Friday, July 25, 2014

The Southwest Drought

The New York Times occasionally runs a series of maps and charts examining a variety of issues, including their latest, Mapping the Spread of Drought Across the U.S.

Drought severity across the U.S. on July 22, 2014.  Source: New York Times.  
 Drought is an under appreciated natural disaster.  The onset and end are not typically sudden, but the costs can be quite high.  If you scan the list of billion dollar weather disasters since 1980, drought appears 18 times, with combined loses of almost $250 billion in current dollars.

Droughts are often through to be periods of abnormally low rain, but they are actually quite multifaceted with considerable geographic variability.  There's more to the story than precipitation as the conditions that lead to low soil moisture are also affected by temperature and other weather, climate, and soil factors.  Although there are many different ways to both define and determine the severity of drought, the most widely used index is the Palmer Drought Severity Index (PDSI), which attempts to account for a variety of factors that affect soil moisture.

Plots like the one above derive from the U.S. Drought Monitor, which blends a number of drought measures and expert judgement.

The Southwest is currently in the grips of widespread drought, with drought conditions rated as exceptional over portions of California and Nevada (the "more" region above).  To the first order, this drought reflects the influence of climate variability.  As concluded by Hoerling et al. (2013) in the Assessment of Climate Change in the Southwest United States:
"It is likely that most of the recent dryness over the Southwest is associated with natural, decadal coolness in tropical Pacific sea-surface temperatures, and is mostly unrelated to influences of increased greenhouse gases and aerosols." 
In other words, more persistent La Nina conditions have played an important role in the long-term drought conditions.  This is not to say that global warming has had no influence on the drought.  It is an exacerbating factor with higher temperatures, by contributing to soil drying, increasing in drought coverage and intensity.

Thus, we should be cautious in attributing the current drought to global warming.  On the other hand, we also shouldn't assume that all is well and good in the coming century.  The evidence suggests a decline in water resources over the Southwest over the long term.  As discussed by Gershunov et al. (2013) in that same Assessment of Climate Change in the Southwest United States:
"Drought, as expressed in Colorado River flow, is projected to become more frequent, more intense, and longer lasting, resulting in water deficits not seen during the instrumented record (high confidence)" 
"In terms of soil moisture, drought is expected to generally intensify in the dry season due to warming (high confidence)"

Thursday, July 24, 2014

Hot Stuff

Here's four hot stuff factoids for your Pioneer Day enjoyment:

  • Yesterday's high at the Salt Lake City International Airport was 103ºF, which is tied with July 14th for the hottest day of the year so far.
  • Climatologically, this is the hottest period of the year.  From 18 July to 2 August, the average high temperature at the Salt Lake City International Airport is 94ºF and the average low is 66ºF. 
  • The overnight (through 6 AM) minimum temperature at the Salt Lake City International Airport was only 80ºF, although temperatures did dip to 79ºF just after 7 AM.  I woke up in the middle of the night and heard the air conditioning cranking and thought, whoa, it must be hot!
  • Globally, June was the hottest recorded in the instrumented record.
Source: NCDC
The heat miser is winning.

Wednesday, July 23, 2014

Early Results: Perspectives on Daylight Savings Time

As some of you are aware, the Utah Legislature is presently investigating whether or not to put an end to daylight savings time, the setting of clocks forward in the spring so that the sun rises and sets at a hour of the day during the spring, summer, and fall months. I am a fan of the later sun rise and set relative to the local-time clock, but others out there may feel differently.

The Utah Governor's Office of Economic Development is currently conducting an online survey on views on daylight savings time that can be completed at by both Utah residents and non-residents (yes, the latter is important as we have a big tourism economy).  You can vote and add comments until August 15th.  I wonder if that means August 15 defined using UTC, MDT, or MST?

Results and comments through yesterday morning are now available on the GOED website and they show that the daylight time lovers are currently getting slaughtered.  With over 26,000 responses, a whopping 67% of the respondents wish to align with Arizona and stay on standard time all year.  Only 15% want to maintain current practice.  18% say stay on daylight savings time all year.

Of course, this is a voluntary survey, which tends to invoke response from those with the strongest opinions.  It would be interesting to see what the results would be of a random sample of Utah residents and non-residents.  Ultimately, the decision to could be put up for a vote, and that might be even more interesting.

For your entertainment purposes, more than 13,000 specific comments are available here.  Here are a few I've self selected just for fun.  I especially like the third and fourth.
"Changing time by legislation is so silly to me. Time should never change, it's a cosmic reality, not a law of men. Fooling ourselves about the real time of day is a bit insane." 
"Daylight Savings is silly for a country which calls itself free. If you want to get up an hour earlier for an hour more of sunlight, then do it; it is your prerogative. But it is a form of totalitarianism to force everyone to get up an hour earlier." 
"If DST was a face, I would punch it as hard as I could." 
"I have not changed my clocks in 4 years. I have hated daylight savings for years. What is the point. "
One thing is apparent from reading the comments, everyone hates the change twice a year.  At least we an agree on something!

Monday, July 21, 2014

Clear Views, Clean Air

After several days of smoke inundation, it was great to wake up this morning to clear views and clean air.

In addition to yesterday's storms, we've had a shift in the large-scale wind direction after several days of northwesterly flow, as evident in wind observations from the top of the Collins chair at Alta Ski Area.  The transition to southwesterly flow has resulted in a smoke-free airstream for the Wasatch Front.

Overnight PM2.5 observations from the University of Utah showed the lowest PM2.5 levels in a few days, with values sitting near 0.

Enjoy the clean air!

Sunday, July 20, 2014

The Pots o' Gold Are on Campus

A spectacular rainbow display could be seen looking toward the east bench this evening.  From my vantage point, the pots o' gold produced by the primary and secondary bows were on the University of Utah Campus, including one near Rice-Eccles Stadium.  No word on whether or not President Pershing was scouring the grounds hoping to add to the U's endowment.

The primary bow was spectacular and featured at least one and possibly two supernumerary bows, purple arcs on the inside of the bow. I've had to doctor-up the photo below to bring the most obvious supernumerary bow out.

Saturday, July 19, 2014

Coast to Coast Smoke

Smoke from the western fires of the U.S. and Canada has now spread coast-to-coast.  If you look closely, you can see it in the visible satellite image below over eastern Canada and Maine.
The National Environmental Satellite, Data and Information Service (NESDIS) provides a nice interactive map for examining fire and smoke hazards.  The screenshot below shows the active fires (red dots), areas with moderately dense smoke (yellow) and areas with thin smoke (green).  Coast to coast coverage is achieved thanks to a fire near the California coast and then large-scale transport of smoke from fires in the western U.S. and Canada across the continent.

Some views of the smoke from MODIS follow (source: NASA).

Smoke plumes over Oregon 
Dense smoke over the Columbia Basin
Smoke over the northern Plains (Lakes Superior and Michigan at right for reference)
Smoke over Labrador, Canada
Sadly, fires have destroyed an estimated 100 homes in north-central Washington.