Mohammad Reza Alizadeh, Massachusetts Institute of Technology (MIT) and Mojtaba Sadegh, Boise State University

As wildfire risk rises in the West, wildland firefighters and officials are keeping a closer eye on the high mountains – regions once considered too wet to burn.

The growing fire risk in these areas became startling clear in 2020, when Colorado’s East Troublesome Fire burned up and over the Continental Divide to become the state’s second-largest fire on record. The following year, California’s Dixie Fire became the first on record to burn across the Sierra Nevada’s crest and start down the other side.

We study wildfire behavior as climate scientists and engineers. In a new study, we show that fire risk has intensified in every region across the West over the past four decades, but the sharpest upward trends are in the high elevations.

High mountain fires can create a cascade of risks for local ecosystems and for millions of people living farther down the mountains.

Since cooler, wetter high mountain landscapes rarely burn, vegetation and dead wood can build up, so highland fires tend to be intense and uncontrollable. They can affect everything from water quality and the timing of meltwater that communities and farmers rely on, to erosion that can bring debris and mud flows. Ultimately, they can change the hydrology, ecology and geomorphology of the highlands, with complex feedback loops that can transform mountain landscapes and endanger human safety.

Four decades of rising fire risk

Historically, higher moisture levels and cooler temperatures created a flammability barrier in the highlands. This enabled fire managers to leave fires that move away from human settlements and up mountains to run their course without interference. Fire would hit the flammability barrier and burn out.

However, our findings show that’s no longer reliable as the climate warms.

We analyzed fire danger trends in different elevation bands of the Western U.S. mountains from 1979 to 2020. Fire danger describes conditions that reflect the potential for a fire to ignite and spread.

Over that 42-year period, rising temperatures and drying trends increased the number of critical fire danger days in every region in the U.S. West. But in the highlands, certain environmental processes, such as earlier snowmelt that allowed the earth to heat up and become drier, intensified the fire danger faster than anywhere else. It was particularly stark in high-elevation forests from about 8,200 to 9,800 feet (2,500-3,000 meters) in elevation, just above the elevation of Aspen, Colorado.

We found that the high-elevation band had gained on average 63 critical fire danger days a year by 2020 compared with 1979. That included 22 days outside the traditional warm season of May to September. In previous research, we found that high-elevation fires had been advancing upslope in the West at about 25 feet (7.6 meters) per year.

Cascading risks for humans downstream

Mountains are water towers of the world, providing 70% of the runoff that cities across the West rely on. They support millions of people who live downstream.

High-elevation fires can have a significant impact on snow accumulation and meltwater, even long after they have burned out.

For example, fires remove vegetation cover and tree canopies, which can shorten the amount of time the snowpack stays frozen before melting. Soot from fires also darkens the snow surface, increasing its ability to absorb the Sun’s energy, which facilitates melting. Similarly, darkened land surface increases the absorption of solar radiation and heightens soil temperature after fires.

The result of these changes can be spring flooding, and less water later in the summer when communities downstream are counting on it.

Fire-driven tree loss also removes anchor points for the snowpack, increasing the frequency and severity of avalanches.

Frequent fires in high-elevation areas can also have a significant impact on the sediment dynamics of mountain streams. The loss of tree canopy means rainfall hits the ground at a higher velocity, increasing the potential for erosion. This can trigger mudslides and increase the amount of sediment sent downstream, which in turn can affect water quality and aquatic habitats.

Erosion linked to runoff after fire damage can also deepen streams to the point that excess water from storms can’t spread in high-elevation meadows and recharge the groundwater; instead, they route the water quickly downstream and cause flooding.

Hazards for climate-stressed species and ecosystems

The highlands generally have long fire return intervals, burning once every several decades if not centuries. Since they don’t burn often, their ecosystems aren’t as fire-adapted as lower-elevation forests, so they may not recover as efficiently or survive repeated fires.

Studies show that more frequent fires could change the type of trees that grow in the highlands or even convert them to shrubs or grasses.

Wet mountain areas, with their cooler temperatures and higher precipitation, are often peppered with hot spots of biodiversity and provide refuges to various species from the warming climate. If these areas lose their tree canopies, species with small ranges that depend on cold-water mountain streams can face existential risks as more energy from the Sun heats up stream water in the absence of tree shading.

