flooding

Houston’s long history of flooding

Houston, Texas, seat of Harris County, has a long history of flooding because the city was built on a flood plain. The deluge generated by hurricane Harvey in August, 2017, is only the latest episode.

Houston lies within a coastal plain about 50 miles northwest of Galveston. The area has very flat topography which is cut by four major bayous that pass through the city: Buffalo Bayou, which runs into downtown and the Houston Ship Channel; and three of its tributaries: Brays Bayou, which runs along the Texas Medical Center; White Oak Bayou, which runs through the Heights and near the northwest area; and Sims Bayou, which runs through the south of Houston and downtown Houston. The ship channel goes past Galveston and into the Gulf of Mexico.

The land around Houston consists of sand, silt, and clay deposited by local rivers.

The sedimentary layers underneath Houston ultimately extend down some 60,000 feet, with the oldest beds deposited during the Cretaceous. Between 30,000 feet and 40,000 feet below the surface is a layer of salt, the primary source of salt domes which dot the metropolitan area. Since salt is more buoyant than other sediments, it rises to the surface, creating domes and anticlines and causing subsidence due to its removal from its original strata. These structures manage to capture oil and gas as it percolates through the subsurface. [source]

Groundwater pumping also causes subsidence in parts of the city. (See: Geologists find parts of Northwest Houston, Texas sinking rapidly )

Hurricane damage in Houston:

As described by the Harris County Flood Control District (HCFCD) [link]:

When the Allen brothers founded Houston in 1836, they established the town at the confluence of Buffalo and White Oak Bayous. Shortly thereafter, every structure in the new settlement flooded. Early settlers documented that after heavy rains, their wagon trips west through the prairie involved days of walking through knee-deep water. Harris County suffered through 16 major floods from 1836 to 1936, some of which crested at more than 40 feet, turning downtown Houston streets into raging rivers.

Houston was flooded during the September, 1900, hurricane which wiped out Galveston.

In December of 1935 a massive flood occurred in the downtown Houston as the water level height measured at Buffalo Bayou in Houston topped out at 54.4 feet which was higher than Harvey. There have been 30 major floods in the Houston area since 1937 when the flood control district was established in spite of construction of flood control measures.

In June, 2001, Harris County suffered widespread flooding due to hurricane Allison. According to HCFCD, before leaving the area, Allison would dump as much as 80 percent of the area’s average annual rainfall over much of Harris County, simultaneously affecting more than 2 million people. When the rains finally eased, Allison had left Harris County, Texas, with 22 fatalities, 95,000 damaged automobiles and trucks, 73,000 damaged residences, 30,000 stranded residents in shelters, and over $5 billion in property damage in its wake.

Some climate alarmists are claiming that global warming has played a part in the flooding produced by hurricane Harvey. Dr. Roy Spencer debunks that notion here and here. Storms of or greater than Harvey’s magnitude have happened before. Storm damage is not due entirely to weather. Some is due to local infrastructure.

It all boils down to the luck of the draw: if you choose to inhabit a flood plain, you will get wet from time to time.

P.S. Prior to Harvey, which made landfall as a Category 4 storm, the U.S. had gone a remarkable 12 years without being hit by a hurricane of Category 3 strength or stronger. Since 1970 the U.S. has only seen four hurricanes of Category 4 or 5 strength. In the previous 47 years, the country was struck by 14 such storms.

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Rate of sea level rise is controlled by natural oscillations

A new paper by Dr. Nicola Scafetta of Duke University examines the relationship of natural, solar-driven ocean oscillations such as the Pacific Decadal Oscillation (PDO), Atlantic Multidecadal Oscillation (AMO), and the North Atlantic Oscillation (NAO) to the changes in rate of sea level rise. He finds no correlation with atmospheric carbon dioxide or temperature.

Before I get into the Scafetta paper, here is some background.

Measuring sea level is more complicated than pounding a stake into a beach. Ideally, global sea level would be a rotating oblate ellipsoid of polar radius of 6365.752 km and equatorial radius of 6378.137 km in absence of any other forces. Gravity distorts this ideal shape to make it lumpy.

There are daily and seasonal variations, and storm surges in addition to the oscillations mentioned above. There are tectonic events: is the ocean rising or is the land sinking? Also, extraction of groundwater near coasts may cause the land to sink and present an apparent rise in sea level. All these confounding factors can produce a local rate of sea level change very different from global rate of change.

post-glacial-sea-level-riseSince the end of the last glacial epoch, sea level has risen 120 meters (393 feet), about one meter per century. Sea level is still rising at the rate of 1- to 3mm per year, according to NOAA, about the thickness of one or two pennies.

As you can see from the figure, the rate of sea level rise has changed on broad time scales. Scafetta has found patterns of acceleration and deceleration of rise at much smaller time scales.

