El Niño continued for a third straight month, with no signs of weakening or dissipating. Forecasts keyed in on persistent sea surface temperature (SST) anomalies (Figs. 1–2), along with weakening trade winds, ongoing convective activity, and El Niño-related ocean-atmosphere coupling. If these conditions continue, we are likely to see the effects of a moderate El Niño event–or stronger if conditions continue to strengthen. Spring forecasts have a higher degree of uncertainty, owing to the so-called spring predictability barrier, a likely source of vacillations in recent forecasts.
Current forecasts offer a consistent and bullish forecast compared to last month, when they were integrating mixed signals regarding the strength of El Niño. On May 12, the Japan Meteorological Agency reversed course with an observation that strengthening El Niño conditions in the equatorial Pacific reflected an ongoing El Niño event that was likely to last through at least fall 2015. On May 12, the Australian Bureau of Meteorology upgraded its tracker to official El Niño status, identifying persistent SST anomalies, weak trade winds, and increasing ocean-atmospheric coupling serving as indicators this El Niño event was strong enough to extend into 2015. On May 14, the NOAA-Climate Prediction Center (CPC) extended its El Niño advisory with a 90 percent chance that El Niño will continue through summer 2015 and an 80 percent chance the event will last through 2015 (Fig. 3). The CPC pointed to positive SST anomalies, along with ongoing ocean-atmospheric coupling and dateline convection activity, as indicators of a weak to moderate El Niño event that will likely continue for most of 2015. On May 21, the International Research Institute for Climate and Society (IRI) and CPC forecasts confirmed we are in the midst of an El Niño event that appears to be strengthening, with the current forecast suggesting a moderate to strong El Niño event persisting into 2016. The North American multi-model ensemble shows a moderate event extending through the spring, with potential for a strong event by summer or early fall (Fig. 4).
After a series of fits and starts, the pieces finally seem in place for the El Niño event forecasters expected to start last year. This is partially evidenced by the recent above-average precipitation and below-average temperatures in Arizona and New Mexico in late April and early May—exactly the sort of springtime weather we might expect to see if El Niño conditions were present and affecting our weather patterns. If the event persists into fall and winter 2015, and particularly if it remains a moderate to strong event, we will likely see patterns of above-average precipitation in the Southwest. There is also the possibility of a repeat of the 2014 tropical storm season, in which conditions favorable to El Niño were thought to have driven the increased tropical storm activity in the Southwest.
It may not be news to anyone who follows weather forecasting and climate outlooks, but winter 2014–2015 did not play out as expected. Last year, long-term seasonal forecasts keyed in on conditions favorable to the development of an El Niño event and suggested we were more likely to see above-average precipitation in our winter months. This was welcome news to a region that has been affected by a long-term and persistent drought, but rather than sustained above-average precipitation, we saw highly variable precipitation between October 2014 and April 2015 (Fig. 1) and cumulative water year-to-date precipitation that is below average across much of Arizona and parts of New Mexico (Fig. 2 on page 2). Temperature was much less variable, with record or near-record warm average temperatures across most of the western U.S. (Fig. 4 on page 2). So what does this mean for some key areas of concern in the Southwest?
Snowpack and water supply: The combination of below-average winter precipitation and above-average winter temperatures across the western U.S. meant there was less snow in the mountains and that it melted sooner in the season, which has implications for 2015 water supply. There was below-average precipitation overall, and precipitation that did occur often fell as rain instead of snow, with some losses to infiltration (owing to drier soils and the long-term drought) and sublimation (snow essentially evaporating associated with above-average temperatures and low relative humidity). Above-average temperatures also drove earlier-than-normal snowmelt, with most of the western U.S. recording well below-average snow, and many areas were snow-free far in advance of normal.
Wildfire: The repeated incursions of precipitation associated with an above-average eastern Pacific tropical storm season and rainfall tied to typical monsoon patterns drove the growth of fine fuels in the Southwest. This presents an increased fire risk when these fuels dry out, especially when the monsoon is ramping up and we see instances of dry lightning during building storms. The counterpoint is our recent pattern of mild temperatures, increased humidity, and the occasional rainstorm, all of which have tamped down the wildfire risk in the Southwest. This can change quickly if we get the sustained period of windy weather with low relative humidity and high ambient temperatures that is typical of late May and early June.
Pollen, Air Quality, and Human Health: The combination of precipitation last fall and elevated winter temperatures resulted in a banner year for wildflowers in the Southwest but also high pollen counts. Seasonal allergy sufferers will almost certainly already be aware of this, but cumulative exposure to an increasing level and diversity of pollen likely affects those with only infrequent or occasional allergy symptoms as well.
Precipitation: In the past 30 days, most of New Mexico and much of central Arizona recorded well above-average precipitation (Fig. 1). Climatologically, this is one of the drier times of year for the Southwest, so any substantive precipitation during this timeframe is generally unexpected but welcome, as it helps tamp down fire risk. Water year observations since October 1 demonstrate the persistent and ongoing drought, with most western states, including Arizona, recording large areas of below-average to well below-average precipitation (Fig. 2). New Mexico and the eastern side of Colorado, Wyoming, and Montana have benefitted from some late season storms, but that rainfall on the other side of the Continental Divide, does not necessarily help the water situation in the Southwest.
Temperature: Lingering storms and above-average humidity contributed to mild and pleasant conditions across the Southwest, with temperature anomalies in Arizona and New Mexico between 2 and 6 degrees below average across the region in the past 30 days (Fig. 3). This counters more than six months of record or near-record warm average temperatures that have persisted in the Southwest and the western U.S. since the water year began on October 1 (Fig. 4).
