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After a Brief Respite, Climate Change Enhanced Drought is Returning to the U.S.

Unseasonable warmth across the American West and overall dry conditions across the South is causing drought to expand throughout many parts of the United States.

According to the U.S. Drought Monitor, most of the southern half of the United States is presently experiencing abnormally dry or drought conditions. Meanwhile, an intense drought that has remained in place over the Dakotas and Montana for multiple months continues to persist.

Severe drought conditions are now present in the south-central U.S. with exceptional and extreme drought expanding through Arkansas, Oklahoma, Texas, Louisiana and Missouri. Deepening drought in California and Texas are notable due to the fact that Southeast Texas recently experienced record rainfall due to Hurricane Harvey and California experienced a very wet winter and spring period from 2016 to 2017. Somewhat milder drought is also spreading through the Southeast.

Re-expanding Southern California drought is also enhancing record wildfire activity in that state.

Much Warmer than Normal Temperatures

A strengthening La Nina in the Equatorial Pacific is helping to generate a drought tendency for the Southern U.S. However, various climate change related features including above normal temperatures and a persistent high pressure ridge in the West are lending intensity to the rising drought regime.

(U.S. 30 day average shows much warmer than normal conditions for the lower 48 with extreme warmth prevalent over the American West. Image source: Global and Regional Climate Anomalies.)

Over the past 30 days, temperatures for the U.S. as a whole have been 1.52 C above average (see image above). Much of this excess heat has been concentrated over the West, with mountain and Pacific regions seeing between 4 and 5 C above average temperatures.

Excess heat of this kind helps to speed the drying of soils and vegetation by increasing the rate of evaporation. A condition that can lead to flash drought — whose incidence has been expanding in lock-step with the human-forced warming of the globe.

A Ridiculous Ridge

Linked to the western heat and drought is a strong and persistent high pressure ridge. One that has hit a very intense 1041 hPa pressure as of Monday afternoon over the U.S. Mountain West.

(Very intense high pressure ridge over the U.S. west is presently locking in both warmer than normal and drier than normal conditions. Image source: Earth Nullschool.)

Persistent ridging of this kind was a key feature of the recent 2012 through 2017 California drought. Some climate studies have identified a tendency of these kinds of strong western ridges to form as Arctic sea ice recedes. And during the past decade, strong high pressure ridges have been a rather consistent and significant climate feature for the U.S. West. It is also notable that formation of more powerful ridging features during the fall and winter help to strengthen the Santa Ana winds — which fan California wildfires.

Present drought is nowhere near as intense as it has been during recent years. Especially in California which during 2017 has experienced a bit of a respite. However, with La Nina gaining traction in the Pacific, with global temperatures now in a range between 1.1 and 1.2 C above 1880s averages, and with persistent ridging again taking hold over the U.S. West, the risk of a return to intense drought — especially for the Southwest — is increasing.

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From Record Floods to Drought in Three Months: Unusually Hot, Dry Conditions Blanket South

Back during late August of 2017, Hurricane Harvey dumped as much as 60.48 inches of rain over southeast Texas. Harvey was the wettest tropical cyclone on record ever to strike the U.S. — burying Houston and the surrounding region under multiple feet of water, resulting in the loss of 91 souls, and inflicting more than 198 billion dollars in damages.

Harvey was the costliest natural disaster ever to strike the U.S. Its tropical rains were the heaviest ever seen since we started keeping a record. But strangely, almost inexplicably, just a little more than three months later, the region of southeast Texas is now facing moderate drought conditions.

(Just three months after Harvey’s record rains, Southeast Texas is experiencing drought. No, this is not quite normal despite a mild La Nina exerting a drying influence. Image source: U.S. Drought Monitor. Hat tip to Eric Holthaus.)

How did this happen? How did so much water disappear so soon? How could an instance of one of the most severe floods due to rainfall the U.S. has ever experienced turn so hard back to drought in so short a time?

In a sentence — climate change appears to be amplifying a natural switch to warmer, drier weather conditions associated with La Nina.

Climate change, by adding heat to the Earth’s atmosphere and oceans fundamentally changes the flow of moisture between the air, the ocean and the land. It increases the intensity of both evaporation and precipitation. But this increase isn’t even. It is more likely to come about in extreme events. In other words, climate change increases the likelihood of both more extreme drought and more extreme rainfall.

Of course, climate change does not exist in a vacuum. Base weather and climate conditions influence climate change’s impact. At present, with La Nina emerging in the Pacific, the tendency for the southern U.S. would be to experience warmer and drier conditions. But in a normal climate, these conditions would tend to be milder. In the present climate — warmed up by fossil fuel burning — the tendency is, moreso, to turn toward an extreme. In this case, an extreme on the hot and dry end of the climate spectrum.

For the region of Southeast Texas flooded so recently by Harvey’s record rains, it means that a turn from far too wet to rather too dry took just a little more than 3 months.

(Both temperature and moisture took a very hard turn over the past 30 days. Such extremely warm and dry conditions increase the likelihood of flash drought. A climate feature that has become far more frequent as the Earth has warmed. Image source: NOAA.)

