climate change on UAE - Stockholm Environment Institute-US Center

4.6. Scenarios and Key
Assumptions
It is impossible to know definitely the path of
economic growth, demographic <strong>change</strong>s, water
use patterns and priorities, etc. throughout
the ADE over the next 30 to 40 years. For this
reason, the analyst must make assumptions
regarding the future and then investigate what
those assumptions might mean for the water
supply and demand balance. In this study,
these assumptions are bundled into a set of
Scenarios that fall into three broad categories,
labeled “Optimistic”, “Pessimistic”, and
“Middle-of-The-Road”. For each of these three
broad Scenarios, we will make assumptions
about the drivers of future water demand,
including population growth rates, per-capita
water use, and <strong>climate</strong> <strong>change</strong>. Accompanying
these drivers are assumptions regarding
future water use priorities such as possible
reductions in agriculture and amenity watering,
and future water supply sources such as new
desalinization capacity or the development of
strategic reserves through aquifer storage and
recovery projects. These later assumptions will
be referred to as “adaptation options”, and will
be included as part of our Scenarios, which are
summarized in the scenario matrix of Table ‎4‐8
(Page 113). The study horizon for our analysis
is 2008 to 2050.
4.7. Developing Climate Change
Scenarios
As explained previously, there is strong scientific
consensus that the earth has been warming,
that this warming is driven substantially by
human emissions of greenhouse gases, and that
warming will continue. Climate models project
that temperatures will increase globally by 1
to 2ºC in the next 20-60 years. The projections
are fairly consistent for the next 20 years, with
a 1ºC increase, but exhibit larger uncertainty
Table ‎4‐6. 5 GCM outputs projected maximum/
minimum <strong>change</strong>s.
Temperature
Precipitation
+1.7 to 2.7°C (2050) -21% to +10% (2050)
+3.1 to 4.8 ° C (2100) -38% to +18% (2100).
in the 40-year projections. Scientists agree on
some of the important broad-scale features
of the expected hydrologic <strong>change</strong>s, the most
likely of which will be an increase in global
average precipitation and evaporation as a
direct consequence of warmer temperatures.
Regional <strong>change</strong>s, however, are more uncertain
and in fact could be quite different from regionto-region,
with some place experiencing more
and others less precipitation. Generally, Global
Climate Models agree that the mid-latitudes
and sub-tropics will be warmer.
Climate Scenarios are rooted in downscaled
General Circulation Models (GCM), which
provided a maximum and minimum projected
<strong>change</strong> in temperature & precipitation for Abu
Dhabi in 2050 and 2100. Below, we report the
projected maximum/minimum <strong>change</strong>s for 4
Scenarios (A1, A2, B1, and B2). For each of the
4 Scenarios (A1, A2, B1, and B2), the projected
maximum/minimum <strong>change</strong>s are based on
5 GCM outputs (CCC196, CSI296, ECH496,
GFDL90, and HAD2TR95) area as follows:
These projected <strong>climate</strong> <strong>change</strong>s are used as
guidelines in the development <strong>climate</strong> <strong>change</strong>
Scenarios that are used by the WEAP model
to simulate ADE water supplies and demands.
We developed three <strong>climate</strong> <strong>change</strong> sequences,
given as time series of monthly mean air
temperature and total monthly precipitation
for the period 2005 through 2050. While GCMs
are able to simulate large-scale <strong>climate</strong> features
realistically, they typically exhibit biases
at regional-scales. The regional biases are
problematic for analysis of <strong>climate</strong> implications
for hydrology and water resources (Maurer,
2007).
Recognizing the regional limitations of GCMs
has led to the application of “downscaling”
as a means of trying to understand how local
scale processes, of greater interest to water
resource planners, might respond to largerscale
weather and <strong>climate</strong> <strong>change</strong>s (Wilby et al.,
2004). Regardless of the technical approach,
the primary goal is to process or interpret the
GCM output so that it reflects the large-scale
features and temporal trends from the GCM
simulation, but also the historical patterns
of <strong>climate</strong> variables at the regional and local
scale (Wood et al., 2004). Downscaling can
produce more sub-regional detail and eliminate
Impacts, Vulnerability & Adaptation for
Water Resources in Abu Dhabi
111