ILLUSTRATED FLORA OF EAST TEXAS - Brit - Botanical Research ...

CLIMATE OF EAST TEXAS/INTRODUCTION 71
(Bomar 1995). Houston and nearby areas have unfortunately experienced more recent inundations,
including those resulting from Tropical Storm Allison. This storm, which stalled over
the Houston area for five days in June of 2001, produced as much as 37 inches (94 cm) of
rain and caused devastating flooding. The results included 22 fatalities in Texas and approximately
$5 billion in damages, making it the costliest tropical storm in U.S. history (National
Weather Service 2003a, 2003b).
It should be noted that flooding in urban areas such as Houston is exacerbated by
human-caused changes in hydrology (e.g., paving over large areas, and thus dramatically
increasing runoff), while natural vegetation in many flood-prone areas (e.g., parts of the Big
Thicket) absorbs water, reduces flood damage, is well-adapted to recurrent flooding and
inundation, and is seldom permanently affected. In addition, Houston may possibly influence
its own rainfall patterns. The “urban heat island” effect has long been known (e.g., Howard
1833; Streutker 2003). Caused by heat generation associated with human activities and the
greater absorption of heat by asphalt, concrete, and buildings than by natural landscapes,
cities are often warmer than surrounding areas. On hot summer days, urban air can be
2–10°F (1.1–5.6°C) hotter than the nearby countryside (Environmental Protection Agency
2003). However, it has recently been suggested that major cities, with their large amounts of
rising hot air and turbulence caused by tall buildings, may actually generate convective
clouds, thunderstorms, and rainfall locally. This appears particularly likely when there is a
nearby source of moist air (e.g., the Gulf of Mexico) (NASA 2000; Goddard Space Flight
Center 2003; Kluger 2003; Shepherd & Burian 2003). There is also an issue with ground subsidence
along the Texas Gulf Coast. The excessive pumping of groundwater, combined with
the increased weight from city development, has lowered the elevation of major coastal cities
like Houston, leading to a heightened potential for increasingly damaging floods (D. Finfrock,
pers. comm.; Neighbors 2003). Houston’s repeated bouts with natural disasters thus seem to
be at least partly the result of a number of either predictable or human-caused problems—a
large population living in a low-lying, naturally flood-prone coastal area, continuing hydrologic
modifications making flooding ever more likely, ground subsidence, and human-induced
weather changes.
In a different part of East Texas, the incredibly sticky “black waxy” soil of the Blackland
Prairie is particularly problematic during wet weather. Personal accounts (e.g., Mosely in
Yelderman 1993) described how under wet conditions the dirt roads were virtually impassable
and families actually went hungry until the ground dried enough for people to get to
town to obtain food. Drought, on the other hand, is a bigger problem in the western part
of East Texas, with the lack of water probably always being a limiting factor for humans as
well as plants and animals. The relatively impermeable clay soils, the lack of dependable
shallow water-bearing layers, and the scarcity and transitory nature of surface streams made
the early Blacklands a particularly inhospitable environment. This difficulty was noted in
the early explorer accounts, such as the one by D.P. Smythe (1852) who described a trip
across the Blacklands:
The soil improves now at every step becoming more level, and uniformly of a dark rich color, but the
water is very bad and scarce, drying up entirely during the heat of the summer.… During the
forenoon of today we must have traveled some twenty miles without passing over a spot of thin soil;
being chiefly the black stiff ‘hog wallow’ prairie, rolling just enough to drain itself, but entirely
destitute of water during the summer.…
Josiah Gregg, another early explorer who traveled in the area in 1841–1842, indicated that in
addition to droughts, the lack of springs or dependable water was “one of the greatest defects
of this country” (Fulton 1941).
Even today, the concentration of rainfall in spring and fall, coupled with hot dry summers,
makes the water problem acute on the Blackland Prairie (Yelderman 1993). Currently, access