While the risk is rising fastest in the high mountains, most of the West is now at increasing risk of fires. With continuing greenhouse gas emissions fueling global warming, this trend of worsening fire danger is expected to intensify further, straining firefighting resources as crews battle more blazes.

Mohammad Reza Alizadeh, Postdoctoral Researcher in Environmental Engineering, Massachusetts Institute of Technology (MIT) and Mojtaba Sadegh, Assistant Professor of Civil Engineering, Boise State University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

The Lower 48 saw a 3% rise in S/VS, w/ big jumps in the Mid-Atlantic and Northeast. The Central/Southern Plains continue to have high levels of S/VS. Most of the West and Southeast (except FL) have low levels.

Click the link to read the article on the Aspen Journalism website (Heather Sackett):

Fueled by a deep snowpack that hit record highs in some areas, spring streamflow is forecasted to be well above average across the Western Slope.

According to the April Water Supply Outlook Report from the National Resources Conservation Service, streamflows are forecast to be 184% of median in the Yampa/White/Little Snake River basin; 173% of normal in the Gunnison River basin; 171% of median in the San Miguel/Dolores/Animas/San Juan basin. The mainstem of the Colorado River headwaters lagged behind other areas of the West Slope with a predicted 118% of normal streamflow.

The Roaring Fork River basin is forecast to hit 136% of median streamflow; the Eagle River basin is at 105% of average and the Blue River is at 94% of median. At the confluence of the Roaring Fork and Colorado rivers in Glenwood Springs, streamflow is forecast to be about 140% of normal.

“I think the biggest takeaway is that really substantial March precipitation across the state, particularly in western Colorado, really boosted the streamflow forecast,” said Karl Wetlaufer, a hydrologist and assistant supervisor with the NRCS Colorado Snow Survey. “A pretty substantial proportion of western Colorado SNOTEL sites had record-high or second-highest snowpack accumulations for the month of March and that was going on top of a snowpack that was already quite substantial.”

SNOTEL, or snow telemetry, sites are remote sensing stations throughout the West’s mountainous watersheds that collect weather and snowpack data. Most sites have been collecting data for about the last 30 or 40 years. According to the report, up to 30% of the SNOTEL sites in the state reached a record or near-record snow depth and snow-water equivalent. Snow-water equivalent (SWE) is a measure of how much water is contained in the snowpack.

The southwest corner of the state was the big winner for March precipitation, with the combined San Miguel/Dolores/Animas/San Juan river basins receiving 326% of median snowfall. The Sharkstooth SNOTEL site in the Dolores basin ended March with a whopping 532% of median precipitation.

With warmer temperatures this week, it’s likely that much of the Western Slope has already turned the corner, hitting peak snowpack and beginning to melt out. In the Roaring Fork basin, most SNOTEL sites started seeing a decrease in snowpack around April 9 or 10.

“It’s definitely looking like this may have been peak snowpack statewide in the last week or so,” Wetlaufer said. “You can always get another pulse that can top it, but I think it would take a significant input of snow to achieve a new peak beyond what we have seen.”

As that snow turns to water it will begin to fill Colorado’s depleted reservoirs. For many of the reservoirs, Wetlaufer said, inflow is forecast to be more than the reservoir’s total capacity.

“It’s encouraging that this year will most certainly help to fill most if not all reservoirs,” he said.

After two years of drought, in March 2022, Ruedi Reservoir on the Fryingpan River above Basalt hit its lowest level in two decades. This year, Ruedi is on track to fill, with a forecasted 107% of average inflow. The reservoir is currently at about 61% full.

“We should have the best opportunity to reach a full fill since 2019,” said Tim Miller, a hydrologist with the U.S. Bureau of Reclamation, which operates Ruedi Reservoir.

As spring progresses, water managers will get a clearer picture of what this year will bring. Scientists are gaining a better understanding that what happens in the weeks following peak snowpack can have an outsize influence on the year’s water supply and that the April numbers may no longer be a reliable benchmark.

In particular, timing of the melt out can be hard to predict. High temperatures, lots of sun and dust on snow, which increases the melt rate, could all combine to cause flooding in some areas.

