Wednesday, June 22, 2016

What does our drought look like so far this year?

If you lived in the Inland Northwest last year, you will remember the extent of the severe drought which played a huge role in the extreme fire season that we experienced. When fire season ended last year, 913,430 acres burned, which broke the record that was previously set in 2014 of 367,199 acres. 

There are many factors to look at when trying to identify if we're facing a drought season again, and will it be as severe as last year. One of the largest factors is the snow pack that our mountains received. Washington and the Idaho Panhandle received more snowfall than the previous year but not quite to the level that would be considered normal. Although Spokane is not in the mountains, it is a good representation of how the snowfall varied from the previous year. Spokane typically receives an average of 44.9" of snow, but the winter of 2014-2015 brought only 17.6" of snow. This last winter brought 34.2" of snow, double what the previous winter received,with 24.1" of snow accumulating in December alone. Even though that is still below average, that has helped slow the onset of another extreme drought like last year. 

When we started May off last year, the drought was already in effect for most of the Inland Northwest. Compare that to this year, we are already looking at better conditions, but that does not mean that those conditions won't worsen over the next few months. At the start of May 2015, we can see that all of Idaho, Oregon, and a large portion of Washington had some sort of drought that was effecting the area. When we look at the same week in 2016, only a small portion of Washington and Idaho is classified as a D0 (abnormally dry). Oregon has a worse drought in May 2016 compared to how Washington and Idaho look but they are still better off than they look from 2015 with levels only reaching a D1 (moderate drought)
U.S. Drought Monitor: May 2015 (left) vs. May 2016 (right)

When we fast forward a month and a half, we can see that the drought back in 2015 worsened for most of the West. In 2015, the southern portion of Washington stayed in a severe drought while the north eastern portion was upgraded from a moderate drought to a severe drought. When we look at how look at how 2016 has advanced, Washington went from have a D0 (abnormally dry) over the southern portion along the Oregon boarder to a D0 across most of the State as well as the Idaho Panhandle. The Southern portion that was only at a D0 has been upgraded to a D1 (moderate drought). Although it looks like we will have some type of drought over Washington, we will have to see how it advances over the coming months.
U.S. Drought Monitor: June 2015 (left) vs. June 2016 (right)

Due to the drought that was already in place in May of last year, many of what we call fire fuels, were ready to burn starting early in the season. We have a classification for what we call fire fuels based on the size of the object. We have 10 hour fuels (1/2" diameter), 100 hour fuels (1-3" diameter), and 1000 hour fuels (3-8" diameter).The fuels hours represent the modeled moisture content of dead fuels based on the min and max temperature of the day, relative humidity as well as the precipitation from the previous 24 hours. We are going to look at the 100 hour fuels which, based on our classification, would be small trees. 

When we look at the two maps below, we can see that at the beginning of May, a majority of our fuels contained less moisture than the previous year. The fuels in the Idaho Panhandle during this time frame contained much more moisture than the previous year, limiting their burn ability. The fuels East of the Cascades were also contained more moisture than last year, although it is not much more.
100 Hour Fuels: May 5, 2015 vs. May 3, 2016

When we compare that to this week in June, we can see that there has not been a large change in the fuels for the Idaho Panhandle or the Eastern portion of Washington. This is mainly due to the cool off that we had this last week that brought moisture to most of the area. Before the cool off that started on June 10th, the fuels were drier than 2015. The current forecast for the next week is showing a drier and warmer forecast for most of the area, meaning that our fuels are going to be drying out once again.
100 Hour Fuels: June 16, 2015 vs. June 14, 2016

These next maps show what the stream levels looked like in 2016 and how that they compare with last year. We can see that there were more locations in the Cascades that were much below normal than in 2016. However, that does not mean that we are not going to experience some level of drought this year. We are going to look at a few of these locations in more depth and try to understand how we currently compare to last year.  

Stream flow levels: 2015 (left) vs. 2016 (right)

The first river we will look at is the Spokane River. We can look at how June 13, 2016 compares to the exact day a year ago. We can see that with very little snowfall during the winter of 2014-2015 that the river was already at low levels even during the middle of June. Compare that to a year when there was more snowfall on the ground and you can tell that the stream flow is much higher. Although the Spokane River flow is currently only in the 7th percentile of where we should be in mid-June, we are still starting out the summer better this year than we were at this time last year. 
Spokane River Stream flow from January 1, 2015- June 13, 2016

Wenatchee was another location where the stream flow level was much below normal, but compared to where we were last year, we have made a slight improvement. We can also see that the stream flow for this spring was higher than last year thanks to the snowpack in the mountains. 

Wenatchee River  Stream flow from January 1, 2015- June 13, 2016

When we look at the Kettle Rive up near Ferry, WA, we are seeing a very similar trend to Wenatchee. There is a increase in the stream flow but it is not quite as impressive as the Spokane River. We can also see that there was higher spring runoff thanks to the higher snowpack in that basin this past winter.
Kettle River Stream flow from January 1, 2015- June 13, 2016

The last location we are going to look at is St. Joe River in Calder, ID. We can see that the stream flow is about the same level for both 2015 and 2016 but the timing of the peak was different. For 2015, the peak flow was around March and April while in 2016 it was more towards May and lasted a lot longer. The current flow in the St Joe is in the 11th percentile of what we would expect for this time of the year.

St. Joe River Stream flow from January 1, 2015- June 13, 2016

As you can see, the stream flow for almost all locations across the Inland Northwest have had improvement from last year. It's important to note that although we do have more flow in many locations than we did at this time last year, many rivers are still far below their average flows and will continue to drop through the summer. This means that we can expect to hit low flows earlier in the season, which can have impacts on water rights, fish, and groundwater levels, among other things. 

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