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Tag Archive: flooding

  1. Forest grazing counteracts the effectiveness of trees to reduce flood risk

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    • Planting trees can reduce flood risk, but a high intensity forest land use, such as grazing, can counteract the positive effect
    • Infiltration rates were between ten and a hundred times higher under trees, when the forested area remained relatively undisturbed, compared with adjacent pasture
    • Forest buffer zones, with restricted access, strategically placed to intercept surface runoff before it reaches the stream may be more effective than larger scale planting when the forested areas are used for other purposes

    October 10, 2017 Lancaster University read full ScienceDaily article here

    As the frequency and severity of flooding becomes an increasing problem, land managers are turning to natural flood management measures, such as tree planting, to reduce the risk. When rainfall exceeds the rate at which water can enter the soil it flows rapidly over the land’s surface into streams and rivers. Trees can help to reduce the risk of surface runoff by increasing the number of large pores in the soil through which water can drain more easily. Land use, such as grazing, also affects the soil’s ability to absorb water; however, while the effect of land use on surface runoff has been well studied in grasslands, little is known about the effect of land use in forests.

    …Researchers found that infiltration rates were between ten and a hundred times higher under trees, when the forested area remained relatively undisturbed, compared with adjacent pasture. Where sheep were allowed to graze under the trees there was no observable difference from the pasture.

    They also compared forest types — conifer forest planted with Scots Pine and broadleaved forest planted with sycamore — and found that infiltration rates were significantly higher under Scots Pine than under sycamore, but only when the forest was ungrazed…

    …”Tree planting can make an important contribution to flood risk management, but forest buffer zones, with restricted access, strategically placed to intercept surface runoff before it reaches the stream may be more effective than larger scale planting when the forested areas are used for other purposes.”…

    K.R.Chandler, C.J.Stevens, A.Binley, A.M.Keith. Influence of tree species and forest land use on soil hydraulic conductivity and implications for surface runoff generation. Geoderma, 2017 DOI: 10.1016/j.geoderma.2017.08.011

  2. What would an entirely flood-proof city look like? From China to New Jersey

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    • As the recent floods from Bangladesh to Texas show, it’s not just the unprecedented magnitude of storms that can cause disaster: it’s urbanisation.
    • From sponge cities in China to ‘berms with benefits’ in New Jersey and floating container classrooms in the slums of Dhaka, we look at a range of projects that treat storm water as a resource rather than a hazard.

    by Sophie Knight Sept. 25 2017 read full GuardianUK article here

    They call it “pave, pipe, and pump”: the mentality that has dominated urban development for over a century. Along with the explosion of the motorcar in the early 20th century came paved surfaces. Rainwater – instead of being sucked up by plants, evaporating, or filtering through the ground back to rivers and lakes – was suddenly forced to slide over pavements and roads into drains, pipes and sewers. Their maximum capacities are based on scenarios such as 10-year storms. And once they clog, the water – with nowhere else to go – simply rises.

    The reality of climate change and more frequent and intense downpours has exposed the hubris of this approach. As the recent floods from Bangladesh to Texas show, it’s not just the unprecedented magnitude of storms that can cause disaster: it’s urbanisation.

    …With climate change both a reality and threat, many architects and urbanists are pushing creative initiatives for cities that treat stormwater as a resource, rather than a hazard….

    …In China, the government has commissioned the construction of 16 “Sponge Cities” to pilot solutions for the freshwater scarcity and flooding suffered in many cities as a result of rapid urbanisation. Chicago architectural firm UrbanLab was commissioned to design the masterplan for Yangming Archipelago in Hunan province: a new centre within the larger city of Changde, devised as a “new model for the future”.

    The area, a low-lying land river basin that experiences heavy rainfall, is regularly flooded. Instead of incorporating defences against water, UrbanLab put space for it to flow at the centre of its urban plan, putting major buildings on islands in an enormous central lake. Canal-lined streets that UrbanLab call “Eco-boulevards” connect the eight districts – the process is visualised in this video.

    UrbanLab says their vision combines a dense metropolis with a nature setting: “As a functional center, Yangming Archipelago will serve as an urban model, we expect it to lead the way to a new way of thinking about the city of the future.”