“I think the timing of this runoff is something I would advise people to watch closely, both for reservoir management and for the flood potential,” Wetlaufer said. “With this much water stored in the snowpack across western Colorado, if it does come down all at once, the rivers are most certainly going to be flowing fast and furious.”

Dave Kanzer, director of science and interstate matters with the Colorado River Water Conservation District, said the good news is that there should be enough water for nearly all users in western Colorado this season and that most reservoirs, including Paonia, Ridgway, Granby and others, should fill and spill. But regionally, even this winter’s record-breaking snowstorms won’t be enough to replenish the nation’s two largest reservoirs Lake Powell and Lake Mead, which are 23% and 28% full, respectively.

The March forecasts from the Bureau of Reclamation, which manages Powell and Mead, predicted that the most probable estimate of inflow into Lake Powell this year would be 10.9 million acre-feet, which is 113% of average. According to Reclamation’s estimates from March, 10.9 million acre-feet of inflow would result in raising Lake Powell’s elevation to 3,552 feet, or about 33% full, as of Dec. 31, 2023.

“One year does not bust a drought,” Kanzer said.

Click the link to read the article on the NOAA website (Emily Becker):

Well, that was quick! Just two months ago I was writing about La Niña for what seemed like the 97^th month in a row, and then by March La Niña had departed. Today we’re hoisting an El Niño Watch, meaning that conditions are favorable for the development of El Niño conditions within the next 6 months. In fact, there’s a 62% chance of El Niño conditions for the May–July period. Read on for the reasoning behind the outlook, thoughts about the potential strength of El Niño, and implications for global weather and climate.

Let’s run some numbers

The March average sea surface temperature in the Niño-3.4 region, our primary monitoring region for ENSO (El Niño/Southern Oscillation, the whole El Niño-La Niña system), was 0.2° Celsius (~0.4˚Fahrenheit) below the long-term average, according to ERSSTv5. This is solidly in the ENSO-neutral range, that is, between -0.5 and 0.5 °C difference from average.

The atmosphere is also looking quite neutral, overall. In March, both the Southern Oscillation Index and the Equatorial Southern Oscillation Index were close to zero. Both of these indexes measure the strength of the atmospheric component of ENSO, via the relative surface pressures in the western and central-eastern Pacific. Negative index values indicate the Walker circulation is weaker than average, an El Niño response, while positive values tells us the west-east pressure difference is greater than average, indicating a strengthened Walker circulation—a La Niña response. Near-zero, like the current values, tells us that the atmospheric patterns are near average over the tropical Pacific Ocean.

Onward!

That’s where we are… but where are we going?? There’s a 62% chance that El Niño will develop during the May–July period, and more than 80% chance of El Niño by the fall.

We spend a lot of time and effort monitoring and predicting ENSO because it can give us an idea about upcoming potential weather and climate conditions (and because it is a fascinating natural system!). When El Niño or La Niña are holding court in the tropical Pacific, they can affect global temperature and rain/snow patterns in specific ways, with the strongest impacts during the winter. Since ENSO can be predicted months in advance, we can start playing the odds on what sort of climate patterns can be expected. There is a lot of variety, and no prediction is ever perfect! But it’s currently the best tool we have to anticipate upcoming seasonal conditions.

I’ll get back to the potential impacts of El Niño in a minute—first, let’s discuss this confident forecast. Forecasts made during the spring are often less accurate than those made other times of the year. ENSO tends to change phase during the spring, and the tropical Pacific ocean-atmosphere system can be more susceptible to smaller pushes like short-term weather variations, contributing to the “spring predictability barrier.” So it seems the forecasters are really feeling their oats this month, to be giving El Niño such relatively high odds. What’s behind this?

First, the latest runs from our computer climate models are providing very high probabilities that El Niño will develop this year. When there is a lot of agreement among the models, we tend to give more credence to their predictions. For some examples, here’re Niño-3.4 forecasts from the European multi-model ensemble, Australia’s ACCESS-S2, and the North American Multi-Model Ensemble.