Snowpack & Streamflow Forecasts: The late-season push for cooler than average weather had little impact on snowpack, and as of May 13, snow water equivalent (SWE) was far below average across the western U.S. (Fig. 5). Above-average temperatures and below-average precipitation, both contributing to a meager snowpack, were primary drivers in this pattern and resulted in below-average forecasts for streamflow (Fig. 6)
Drought & Water Supply: The U.S. Drought Monitor highlights persistent drought conditions across the West, with particularly severe conditions in California and Nevada, and emphasizes primarily long-term drought conditions across most of Arizona and much of New Mexico. Total reservoir storage was 44 percent in Arizona and 26 percent in New Mexico (see reservoir storage on for details). Below-average snowpack and above-average temperatures have resulted in earlier-than-normal melt-out in numerous areas and losses associated with sublimation and infiltration.
Wildfire: Mild spring weather, above-average precipitation, and relative humidity have resulted in reduced wildfire risk in Arizona and New Mexico so far this season. This can change quickly, especially since precipitation during the 2014 tropical storm season contributed to abundant fine fuels, which can escalate wildfire risk when the region eventually dries out. An early or even on-time start to the monsoon could limit the window of highest wildfire risk, but a delayed start could extend it, especially given the dry lightning associated with summer storms.
Precipitation & Temperature Forecasts: The May 21 NOAA-Climate Prediction Center seasonal outlook predicts above-average precipitation this spring into summer for much of the Southwest and Intermountain West, although California and most of Arizona are notable exceptions. Temperature forecasts remain split across the region, with elevated chances for above-average temperatures along the West Coast and eastward into Arizona (and most of the western U.S.), and increased chances for below-average temperatures in western Texas and into eastern New Mexico.
We're introducing a new podcast series that focuses on quick and timely reporting on important climate news and information. We will emphasize stories that relate to the southwest, but we'll also include other climate related news that illustrate the impact of climate on national or global scales. And Mike, Zack, and Ben will still take a deeper look at southwestern climate issues in the monthly CLIMAS Southwest Climate Podcast. This episode, we're focused on record warm temperatures, drought, and snowpack across the west, along with a few stories that illustrate the downstream impact of these conditions.
2014 Was a Record Warm Year - 2015 May Challenge This Record
Globally, 2014 was the warmest year on record. This pattern was repeated in the southwest, where Arizona, California, and Nevada all had record warm average temperatures in 2014, while New Mexico, Utah, Idaho, Washington, and Oregon were all in the top 5 of warmest years on record (Fig. 1).
2015 is continuing this trend, where the January – March 2015 saw record warm average temperatures for 7 states, Arizona, California, Nevada, Utah, Wyoming, Washington and Oregon, while Montana, Idaho, Colorado and New Mexico were all in the top 10 warmest on record(Fig. 2).
Both states do get water from the Colorado River (Fig. 4), but as of yet, neither has seen mandatory reductions, although water managers are closely monitoring Lake Mead with projections it might drop to 1075’ within the next few years (Fig. 4 inset) – which would trigger mandatory reductions in some allocations. Arizona water leaders are concerned about the drought, but they have been planning for possible shortages for decades.
Bark Beetles are attacking trees that are stressed by climate change
Drought and warmer temps aren’t the only things that come with climate change. These changes also alter the ecosystem dynamics as plants and animals respond to climate stressors. Bark Beetles are tiny winged beetles that have been attacking North American forests for a long time. But lately these beetles have gone into overtime and are attacking trees that are stressed by climate change (Fig. 5).
Trees that were “born” during mini-ice age in 1800s are stressed by warming trends and the beetles are exploiting the reduced defenses associated with this stress. They are sometimes felling as many as 100,000 trees a day. Other genetic sub-populations that are more adapted to warmer temperatures are more resilient and the beetles don’t hit them as hard (or at all). Because of droughts and shorter winters, the trees are more stressed, and fewer beetles are killed off in winter freezes, and bark beetles have killed billions of trees in what will probably be the largest forest insect outbreak ever. 10 times the size of any past outbreak.
Some real estate agents have seen the prices of home plummet from “viewshed contamination” in areas destroyed by the bugs (Fig. 6). As climate change continues to warm the forests in North America, these bugs are expected to continue to thrive. This means more beetles in the future, preying on bigger chunks of forested areas across the county.
One way to understand this snow deficit is to look at Tahoe City, California. From October 1, 2014 through March 31st 2015 only 19.5 inches of snow had fallen. That is 143.1 inches below average. Almost 12 feet less of snow! An airborne snow survey was conducted by NASA’s Jet propulsion Laboratory over the Tuolumne River Basin on March 25th and the snowpack water content is 34 billion gallons less than last spring. California has had a wetter April but as is the case with the drought across the western united stats - to make a dent in a multiyear drought, it requires multiple years of above average precipitation.
20 percent of California’s generation came from hydropower during the first 6 months of each year from 2004 to 2013. However, during the first half of 2014, only 10 percent of California’s generation came from hydropower. (Fig. )
California is turning to natural gas to make up for the loss in generation. When a month’s hydropower generation dips under 10-year average levels, monthly natural gas generation often rises above its average. Wind and solar are also helping in the fight. Wind generation surpassed hydro generation in California for the first time in February and March of 2014. (Fig. )
According to the National Climate Assessment and other recent publication, warmer air temperatures and more frost-free days have advanced the start time of pollen production. This is leading to an earlier and longer pollen season. Also because the levels of CO2 have increased, this has enhanced photosynthesis making pollen-producing plants bigger. Bigger plants, more pollen, more allergies. Warming temperatures have changed the spatial distribution of pollen. Ragweed, a rare type of pollen for the United Kingdom, was reported at record levels for the first time in the East Midlands in September of 2014. In 2001 7.3 percent of the U.S. suffered from asthma. In 2010 the number rose to 8.4 percent. The scientific community believes climate change could be contributing to this change.