    The two-mile Pilsen Sustainable Street, commissioned by the Chicago Department of Transportation to improve the urban ecosystemPermeable pavements: Chicago’s ‘green alleys’

     

    The bioswale, an environmentally-friendly form of drainage through landscape, at the Pilsen Sustainable Street on Cermak Rd.
    Bioswale along cermak road
    • Rainwater travels through the self-cleaning, pollution-reducing sidewalk before going on to feed surrounding plants…

    …In New Jersey and New York…in response to Sandy, ZUS partnered with MIT’s Center for Advanced Urbanism and De Urbanisten to devise New Meadowlands: a masterplan for combining flood resilience with recreational amenities through marshes and a system of parallel raised banks called berms.

    Between the outer berm and the sea, the restored wetlands would soak up seawater and slow down tidal waves, preventing them from hitting the dikes at high speed. The stretch of berms would serve as a wildlife refuge, filling up with rainwater during periods of heavy rain before draining out. And on the insider of the inner berm, ditches and ponds would retain rainwater, preventing it from causing sewers to overflow….

    A terrace in Little Ferry, one of the first sites for the pilot project of New MeadowlandsBerms with benefits

     

    Floating pods – and beyond…

    Waterstudio’s Floating City Apps in a slum
  3. ‘Horizontal hurricanes’ – atmospheric rivers pose extreme storm risk but also drought-busting opportunity for California; plans for new 2-3 week forecast and ranking system similar to hurricanes

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    • Severe atmospheric rivers in California could mean 23 days of rain and wind  causing floods and landslides to the tune of $300 billion in property damage per past USGS modeling
    • Atmopheric rivers — while carrying the potential for more damage — will also help California maintain typical rainfall levels amid a drying climate.
    • plan to begin publishing regular 14-day to 21-day outlooks on atmospheric rivers as soon as this winter along with new rating system for intensity on a scale of 1 to 5, similar to hurricanes.

    By Kurtis Alexander September 27, 2017 read full SF Chronicle article here

    …California is facing its own threat of bigger and more destructive storms. Mounting research, much of it done in the wake of the near-record rains that pulled California out of a five-year drought this past winter, shows that seasonal soakers may not come as often as they used to, but could pack more punch when they do arrive.

    ….The massive weather systems that rise out of the Pacific Ocean, now popularly called atmospheric rivers, can drop as much water as Hurricane Irma dumped on Florida this month — billions of gallons that submerged cities and towns.

    …U.S. Geological Survey ran a simulation of what a sequence of severe atmospheric rivers might look like in California…. 23 days of rain and wind that caused floods and landslides to the tune of $300 billion in property damage….big drenchers earlier this year…caused mass flooding in San Jose and other cities and triggered a near-catastrophe at Lake Oroville when a pair of dam spillways failed.

    …A group of Southern California scientists, some of whom are partnering with Sonoma County, plan to begin publishing regular 14-day to 21-day outlooks on atmospheric rivers as soon as this winter. Current forecasts typically don’t anticipate the events more than a week out.

    …Marty Ralph, director of the Center for Western Weather and Water Extremes at UC San Diego’s Scripps Institution of Oceanography, is also working to develop a rating system for the storms.  The blasts will be evaluated for intensity on a scale of 1 to 5, similar to hurricanes. A test run of the ratings last winter pegged the strong atmospheric river in February, which contributed to the damage at Oroville Dam, as a category 5 eventResearch published in the journal Geophysical Research Letters in August, which Ralph participated in, indicates that atmospheric rivers are carrying increasing amounts of water.

    …Sometimes called horizontal hurricanes, atmospheric rivers are exactly what they sound like: airborne channels of water that develop over the Pacific Ocean and are pushed along by strong winds toward the West Coast during the winter….providing as much as 50 percent of the state’s annual rainfall in a matter of days — dumpings that are critical to water supplies but, at times, bring on disaster…

    Another study [published in September] in the journal Scientific Reports, suggests that the swelling intensity of atmospheric rivers — while carrying the potential for more damage — will also help California maintain typical rainfall levels amid a drying climate….

