| 1. |
- Gao, Yanhong, et al.
(författare)
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Comparison between past and future extreme precipitations simulated by global and regional climate models over the Tibetan Plateau
- 2018
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Ingår i: International Journal of Climatology. - : Wiley. - 0899-8418 .- 1097-0088. ; 38:3, s. 1285-1297
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Tidskriftsartikel (refereegranskat)abstract
- Past studies on regional climate change over the Tibetan Plateau (TP) have mainly looked at changes in the mean climate. This study focuses on past and future extreme precipitations, simulated by global and regional climate models over the TP. To assess the influence of large-scale forcing on dynamic downscaling using Weather Research and Forecasting (WRF) model, downscaling results for the historical period (1980–2005) with ERA-Interim reanalysis and CCSM4 as forcings are evaluated against a gridded observational data set. These are inter-compared before future projections for the period 2005–2100 under two scenarios (RCP4.5 and RCP8.5). The followings are obtained: (1) the reanalysis greatly overestimates not only the mean, but also extreme precipitation. The overestimation in CCSM4 is even larger than that of the reanalysis. (2) The two downscalings outperform their forcings, reflected by reduced overestimation for extreme precipitation frequency, increased spatial pattern correlations and more accurate linear trends, especially for the downscaling driven by CCSM. This demonstrates the constraining power of the fine-scale modelling and the importance of more realistic representations of surface forcing and related processes in the TP. (3) CCSM4 projects a general wetting across the whole TP with increases of heavy precipitation as well as the wetting intensification with warming. WRF also projects an overall wetting, but the wetting is less sensitive to the warming and there is more of an increase in light precipitation frequency. More importantly, a diverse pattern with wetting in the north and drying in the south is found in the dynamical downscaling in contrast to the uniform wetting in its forcing.
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| 2. |
- Gao, Yanhong, et al.
(författare)
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Modeling of Regional Climate over the Tibetan Plateau
- 2017
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Ingår i: Oxford Research Encyclopedia of Climate Science. - : Oxford University Press.
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Tidskriftsartikel (refereegranskat)abstract
- The modeling of climate over the Tibetan Plateau (TP) started with the introduction of Global Climate Models (GCMs) in the 1950s. Since then, GCMs have been developed to simulate atmospheric dynamics and eventually the climate system. As the highest and widest international plateau, the strong orographic forcing caused by the TP and its impact on general circulation rather than regional climate was initially the focus. Later, with growing awareness of the incapability of GCMs to depict regional or local-scale atmospheric processes over the heterogeneous ground, coupled with the importance of this information for local decision-making, regional climate models (RCMs) were established in the 1970s. Dynamic and thermodynamic influences of the TP on the East and South Asia summer monsoon have since been widely investigated by model. Besides the heterogeneity in topography, impacts of land cover heterogeneity and change on regional climate were widely modeled through sensitivity experiments.In recent decades, the TP has experienced a greater warming than the global average and those for similar latitudes. GCMs project a global pattern where the wet gets wetter and the dry gets drier. The climate regime over the TP covers the extreme arid regions from the northwest to the semi-humid region in the southeast. The increased warming over the TP compared to the global average raises a number of questions. What are the regional dryness/wetness changes over the TP? What is the mechanism of the responses of regional changes to global warming? To answer these questions, several dynamical downscaling models (DDMs) using RCMs focusing on the TP have recently been conducted and high-resolution data sets generated. All DDM studies demonstrated that this process-based approach, despite its limitations, can improve understandings of the processes that lead to precipitation on the TP. Observation and global land data assimilation systems both present more wetting in the northwestern arid/semi-arid regions than the southeastern humid/semi-humid regions. The DDM was found to better capture the observed elevation dependent warming over the TP. In addition, the long-term high-resolution climate simulation was found to better capture the spatial pattern of precipitation and P-E (precipitation minus evapotranspiration) changes than the best available global reanalysis. This facilitates new and substantial findings regarding the role of dynamical, thermodynamics, and transient eddies in P-E changes reflected in observed changes in major river basins fed by runoff from the TP. The DDM was found to add value regarding snowfall retrieval, precipitation frequency, and orographic precipitation.Although these advantages in the DDM over the TP are evidenced, there are unavoidable facts to be aware of. Firstly, there are still many discrepancies that exist in the up-to-date models. Any uncertainty in the model’s physics or in the land information from remote sensing and the forcing could result in uncertainties in simulation results. Secondly, the question remains of what is the appropriate resolution for resolving the TP’s heterogeneity. Thirdly, it is a challenge to include human activities in the climate models, although this is deemed necessary for future earth science. All-embracing further efforts are expected to improve regional climate models over the TP.
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| 3. |
- Gao, Yanhong, et al.
(författare)
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Quantification of the relative role of land-surface processes and large-scale forcing in dynamic downscaling over the Tibetan Plateau
- 2017
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Ingår i: Climate Dynamics. - : Springer Science and Business Media LLC. - 0930-7575 .- 1432-0894. ; 48:5, s. 1705-1721
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Tidskriftsartikel (refereegranskat)abstract
- © 2016 Springer-Verlag Berlin HeidelbergDynamical downscaling modeling (DDM) is important to understand regional climate change and develop local mitigation strategies, and the accuracy of DDM depends on the physical processes involved in the regional climate model as well as the forcing datasets derived from global models. This study investigates the relative role of the land surface schemes and forcing datasets in the DDM over the Tibet Plateau (TP), a region complex in topography and vulnerable to climate change. Three Weather Research and Forecasting model dynamical downscaling simulations configured with two land surface schemes [Noah versus Noah with multiparameterization (Noah-MP)] and two forcing datasets are performed over the period of 1980–2005. The downscaled temperature and precipitation are evaluated with observations and inter-compared regarding temporal trends, spatial distributions, and climatology. Results show that the temporal trends of the temperature and precipitation are determined by the forcing datasets, and the forcing dataset with the smallest trend bias performs the best. Relative to the forcing datasets, land surface processes play a more critical role in the DDM over the TP due to the strong heating effects on the atmospheric circulation from a vast area at exceptionally high elevations. By changing the vertical profiles of temperature in the atmosphere and the horizontal patterns of moisture advection during the monsoon seasons, the land surface schemes significantly regulate the downscaled temperature and precipitation in terms of climatology and spatial patterns. This study emphasizes the selection of land surface schemes is of crucial importance in the successful DDM over the TP.
