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Desertification and Land Degradation Processes
Published in Ajai, Rimjhim Bhatnagar, Desertification and Land Degradation, 2022
The wind is the other important agent of soil erosion, and the process of erosion through wind action is called the ‘aeolian process' or simply ‘wind erosion'. In fact, wind erosion has always been occurring as a natural land-forming process (Livingstone and Warren 1996), but in recent times, the geomorphic effects of wind are locally accelerated by anthropogenic interventions. The problem of wind erosion has attracted much more attention since the ‘Dust Bowl' event in the Great Plains of the United States (Cooke and Doornkamp 1974). The aeolian process is common and more pronounced in arid and semi-arid regions of tropical and temperate environments where strong winds can easily mobilize soil particles from the land surface.
General report: Classification of arid soils for engineering purposes
Published in P.G. Fookes, R.H.G. Parry, Engineering Characteristics of Arid Soils, 2020
Arid soils have a number of significant characteristics which result from their conditioning and which influence their behaviour. The most important of these are: Low water content and low water table. This usually results in arid soils being unsaturated and having relatively large pore water suctions.Low organic content. This results in arid soils being poor for agricultural purposes. (Note that dictionary definitions of arid talk about dry, parched, barren, unproductive and so on, usually in an agricultural context.)Many arid soils have a crust which is rich in salts. This arises largely from upward moisture movements in the arid environment. Moisture loss at the top of the profile by evaporation often results in arid soils being cemented or bonded by precipitation of salts.Many arid soils are aeolian, ie. they were transported and sorted by and deposited from wind. This often results in them being poorly graded (ie. with nearly uniform grain size) and having a very loose structure.
Aeolian processes and landforms
Published in Richard J. Chorley, Stanley A. Schumm, David E. Sugden, Geomorphology, 2019
Richard J. Chorley, Stanley A. Schumm, David E. Sugden
Wind velocity near the ground depends largely upon the roughness of the ground surface, and velocity decreases to zero at the surface (Figure 16.3A). The roughness of the ground surface, whether it be due to vegetation or to the irregularity of the surface itself, has a significant effect on wind velocity. The logarithmic plots of Figure 16.3B intercept the Y-axis at some value greater than zero indicating that wind velocity is, in fact, zero at some small height above the ground surface. This height is approximately one-thirtieth of the mean grain diameter on the surface; i.e. if the average diameter of particles on the ground surface is 30 mm, then wind velocity is zero at 1 mm above the ground surface. This is important because the larger particles prevent the movement of the smaller particles by protecting them from the wind. Therefore, a rough surface or a surface covered with an armour of scattered boulders or cobbles is very effective in reducing aeolian erosion. Figure 16.4 shows the aeolian transport of various sediment sizes with height above the surface, as collected in vertical sand traps in Coachella Valley, California, during 146 days prior to 11 December 1953 (Sharp, 1964). This indicates the small range of sizes being moved, the predominance of fine and medium sand and that most of the transport takes place quite close to the ground surface.
Monitoring interannual dynamics of desertification in Minqin County, China, using dense Landsat time series
Published in International Journal of Digital Earth, 2020
Xiaolin Zhu, Kwok Huen Leung, Wing Sze Li, Lek Kin Cheung
Climate change, especially global warming and acidification, can increase evaporation of water and dry the soil, which, in turn, can decrease the vegetation cover and then cause land degradation. The geographic location is another natural factor associated with land degradation. Northwest China is located far from the sea, and the precipitation is low, erratic and concentrated mostly in the warmer months with high interannual variations. The low and irregular precipitation, along with Aeolian soil texture, erodible land surface, and strong and frequent winds, provides the dynamic force for soil erosion (Tao 2014). Figures 10 and 11 show the temporal trend of annual average temperature and precipitation in Minqin County. The temperature in Minqin County is increasing from 1987 to 2013, while the precipitation shows no significant change trend. Given the annual change of temperature and precipitation, the study area should become gradually drier over the study period. Under this scenario, the desertification would become more serious. As a result, the vegetation coverage and greenness would have declined over the past 31 years. However, the Landsat EVI data show an increasing trend. Therefore, climate may not be the dominant factor influencing the vegetation in Minqin County from 1987 to 2017, or the negative effect of climate has been weakened by the governmental policies against desertification that will be discussed in the following paragraphs.
