smoldering cigarette butt. (It’s a little more complicated than that, but you get the idea.)
A Northwest Climate Toolbox tool called the Climate Mapper includes the Energy Release Component, mapping what is a metric of fire potential onto our region (see the map above). Okay, let’s unpack how to read the metric.
The Energy Release Component is calculated in units of heat energy (British Thermal Units) per square foot. Pat yourself on the back if those units are meaningful to you. For everyone else, we translate this data into more usable information using percentiles.
Percentiles are a ranking system of all days of the year, where the lowest value on record is the 0 percentile and the highest is the 100th percentile. The map above shows Energy Release Component percentiles for August 6th of this year.
Fire management often uses the 90th and 97th percentile to qualify days with high and extreme values, respectively. We’ve color coded the percentiles of the Energy Release Component from light brown (not a big threat of fire) to dark brown (a big threat of fire). The map, as you’ve probably noticed, has a lot of dark brown right now. This represents a wide swath of high to extreme fire danger extending across much of Oregon, Washington, Montana, and northern Idaho, covering both forested and grasslands.
What’s more, the map also shows active large fires burning in our region (these are the little fire icons, in case that wasn’t clear).
The ability to map extreme fire danger can help locate hotspots where large fires are more likely to occur. This is important and brings us back to this year’s fire season and where predictions might have gone wrong.
We know that this past winter was especially wet in the Northwest. And generally speaking, wet winters aren’t immediately followed by bad fire seasons. Ample winter precipitation, particularly mountain snow, keeps vegetation moist and less fire prone, tending to put a damper on early fire season activity. That’s at least what you might expect. But it’s more complicated than that and requires us to consider how the ingredients for fire differ across the region. Let’s start in the drier grasslands that cover much of southern Idaho, eastern Washington, and eastern Oregon.
Following a wet winter, fine fuel — especially grasses — grows quickly, thriving on the extra moisture. This pattern is very important in normally arid regions where fire activity is often limited by not having enough vegetation for fire to spread. But heat things up and dry things out, and this bumper crop of vegetation becomes a potential fuel source, heightening fire risk.
The ingredients for fire in forests are different. In our Northwest forests, there is often enough vegetation for fires to spread. However, fuels often remain wet enough throughout summer to limit fire activity. Forest fires typically burn when warmer and drier-than-normal conditions allow fuels to dry out and become ripe for carrying fire. We’ve seen more and more of these types of summers in the past couple decades, most recently during 2015, one of the bigger fire seasons in the last century across the Northwest.
Okay, let’s recap.
The main climate ingredient for wildfire activity in Northwest grasslands is ample winter precipitation, while the main climate ingredient in forest fires is a hot, dry summer. This past winter and summer served up both ingredients.
We very abruptly went from a cold, wet winter and soggy spring into the fiery and smoky fry pan of summer. After the very long and wet winter, not many anticipated such an abrupt transition. Instead, the fire outlook for the region issued in April by the National Interagency Fire Center called for a benign fire season, most notably for the region’s forests.
Since mid-May, much of the region has received less than half the amount of precipitation it typically gets. As of August 6th, many locations have logged impressive streaks of over 50 days without a wetting precipitation event, a variable we also mapped for this post using the Climate Mapper.
The dry spell coincided with warmer-than-normal conditions across the region, which helped escalate fire risk. Long story short, the abrupt transition from our cool, wet winter to a warm, dry summer has turned what was anticipated to be a dud of a fire season in our forests to a fairly active one.
Predictions, of course, are not prophecies. They are, at best, educated guesses. That said, a growing body of research has demonstrated that fire danger metrics like those used in the Northwest Climate Toolbox are good proxies for tracking regional fire activity.
So by all means, feel free to get online on try out the tools that we have developed. Let us know what you think. And we’ll keep you updated on developments in the fire season and show you some more of our work along the way.
This post is the first in an ongoing series we are calling Northwest Climate Currents. Northwest Climate Currents will use the Northwest Climate Toolbox and the data it collects to help us unpack and prepare for our region’s climate events. The Northwest Climate Toolbox is part of CIRC’s Climate Tools effort.