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| 4. |
- Liang, Yajun, et al.
(författare)
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Migraine, Cognitive Decline, and Dementia in Older Adults : A Population-Based Study.
- 2022
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Ingår i: Journal of Alzheimer's Disease. - : IOS Press. - 1387-2877 .- 1875-8908. ; 88:1, s. 263-271
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND: The potential impact of migraine on cognitive aging among older adults remains controversial.OBJECTIVE: To examine the relationship of migraine and subtypes with cognitive decline and dementia in an older Swedish population.METHODS: This population-based study included 3069 participants (age≥60) from the Swedish National study on Aging and Care in Kungsholmen, Stockholm. Baseline examination was conducted in 2001-2004, and participants were followed every 3 or 6 years until 2013-2016. Data were collected through face-to-face interviews, clinical examinations, laboratory tests, and linkage with registers. Global cognitive function was measured with the Mini-Mental State Examination (MMSE). Dementia was diagnosed according to the DSM-IV criteria. Migraine and subtypes were defined following the international classification system. Data were analyzed using logistic regression, Cox regression, and linear mixed-effects models.RESULTS: At baseline, 305 participants were defined with non-migraine headache and 352 with migraine. The cross-sectional analysis showed that the multivariable-adjusted odds ratio (95% confidence interval) of prevalent dementia was 0.49 (0.20-1.21) for migraine and 0.66 (0.26-1.66) for migraine without aura. The longitudinal analysis showed that the multivariable-adjusted hazard ratios of incident dementia associated with migraine and subtypes ranged 0.68-0.89 (p > 0.05). Furthermore, migraine and subtypes were not significantly associated with either baseline MMSE score or MMSE changes during follow-ups (p > 0.05). The nonsignificant associations did not vary substantially by age, APOEɛ4 allele, cerebrovascular disease, and antimigraine treatment (p for interactions > 0.05).CONCLUSION: This study shows no evidence supporting the associations of migraine and its subtypes with cognitive decline and dementia among older adults.
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| 5. |
- Xu, Jianwei, et al.
(författare)
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Evaluation of global climate models for downscaling applications centred over the Tibetan Plateau
- 2017
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Ingår i: International Journal of Climatology. - : Wiley. - 0899-8418 .- 1097-0088. ; 37:2, s. 657-671
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Tidskriftsartikel (refereegranskat)abstract
- © 2016 Royal Meteorological Society.Quality of a downscaling depends primarily on the quality of the driving global climate model (GCM). In this study, historical atmospheric conditions simulated by 14 GCMs in CMIP5 are evaluated for downscaling applications centred over the Tibetan Plateau (TP) with ERA-Interim reanalysis as reference. Another reanalysis NCEP-DOE is also used to estimate the uncertainty associated with the reanalyses. Performances of six frequently used GCM variables, involving atmospheric circulation, air temperature and humidity, are evaluated in terms of biases, spatial correlation coefficient, mean absolute error as well as distinct seasonal features. To detect distributional biases, the two-sample Kolmogorov-Smirnov test (KS test) is applied to both the original time series and their anomalies on the monthly scale. A spatial ranking scheme is finally applied to objectively quantify overall relative merits of the GCMs over this region. We found that differences between two reanalysis datasets are negligible over this region. Regarding the GCMs' performances, the biases of the simulated variables show remarkable differences among models. Sea level pressure and 500 hPa geopotential height are well simulated by all the GCMs, whereas specific humidity at 600 hPa has a significant dry bias and temperature at 500 hPa has a sizable cold bias. The spatial pattern of the upper-tropospheric circulation is relatively poorly simulated. The KS test suggests that the climatic mean and higher order moments play about an equal role in causing the errors. According to the ranking scores, CCSM4, CNRM-CM5, MPI-ESM-LR, NorESM1-M, MIROC4h, MPI_ESM_MR and CSIRO-MK are relatively superior to other GCMs for this region.
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| 6. |
- Zhang, Guoqing, et al.
(författare)
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Extensive and drastically different alpine lake changes on Asia's high plateaus during the past four decades
- 2017
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Ingår i: Geophysical Research Letters. - 0094-8276. ; 44:1, s. 252-260
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Tidskriftsartikel (refereegranskat)abstract
- Asia's high plateaus are sensitive to climate change and have been experiencing rapid warming over the past few decades. We found 99 new lakes and extensive lake expansion on the Tibetan Plateau during the last four decades, 1970–2013, due to increased precipitation and cryospheric contributions to its water balance. This contrasts with disappearing lakes and drastic shrinkage of lake areas on the adjacent Mongolian Plateau: 208 lakes disappeared and 75% of the remaining lakes have shrunk. We detected a statistically significant coincidental timing of lake area changes in both plateaus, associated with the climate regime shift that occurred during 1997/1998. This distinct change in 1997/1998 is thought to be driven by large-scale atmospheric circulation changes in response to climate warming. Our findings reveal that these two adjacent plateaus have been changing in opposite directions in response to climate change. These findings shed light on the complex role of the regional climate and water cycles, and provide useful information for ecological and water resource planning in these fragile landscapes.
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