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A desert is a barren area of landscape where little precipitation occurs and, consequently, living conditions are hostile for plant and animal life. The lack of vegetation exposes the unprotected surface of the ground to denudation. About one-third of the land surface of the Earth is arid or semi-arid. This includes much of the polar regions, where little precipitation occurs, and which are sometimes called polar deserts or "cold deserts". Deserts can be classified by the amount of precipitation that falls, by the temperature that prevails, by the causes of desertification or by their geographical location. Deserts are formed by weathering processes as large variations in temperature between day and night put strains on the rocks, which consequently break in pieces. Although rain seldom occurs in deserts, there are occasional downpours that can result in flash floods. Rain falling on hot rocks can cause them to shatter, and the resulting fragments and rubble strewn over the desert

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Related publications (5)

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

Calibration of ground surface albedo models

Pierre-Jean Alet, Christophe Ballif, Arttu Matias Tuomiranta

The emergence of bifacial photovoltaics as a serious option for large-scale power generation makes the accuracy of the in-situ estimation of ground surface albedo increasingly critical. Recent studies have evaluated the performance of different models but an investigation of how these models should be calibrated is missing. This paper proposes geographically generalised parametrisations for time-variant albedo models of vegetated and desert surfaces based on a worldwide database and reports their performance compared to site-specific, unbiased parametrisations. These geographically generalised formulations can be used as an alternative for lengthy calibration campaigns as their only parameters can be easily measured. The paper also presents a simple method for deriving white-sky albedo without the need for diffuse irradiance data. The method is founded both theoretically and empirically. If on-site measurements can be collected to calibrate a model, the duration of the campaign is usually a few weeks at the maximum. This paper first shows evidence of the strong impact of the timing on calibration performance and accordingly gives practical guidelines on the most suitable measurement seasons and weather conditions. In general, early-summer months appear to be the most appropriate time for calibrating most models. Atmospheric turbidity during the campaign period, however, should be either minimised or maximised depending on the site and the model. Finally, in case no flexibility exists in timing the calibration, simple models with few parameters should be deployed. Geometric mean shows the most robust performance at most sites.

PERGAMON-ELSEVIER SCIENCE LTD2022

Geometric Alignments of the Subgrid-Scale Force in the Atmospheric Boundary Layer

Chad Higgins, Charles Vivant Ignacio Meneveau, Marc Parlange

priori tests of subgrid-scale (SGS) models for large-eddy simulations (LES). The experimental arrangements and data collected have facilitated studies of variables such as the filtered strain rate, SGS stress and dissipation, and the eddy viscosity coefficient. However, the experimental set-ups did not permit analysis of the divergence of the SGS stress (the SGS force vector), which is the term that enters directly in the LES momentum balance equations. Data from a field experiment (SGS2002) in the west desert of Utah, allows the calculation of the SGS force due to the unique 4 × 4 sonic anemometer array. The vector alignment of the SGS force is investigated under a range of atmospheric stabilities. The eddy viscosity model is likely aligned with the measured SGS force under near-neutral and unstable conditions, while its performance is unsatisfactory under stable conditions.

2009

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