South Texas, however, is just one pin in the map of a larger trend toward drought that is now blanketing the South. Over the past month, precipitation levels were less than 50 percent of normal amounts in most locations with a broad region over the south and west experiencing less than 10 percent of the normal allotment of moisture. Meanwhile, 90-day precipitation averages are also much lower than normal across the South.

Precipitation is a primary factor determining drought. But temperature can mitigate or worsen drought conditions. Higher temperatures cause swifter evaporation — driving moisture out of soils at a faster rate. And average temperatures across the south have been quite warm recently. With one month averages ranging from 1 C above normal over most of the south to a whopping 8 C above normal over parts of New Mexico. As with lower than normal precipitation, higher than normal temperatures have also extended into the past 90 day period across most of the South.

 

(Moderate drought conditions are widespread as severe to extreme drought is starting to crop up in the South-Central U.S. With La Nina likely to continue through winter and with global temperatures in the range of 1.1 to 1.2 C above pre-industrial averages, there is risk that conditions will intensify. Image source: U.S. Drought Monitor.)

The upshot is that moderate drought is taking hold, not just in southeast Texas, but across the southwest, the southeast, and south-central U.S. Severe to extreme drought has also already blossomed from northern Texas and Louisiana through Oklahoma, Arkansas and Missouri. This is relatively early to see such a sharp turn, especially considering the fact that La Nina conditions have only lasted for a short while and have, so far, been rather mild on the scale of that particular climate event.

Furthermore, like Texas, many of these drying regions experienced extreme rainfall events during spring and summer. Such events, however, were not enough to stave off a hard shift to drought in a world in which human-caused climate change is now driving both droughts and more extreme rainfall events to rising intensity.

(Predicted temperature and precipitation variance from normal over next three months. Climate change is likely to enhance this variability related feature. Image source: NOAA.)

With La Nina likely to remain in place throughout winter, the typical climate tendency would be for continued above average temperatures across the south and continued below average rainfall for the same region. Present human-caused global warming through fossil fuel burning in the range of 1.1 to 1.2 C above pre-industrial averages will tend to continue to amplify this warm, dry end of the natural variability cycle (for the southern U.S.).

In other words, there is not insignificant risk that the hard turn away from record wet conditions in the South will continue and that severe to very severe drought conditions will tend to spring up and expand.

RELATED STATEMENTS:

Smoke Blankets Western North America, 106 F Temps in Portland, Flash Northern Plains Drought Threatens U.S. Wheat Crop

The climate change related impacts from continued fossil fuel burning just keep on ramping up.

Last Thursday, the mercury struck 106 degrees Fahrenheit in Portland, Oregon. The reading, just one degree shy of the hottest temperature ever recorded for the city, came after the thermometer soared to the 103 F mark on Wednesday. The extreme heat prompted some locals to re-name the typically wet and cool city — ‘Hotlandia’ — even as a broader severe heatwave blanketed most of the U.S. West.

(Smoke covers large portions of the U.S. West following record heat in many locales. Image source: NASA Worldview.)

During the weekend, the heat shifted north and east — thrusting 90+ degree (F) temperatures into British Columbia where severe wildfires have been raging throughout the summer. As a result, fire intensity spiked once again and great plumes of smoke today blanketed hundreds of miles of western sky.

In total, more than 575,000 hectares have burned in British Columbia so far this year. This is about 6 six times the average rate of wildfire burning for a typically wet and cool region. An intensification of the fire regime that came on as temperatures warmed, climates changed, and indigenous plants found themselves thrust into conditions outside those they’re adapted to.

The extreme heat was brought on by the kind of combined Pacific Ocean warming and upper level high pressure ridge amplification that some researchers have linked to human-caused climate change. And the overall impacts of the system have been as outlandish as they are notable.

(Extreme heat blankets the U.S. on Thursday, August 3rd. Image source: The National Weather Service.)

Further east, the high plains have suffered from extraordinarily dry conditions throughout spring and summer. Since April, rainfall totals have been reduced by 50 percent or more. The drying began with the start of growing season and has continued on through early August. After a rapid intensification during recent weeks, 62 percent of North Dakota and 38 percent of Montana are now blanketed by severe drought conditions or worse.

The drought’s center mass is near the Missouri River Basin — a primary water shed for the northern plains states. Since April, these key regions have seen as little as one quarter the usual precipitation amount. This equals the driest growing season ever recorded for some locations. And overall conditions are about as bad as they have been at any time in the past 100 years.

The result has been the emergence of a very intense flash drought. One of a type that has become more common as atmospheric temperatures have increased and as evaporation from waters and soils has intensified. At Lodgepole Montana, the heat and drought were enough to ignite a 422 square mile wildfire. Covering an area 1/3 the size of Rhode Island, the fire is Montana’s largest blaze since 1910. The fire is now, thankfully, 98 percent contained. More worrisome, the massive blaze is now accompanied by 9 smaller sister fires throughout the state. And all before the peak of fire season.