    During the height of the drought, California went as long as a year without seeing a single atmospheric river. But the state was hit by more than 30 of the systems last winter, according to Scripps researchers. That explains why the season was one of the wettest on record….

    Alexander Gershunov, Tamara Shulgina, F. Martin Ralph, David A. Lavers, Jonathan J. Rutz. Assessing the climate-scale variability of atmospheric rivers affecting western North America. Geophysical Research Letters. Volume 44, Issue 15 16 August 2017. Pages 7900–7908 DOI: 10.1002/2017GL074175

  4. Cartoons- climate change, flooding

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    http://www.gocomics.com/mattdavies/2017/08/31

    http://www.gocomics.com/nickanderson/2017/09/01

    cartoon

    http://www.philly.com/philly/opinion/signe/20170830_Daily_Signe_Cartoon_08_30_17.html

    http://www.gocomics.com/joelpett/2017/08/26

    http://www.gocomics.com/claybennett/2017/08/30

  5. Houston’s flooding shows what happens when you ignore science and let developers run rampant

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    • The watershed of the White Oak Bayou river, which includes much of northwest Houston, is a case in point. From 1992 to 2010, this area lost more than 70% of its wetlands, according to research (pdf) by Texas A&M University.
    • The vanished wetlands wouldn’t have prevented flooding, but they would have made it less painful, experts say.
    • Wet land needs wetlands….Prairies, which also act as floodwater sponges, have been decimated too.

    Since Houston, Texas was founded nearly two centuries ago, Houstonians have been treating its wetlands as stinky, mosquito-infested blots in need of drainage.

    Even after it became a widely accepted scientific fact that wetlands can soak up large amounts of flood water, the city continued to pave over them. The watershed of the White Oak Bayou river, which includes much of northwest Houston, is a case in point. From 1992 to 2010, this area lost more than 70% of its wetlands, according to research (pdf) by Texas A&M University.

    In the false-color satellite images below, plants and other vegetation appear green, while urbanized and developed areas appear blue and purple. Drag the slider to see how northwest Houston has changed since 1986.

    ….In recent days, the flooding caused by Hurricane Harvey has raised water levels in some parts of the watershed high enough to completely cover a Cadillac. The vanished wetlands wouldn’t have prevented flooding, but they would have made it less painful, experts say….

    ….Between 1992 and 2010 alone nearly 25,000 acres (about 10,000 hectares) of natural wetland infrastructure was wiped out, the Texas A&M research shows. Most of the losses were in Harris County, where almost 30% of wetlands disappeared.

    Altogether, the region lost the ability to handle nearly four billion gallons (15 billion liters) of storm water. That’s equivalent to $600 million worth of flood water detention capacity, according to the university researchers’ calculations.

    To be sure, that’s a drop in the bucket of what Harvey will eventually unleash. The estimate was already at nine trillion gallons a couple of days after the storm made landfall. But saving and restoring wetlands is nonetheless an important part of making Houston more storm resistant, says Mary Edwards, a wetlands specialist at Texas A&M’s AgriLife Extension.

    …It’s not just wetlands that are being destroyed. Prairies, which also act as floodwater sponges, have been decimated too. Below, maps show the change in the Katy Prairie, west of downtown Houston. By 1996, much of it was gone, but another 10% had been lost by 2010, while the developed acreage grew by 40%, data from HARC shows….

  6. As Hurricane Harvey hits Gulf Coast, Central Valley must prepare for the coming storm- Editorial

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    • The Big One in the form of a superstorm may come this winter, or the next or the one after that. But it is headed this way.
    • New plan calls for multi-benefit floodplain management, expanding bypasses and limiting building
    • Giving rivers and floodways more room to carry flood waters is the best way to protect communities from dangerous floods, and giving rivers more room provides multiple benefits, including clean water, parks, and habitat for fish and wildlife.
  7. Four things Houston-area leaders must do to prevent future flooding disasters

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    Read full article in the Texas Tribune

    …This may seem like a freak occurrence. But it’s the third catastrophic flooding event this region of 6.5 million people has experienced in three years. And scientists and other experts say that much of the devastation could have been prevented. …They say local officials need to account for more frequent and intense rains that are sure to come with climate change, rather than looking to what has happened in the past in their search for solutions.

