Dongxian Kong

Assessment of CMIP5 climate models and projected temperature changes over Northern Eurasia

Assessing the performance of climate models in surface air temperature (SAT) simulation andprojection have received increasing attention during the recent decades. This paper assesses theperformance of the Coupled Model Intercomparison Project phase 5 (CMIP5) in simulatingintra-annual, annual and decadal temperature over Northern Eurasia from 1901 to 2005. Weevaluate the skill of different multi-model ensemble techniques and use the best technique toproject the future SAT changes under different emission scenarios. The results show that most ofthe general circulation models (GCMs) overestimate the annual mean SAT in Northern Eurasiaand the difference between the observation and the simulations primarily comes from the winterseason. Most of the GCMs can approximately capture the decadal SAT trend; however, theaccuracy of annual SAT simulation is relatively low. The correlation coefficient R between eachGCM simulation and the annual observation is in the range of 0.20 to 0.56. The Taylor diagramshows that the ensemble results generated by the simple model averaging (SMA), reliabilityensemble averaging (REA) and Bayesian model averaging (BMA) methods are superior to anysingle GCM output; and the decadal SAT change generated by SMA, REA and BMA are almostidentical during 1901–2005. Heuristically, the uncertainty of BMA simulation is the smallestamong the three multi-model ensemble simulations. The future SAT projection generated by theBMA shows that the SAT in Northern Eurasia will increase in the 21st century by around1.03°C/100yr, 3.11°C/100yr and 7.14°C/100yr under the RCP 2.6, RCP 4.5 and RCP 8.5scenarios, respectively; and the warming accelerates with the increasing latitude. In addition, thespring season contributes most to the decadal warming occurring under the RCP 2.6 and RCP4.5 scenarios, while the winter season contributes most to the decadal warming occurring underthe RCP 8.5 scenario. Generally, the uncertainty of the SAT projections increases with time inthe 21st century.S Online supplementary data available from stacks.iop.org/ERL/9/055007/mmediaKeywords: CMIP5, multi-model ensembles, Northern Eurasia, temperature

Would the ‘real’ observed dataset stand up? A critical examination of eight observed gridded climate datasets for China

This research compared and evaluated the spatio-temporal similarities and differences of eight widely used gridded datasets. The datasets include daily precipitation over East Asia (EA), the Climate Research Unit (CRU) product, the Global Precipitation Climatology Centre (GPCC) product, the University of Delaware (UDEL) product, Precipitation Reconstruction over Land (PREC/L), the Asian Precipitation Highly Resolved Observational (APHRO) product, the Institute of Atmospheric Physics (IAP) dataset from the Chinese Academy of Sciences, and the National Meteorological Information Center dataset from the China Meteorological Administration (CN05). The meteorological variables focus on surface air temperature (SAT) or precipitation (PR) in China. All datasets presented general agreement on the whole spatio-temporal scale, but some differences appeared for specific periods and regions. On a temporal scale, EA shows the highest amount of PR, while APHRO shows the lowest. CRU and UDEL show higher SAT than IAP or CN05. On a spatial scale, the most significant differences occur in western China for PR and SAT. For PR, the difference between EA and CRU is the largest. When compared with CN05, CRU shows higher SAT in the central and southern Northwest river drainage basin, UDEL exhibits higher SAT over the Southwest river drainage system, and IAP has lower SAT in the Tibetan Plateau. The differences in annual mean PR and SAT primarily come from summer and winter, respectively. Finally, potential factors impacting agreement among gridded climate datasets are discussed, including raw data sources, quality control (QC) schemes, orographic correction, and interpolation techniques. The implications and challenges of these results for climate research are also briefly addressed.

Functional degradation of the water-sediment regulation scheme in the lower Yellow River: Spatial and temporal analyses.

