Livelihood Security: Climate change, conflict and migration in - UNEP

ated to increase processing time. Building on a critical VHI threshold (VHI values < 35 indicate
severe drought conditions), the datasets were reclassified in a subsequent step. Based on these
reclassified layers (0: VHI > 35; 1: VHI < 35), finally, the number of drought affected seasons
was calculated for each cell (16 x 16 km) for the period 1985 to 2009.
DFO - FLOOD DATA
As the data is provided in Mapinfo Interchange Format on the DFO website, the first step was
to convert the data to a common vector format. In a next step a subset of the data was
created, showing the major flood events in the region of interest as polygons. Finally, a net
of artificial cells was created in order to calculate the number of flood events per cell for the
years 1985 to 2009.
CSI-CGIAR – SRTM v4 ELEVATION DATA
As the SRTM v4 global digital elevation model (GDEM) is provided in 5 degree resolution tiles,
the first step – after downloading the tiles - was to mosaic the tiles covering the target region.
APD & GPWv3 - POPULATION DATA
Population count data was acquired from different sources. Data from 1960 to 2000 was
acquired from the UNEP African Population Database (APD) website, while data from 1990 to
2010 was downloaded from the Gridded Population of the World (Version 3) portal. To determine
if the GPWv3 data could be utilized to update the available time-series of population
data as provided by UNEP-APD, Pearson’s correlation of both datasets (UNEP-APD and GPWv3)
was calculated for three larger test areas. Following this approach the overall population trend
was calculated for two periods: 1) 1970-2010 and 2) 1980-2010.
PRIO-CSCW – CONFLICT SITE DATA
After the dataset was downloaded from the PRIO-CSCW website, a subset of the data for the
region of interest was created. Then, based on the given centre-point coordinates and the
radius variable, the estimated spatial extent of the conflicts in the target area were calculated.
In order to have additional information on the number of conflicts a dissect (number of overlaps)
was calculated based on the subset.
Cartographic representation
Following analysis of the data, the resulting geospatial information layers were cartographically
refined in order to obtain a more intuitive and appealing characterization of the results,
making both interpretation and communication easier. Depending on the quality and format
of the dataset different approaches were applied:
•
•
•
Angular polygon layers were smoothed making use of Bezier interpolation techniques.
Coarse grids, such as the temperature or precipitation trend dataset (0.5 degree resolution),
were converted to point layers in order to apply spatial interpolation techniques (ordinary
kriging) to create a continuous surface of finer resolution (i.e. 0.1 degree resolution). Where
necessary, a low-pass filter was utilized to further smooth the entire raster. In a next step the
refined grids were re-converted to polygons. Finally, the polygons were smoothed making
use of Bezier interpolation techniques.
Finally, where necessary, representation tools were utilized to enhance the visual
representation of the resulting geospatial information layers.
Livelihood Security: Climate Change, Migration and Conflict in the Sahel
83