    Here’s what local leaders could have done to protect the region — and what they must do to prevent such disasters in the future.

    Preserve and restore as much prairie land as possible

    Much of northwest Houston used to be covered in prairie land, where tall grasses could absorb huge amounts of floodwater….

    Restrict development in floodplains and buy flood-prone homes

    Buildings continue to go up in vulnerable floodplains all over Harris County. A few years ago the city of Houston tried to ban new development in the most flood-prone areas. …

    Plan for climate change

    In planning for flooding from future storms, local officials largely look to past rainfall totals and weather patterns. But climate change will heighten the risks that the region already faces. That’s particularly true because it sits so close to the Gulf of Mexico, where sea levels are rising and waters have been warming as the planet gets hotter….“The exact same storm that comes along today has more rain associated with it than it would have 50 or 100 years ago,” renowned climate scientist Katharine Hayhoe told The Texas Tribune last year. Hayhoe said Houston needs to plan for more frequent and intense rainstorms, just like many other cities in the country….

    Educate the public

    Hundreds of thousands of people have moved to the Houston area in recent decades; it’s consistently ranked as one of the nation’s fastest-growing cities. But people who move to flood-prone areas are often unaware of the risks….

  8. Houston’s Flood Is a Design Problem

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    • It’s not because the water comes in. It’s because it is forced to leave again.
    • Reducing impervious surfaces and improving water conveyance has a role to play
    • most important step is to reduce the velocity of water when it is channelized, so that it doesn’t deluge other sites. And then to stop moving water away from buildings and structures entirely, and to start finding new uses for it in place.
    • China’s “sponge cities” as a dramatic example—a government-funded effort to engineer new, permeable materials to anticipate and mitigate the flooding common to that nation….

    Ian Bogost  The Atlantic  August 29 2017  Read full article here

    …But the impact of flooding, particularly in densely developed areas like cities, is far more constant than a massive, natural disaster like Harvey exposes. The reason cities flood isn’t because the water comes in, not exactly. It’s because the pavement of civilization forces the water to get back out again.

    Under normal circumstances, rain or snowfall soaks back into the earth after falling. It gets absorbed by grasslands, by parks, by residential lawns, by anywhere the soil is exposed. Two factors can impede that absorption. One is large quantities of rain in a short period of time. The ground becomes inundated, and the water spreads out in accordance with the topography. The second is covering over the ground so it cannot soak up water in the first place. And that’s exactly what cities do—they transform the land into developed civilization.

    Roads, parking lots, sidewalks, and other pavements, along with asphalt, concrete, brick, stone, and other building materials, combine to create impervious surfaces that resist the natural absorption of water. In most of the United States, about 75 percent of its land area, less than 1 percent of the land is hardscape. In cities, up to 40 percent is impervious….

    …In Houston’s case, catastrophic floods have been anticipated for some time. The combination of climate change, which produces more intense and unpredictable storms, and aggressive development made an event like this week’s almost inevitable. The Association of State Floodplain Managers has called for a national flood risk-management strategy, and the Houston Chronicle has called flood control the city’s “most pressing infrastructure need.” …

    …Houston poses both a typical and an unusual situation for stormwater management. The city is enormous, stretching out over 600 square miles. It’s an epitome of the urban sprawl characterized by American exurbanism, where available land made development easy at the edges. Unlike New Orleans, Houston is well above sea level, so flooding risk from storm surge inundation is low. Instead, it’s rainfall that poses the biggest threat.

    A series of slow-moving rivers, called bayous, provide natural drainage for the area. To account for the certainty of flooding, Houston has built drainage channels, sewers, outfalls, on- and off-road ditches, and detention ponds to hold or move water away from local areas. When they fill, the roadways provide overrun. The dramatic images from Houston that show wide, interstate freeways transformed into rivers look like the cause of the disaster, but they are also its solution, if not an ideal one. This is also why evacuating Houston, a metropolitan area of 6.5 million people, would have been a terrible idea. This is a city run by cars, and sending its residents to sit in gridlock on the thoroughfares and freeways designed to become rivers during flooding would have doomed them to death by water.

