scholarly journals Modeling the contributing factors of desertification and evaluating their relationships to soil degradation process through Geomatic techniques

2015 ◽  
Vol 7 (4) ◽  
pp. 3735-3771 ◽  
Author(s):  
P. Shoba ◽  
S. S. Ramakrishnan

Abstract. Desertification is a prolonged stage of land degradation which converts the productive ecosystem to fragile by three crucial events namely evapotranspiration, rainfall and negative human intrusion. The present study concentrates on identifying the causative factors of desertification namely temperature, wind, rainfall and human pressure, distinguishing the desertified land from degraded land and assessing the way from which the soil degradation process gets accelerated by those factors by employing the datasets such as long term (2001–2011) and short term (2012–2015) Meteorological data and Landsat ETM+ and OLI satellite imageries of crop growing period (June–October) into geostatistical methods and newly proposed remote sensing models which yielded good accuracy with in situ observations (R2 = 0.8). In temperature induced desertified region, the rate of increment of the saline affected region was magnified significantly from 16 to 74 % (2001–2015) due to the presence of native fluoride concentration and extreme temperature event over a period of time. The long term exaggeration of soil moisture stress (19 to 90 %) has been notified in the areas that were susceptible to wind induced desertification, due to high evaporation rate invoked by extreme wind event for a substantial period. Similarly rainfall induced desertified regions have also been experiencing high soil moisture stress (4 to 70 %) because of the insufficient reception of rainfall. High human made soil salinity (36 %), human occupancy (16 %), followed by moisture stress (7 %) are observed in the human affected region because of growing population and improper land management of the already fragile land.

Solid Earth ◽  
2016 ◽  
Vol 7 (2) ◽  
pp. 341-354 ◽  
Author(s):  
P. Shoba ◽  
S. S. Ramakrishnan

Abstract. Desertification is a prolonged type of land degradation which converts the productive ecosystem to a fragile one by two crucial factors, namely, climate and negative human intrusion. The present study concentrates on identifying the causative factors of desertification, namely temperature, wind, rainfall scarcity and human pressure. It also concentrates on distinguishing the desertified land from degraded land and assessing the way in which the soil degradation process becomes accelerated by these factors, by employing data sets such as meteorological data and Landsat ETM+ (Enhanced Thematic Mapper) and OLI (Operational Land Imager) satellite images of the crop-growing period (June–October) in geostatistical methods and newly proposed remote sensing models, which yielded good accuracy with in situ observations (R2 = 0.8). The study was centered on two time periods, 2001–2011 (11 years) and 2012–2015 (4 years). In rainfall–temperature/drought-induced desertified region, the rate of salt-affected soils increased significantly from 12 to 58 % (2001–2015) due to the presence of native fluoride concentration and extreme temperature events. The region has also been experiencing high soil moisture stress (5 to 33 %) because of the insufficient occurrence of rainfall over a period of time. A longer term exacerbation of soil moisture stress (19 to 90 %) has been noted in the areas that were susceptible to wind-induced desertification, due to a high evaporation rate caused by extreme wind events for a substantial period. High human-induced soil salinity (36 %), human occupancy (16 %), followed by moisture stress (7 %) are observed in the human-affected region because of growing population and improper land management of the land that is already fragile.


2020 ◽  
Vol 92 (2) ◽  
pp. 295-306 ◽  
Author(s):  
Wiebke Niether ◽  
Alexandra Glawe ◽  
Katharina Pfohl ◽  
Noah Adamtey ◽  
Monika Schneider ◽  
...  

Abstract Understanding water stress signaling mechanisms and screening for tolerant cocoa cultivars are major challenges when facing prolonged dry and rainy seasons in cocoa-producing areas. While abscisic acid (ABA) and proline are supposed to enhance drought tolerance in cocoa, the role of polyamines remains unclear. The aim of this study was to investigate the biochemical response and phenological adaptation of cocoa (Theobroma cacao) on different soil moisture conditions, with a focus on short-term (20 days) and long-term (89 days) stress conditions, and to compare the performance of three cocoa cultivars. In a split plot design with four blocks, cocoa seedlings of an international high-yielding cultivar (TSH-565) and two locally selected cultivars (IIa-22 and III-06) from the drought-exposed Alto Beni region, Bolivia, were arranged in pots under a roof shelter (cultivar: three levels). The seedlings were exposed to strong (VERY DRY) and moderate (DRY) soil moisture deficits, water logging (WET) and regular irrigation (MOIST) that served as a control (moisture: four levels). We examined the growth performance and the levels of ABA, proline, and polyamines in the leaves. Growth was reduced already at a moderate drought, while severe drought enhanced seedling mortality. Severe drought increased the levels of ABA by 453% and of proline by 935%, inducing a short-term stress response; both compounds were degraded over the long-term period. The polyamine concentration was unrelated to soil moisture. The cocoa cultivars did not differ in their biochemical response to soil moisture stress (proline: p-value = 0.5, ABA: p-value = 0.3), but the local cultivar III-06 showed a stronger height growth increment than the international cultivar TSH-565 (237%, p-value = 0.002) under drought conditions.


2009 ◽  
Vol 6 (8) ◽  
pp. 1423-1444 ◽  
Author(s):  
T. Keenan ◽  
R. García ◽  
A. D. Friend ◽  
S. Zaehle ◽  
C. Gracia ◽  
...  

Abstract. Water stress is a defining characteristic of Mediterranean ecosystems, and is likely to become more severe in the coming decades. Simulation models are key tools for making predictions, but our current understanding of how soil moisture controls ecosystem functioning is not sufficient to adequately constrain parameterisations. Canopy-scale flux data from four forest ecosystems with Mediterranean-type climates were used in order to analyse the physiological controls on carbon and water flues through the year. Significant non-stomatal limitations on photosynthesis were detected, along with lesser changes in the conductance-assimilation relationship. New model parameterisations were derived and implemented in two contrasting modelling approaches. The effectiveness of two models, one a dynamic global vegetation model ("ORCHIDEE"), and the other a forest growth model particularly developed for Mediterranean simulations ("GOTILWA+"), was assessed and modelled canopy responses to seasonal changes in soil moisture were analysed in comparison with in situ flux measurements. In contrast to commonly held assumptions, we find that changing the ratio of conductance to assimilation under natural, seasonally-developing, soil moisture stress is not sufficient to reproduce forest canopy CO2 and water fluxes. However, accurate predictions of both CO2 and water fluxes under all soil moisture levels encountered in the field are obtained if photosynthetic capacity is assumed to vary with soil moisture. This new parameterisation has important consequences for simulated responses of carbon and water fluxes to seasonal soil moisture stress, and should greatly improve our ability to anticipate future impacts of climate changes on the functioning of ecosystems in Mediterranean-type climates.


2011 ◽  
Vol 63 (6) ◽  
pp. 392-392 ◽  
Author(s):  
Anil Gunaratne ◽  
Upul Kumari Ratnayaka ◽  
Nihal Sirisena ◽  
Jennet Ratnayaka ◽  
Xiangli Kong ◽  
...  

1954 ◽  
Vol 41 (4) ◽  
pp. 316-320 ◽  
Author(s):  
Dorothy H. Woodhams ◽  
Theodore T. Kozlowski

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