(Flash drought — a new phenomenon brought on by human-forced climate change — emerges in Montana. Image source: The US Drought Monitor and Grist.)

But perhaps the worst of the drought-related damage has impacted the region’s wheat crops. And reports now indicate that fully half of the Northern Plains wheat crop is presently under threat. Overall current damage estimates for the Northern Plains drought alone are spiking above 1 billion dollars and states are now seeking emergency funding from a relief pool that the Trump Administration recently cut.

But regardless of Trump’s views on climate change or his related lack of preparedness, the damages and risks just continue mounting. Montana resident Sarah Swanson recently noted in Grist:

“The damage and the destruction is just unimaginable. It’s unlike anything we’ve seen in decades.”

Sadly, with atmospheric carbon levels in the range of 407 ppm CO2 and 492 ppm CO2e, and with fossil fuel burning still continuing, these kinds of devastating droughts, heatwaves, and fires will just keep on getting worse.

Links:

NASA Worldview

The US Drought Monitor

The National Weather Service

The National Interagency Fire Center

Portland Heatwave

Flash Drought Could Devastate Half the U.S. Wheat Harvest

Drought Spreads Across U.S. Plains

Western Heatwave Breaks Records Across Oregon and Washington

Canada’s Interagency Fire Center

Drought, Climate Change Spur Severe Election Day Wildfire Outbreak Across Four-State Area

It’s November. A month when the United States should be cooling down toward winter-like conditions. But for the mountainous region along the four-state area bordering Kentucky, North Carolina, Georgia and Tennessee, the climate are anything but fall-like. There, enormous wildfires are now raging, spilling out massive plumes of choking smoke into the abnormally warm air over lands that have been flash-dried by climate change related heat.

Massive Wildfires Strike Dry Lands

large-wildfires-smokey-mountains-november-7

(Very large wildfires burning across the Smokey Mountain region on November 7. Image source: LANCE MODIS.)

In the above satellite image, taken by NASA on November 7, 2016, we see multiple fires with fronts ranging from 1 to 5 miles wide erupting over the Smokey Mountain region of North Carolina, Tennessee, Georgia and Kentucky. Some fires appear to straddle the border with Virginia. Large fires also burn further east between Ashville and Charlotte. Together, these fires are emitting smoke plumes that currently stretch upwards of 350 miles — wafted north and west by warm, southerly winds.

Fire warnings and public announcements urging people to not light campfires were given back on November 1. The National Interagency Fire Center (NIFC) provided initial information on multiple fires sparking throughout this four state region on November 4th. MODIS satellite shots for the 4th show that these fires were then much smaller — barely visible in the imagery. Image and ground based reports now indicate that the fires became considerably larger and more threatening over the weekend.

(The view over western North Carolina yesterday afternoon as wildfires burned through the mountainous region.)

By Monday, local news agencies were reporting the outbreak of 170 fires in Georgia alone with 4,000 acres already burned in the northern part of the state. In Tennessee 96 currently active fires are reported to have consumed 9,000 acres. Campbell, in the eastern part of the state, was particularly hard-hit with over 3,400 acres burned as of this afternoon and declining air quality setting off Code Red Alerts. In Kentucky, 11,000 acres had been consumed as of Monday. North Carolina, meanwhile, called up 350 firefighters to fight multiple large and growing blazes.

Flash Drought, Extreme Warmth

Over September and October, the eastern two-thirds of the U.S. has been both extremely warm and extreme dry. Temperatures for the month of October have ranged between 5 and 12 degrees Fahrenheit above average for a majority of the lower 48 states.

us-drought-monitor-thursday-nov-3

(Extreme heat over the southeastern U.S. has helped to promote flash drought conditions together with very large wildfires now burning in North Carolina, Tennessee, and Kentucky. Image source: The U.S. Drought Monitor.)

Together with the heat has come a rapid emergence of drought conditions. In particular, Mississippi, Alabama, Georgia, South Carolina, North Carolina, Tennessee and Kentucky have experienced increasingly extreme conditions. In Kentucky, for example, the week ending on November 1st saw the state’s drought coverage more than triple jumping from 24 percent to 81 percent of the state’s land area within just seven days.

Flash drought is a new feature of climate change brought on by increasing rates of evaporation due to warming lands and airs. The extra warmth draws moisture out of soil and vegetation more rapidly and can spark the emergence of extreme conditions on short time-scales. The current flash drought was already causing problems in the Southeast before the recent spate of wildfires. However, given the intense, unseasonal warmth and the speed at which the lands have dried, the present fire outbreak represents a serious and unusual hazard for this time of year.

Links:

LANCE MODIS

The National Interagency Fire Center

The U.S. Drought Monitor

North Georgia Fire Outbreak

Tennessee Air Quality Alert as Wildfires Belch Smoke

Kentucky Wildfire Outbreak

Wildfires Burn in Western North Carolina

Hat tip to Colorado Bob

Hat tip to NCFireFighters

Hat tip to Titania

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