But it’s not just model advice supporting the forecast. We always keep an eye on the temperature of the water under the surface of the tropical Pacific. After many months cooler than average, the amount of warmer subsurface water has increased over the past month as a downwelling Kelvin wave—an area of warmer water that sloshes from the west to the east beneath the surface—traverses the tropical Pacific.

This warm subsurface will provide a source of warmer water to the surface over the next couple of months and helps provide confidence in the forecast.

Further bolstering the chance for El Niño is a short-term forecast for the Madden-Julian Oscillation (MJO). The MJO is an area of storminess that travels west-to-east along the equator. It’s flanked by wind anomalies, as surface level winds rush toward the area of storminess. The MJO is predicted to be in a phase that will weaken the trade winds (the consistent east-to-west winds near the equator) over the next couple of weeks. Weaker trade winds allow the surface to warm and can contribute to the growth or propagation of downwelling Kelvin waves.

One more observation supporting the potential development of El Niño is the currently very warm far-eastern Pacific. The Niño-1+2 index, which measures the sea surface temperature off the coast of Peru, was near-record warm in March. A coastal El Niño like this can precede a larger El Niño event, although not always.

To summarize, there are several signs pointing to the development of El Niño, including model predictions and the current state of the ocean and atmosphere. It’s still possible that a developing El Niño will sputter out, and the forecast includes around a 1-in-8 chance of neutral conditions in the late fall. However, from our current vantage point, there is enough evidence to support a confident forecast for El Niño.

How strong of an El Niño are we talking?

That’s a lot of support for El Niño developing, but how strong it will get if it forms is a different question. Some of the models are predicting pretty extraordinary Niño-3.4 values, but we put a lot less trust in those predictions—models tend to overestimate, especially in the spring. The ENSO team has a method of predicting the strength of an El Niño or La Niña event that combines human forecasts and model predictions. This method has shown promise so far, although we’ve only been using it for a couple of years. (Lots more detail in Tom’s post on the topic.) By that method, the current chance for a strong El Niño (Niño-3.4 greater than 1.5 °C) is about 4 in 10; a clearer picture of the potential strength of El Niño will develop as we emerge from the spring barrier.

What would an El Niño mean for global climate?

Right, I promised to get back to impacts! El Niño influences the Atlantic and Pacific hurricane seasons, usually leading to fewer tropical storms and hurricanes in the Atlantic and more than average in the Pacific. In the case of the Atlantic, El Niño increases vertical wind shear—the change in wind direction and strength from the surface to higher in the atmosphere—which can impede a hurricane’s growth. NOAA’s hurricane outlook comes out next month, so keep your eyes peeled for that.

You can check out some of the El Niño-related expected temperature and precipitation patterns during June–August and December–February here. We’ll get into more detail about these potential patterns in coming months.

One last comment! ENSO has a strong relationship with the global average temperature: in general, the warmest year of any decade will be an El Niño year, and the coolest a La Niña one. Global warming means that we can’t just say “El Niño years are warmer than La Niña,” since recent La Niña years (we’re looking at you, past 3 years!) have featured much higher global averages than El Niño years from the 1990s and earlier. 2022 was the 6^th warmest year since records began in 1880, and that was with a non-stop La Niña. If El Niño develops this year, it increases the odds of record-warm global temperature.

Click the link to read the discussion on the Climate Prediction Center website:

ENSO Alert System Status: El Niño Watch

Synopsis: ENSO-neutral conditions are expected to continue through the Northern Hemisphere spring, followed by a 62% chance of El Niño developing during May-July 2023.

During the last month, above-average sea surface temperatures (SSTs) became more prominent in the western and far eastern equatorial Pacific Ocean. The latest weekly Niño-3.4 index value was 0.0ºC, but the Niño1+2 index value was +2.7ºC, indicating significant warming along the South American coast. Area-averaged subsurface temperatures also increased over the past month, reflecting the dominance of above-average subsurface temperatures across the equatorial Pacific Ocean. For the monthly average, upper-level and low-level winds were near normal across most of the equatorial Pacific Ocean. However, low-level westerly wind anomalies were evident in the first half of March associated with subseasonal activity. Suppressed convection was evident over the central tropical Pacific and over parts of Indonesia. While the warming near coastal South America was striking, the basin-wide coupled ocean-atmosphere system was consistent with ENSO-neutral.

