climate change on UAE - Stockholm Environment Institute-US Center

Annex 1: Elevation Data
Sensitivity
Analysis
Introduction: the influence of digital
elevation models (DEMs) on models of sea level
rise.
Topographic information is integral to analyses
in many fields of research including ecology,
hydrology, agriculture, geology and others. With
technological advances, many researchers have
transitioned to using digital elevation models
(DEMs) for computer-based processing. A DEM
is merely numerical representation of surface
elevations over a region of terrain (Cho and
Lee, 2001). There are multiple ways to derive
DEMS- from time-consuming digitization
processes of paper quadrangle maps to shuttle
radar missions. A body of literature has emerged
around both assessments based on DEM source
(Hodgson et al., 2003) as well as the impact
of DEM resolution on the results of research
projects.
DEMs are used in an array of projects. Elevation
data contributes to site suitability analysis for
property development, transportation networks
and other infrastructural developments, as
well as identifying ecosystem and biodiversity
conservation or migration. Researchers also
use coastal DEMs to identify the extent of
areas vulnerable to sea level rise and storm
surges. As scientists have begun realizing that
the pace of <strong>climate</strong> <strong>change</strong> is much faster than
initially expected, there is an urgent need for
more accurate modeling of regional and abrupt
sea level rise, coastal inundation of flood plains
from storm surges, and a range of other <strong>climate</strong>
<strong>change</strong> impacts.
DEM Comparisons
Jarvis et al. (n.d.) explored different DEM
through a serious of case studies in Ecuador,
Honduras, and Columbia. In Ecuador, the
researchers analyzed the SRTM DEM
against the global, GTOPO30 data set and in
Honduras the compared the SRTM against
cartographically derived TOPOGRID at
1:50,000 1 . SRTM is vast improvement on global
DEM (GTOPO), and care should be taken
when interpolating SRTM holes with GTOPO
data. The researchers found that based on
their analysis of specific locations that SRTM
data are was accurate to +/- 16-meters. After
comparing SRTM values against an existing
GPS database of elevation points, the team
found that SRTM values were close to GPS
values 80% of the time. On average, the SRTM
differed from the TOPOGRID by 8 meters and
from the GPS points by 20meters.
The researchers found that terrain heavily
influenced the elevation difference between the
DEMs. In addition, as hydrologic properties
are inherently tied to terrain, the quality of
terrain data affects the accuracy of hydrologic
models. Researchers agreed that the 1:10,000
cartographic derived DEM is the best scale
especially when dealing with hydrological
models; however, high-resolution cartographic
data exists for few areas in tropical countries.
Even in countries with a strong tradition of
cartographic mapping, like the US, age of
cartographic maps on which national DEMs are
based adds another dimension to the accuracy
of models; for example, 1950s contour lines in
one region may not accurately reflect more
recent land <strong>change</strong>s.
Typically, in tropical countries, the SRTM
overestimates for northeast facing slopes and
underestimates for southwest facing slopes;
an occurrence that correlates with shuttle
flight path directions. In general, the SRTM
data tended to have more surface detail
and roughness than the TOPOGRID. For
hydrological modeling, the SRTM performs well
Impacts, Vulnerability & Adaptation for
Coastal Zones in the United Arab Emirates
1 The cartographically derived maps were digitized by the Centro International de Agricultura Tropical (CIAT). The entire
country, 280 topographic sheets and an additional 250 maps from the national forestry commission that needed rectifying were
digitized at a 1:50,000 scale (with 100m contour lines, and 10m contour lines