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University of Twente (2019)

Spatial temporal relationship between elephant movements and the surface water availability in the Amboseli ecosystem.

Chen Na

Titre : Spatial temporal relationship between elephant movements and the surface water availability in the Amboseli ecosystem.

Auteur : Chen Na

Etablissement de soutenance : University of Twente

Grade : Master of Science in Geo-Information Science and Earth Observation 2019

Résumé
African elephants (Loxodonta Africana) are water dependent-species that can drink up to 50 gallons of water per day. Also, elephants need water for thermoregulation since they are susceptible to high temperature and sunburn. In particular, the movements of elephants are constrained by the limited surface water resources in the dry season. Despite the importance of surface water availability to elephants, lack of detailed surface water information in dry and wet season hampers further understanding of relationships between surface water and elephant movements. Remote sensing data had been widely and successfully used in the mapping of surface water. This study first mapped the surface water in the dry season and wet season over the Amboseli ecosystem used the Sentinel-1 radar image, Sentinel-2 optical image, and the combination of both based on random forest method. Then kappa coefficients of using Sentinel-1, Sentinel-2 or the combination of both were compared to identify the surface water maps that have the highest kappa coefficient for further analysis. Next, the Sentinel surface water maps were compared with existing surface water products (ILRI and JRC), after which, the distance of elephants to the nearest surface water during dry and wet season were quantified and compared. Finally, speeds of elephant movements have been calculated, classified into three categories regarding the distances of elephants to the nearest surface water and difference in the speeds was tested. These three categories are close to water (< 3km) ; Medium to water (3km - 6km) ; far from water (> 6km). Results are as follows, 1) the kappa coefficient of mapping surface water in the Amboseli ecosystem using the combination of Sentinel-1 radar and Sentinel-2 optical data is significantly higher than the one used Sentinel-1 data ; 2) There is not a significant difference between the kappa coefficients of using Sentinel2 optical data and the combination of Sentinel-1 and Sentinel-2 data. 3) A significant difference was observed in surface water distribution pattern among the three surface water products (Sentinel, ILRI and JRC). 4) The mean distance of elephants to the nearest surface water extracted from the Sentinel water products during the dry season and wet season are 6.7 km and 4.2 km, respectively ; 5) The distance of elephant to the nearest surface water is longer in the dry season compared with that in the wet season ; 6) A significant difference exists in the speeds of the elephant movement between close and far distance classes during the dry and wet season. The study mapped the surface water in the Amboseli ecosystem and suggested that elephant in the Amboseli ecosystem moved faster when they are closer to surface water. Findings of the relationship between the elephant movements and surface water availability are essential for understanding the movements of elephants as well as developing conservation strategies for wildlife and surface water resources.

Mots clés : Surface water, elephant movement, Sentinel-1, Sentinel-2, DEM, Amboseli ecosystem, random forest

Version intégrale (ITC)

Page publiée le 31 octobre 2019