The most recent IRI plume favors a transition to El Niño, beginning June-August 2023 and persisting into the winter. While the lower accuracy of forecasts during the spring can result in surprises, the recent oceanic Kelvin wave plus recurring westerly wind anomalies are anticipated to further warm the tropical Pacific Ocean. The coastal warming in the eastern Pacific may foreshadow changes across the Pacific basin. Therefore, an El Niño Watch has been issued, and the range of possibilities toward the end of the year includes a strong El Niño (4 in 10 chance of Niño-3.4 1.5C) to no El Niño (1 in 10 chance). In summary, ENSO-neutral conditions are expected to continue through the Northern Hemisphere spring, followed by a 62% chance of El Niño developing during May-July 2023.

Click on a thumbnail graphic to view a gallery of drought data from the US Drought Monitor website.

Click the link to go to the US Drought Monitor website. Here’s an excerpt:

This Week’s Drought Summary

This U.S. Drought Monitor (USDM) week saw continued improvements on the map across areas of the West including California, Nevada, Idaho, Montana, and Utah. In the Plains states, drought-related conditions degraded in the southern Plains in Kansas and Oklahoma. In Kansas, the past 9-month period (July 2022-March 2023) has been the 4th driest on record, according to the NOAA National Centers for Environmental Information (NCEI). In the northern Plains, the conditions on the map improved in response to recent significant winter storm events that helped to boost snowpack conditions in North Dakota where numerous weather stations broke all-time snow depth records for April, according to the North Dakota State Climate Office. In the South, a mix of improvements and degradation characterized the region’s drought status this week. Significant improvements were observed in South Texas, parts of the Hill Country, and the Gulf Coast regions where locally heavy rainfall accumulations (2 to 8+ inches) were logged. Conversely, areas of western Texas and the Panhandle saw continued degradations in response to short and longer-term precipitation shortfalls. In the Southeast, above-normal temperatures (4 to 8 deg. F) and generally dry conditions persisted across drought-affected areas of Florida. Further to the north in the Carolinas and areas of southern Virginia, improvements were made related to widespread shower activity, including some locally heavy accumulations (2 to 5+ inches), observed this past week. In the Mid-Atlantic and Northeast, short-term dry conditions and widespread low streamflow activity led to areas of degradation in Virginia, Maryland, New Jersey, New York, Connecticut, and Rhode Island. Looking at the latest climatological data released by NOAA NCEI, March precipitation across the contiguous U.S. ranked in the wettest third of the historical record (129 years) with well above-normal precipitation (falling in the top 10th percentile) observed regionally across much of the western U.S. including in California (7th wettest), Nevada (6th wettest), and Utah (3rd wettest). Meanwhile, drier-than-normal conditions for March were observed across much of the Eastern Seaboard including in Virginia, which saw its 8th driest on record. In terms of average temperatures, temperatures were above normal for March across all of the Eastern Seaboard as well as across the southern Gulf Coast states where Florida observed its 8th warmest on record. In the northern Plains and across the West, cooler-than-normal temperatures prevailed with notable anomalies observed in California (5th coldest), Nevada (5th coldest), Oregon (3rd coldest), and Utah (7th coldest). Looking at snowpack conditions across the West, record-breaking snowpack conditions were observed in the Sierra Nevada, Great Basin, ranges of the Colorado Plateau in Utah and northern Arizona, and in the central and southern Rockies of western Colorado, northern Utah, and southeastern Idaho…

High Plains

On this week’s map, deterioration occurred in the southern extent of the region in Kansas where both short and long-term precipitation deficits exist (ranging from 4 to 16 inches during the past 12-month period). Moreover, other drought-related indicators, such as surface and root zone soil moisture, are showing very low moisture levels (ranging from the 2nd to the 20th percentile) across Kansas as well as much of Nebraska, according to NASA Short-term Prediction Research and Transition Center (NASA SPoRT). In the Dakotas, deep snowpack conditions were observed this month as well as recent rapid melting which has boosted soil moisture levels significantly (leading to improvement on the map) as well as concerns over major flooding. Flood warnings have been issued for numerous rivers across the Dakotas as temperatures are expected to soar into the low 90s today (April 12) in southeastern South Dakota. According to NOAA NCEI, North Dakota logged its 32nd wettest March on record while Nebraska observed its 28th driest and Kansas its 14th driest. In terms of average temperatures, North Dakota observed its 5th coldest March and South Dakota its 16th coldest on record, For the 12-month period (April 2022-March 2023), Nebraska experienced its 11th driest on record while Kansas its 17th driest…

