15.3.2.9. U.S.-Mexican Border
The U.S.-Mexican border is characterized by a semi-arid climate, with higher
precipitation toward both coasts. Evaporation exceeds precipitation for many
months of the year, causing a soil moisture deficit. Many studies relate climate
and hydrology along the U.S. border states (Green and Sellers, 1964; Hastings
and Turner, 1965; Norwine, 1978; Cayan and Peterson, 1989) and along the Mexican
border states (Mosiño and García, 1973; Schmidt, 1975; Acosta,
1988; Cavazos, 1998). The western border has an annual rainfall of about 250
mm yr-1, with temperatures ranging from 10 to 28°C.
The Arizona-Sonora border has a much more extreme and desert climate, with only
80 mm yr-1 of precipitation and maximum temperatures
reaching 45°C. Around the Ciudad Juarez (Mexico)-El Paso (Texas) border,
annual precipitation is around 220 mm, with maximum temperatures reaching 40°C.
Finally, in the easternmost part of the border (Brownsville, Texas-Matamoros,
Mexico), annual precipitation is close to 675 mm, with temperatures ranging
from 11 to 38°C.
There is large climate variability along the U.S.-Mexican border states.
Drought and floods occur frequently (Powell Consortium, 1995), some influenced
by the occurrence of El Niño (Cavazos and Hastenrath, 1990; Cayan and
Webb, 1992). The Mexican states along the border are highly vulnerable to drought,
particularly along the Rio Grande region, areas with low precipitation rates
(less then a 100 mm yr-1) (Mundo and Martínez
Austria, 1993; Hernández, 1995; Mendoza et al., 1997). Strong
El Niño events during the summer result in severe water deficit in northern
Mexico (Magaña and Quintanar, 1997), and serious negative impacts in
agricultural activities. Such vulnerable conditions during drought periods have
resulted in legal disputes between Mexico and the state of Texas with regard
to rights to Rio Grande water.
It is unclear what the signs of future changes in precipitation and water availability
will be along the border (Mearns et al., 1995; Magaña et al.,
1997; Mendoza et al., 1997). Some scenarios suggest increased winter
precipitation and decreased summer precipitation (Magaña et al.,
1998). Without reliable predictions of precipitation changes across drainage
basins, little confidence can be placed in hypothesized effects of global warming
on annual runoff (Karl and Riebsame, 1989). Therefore, to examine potential
impacts of climate change on water availability, most studies make use of long
instrumental records of precipitation and streamflow. Some analyses indicate
that in recent decades there is a positive trend in streamflow and even precipitation,
corresponding to more water availability along the U.S.-Mexican border
(Magaña et al., 1998; Magaña and Conde, 2000). However,
demand for water in agriculture, industries, and cities is increasing steadily,
surpassing recent increases in water availability (Mundo and Martínez
Austria, 1994).
The signal of climate change along the U.S.-Mexican border may be exacerbated
along the Mexican side by differences in land use. Along the U.S. side, the
presence of gardens and green areas lead to a cooler environment relative to
the Mexican side. Currently, maximum temperatures in contiguous border towns
may differ by as much as 3°C as a result of different characteristics in
vegetation (Balling, 1988). This cross-border contrast is possible because water
consumption in U.S. border cities is four times larger than in Mexican border
cities. Surface water distribution along the border (Rio Grande and Colorado
watersheds) is regulated by the Binational Treaty of 1944. Yet, there are no
regulations for subsurface water (Sanchez, 1994).
15.3.2.10. The U.S.-Caribbean Border
Some of the U.S.-Caribbean border problems that may increase as a result
of climate change are related to:
- Effects of sea-level changes on coastal ecosystems
- Effects of temperature increases on terrestrial and aquatic ecosystems,
including possible effects on economically important species
- Effects of climate change on socioeconomic structures and activities.
Considering the high population density in part of the Caribbean islands and
coastal areas, human settlements will be highly affected by sea-level rise and
saline intrusion (Vincente et al., 1993). Coral reefs in the region may
be severely affected by coral bleaching induced by warmer water temperatures
(Milliman, 1993).
Tourism is a major economic activity in most of the region. A change in rainfall
patterns, tropical storms, and warming of the climate in temperate countries
may affect the comparative advantages of this sector in the region (Alm et
al., 1993). Narrow beaches combined with projected sea-level rise contribute
to the vulnerability of the tourism sector to changes in climate (Gable, 1997).
Potential consequences of changes in extreme events (e.g., hurricanes) are
not well-defined. Other trends, such as changing demographic patterns, may exacerbate
impacts. Recent large losses of life from rainfall-induced floods, mudflows,
and landslides reflect increasing concentrations of residents in high risk areas
(Rodriguez, 1997; Pulwarty, 1998).
|