climate change on UAE - Stockholm Environment Institute-US Center

e defined climatically (Boer, 1997), although
increasingly harsh land use practices along
the coast may rapidly overtake contemporary
<strong>climate</strong> as an ecosystem driver. In undisturbed
savannas, the frequency and intensity of
rainfall and temperature fluctuations drive the
distribution of grasses, trees and shrublands.
Land uses and disturbances add a level of
complexity to the story: Grazing dynamics
(both intensity and timing) can quickly shift
can force semi-arid grasslands towards either
shrub or grassy monocultures; fire frequency
alters the balance of shrubs and grasslands;
and human disturbances, such as road building
and mineral extraction, commonly introduce
exotic and invasive species. In the UAE, some
exotics have been introduced for horticultural
purposes (such as Prosopis juliflora, an acacia)
and are spreading invasively (Essa et al., 2006).
To date, the most significant threats to the
dryland ecosystems of the UAE have been from
land use and development practices: camel
overgrazing of sensitive vegetation (Gallacher
and Hill, 2008), rapid urban development (Brown
et al., 2004), and unchecked groundwater
extraction (Zoebisch and DePauw, 2004; Brook
et al., 2005). However, <strong>change</strong>s in the already
extreme climatic conditions of the UAE could
significantly impact the already strained
ecosystem. The semi-arid Sudanian coastal
belt could see rainfall reductions, or shifts in
intensity and timing, which could lead to shifts
in the dominance of grasses, shrubs, and trees,
or even a loss of biota altogether.
Many researchers (Ogle and Reynolds, 2004;
van de Koppel et al, 2004; Holmgren, 2006)
have found that in desert ecosystems, plant
functional types respond to precipitation pulses
differently: relatively small amounts of rainfall
trigger growth and respiration in biological soil
crusts at the top several centimeters of soil,
while less common, but larger precipitation
events trigger the growth of grasses and
sedges. These grasses survive drought years by
producing large seed stores in rainy years which
then sprout in future rainy years.
Finally, rare heavy rainfall events can migrate
through soils into groundwater and contribute
to the growth of trees and shrubs with deep
taproots. These shrubs survive drought through
senesce and dormancy. However, extended
droughts can begin to reduce the ability of even
the most drought tolerant grasses to survive
with no rainfall. Some arid systems (such as soil
biota) have been shown to display a heartiness
threshold, failing to thrive when temperatures
increase without a concurrent increase in
precipitation (respiration increases with
temperature and a negative carbon balance
leads to senescence; Xu et al., 2004). Recent
observations show that the Sahara desert was
previously a wooded savanna ecosystem, which
dried out significantly about 4,300 years ago,
and then lost all vegetation cover approximately
2,700 years ago (Claussen et al., 1999; Kröpelin
et al., 2008).
Increasing aridity, when coupled with intensive
land use, is particularly damaging. In arid
regions, herbivores play an important role in
maintaining biodiversity and providing nutrients
to soils, but in wet years, both native herbivores
and livestock can increase dramatically, leading
to overgrazing in following years (Holmgren,
2006). The Millennium Ecosystem Assessment
on Desertification (MEA, 2005) suggests that
transitions from low to high pressure grazing
force a rapid transition from grasslands to
shrublands, with a subsequent increase in
erosion, loss of biodiversity, productivity, and
ecosystem services, such as groundwater
recharge. A potential <strong>climate</strong>-<strong>change</strong> induced
threshold then may be induced by either
a changing balance of temperature and
precipitation, or relatively small <strong>change</strong>s in
<strong>climate</strong> coupled with increasing land use and
grazing pressures in the UAE.
8.4. Adaptation to <strong>climate</strong> <strong>change</strong>
in drylands
The IPCC defines <strong>climate</strong> <strong>change</strong> adaptation
as: 'Adjustment in natural or human systems in
response to actual or expected climatic stimuli or
their effects, which moderates harm or exploits
beneficial opportunities'. An alternative definition
is offered in the inter-agency report, Poverty and
Climate Change, as The ability to respond and
adjust to actual or potential impacts of changing
<strong>climate</strong> conditions in ways that moderate harm
or take advantage of any positive opportunities
that the <strong>climate</strong> may afford.
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Climate Change Impacts, Vulnerability & Adaptation