climate change on UAE - Stockholm Environment Institute-US Center

mm/month
mm/month (prcp)
Figure ‎4‐4. Al Ain “average” monthly PET and rainfall over the period 1994-2005.
this cover it was assumed that the Kc value
is relatively low, implying a general strategy
of under-watering. The Forests land use type
makes use of the same crop demand model
used for the Agriculture and Forestry objects in
the WEAP model.
Potential evapotranspiration (PET) is estimated
using the well known Penman Montieth
method (FAO-56) and are given in units of mm/
month. The PET was computed from monthly
observations of average air temperature (OC),
relative humidity (RH), wind speed (m/s),
and solar radiation. In addition, time series of
monthly total precipitation were used to modify
crop water requirements, although in this hyperarid
region, annual evaporation demand far
exceeds annual precipitation, and so the benefits
from rainfall in terms of satisfying crop water
demands are very marginal. Figure ‎4‐4 shows a
plot of the average monthly PET estimate for
the coast (Abu Dhabi) and Interior (Al Ain).
The coastal PET value is substantially lower
than the interior, as the high RH suppresses
PET, while lower RH and substantially higher
air temperatures raises PET in the interior of
Abu Dhabi Emirate. Figure ‎4‐4 also includes
a plot of “average” monthly rainfall over the
period 1994 through 2005 for Al Ain, and should
be referenced with the right y-axis of the figure.
Annual rainfall is only about 1% of annual PET
on average.
4.5. Calibration using observed
data
Having described the general approach to
estimating M&I, agricultural, amenity and
forestry water demands, we now summarize
WEAP’s ability to replicate the broad annual
water supply and demand for two select years,
2003 and 2005. We have chosen these two years
since they correspond to water reporting
years available from the Department of Water
Resources at ERWDA. Table 4-4 summarizes
the reported water use by sector for 2003 and
2005 (gray columns); and the corresponding
modeled water use (columns labeled
“Model”).
Our estimates of Municipal and Industrial
water use are less than the reported water
use, but are consistent with the per-capita
and population estimates given for 2003 and
2005. The discrepancy is likely due to other
uses of desalinized water that are part of the
reported estimate, including irrigation. Our
2003 estimates of agricultural, water, and
amenity uses closely match observations, while
our 2005 estimate of these same sectoral uses
is about 15% higher than those reported. This
discrepancy is a result of higher evaporative
demands in 2005 relative to 2003, which
increased modeled irrigation requirements in
all sectors. In addition, there is a reported 40%
reduction in the western forestry sector “due
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Climate Change Impacts, Vulnerability & Adaptation