| 1. |
- Liu, Sheng, et al.
(författare)
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An improved estimation of soil water and salt dynamics by considering soil bulk density changes under freeze/thaw conditions in arid areas with shallow groundwater tables
- 2023
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Ingår i: Science of the Total Environment. - : Elsevier BV. - 0048-9697. ; 859
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Tidskriftsartikel (refereegranskat)abstract
- Soil bulk density (BD) is a parameter dependent on soil texture, compositions of soil minerals and organic matter and the extent of soil compaction. Seasonal freeze/thaw in arid areas with shallow groundwater tables (AASGT) may significantly change BD and hence soil hydrothermal properties and water holding capacity. Therefore, quantifying soil bulk density changes (BDC) under freeze/thaw conditions can improve estimates of soil water-salt dynamics in AASGT. In this study, we conducted field experiments to investigate the soil water-salt dynamics under freeze/thaw conditions from three typical land-use types (i.e., farmland, woodland, and natural land) in the upper Yellow River basin, China. We proposed a method to estimate BDC, which can better describe the soil water-salt dynamics during the freeze/thaw period. Our results showed marked BDC occurred in all layers within the 0–100 cm profile in natural land, while mainly at the 20–80 cm profile in farmland. During the freezing period, BD in farmland and natural land first decreased rapidly and then remained relatively stable until the thawing period started. After that, BD gradually increased during the thawing period. The largest BDC in farmland and natural land were 0.48 g cm−3 (occurring at the 30–40 cm layer) and 0.43 g cm−3 (occurring at the 80–90 cm layer), respectively, close to 30 % of their initial values. The differences in BDC between the three land-use types were mainly owing to their differences in groundwater table depth, initial soil salt concentration, soil texture, and surface coverage conditions. Moreover, in farmland and natural land, ignoring BDC resulted in different degrees of overestimation or underestimation in soil water content, water fluxes, and soil hydrothermal properties in the selected soil layers. This study demonstrates that considering BDC can improve the accuracy of soil water-salt dynamics estimation in AASGT under freeze/thaw conditions.
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| 2. |
- Wei, Ting, et al.
(författare)
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Developed and developing world responsibilities for historical climate change and CO2 mitigation
- 2012
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Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 109:32, s. 12911-12915
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Tidskriftsartikel (refereegranskat)abstract
- At the United Nations Framework Convention on Climate Change Conference in Cancun, in November 2010, the Heads of State reached an agreement on the aim of limiting the global temperature rise to 2 degrees C relative to preindustrial levels. They recognized that long-term future warming is primarily constrained by cumulative anthropogenic greenhouse gas emissions, that deep cuts in global emissions are required, and that action based on equity must be taken to meet this objective. However, negotiations on emission reduction among countries are increasingly fraught with difficulty, partly because of arguments about the responsibility for the ongoing temperature rise. Simulations with two earth-system models (NCAR/CESM and BNU-ESM) demonstrate that developed countries had contributed about 60-80%, developing countries about 20-40%, to the global temperature rise, upper ocean warming, and sea-ice reduction by 2005. Enacting pledges made at Cancun with continuation to 2100 leads to a reduction in global temperature rise relative to business as usual with a 1/3-2/3 (CESM 33-67%, BNU-ESM 35-65%) contribution from developed and developing countries, respectively. To prevent a temperature rise by 2 degrees C or more in 2100, it is necessary to fill the gap with more ambitious mitigation efforts.
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