Desertification

Desertification is a type of land degradation in drylands in which biological productivity is lost due to natural processes or induced by human activities whereby fertile areas become arid. It is the spread of arid areas caused by a variety of factors, such as climate change and overexploitation of soil as a result of human activity. Throughout geological history, the development of deserts has occurred naturally. In recent times, the potential influences of human activity, improper land management, deforestation and climate change on desertification is the subject of many scientific investigations. Definitions of words As recently as 2005, considerable controversy existed over the proper definition of the term "desertification." Helmut Geist (2005) identified more than 100 formal definitions. The most widely accepted of these was that of the Princeton University Dictionary which defined it as "the process of fertile land transforming into desert typically as a result o

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Constructing the desert. Hotel and coach station (Ouarzazate, Maroc)

Pietro Berta, Adèle Moret

Desertification process keeps on expanding, particularly on the African continent, arid areas cover one third of the surface. At the same time, the world human population increases exponentially. For these reasons, it is important to keep on exploiting these desert zones. Ouarzazate is situated in the south of Morocco in a sub-desert climate. The city is nicknamed “Door of the desert” because of its strategic location: it is situated at the junction of the two roads, which give accessibility to the south of Morocco and the Sahara desert. The region is well known for its architectural patrimony and more recently for the cinema activities. These two different domains make increase the number of visitors in this part of the country and there will soon be a lack of host infrastructure including hotels. The project, a hotel and a coach station, doesn't want to be closed-off on itself, but to take place in the city centre to benefit of the existing activities; at the same time the two programs are close to the main crossroad of the region. This situation is accorded with the way tourists travel in the region: moving a lot in order to discover a maximum of sites spread in the south and staying a short time in the same place. The hotel is inspired by the caravanserai, which was a roadside inn along the trade routes where travellers could rest and recover from the day's journey. It supported the flow of commerce, information and people. It was a place where travellers could acquire new supplies and there were also shops where merchants could dispose of some of their goods. The issue of this project in the desert is to build in a sustainable way using contemporary building construction modes being in the same time inspired by vernacular architecture.

2009

Experimental characterization of vegetation uprooting by flow

Benoît Crouzy, Katharina Maria Edmaier, Paolo Perona

We investigate vegetation uprooting by flow for Avena sativa seedlings with stem-to-sediment size ratio close to unity and vanishing obstacle-induced scouring. By inducing parallel riverbed erosion within an experimental flume, we measure the time-to-uprooting in relation to root anchoring and flow drag forces. We link the erosion rate to the uprooting timescales for seedlings with varying mean root length. We show that the process of continuous erosion leading to uprooting resembles that of mechanical fatigue where system collapsing occurs after a given exposure time. By this analogy, we also highlight the nonlinear role of the residual root anchoring versus the flow drag acting on the canopy when uprooting occurs. As a generalization, we propose a framework to extend our results to time-dependent erosion rates, which typically occur for real river hydrographs. Finally, we discuss how the characteristic timescale of plant uprooting by flow erosion suggests that vegetation survival is conditioned by multiple erosion events and their interarrival time.

2015

Optimisation temps reel en présence d'incertitude et de contraintes

Grégory François

2011

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