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Wageningen University (2020)

Characterising turning points and their drivers in Moroccan Dryland Ecosystems over the Last 20 years

Heger, Rick

Titre : Characterising turning points and their drivers in Moroccan Dryland Ecosystems over the Last 20 years

Auteur : Heger, Rick

Université de soutenance : Wageningen University

Grade : Master of Science (MS) Geo-information Science and Remote Sensing 2020

Résumé partiel
Among the Sustainable Development Goals (SDG), SDG 15.3 : “end desertification and restore degraded land” is of great importance, yet challenging, for drylands all over the world. Especially in Morocco, of which a vast area is dryland, and thus vulnerable to desertification and land degradation. By understanding turning points (i.e., key moments in the ecosystem development where its functioning is significantly changed or altered) in Moroccan dryland ecosystem functioning and their effects on desertification and land degradation, valuable information is produced for better dryland ecosystem conservation. This research aimed to (1) identify and classify turning points in Moroccan dryland ecosystem functioning and (2) to establish a relationship between turning points and their drivers. Moreover, this research intended to (3) identify and classify abrupt changes in vegetation greenness trends on a sub-national scale, namely in the Todgha valley, and to investigate the explanatory value of migration to characterise the detected changes. By applying BFAST01 (a time series segmentation technique) on a 19-year rain-use efficiency time series, turning points were detected. Next, a typology developed for the classification of turning points was used to characterize ecosystem functioning changes in Moroccan drylands. Results showed a hotspot of turning points in the northern part of Morocco, in 2009, encompassing the Moulouya River basin. The majority of turning points (63.2%) were characterized by a steady increase in ecosystem functioning up to the turning point occurrence, after which the increase in ecosystem functioning slowed down. The Hassan II dam might explain the occurrences of these turning points, as the dam possibly led to a reduction of water availability downstream. Further analysis, by means of a binary logistic regression, showed that a combination of proximate (i.e., cropland abandonment, changes in sparse herbaceous land cover, and built-up expansions) and underlying causes (i.e., the occurrence of abnormally dry months and population density increase) had influence over the probability of a turning point occurrence in Moroccan dryland ecosystem functioning. However, the model resulted in a McFadden pseudo-R 2 of only 0.015, so interpretation should be done with care.

Mots Clés : brupt changes, rain-use efficiency, ecosystem functioning, turning point, drylands, drivers


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