Houston, we have a problem
The Houston metropolitan area and included counties
The other day a colleague drew my attention to a very interesting program being led by the University of Hull in the northeast of England. The basic tenet of the program is to note that the Humber Estuary, like other estuaries around the world, has both a concentration of industries that support the local economy but that are intense emitters of green house gases (GHG), and falls into an area of higher exposure to climate change risks particularly rising sea level, because it’s low lying flat topography beside the North Sea.
My colleague’s comment got me thinking about the Houston area, where we have resided for more than 17 years. Is Houston a similar conflagration of causes and effects? In this blog I hope to convince the reader that the answer is yes and moreover there are other additional factors that increase the risk exposure associated with global sea level rise and changing climate patterns. Houston’s exposure to a number of environmental risks such as catastrophic flooding (three 500 year events in as many years) is already being felt and can only get worse, if mitigation and adaption actions are not taken. In a follow up article, “Failure is not an option”, I propose some solutions and a framework for the response.
A geologic cross section across the Gulf Coast and Gulf of Mexico
Soft rocks
Most any geologist can tell you about rising and falling sea livel throughout geologic time. At any one location its typically been a function of rates of subsidence/uplift (tectonics), sedimentation, compaction of those sediments as they’re buried and global changes in sea level largely due to land ice sheet cover. So it is with the Gulf Coast. For 100 million years or more a big hole or basin now called the Gulf of Mexico, created by subsidence, has been progressively filled by sediments shed by the largest continental rivers ancestral to the Mississippi and Rio Grande. Patterns of relative sea rise (transgression) and fall (regression) carry a signature due to global (eustatic) sea level change, but are also controlled by increased rates of river sedimentation, compaction on faults, and general down slope movement of the sediment mass, particularly the more mobile Jurassic salt.
Bathymetry of the Gulf of Mexico from 3D seismic surveys. Source: BOEM
The current Gulf Coast morphology is largely a response to sea level rises in the last 12,000 years or so known as the Holocene) as ice caps and glaciers have receded global sea level has risen. The flooding of a very gently sloping coastal plain has developed a wide and shallow shelf area, only narrowed by the bird’s foot delta of the Mississippi River. South of the shelf the sea floor topography reflects the continued movement of sediment, complicated by plastic movement of salt, pocking the sea bed. North of the shelf is a generally flat, low lying coastal plain that in the last 100 years or so has seen great cities and industrial complexes grow on the estuaries, bayous and cities, most of it supported by oil and gas produced from the thick pile of petroliferous sedimentary rocks in the region.
The delicate interplay of the factors controlling relative sea level continues in our modern time, with the sea winning the competition of factors along much of the Gulf Coast. For example, the gauge at Pier 21 in Galveston, shows an average 6.5 mm rise per year over the last century. Sinking of the land has in places been exacerbated by extraction of water, oil and gas from aquifers and reservoirs in the sediment pile. For example extraction of groundwater to support the petroleum industry in the Galveston Bay Area has led to subsidence rates between 3 and 30 mm per year. The highest subsidence rates observed in the bay are within the lower 15 km of the San Jacinto River/Houston Ship Channel region, where much of the industry is concentrated. This inexorable rise of relative sea level increases the risk from flooding in tidal surges associated with tropical storms. Encroachment of the sea can also lead to other problems such as contamination of fresh water aquifers or backing up of sewers and other underground drainage. Millions of people are exposed to these risks and great swathes of industry and commerce are founded on these soft rocks.
Choked rivers
We’ve certainly seen our fair share of weather in Texas, both in the city and out west in Washington County where we have a horse farm. We’ve been a lot more fortunate than many with those weather events, but we have witnessed extreme flooding. The lower one fifth of our land hugs a creek that a few miles away flows into the Brazos River. The property plat depicts the 100 year flood plan as a strip either side of the creek. An elderly neighbor remembers cotton being grown in the creek bottom. Nowadays it floods several times a year. We’re way upstream from the sea and I suspect that it bad waterway management that has caused this change. While littering seems to be part of the problem, I think it’s undersized culverts and bridge gaps that forces the flood water to un-naturally back up and spill over into the flood plain. In the metropolitan area of Houston - actually the largest city in the US by that measure - the modification of bayous with levees and reservoirs is proving insufficient to handle big precipitation events like Harvey. The problem is exacerbated by the urbanization of surrounding areas, with concrete and asphalt diminishing the ability of the prairie to absorb rain water, which instead runs into the already full bayou system, designed by nature and modified by the Army Corps of Engineers for a different run off pattern. All these factors combine to increase the probability of flooding when there is heavy rain. The effect of these factors has been felt recently - more than a third of the properties that flooded in Houston’s Memorial Day 2015 and Tax Day 2016 floods are located outside areas that the Federal Emergency Management Agency deems to be at high risk of flooding.