West

On the map, another round of improvements was made in drought-affected areas of California, Nevada, Idaho, Montana, and Utah this week. Looking at the October through March period, NOAA NCEI’s latest climatological rankings are showing above-normal precipitation in the West Climate Region (California, Nevada) as well as in the Southwest Climate Region (Four Corners states) coming in at 9th wettest (+6.31-inch anomaly) and 18th wettest (+1.83-inch anomaly), respectively. At a statewide level for the contemporaneous period, California ranked 10th wettest (+8.6 inch-anomaly), Nevada 5th wettest (+3.03-inch anomaly), and Utah 4th wettest (+3.71-inch anomaly). Looking at the latest region-level (2-digit HUC) snowpack data across the West, the NRCS SNOTEL network (April 11) was reporting the following median snow water equivalent (SWE) levels: Pacific Northwest 126%, Missouri 114%, Souris-Red-Rainy 84%, California 258%, Great Basin 246%, Upper Colorado 157%, Arkansas-White-Red 98%, Lower Colorado 417%, and Rio Grande 143%. In the Colorado River Basin, Lake Powell was at 23% of capacity and Lake Mead at 28% of capacity on April 11, according to the U.S. Bureau of Reclamation. In Arizona, the Salt and Verde River system reservoirs were 98% full as compared to 72% full a year ago, according to the Salt River Project. In California, the state’s two largest reservoirs, Shasta Lake and Lake Oroville, are 110% and 117% of their historic averages for the date, respectively. Overall, drought coverage (D1-D4 categories) in California on the map dropped to 8.79% this week as compared to 99.77% at the beginning of the Water Year (October 1, 2022). Likewise, drought coverage on the map in Utah went from 100% (October 1) to 35% this week, and in Nevada from 100% (October 1) to 23%…

South

In the South, drought-related conditions improved in areas of southern Texas in association with some locally heavy rainfall accumulations (up to 8 inches) during the past week. In other areas of the region, drought-related conditions deteriorated in isolated areas of western Oklahoma and Texas in response to precipitation shortfalls at various time scales, low streamflows (<10th percentile), poor groundwater conditions, and impacts within the agricultural sector. For the week, average temperatures across the region were below normal across Louisiana, Oklahoma, and Texas (2 to 10+ degrees F) while Arkansas, Mississippi, and Tennessee were 1 to 5 degrees F above normal. According to NOAA NCEI, the past 12-month period (April 2022-March 2023) was the 5th warmest and 33rd driest on record in the South Climate Region. For March 2023, the region saw its 35th warmest on record with a +3.0-degree F anomaly and its 51st driest on record…

Looking Ahead

The NWS WPC 7-Day Quantitative Precipitation Forecast (QPF) calls for moderate-to-heavy liquid (liquid = rain + SWE) precipitation accumulations ranging from 2 to 5+ inches across western portions of Oregon and Washington while lighter accumulations (< 1 inch) are forecasted for areas of the northern and central Rockies. The remainder of the West is expected to be generally dry during the next 7-day period. In areas of the Upper Midwest and Northeast, light accumulations (< 1 inch) are expected, while light to moderate accumulations (1 to 4+ inches) are forecasted for areas of the Gulf Coast states with the heaviest accumulations expected in southern portions of Louisiana and Mississippi. The CPC 6-10-day Outlooks calls for a moderate-to-high probability of above-normal temperatures across the southern and central Plains, South, Southeast, and the Northeast, while below-normal temperatures are expected across areas west of the Rockies and across areas of the northern Plains and Upper Midwest. In terms of precipitation, below-normal precipitation is expected across the far eastern extent of the Midwest and the southwestern portion of the Northeast region, while above-normal precipitation is forecasted for Plains states, Texas, and the northern two-thirds of the western U.S.