LIGHTNING STRIKES

Several readers of my wildfire blog suggested that I had given lightning strikes short shrift as causes of forest fires.  In fact, lightning as a cause is not even mentioned because it is not in the top four causes, at least until 2015, as reported in the the paper I used, which is cited at the end of this piece. They plot the proportion of number of fires and area burned by cause of ignition in (a) the Santa Monica Mountains and (b) San Diego County. I am not reproducing the plot here for copyright reasons but interested folks can go to the link in the citation (Syphard and Keeley 2015) below.

Most such studies concentrate more on the area burned, than numbers of ignition, presumably because that is the net effect on the public and on the environment.  Lightning as a cause is present in both areas studied by Syphard and Kelley, but the incidences are few and importantly, the areas burned are low when compared with the four largest contributors, arson, campfires, power lines and equipment (this last is a grab bag including chain saws and mowers).  These data beg the question whether something has changed in the last half dozen years to make lightning a bigger factor.  I examined a later (2018) paper by the same authors and found no change in this area.

Then I found a recent story which indicated that between August 16 and August 19, 12,000 bursts of lightning were recorded. Many of these ignited fires, burning more than 1.3 million acres across California.  That is nearly a third of the total area burned to date, certainly not in line with the conclusion that lightning is a minor player.  The Science News story linked above gets into an explanation, with the gist of it being “a bit of bad luck and a landscape primed for fire devastation due to climate change”.  The bad luck part is a combination of two events, each rare for that time of year, and leading to the production of “dry lightning”.  Before getting into what that means, and why it happens, first a quick primer on lightning.

Storm clouds usually form by the collision of colder and warmer air.  Moisture can be in the form of water, ice, or a soft hail.  Air movements cause collision of the species and these collisions produce static charges. The negatively charged particles sink in the cloud and the positively charged ones go to the top.  When the charge balance is sufficient to break down the insulating medium between, a lightning flash occurs, within a cloud or between clouds. The heat generated can be intense, which produces a shock wave, which we hear as thunder.

Image of a dry thunderstorm. Courtesy National Oceanic and Atmospheric Administration

Dry lightning is lightning associated with thunderstorms producing very little rain on the ground.  Ordinarily rain can be expected to render the vegetation less susceptible to ignition.  In a forest with a canopy, 0.1 inches are needed, although as little as a tenth of that is sufficient for open grassland.  Dry thunderstorms do produce precipitation, but evaporation in the hot dry air on the way down results in very little on the ground.

The dry lightning which caused many of the August fires in California this year were described by experts as “freak” events.  Tropical storms far south were wind driven to California to supply cloud forming moisture.  At the same time, the remnants of a Sonoran Desert storm conspired with this tropical moisture to form high storm clouds at elevations of 9000 feet.  Copious lightning was not accompanied by rain on the ground because of the hot and dry conditions below the clouds.  Wildfires were the result.

What are we to make of this and what is the connection to climate change? Prior to the dry lightning events, California was experiencing record-breaking hot and dry conditions.  August 16, the first day of the dry lightning onslaught, somewhat coincidentally, was the date that Death Valley, CA recorded the highest ever temperature measured on the planet: 130 ^o F.  These conditions certainly carry the imprint of climate change.  But connecting dry thunderstorm conditions to climate change is more of a stretch. No modeling to date has been disclosed. Other phenomena, such as increased frequency and intensity of El Nino, are grounded in mechanisms.

I am forced to conclude that lightning as a source of large wildfires is a chance occurrence.  But lightning could strike again, symbolically* and really.

Vikram Rao

*” Lightning’s striking again” in Lightnin’ Strikes, by Lou Christie (1965), written by Lou Christie and Twyla Herbert

Syphard, A. D., & Keeley, J. E. (2015). Location, timing and extent of wildfire vary by cause of ignition. International Journal of Wildland Fire, 24(1), 37. https://doi.org/10.1071/WF14024

FUTURE OF ENERGY AND PARTICULATE MATTER ARE INTERWOVEN

The future of energy is experiencing special scrutiny.  The Economist has a lead story this month.  The timing of this discourse is, of course, occasioned by the Covid-19 related plummet in energy usage.  Most of this is in the transportation sector, but even electricity usage has dropped in step with reduced industrial activity.  The sector responsible for most of the deaths associated with particulate matter (PM), biomass combustion in cookstoves, has likely been unaffected.   The poor, representing most of the affected persons, still cook their food.  Broad assertions regarding the effect of reduced energy consumption on climate change must recognize that this sector remains unaffected.

Over 85% of ambient PM is produced from combustion processes.  The sources fall into three categories: electricity production using coal, transportation, and biomass burning. In the US, coal fired electricity has experienced a sustained drop.  While emission regulations have been a factor in retiring the oldest plants, cheap natural gas has resulted in the retired coal plants not being replaced by similar units.  Shale gas, and gas associated with shale oil, have caused a sustained drop in the price of natural gas in the US to below USD 3 per million BTU.  At those prices, with an expectation of continuation of the low price regime, coal has not been able to compete.  This trend can be expected to continue and ambient PM ought to benefit.

Fuel use in transportation has plummeted during the pandemic.  Some of the behavioral changes resulting in reduction in driving and flying ought to persist.  This trend comes at a time when electric vehicles (EV’s) have reached something of tipping point.  This has resulted from an astonishing reduction in the cost of batteries from USD 1000 per kWh to a possible USD 100 in a year; all this in a scant ten years.  Consequently, electric cars are getting close to parity on price with conventional gasoline driven ones. They already are for luxury vehicles.  This is important because the American consumer is unduly influenced by the “sticker price” as opposed to life cycle costs.  Operating costs of EV’s will be lower than for the comparable conventional vehicle.  A modest family sedan will travel a mile using about 0.25 kWh.  Electricity cost is variable, but in many states nighttime prices are lower due to depressed demand, as low as 4 cents per kWh.  Even at a generous 8 cents, the fuel cost per mile is 2 cent per mile.  The same conventional car delivering 30 miles to the gallon of gasoline will cost 10 cents per mile at USD 3 per gallon.  Maintenance costs are also lower for electric vehicles. 

EV’s will result in lower ambient PM and not only because of zero tailpipe emissions.  The electricity used, if produced from coal, will certainly emit PM.  But being at a point source, capture and disposition is more feasible than at the tailpipe.  The electricity is increasingly likely to be from a renewable source.  But no matter which the source, one feature of EV’s is that the well to wheel energy usage is 65% less for EV’s than a comparable conventional vehicle.  Consider a conventional vehicle delivering 35 miles to the gallon.  An EV of the same capability will be rated at between 110 and 120 miles per gallon equivalent, as is the Chevy Bolt.  Therefore, no matter the source, an EV simply uses less energy per mile. With no change in consumer driving behavior, one could expect a net drop in PM emissions with increasing penetration of EV’s into the fleet.

As matters stand, coal fired electricity is in retreat, at least in the highest electricity consuming nations.  EV’s are increasingly nudging oil into the non-essential realm.  Two of the big three contributors to airborne particulates are headed in the right direction.  Major corporations are placing substantial bets.

British Petroleum (BP) recently announced plans for cutting back on oil production by 40% by 2030.  They also announced an intent to produce a sizeable amount of renewable electricity in the same time frame.  The announcement caused an increase in the price of their stock price.  That would not have been expected a few years ago.  About a dozen years ago BP had announced a similar intent, going so far as to state that BP stood for Beyond Petroleum.  That proved to be more rhetoric than action. Now it appears that the climate is right.  And the climate will indeed be the beneficiary.

Vikram Rao