The location of flooded buildings relative to demarcated Flood Zones
Dirty Air
Earlier this year the American Lung Association released its 20th annual report on the State of the Air in American cities. The news was not good for Houston, where some of the progress made in recent years has been reversed somewhat. Of particular concern is the levels of ozone in the city’s air, which is formed by reaction with NOX and VOX pollutants. Ozone and particle pollution present a variety of health risks to the 7 million Houstonians living in the area, particularly those with pre-existing conditions such as asthma and COPD. About 60% of ozone forms from fumes emitted by transport, the rest from industrial processes such as coal-fired power generation. This is another example of the negative impact of industrial and economic processes in the region that support a healthy economy in the area, but increase environmental risks for the population. While we’ll come back to this point later in the article, it’s worth noting that CO2 emissions often go hand in hand with NOX and VOX pollution. Texas is the highest CO2 emitting state in the nation.
Changing Climate
In the preceding paragraphs I have outlined the increasing environmental risks in the Houston area associated with the negative impacts of industry and commerce. Like the Humber Estuary, the coincidence is not an accident - Houston’s history is founded on the petroleum industry, related heavy industries, and several neighboring sea ports. Population growth has gone hand in hand with economic growth. If these environmental risks weren’t enough to be worried about, global climate change only compounds the threats.
The heat-trapping nature of CO2 and other GHGs has been known about for more than 100 years and has measured from space for decades. CO2 concentrations varied with the cyclicity of ages over the last few million years and in the last 350,000 years that variation has continued. The cycles of ice ages depicted in the chart above are caused by eccentricities in the orbit of the Earth around the sun. As the sunlight incidence on the planet is reduced through thousands of years so the plant grew cooler. In a cooling world CO2 is naturally sequestered in the oceans and biosphere and hence CO2 concentration parallels temperature. These glacial periods come to an abrupt end because of several strongly reinforcing agents that enhance the warming effect of the sun. This includes the reduced reflectivity of the planet’s surface as ice is melted. In addition, CO2 is expelled from the oceans and biosphere as they warm increases heat retention and positively reinforces warming. These “abrupt” ends to glacial periods actually still take thousands of years. For the last 12,000 years or so, the planet has been in an inter-glacial period. It’s known to geologists as the Holocene. The last four inter-glacials have been characterized by C02 levels of about 300 ppm and have lasted about 20,000 years. During the last 150 years or so CO2 in the atmosphere has risen sharply to over 400 ppm, higher than its been for 3 million years, and at a much faster rate . Humanity is wholly responsible for this sharp rise in CO2: through burning of fossil fuels and deforestation. About half the CO2 we’ve generated as ended up in the oceans (increasing acidity) and the other half has increased the C02 concentration in the atmosphere by about 40%. The planet's average surface temperature has risen about 1.62 degrees Fahrenheit (0.9 degrees Celsius) since the late 19th century. And because of ice sheet melting and thermal expansion, global sea level is rising at about 3.2 mm per year.
These globally coherent effects of climate change are projected to grow, at a minimum at similar rates to present, but many models predict increased rates of warming, particularly if emissions continue to grow. No further change is not within these ranges of uncertainty or error bars. These global increases in temperature and sea level only serve to compound the risks described above for the Houston area and surrounding regions of Texas. Coastal flooding and the side effects such as susceptibility to tropical storms will worsen. Temperature increases will accelerate “bad”ozone production. Wildfires in the surrounding regions could not only destroy natural resources, but add to the particle pollution problem in Houston and other population centers in Texas.
Conclusion: it’s not a problem, it’s a growing crisis
While it’s statistically possible of course, three 500 year floods in as many years, has to be addressed. Add in the other natural and manmade environmental risks outlined in this article, I believe I’ve described a crisis. The Houston area, for all its economic vibrancy, is not on a sustainable path. Ignoring global warming, this crisis still needs an integrated and coherent response. Layering on the effects of global climate change increases the current risk exposure and escalation potential of the crisis in the region. Put another way, Houston has to deal with the impacts of unsustainable economic development at both local and global scales.
Any action plan will have both mitigation and adaptation measures. Mitigating actions will reduce emissions, manmade subsidence and so on. A side-product of these actions will be to reduce or eliminate part of the America’s contribution to global climate change. Adaptive actions will include measures to make the area more resilient to the consequences of these risks, such as re-engineered drainage or coastal barriers. A plan for a sustainable Houston will allow economic growth for the good of all today, but not at the cost increasing environmental risks for future generations. The good news that Houston is blessed with capabilities, resources, technology, innovation and spirit to meet this challenge. There is more than enough ability to develop a plan for a more sustainable Houston and execute. We just need to decide to do it.
In a follow up article to this one I will review some of the action planning that is being undertaken in the Houston area and suggest some ideas to accelerate and grow the response. Perhaps most importantly we will need leadership from all sectors of society ready to take on a challenge with no easy answers.