| 1. |
- Bring, Arvid, et al.
(författare)
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Implications of freshwater flux data from the CMIP5 multimodel output across a set of Northern Hemisphere drainage basins
- 2015
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Ingår i: EARTHS FUTURE. - 2328-4277. ; 3:6, s. 206-217
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Tidskriftsartikel (refereegranskat)abstract
- The multimodel ensemble of the Coupled Model Intercomparison Project, Phase 5 (CMIP5) synthesizes the latest research in global climate modeling. The freshwater system on land, particularly runoff, has so far been of relatively low priority in global climate models, despite the societal and ecosystem importance of freshwater changes, and the science and policy needs for such model output on drainage basin scales. Here we investigate the implications of CMIP5 multimodel ensemble output data for the freshwater system across a set of drainage basins in the Northern Hemisphere. Results of individual models vary widely, with even ensemble mean results differing greatly from observations and implying unrealistic long-term systematic changes in water storage and level within entire basins. The CMIP5 projections of basin-scale freshwater fluxes differ considerably more from observations and among models for the warm temperate study basins than for the Arctic and cold temperate study basins. In general, the results call for concerted research efforts and model developments for improving the understanding and modeling of the freshwater system and its change drivers. Specifically, more attention to basin-scale water flux analyses should be a priority for climate model development, and an important focus for relevant model-based advice for adaptation to climate change.
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| 2. |
- Chalov, Sergey R., et al.
(författare)
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Spatio-temporal variation of sediment transport in the Selenga River Basin, Mongolia and Russia
- 2015
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Ingår i: Environmental Earth Sciences. - : Springer Science and Business Media LLC. - 1866-6280 .- 1866-6299. ; 73:2, s. 663-680
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Tidskriftsartikel (refereegranskat)abstract
- Many Asian rivers have been intensively used to boost economic growth, resulting in sudden and drastic changes in sediment transport patterns. However, a few rivers are still undisturbed. The present paper considers the unregulated Selenga River and its basin, located in Russia and Mongolia. The river contributes to 50 % of the total inflow to Lake Baikal. Pending scientific challenges include the quantification of sediment loads and erosion-deposition patterns along the Selenga River system, the understanding of suspended particulate matter composition and the importance of peak flow events for total sediment discharge and heavy metal transport. Field data and hydraulic modeling converge on showing that peak flow events during spring and summer contribute to the main part (70-80 %) of the annual sediment and pollution loads in upstream parts of the basin. The Selenga River carries mostly silt and sand. The average particle size differs by a factor of four between summer floods and base flow periods. The low amount of particulate organic matter (ranging between 1 and 16 % in the studied rivers) is consistent with the significant role of sediments originating from mining areas and in-channel sources. The bed load transport in the downstream part of the river basin is high (up to 50 % of the total transport), and channel storage plays an important role in the total sediment transport to Lake Baikal. Reported statistically significant multi-decadal declines in sediment fluxes in the downstream Selenga River can be attributed to the abandonment of cultivated lands and (most likely) to changing hydroclimatic factors.
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| 3. |
- Pietroń, Jan, et al.
(författare)
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Model analyses of the contribution of in-channel processes to sediment concentration hysteresis loops
- 2015
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Ingår i: Journal of Hydrology. - : Elsevier BV. - 0022-1694 .- 1879-2707. ; 527, s. 576-589
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Tidskriftsartikel (refereegranskat)abstract
- Sediment concentration (SC)-water discharge (Q) relations in rivers are typically governed by multiple and relatively complex processes. Due to hysteresis effects, sediment discharges can differ for similar or equivalent water discharges, which causes scatter in empirical datasets and may decrease the predictive power of SC rating curves. Such hysteresis effects must therefore be understood and accounted for to make dependable predictions for river system management. The overall objectives of this study are to develop modelling approaches suitable for reproducing and predicting hysteresis effects at larger scales and to investigate the possible contribution of in-channel processes (erosion and deposition) to sediment concentration hysteresis loops. To investigate relevant field-scale conditions, we develop a one-dimensional dynamic sediment transport model of the downstream Tuul River (northern Mongolia), investigating in-channel processes along a 141 km stretch during a hydrological year. The results show that the present modelling approach can reproduce both anti-clockwise and clockwise hysteresis effects. Importantly, in-channel processes alone can cause considerable anti-clockwise hysteresis effects without being reinforced by catchment processes such as hillslope erosion. Such specific contributions from in-channel processes introduced data scatter into the sediment rating curves, decreasing their R-2-values from unity to approximately 0.5 to 0.6. More generally, possible changes in the number or magnitude of high-flow events, caused by climatic or other anthropogenic factors, could influence total sediment deposition, which was primarily found to occur during relatively short high-flow events. Such potential changes also have important implications for the possible spreading of polluted sediments.
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