    Accounting for a 100-year, 500-year, or “million-year” flood, as some are calling Harvey’s aftermath, is difficult and costly. Stiftel confirms that it’s almost impossible to design for these “maximal probable flood events,” as planners call them. Instead, the hope is to design communities such that when they flood, they can withstand the ill effects and support effective evacuations to keep people safe. “The Houston event seems like an illustration that we haven’t figured it out,” Stiftel says.

    Many planners contend that impervious surface itself is the problem. The more of it there is, the less absorption takes place and the more runoff has to be managed. Reducing development, then, is one of the best ways to manage urban flooding. The problem is, urban development hasn’t slowed in the last half-century. Cities have only become more desirable, spreading outward over the plentiful land available in the United States….

    ….In other cases, floodplains have been managed through redevelopment that reduces impervious surfaces. Natural ground cover, permeable or semi-permeable pavers, and vegetation that supports the movement of water offer examples. These efforts dovetail with urban redevelopment efforts that privilege mixed-use and green space, associated with both new urbanism and gentrification. Recreation lands, conservation lands and easements, dry washes, and other approaches attempt to counterbalance pavement when possible. Stiftel cites China’s “sponge cities” as a dramatic example—a government-funded effort to engineer new, permeable materials to anticipate and mitigate the flooding common to that nation….

    ….Reducing impervious surface and improving water conveyance has a role to play, but the most important step in sparing cities from flooding is to reduce the velocity of water when it is channelized, so that it doesn’t deluge other sites. And then to stop moving water away from buildings and structures entirely, and to start finding new uses for it in place.

    That can be done by collecting water into cisterns for processing and reuse—in some cases, Debo explains, the result can even save money by reducing the need to rely on utility-provided water. Adding vegetation, reclaiming stormwater, and building local conveyance systems for delivery of this water offer more promising solutions….

    ….Instead of looking for holistic answers, site-specific ones must be pursued instead. Rather than putting a straight channel through a subdivision, for example, Debo suggests designing one to meander through it, to decrease the velocity of the water as it exits

    …But there are some regions that just shouldn’t become cities. “Parts of Houston in the floodway, parts of New Orleans submerged during Katrina, parts of Florida—these places never should have been developed in the first place,” Debo concludes. Add sea-level rise and climate-change superstorms, and something has to give.

    …Residential homeowners who install a new cement patio or driveway might not even realize that they are channeling water down-grade to their neighbors, or overwhelming a local storm drain. Citizens can also influence stormwater issues within their municipalities. Many folks know that they have a local city council and school board, but local planning, zoning, and urban design agencies also hold regular public meetings—unfortunately, most people only participate in this aspect of local governance when they have an axe to grind. For the average American concerned with the deluge, the best answer is to replace an occasional, morbid curiosity with flooding with a more sophisticated, long-term interest in stormwater management.

  9. Did Climate Change Intensify Harvey? Yes- amplifying worst effects

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    Robinson Meyer  read full article in The Atlantic

    Every so often, the worst-case scenario comes to pass.  As of Sunday afternoon, the remnants of Hurricane Harvey seem likely to exceed the worst forecasts that preceded the storm. The entire Houston metropolitan region is flooding: Interstates are under feet of water, local authorities have asked boat owners to join rescue efforts, and most of the streams and rivers near the city are in flood stage….“Local rainfall amounts of 50 inches would exceed any previous Texas rainfall record. The breadth and intensity of this rainfall are beyond anything experienced before,” said a statement from the National Weather Service. “Catastrophic flooding is now underway and expected to continue for several days. ”…
    This means that thousands of people—and perhaps tens of thousands of people—are facing a terrifying and all-too-real struggle to survive right now. In an age when the climate is changing rapidly, a natural question to ask is: What role did human-caused global warming play in strengthening this storm?Climate scientists, who specialize in thinking about the Earth system as a whole, are often reticent to link any one weather event to global climate change. But they say that aspects of the case of Hurricane Harvey—and the recent history of tropical cyclones worldwide—suggest global warming is making a bad situation worse.…Climate change is caused by the release of greenhouse gases like carbon dioxide and methane into the atmosphere. These gases prevent some of the sun’s rays from bouncing back into space, trapping heat in the planetary system and raising air temperatures all over the world….

