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- Chen, Tao, et al.
(författare)
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Comprehensive applicability evaluation of multi-source snow depth datasets over the Tibetan Plateau
- 2022
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Ingår i: Journal of Glaciology and Geocryology. - 1000-0240. ; 44:3, s. 795-809
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Tidskriftsartikel (refereegranskat)abstract
- Snow cover over the Tibetan Plateau has an important impact on the regional climate and water cycle. At present, the existing snow cover datasets have great uncertainty across this region, so the applicability assessment is indispensable in order to make best use of the advantages and bypass the disadvantages. In this study, a comprehensive quantitative evaluation of multiple variables and multiple evaluation indicators was carried out for three snow depth datasets over the Tibetan Plateau against the meteorological station observations（OBS）. The three snow depth datasets include one passive microwave remote sensing dataset（CHE）and two reanalysis datasets（ERA5-Land and MERRA2）. The variables are the annual mean snow depth, the annual maximum snow depth, and the annual snow cover days. In addition, the evaluation indicators are seasonal cycle, climatology, maximum value, standard deviation, interannual variation, and trend. A rank score（RS）value of 0~1 is computed for each evaluation indicator of each variable, the larger value of RS indicate relatively better performance of a snow depth dataset. Assessment results imply that, comprehensively considered, MERRA2 exhibits best agreement with OBS, followed by ERA5-Land, and finally CHE. Evaluate based on the RS of each variable, MERRA2 shows better performance on annual maximum snow depth and annual snow cover days, CHE shows better performance on annual mean snow depth. Evaluate based on the RS of each evaluation indicator, CHE shows advantages in describing trend, ERA5-Land exhibits better agreement with OBS on interannual variation, and MERRA2 show better performance on the rest of the indicators including seasonal cycle, climatology, maximum value and standard deviation. The RS statistics in terms of regional average and spatial distribution show that CHE performs better in the former, and ERA5-Land performs better in the latter. On the other hand, there are obvious deficiencies in all three snow depth datasets. MERRA2 has insufficient ability to characterize the interdecadal variation in snow cover, and its qualitative results for trend in snow cover is inconsistent with OBS, the reason for the first deficiency needs to be further studied and the second deficiency may be mainly related to its simulation capability to precipitation trend. ERA5-Land significantly overestimates the snow cover over the Tibetan Plateau, this may be mostly related to its data assimilation scheme. CHE has poor ability to characterize the spatial distribution of snow cover, coarse spatial resolution of passive microwave remote sensing may be the main reason. The conclusions are only applicable to the central and eastern part of the Tibetan Plateau due to the scarcity of meteorological station in west part of the Tibetan Plateau. Based on the remote sensing and reanalysis data, there is great uncertainty in the trend of snow cover in the western part of the Tibetan Plateau. These systematic classification evaluation of the three representative snow depth datasets provides information on data selection and data refinement.
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- Shi, Fangzhong, et al.
(författare)
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Seasonal compensation implied no weakening of the land carbon sink in the Northern Hemisphere under the 2015/2016 El Niño
- 2024
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Ingår i: Science China Earth Sciences. - 1674-7313 .- 1869-1897. ; 67:1, s. 294-308
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Tidskriftsartikel (refereegranskat)abstract
- The recurrent extreme El Niño events are commonly linked to reduced vegetation growth and the land carbon sink over many but discrete regions of the Northern Hemisphere (NH). However, we reported here a pervasive and continuous vegetation greening and no weakened land carbon sink in the maturation phase of the 2015/2016 El Niño event over the NH (mainly in the extra-tropics), based on multiple evidences from remote sensing observations, global ecosystem model simulations and atmospheric CO2 inversions. We discovered a significant compensation effect of the enhanced vegetation growth in spring on subsequent summer/autumn vegetation growth that sustained vegetation greening and led to a slight increase in the land carbon sink over the spring and summer of 2015 (average increases of 23.34% and 0.63% in net ecosystem exchange from two independent datasets relative to a 5-years average before the El Niño event, respectively) and spring of 2016 (6.82%), especially in the extra-tropics of the NH, where the water supply during the pre-growing-season (November of the previous year to March of the current year) had a positive anomaly. This seasonal compensation effect was much stronger than that in 1997 and 1998 and significantly alleviated the adverse impacts of the 2015/2016 El Niño event on vegetation growth during its maturation phase. The legacy effect of water supply during the pre-growing-season on subsequent vegetation growth lasted up to approximately six months. Our findings highlight the role of seasonal compensation effects on mediating the land carbon sink in response to episodic extreme El Niño events.