Scafetta studied six long-term tidal gauge records sited to represent all of the world’s oceans. He found the rate of sea level rise “…to be characterized by significant oscillations at the decadal and multidecadal scales up to about 110-year intervals. Within these scales both positive and negative accelerations are found if a record is sufficiently long. This result suggests that acceleration patterns in tide gauge records are mostly driven by the natural oscillations of the climate system. The volatility of the acceleration increases drastically at smaller scales such as at the bi-decadal ones.”

“Tide gauge accelerations oscillate significantly from positive to negative values mostly following the PDO, AMO and NAO oscillations. In particular, the influence of a large quasi 60–70 year natural oscillation is clearly demonstrated in these records.”

A conclusion from this paper has implications for climate model predictions: “at scales shorter than 100-years, the measured tide gauge accelerations are strongly driven by the natural oscillations of the climate system (e.g. PDO, AMO and NAO). At the smaller scales (e.g. at the decadal and bi-decadal scale) they are characterized by a large volatility due to significant decadal and bi-decadal climatic oscillations. Therefore, accelerations, as well as linear rates evaluated using a few decades of data (e.g. during the last 20-60 years) cannot be used for constructing reliable long-range projections of sea-level for the twenty first century.”

The cyclical nature of the rate of sea level rise, and its quite variable accelerations and decelerations at different time scales may explain why different researchers get different rate values. So, scary stories saying we are doomed because of acceleration in the rate of sea level rise, such as the ‘science fiction” stories linked below, should be taken with a grain of salt.

Reference: Scafetta, N., 2013, Multi-scale dynamical analysis (MSDA) of sea level records versus PDO, AMO, and NAO indexes, Climate Dynamics, DOI 10.1007/s00382-013-1771-3.

See the full paper here.

See also:

Science Fiction from the University of Arizona?

More science fiction from the University of Arizona

University of Arizona dances with sea level

Sea Level Rising?

Sea Level Rise in the South Pacific: None

Sea Level Rise Declining says EU

Obama parts the waters, sea level drops

Size matters in sea level studies

Sea level rising fast along American East Coast – or not

El Niño, bristlecone pines, and drought in the Southwest

While the Southwest is experiencing drought conditions, unusual flooding is occurring along the Mississippi River.  This is part of the natural La Niña cycle.

Research from the University of Hawaii’s International Pacific Research Center  has found an 1100-year correlation between El Niño-La Niña cycles and tree rings in bristlecone pines in the American Southwest.  This may allow better prediction of the cycles and a better understanding of past cycles and their implications.

El Niño and its partner La Niña, the warm and cold phases in the eastern half of the tropical Pacific,  play havoc with  climate worldwide. Predicting El Niño events more than several months ahead is now routine, but predicting how it will change  in a warming world has been hampered by the short instrumental record. An international team of climate scientists has now shown that annually resolved tree-ring records from North America, particularly  from  the US Southwest, give a continuous representation of the intensity of El Niño events over the past 1100 years and can be used to improve El Niño prediction.

Tree rings in the US Southwest, the team found, agree well with the 150-year instrumental sea surface temperature records in the tropical Pacific. During El Niño, the unusually warm surface temperatures in the eastern Pacific lead to changes in the atmospheric circulation, causing unusually wetter winters in the US Southwest, and thus wider tree rings; unusually cold eastern Pacific temperatures during La Niña lead to drought and narrower rings. The tree-ring records, furthermore, match well existing reconstructions of the El Niño-Southern Oscillation and correlate highly, for instance, with [oxygen 18] isotope concentrations of both living corals and corals that lived hundreds of years ago around Palmyra in the central Pacific.

The graph below shows the correlation.

El nino amplitude from tree rings

The tree rings reveal that the intensity of El Niño has been highly variable, with decades of strong El Niño events and decades of little activity. The weakest El Niño activity happened during the Medieval Climate Anomaly in the 11th  century, whereas the strongest activity has been since the 18th  century.

These different periods of El Niño activity are related to long-term changes in Pacific climate. Cores taken from lake sediments in the Galapagos, northern Yucatan, and the Pacific Northwest reveal that the eastern–central tropical Pacific climate swings between warm and cool phases, each lasting from 50 to 90 years. During warm phases, El Niño and La Niña events were more intense than usual. During cool phases, they deviated little from the long-term average as, for instance, during the Medieval Climate Anomaly when the eastern tropical Pacific was cool.

While correlation does not necessarily prove causation, these results are compelling.  Many factors such as temperature and amount of precipitation affect the width of tree rings.  The researchers say in this case, that precipitation is the controlling factor.  They rely on Liebig’s Law  which states that yield is proportional to the amount of the most limiting nutrient, and in the desert southwest, water is the limiting factor.

We are currently experiencing the La Niña phase which means a dry southwest and colder, wetter conditions in the north and mid-west.

For more background on drought see: Drought in the West.