Desertification detection model in Naiman Banner based on the albedo-modified soil adjusted vegetation index feature space using the Landsat8 OLI images
Published in Geomatics, Natural Hazards and Risk, 2020
Ye Wen, Bing Guo, Wenqian Zang, Dazhuan Ge, Wei Luo, Huihui Zhao
Naiman Banner (42°14′−43°32′N, 120°19′−121°35′E) is located in Horqin Sandy Land, which is a typical region with a semi-arid and semi-humid agro-pastoral ecotone in China. The climate of this region is characterized by cold winter and hot and rainy summer with an annual average temperature of 6.0 °C–6.5 °C and an average precipitation of 366 mm. The low mountains and hills are located in the south part, whereas the wind-erosion-accumulated sands and alluvial plains dominate the middle and north parts, respectively. During the previous decades, this region has experienced extensive aeolian desertification under the joint actions of climate change and human activities, including overgrazing, over-reclamation, and unreasonable utilization of water resources. Therefore, the effects and applicability of different feature space models (including nonlinear and linear models) for monitoring the desertification information were compared and analyzed. In this study, the MSAVI and albedo were inversed by utilizing the Landsat 8 OLI image to construct linear and nonlinear feature space models. Subsequently, comparisons and analysis were conducted to propose an optimal desertification monitoring model.
Reflectance spectroscopy and ASTER mapping of aeolian dunes of Shaqra and Tharmada Provinces, Saudi Arabia: Field validation and laboratory confirmation
Published in International Journal of Image and Data Fusion, 2023
Yousef Salem, Habes Ghrefat, Rajendran Sankaran
Aeolian dune movements in the desert landforms under arid environments lead to sand transportation and encroachment, caused land degradation, and an obstacle to agricultural and infrastructural development, and it is important to study mineralogy, grain size, distribution of the sand deposits to understand the sources, environment, and hazards of the aeolian deposits (Rahdari et al., 2021; Afrasinei et al. 2018, Engel et al. 2018, Gómez et al. 2018, Yang et al. 2019, Aydda et al. 2020, Delgado Blasco et al. 2020, Mahmoud et al. 2020, Nguyen et al. 2021, Zhu et al. 2021). Also, the mapping of dunes allowed understanding the morphology, short-term, and long-term changes and assessing the land encroachment and land degradation of the region (Bullard et al. 2011, White et al. 2015, Afrasinei et al. 2018, Engel et al. 2018, Gómez et al. 2018, Delgado Blasco et al. 2020, Mahmoud et al. 2020). The transportation of sands changed the sedimentation of sand particles in different sedimentary environments (Bagnold 1941, 1951, Ramsey et al. 1999). According to Cooke et al. (1973), the sand sizes changed the dune morphology and a small percentage of coarse grains could perform a sealing process over the dune surface. Wilson (1972) studied the transportation of sands having different grain sizes and stated that the activity expanded the surface of the dunes. Previous studies showed variation in grain sizes on the horns of the dunes and their peaks (Folk 1971, Lancaster 1981). The statistical measurements of sand grains such as mean, median, mode, skewness, kurtosis, etc. were used in several studies to understand the dunes development, occurrence, and movement (Folk and Ward 1957, Folk 1966, Mcbride 1971, Lancaster 1981, Purkait 2006, 2010, Benaafi and Abdullatif 2015, Koeshidayatullah et al. 2016, Amin and Abu Seif 2019, Benaafi et al. 2020, Lopez et al. 2020). The study of reflectance spectroscopy of sands of the dunes has been used to determine sand’s granular size and its mineral composition (Salisbury and Eastes 1985, Paisley et al. 1991, Salisbury and D’Aria 1992, Wald and Salisbury 1995, Clark 1999, Ghrefat et al. 2007, Scheidt et al. 2011).