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- Wang, Yan, et al.
(författare)
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Disaster effects of climate change and the associated scientific challenges
- 2024
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Ingår i: Chinese Science Bulletin. - 1001-6538. ; 69:2, s. 286-300
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Forskningsöversikt (refereegranskat)abstract
- Climate change can be observed in various spheres of the Earth's system, including atmosphere, lithosphere, hydrosphere, biosphere and cryosphere. The interactions among these spheres collectively impact the changes of the climate system. Natural disasters represent the most intense manifestation of the interactions among the Earth's spheres, and they have profound impacts on human society. In this study, we discuss the impact of climate change on natural disasters by examining the characteristics of climate change-induced hazards and the activity patterns of natural disasters. Furthermore, the response mechanisms of natural disasters to climate change are elaborated by exploring the formation and evolution of different types of natural disasters. Additionally, the future trends of disaster-pregnant environment under climate change are estimated, and the future trends of disaster risk are revealed by jointly considering the exposure and vulnerability. The main driving forces and formation conditions of natural disasters vary greatly among different geomorphic units, but they can generally be classified into three categories: Thermally driven disasters, gravitationally driven disasters, and hydrologically driven disasters. For example, heatwaves, tropical cyclones, tornadoes, and wildfires are common examples of thermally driven disasters which are forced by high temperatures or great thermal gradients. In addition, gravitationally driven disasters mainly occur in mountainous areas with significant differences in elevation, such as landslides, snow-ice avalanches and debris flows. The tsunamis caused by seabed movement are also gravity disasters. Furthermore, the disasters such as droughts, regional floods and sea-level rise are primarily driven by the changes in hydraulic conditions, and thus are classified as hydrologically driven disasters. In the context of enhanced climate change, the interactions among multiple spheres of the Earth's system are strengthened, causing the disaster-pregnant environment to evolve towards a more vulnerable state. Thus, the natural disasters present some new characteristics and trends, and the disaster risk shows a sharp increase. The interactions among different types of natural disasters have also become stronger, resulting in a significant rise in the risk of compound and cascading disaster. The differences in driving forces lead to significant variations in the disaster feedback to climate change among the varied geomorphic units. For example, the strengthened interaction between ocean and atmosphere leads to enhanced compound risk and destructive power of marine disasters. Besides, the intensification of water cycle contributes to increased spatial heterogeneity in drought and flood disasters, whose durations, intensities, and magnitudes show significant increasing trends. In addition, the high mountainous areas with altitude-dependent warming and the urban areas with significant heat island effects have obvious amplification effects in the responses to climate warming. This study advocates the goal of improving the accuracy and effectiveness of natural disaster prediction and early warning, and reducing the risk of climate change-related disasters. Five major scientific challenges of climate change-related disaster risk are proposed: (1) The mechanisms of climate change-driven interactions among Earth's spheres and the coupling of internal and external forces; (2) the spatio-temporal patterns of disaster development across different scales; (3) the perception of extreme event information and the data-driven risk identification; (4) the dynamics of disasters and the evolution of risk; (5) the disaster risk management and the resilient social development. By addressing the key issues in these five challenges through comprehensive and diversified approaches, we can deepen our scientific understanding on the Earth's system, adapt to global changes, and reduce disaster risks.
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