    Storms like Harvey are helped by one of the consequences of climate change: As the air warms, some of that heat is absorbed by the ocean, which in turn raises the temperature of the sea’s upper layers.
    Harvey benefitted from unusually toasty waters in the Gulf of Mexico. As the storm roared toward Houston last week, sea-surface waters near Texas rose to between 2.7 and 7.2 degrees Fahrenheit above average. These waters were some of the hottest spots of ocean surface in the world. The tropical storm, feeding off this unusual warmth, was able to progress from a tropical depression to a category-four hurricane in roughly 48 hours.“This is the main fuel for the storm,” says Kevin Trenberth, a senior scientist at the U.S. National Center for Atmospheric Research. “Although these storms occur naturally, the storm is apt to be more intense, maybe a bit bigger, longer-lasting, and with much heavier rainfalls [because of that ocean heat].”……the hurricane churned up water 100 or even 200 meters below the surface, said Trenberth, but this water was still warm—meaning that the storm could keep growing and strengthening. “Harvey was not in a good position to intensify the way it did, because it was so close to land. It’s amazing it was able to do that,” he told me…

    …Trenberth says that the extra heat could make the storm more costly and more powerful, overpowering and eventually breaking local drainage systems.

    The human contribution can be up to 30 percent or so up to the total rainfall coming out of the storm,” he said. “It may have been a strong storm, and it may have caused a lot of problems anyway—but [human-caused climate change] amplifies the damage considerably.”…

    • How Harvey went from a little-noticed storm to a behemoth

    By Sandhya Somashekhar August 27 at 6:06 PM read full Washington Post article

    Even if Harvey had been a milder storm, spinning lazily across the Gulf of Mexico, there would have been reasons for alarm early last week. For starters, the jet stream — the air current that meanders across the continent, pushing storms along a familiar path — flowed far north of Texas, and thus when Harvey crashed into the state there was nothing in the atmosphere to shove it somewhere else. Harvey stalled.

    …Harvey also proved that the Gulf of Mexico — in late August, in a warming climate — can prove explosive for the development of what is generically called a tropical cyclone. In barely more than a day the storm went from a disorganized tropical depression to a significant hurricane and then all the way up to Category 4 — the second-highest rating on the Saffir-Simpson hurricane intensity scale, which is based on wind speed.

    The result: a record-setting storm that within 24 hours plunged much of the nation’s fourth-largest city and its surroundings under feet of choppy brown water. It threatens to submerge even more of the region during the next few days.

    “There are a lot of worst-case-scenario stars that aligned,” said Marshall Shepherd, a professor of atmospheric sciences at the University of Georgia and a past president of the American Meteorological Society. “As bad as it is now, we still have days of this to go.”

    ….A stunning amount of rain has fallen over Texas so far, and it is expected to continue for several more days as the storm creeps along, weakening slightly. In general, things will probably get worse before they get better; some areas might see as many as 50 inches of rainfall when all is said and done, wreaking damage that experts predict could lead to years of recovery across the region.

    As of Sunday afternoon, the storm had deposited 9 trillion gallons over Southeast Texas, as bands of rain picked up moisture from the Gulf. That’s enough water to fill up the Great Salt Lake twice over, meteorology student Matthew Cappucci wrote for The Washington Post….

    Experts say the lack of “steering currents” to move the storm along is unusual and probably responsible for the scale of the flooding. As of Sunday evening, the center of the storm was virtually parked at a spot about 25 miles northwest of the coastal town of Victoria — crawling southeast at 2 miles per hour toward the Gulf.

    With a more common tropical storm, the damage in any one place would be mitigated by the fact that the storms move quickly, spreading the rain over a larger area.

    Perhaps making things worse is something called the “brown ocean effect,” which hypothesizes that storms, which typically get their energy over the ocean or another large body of water, can absorb that energy and moisture from rain-soaked land. “The land, in effect, mimics the energy supply of the ocean,” University of Maryland Baltimore County professor Jeff Halverson wrote for the Capital Weather Gang….

    Related: What you can and can’t say about climate change and Hurricane Harvey