Heavy sedimentation has led to the phenomenon of a secondary perched river in the lower reaches of the Yellow River. The water-sediment regulation scheme (WSRS) using the Xiaolangdi Reservoir was first implemented in 2002 to try to solve this problem. In this study, we analyzed the spatial and temporal effects of the current WSRS (2005-2013) on the lower Yellow River. Our results suggest that the current WSRS is exhibiting a tendency towards functional degradation, meaning that the scheme is no longer as effective as it was initially for the lower Yellow River. Although the main river channel has been fully scoured in the lower reaches since the implementation of the WSRS, we found that the degree of erosion declined gradually in a top-down fashion from the braided reach, through the transitional reach, to the meandering reach. Of the total eroded sediment, 69.64% came from the braided reach and only 6.61% came from the meandering reach. In addition, the reduction in riverbed elevation-a key function of the WSRS-has clearly slowed since 2005. We discuss the mechanisms underlying this functional degradation of the current WSRS and future challenges for the management of the lower Yellow River. Insights gained from this study will likely be of use to those weighing up options for future implementations of the WSRS.

Variations in global temperature and precipitation for the period of 1948 to 2010

Climate change has impacts on both natural and human systems. Accurate information regarding variations in precipitation and temperature is essential for identifying and understanding these potential impacts. This research applied Mann–Kendall, rescaled range analysis and wave transform methods to analyze the trends and periodic properties of global and regional surface air temperature (SAT) and precipitation (PR) over the period of 1948 to 2010. The results show that 65.34xa0% of the area studied exhibits significant warming trends (pu2009<u20090.05) while only 3.18xa0% of the area exhibits significant cooling trends. The greatest warming trends are observed in Antarctica (0.32xa0°C per decade) and Middle Africa (0.21xa0°C per decade). Notably, 62.26xa0% of the area became wetter, while 22.01xa0% of the area shows drying trends. Northern Europe shows the largest precipitation increase, 12.49xa0mm per decade. Western Africa shows the fastest drying, −21.05xa0mm per decade. The rescaled range analysis reveals large areas that show persistent warming trends; this behavior in SAT is more obvious than that in PR. Wave transform results show that a 1-year period of SAT variation dominates in all regions, while inconsistent 0.5-year bands are observed in East Asia, Middle Africa, and Southeast Asia. In PR, significant power in the wavelet power spectrum at a 1-year period was observed in 17 regions, i.e., in all regions studied except Western Europe, where precipitation is instead characterized by 0.5-year and 0.25-year periods. Overall, the variations in SAT and PR can be consistent with the combined impacts of natural and anthropogenic factors, such as atmospheric concentrations of greenhouse gases, the internal variability of climate system, and volcanic eruptions.

Record-Breaking Heat in Northwest China in July 2015: Analysis of the Severity and Underlying Causes

Introduction. In July 2015, northwest China experienced an unusually long and intense heat wave, especially in Xinjiang Autonomous Region (Fig. 19.1a). Maximum daily temperatures (TMX) exceeded 40°C on a record-breaking number of July days in 50 out of 88 counties in Xinjiang, and historical TMX records were broken in 28 counties. The highest TMX was 47.7°C in Turpan. This year also smashed the historical records of heat wave duration in 51 counties. Our paper poses three questions: How extreme was the heat in Northwest China in July 2015 in a historical context? What factors led to the record-breaking heat? Did human-induced climate change increase the odds of abnormally high July heat in Xinjiang?

Environmental impact assessments of the Xiaolangdi Reservoir on the most hyperconcentrated laden river, Yellow River, China

The Yellow River is the most hyperconcentrated sediment-laden river in the world. Throughout recorded history, the Lower Yellow River (LYR) experienced many catastrophic flood and drought events. To regulate the LYR, a reservoir was constructed at Xiaolangdi that became operational in the early 2000s. An annual water–sediment regulation scheme (WSRS) was then implemented, aimed at flood control, sediment reduction, regulated water supply, and power generation. This study examines the eco-environmental and socioenvironmental impacts of Xiaolangdi Reservoir. In retrospect, it is found that the reservoir construction phase incurred huge financial cost and required large-scale human resettlement. Subsequent reservoir operations affected the local geological environment, downstream riverbed erosion, evolution of the Yellow River delta, water quality, and aquatic biodiversity. Lessons from the impact assessment of the Xiaolangdi Reservoir are summarized as follows: (1) The construction of large reservoirs is not merely an engineering challenge but must also be viewed in terms of resource exploitation, environmental protection, and social development; (2) long-term systems for monitoring large reservoirs should be established, and decision makers involved at national policy and planning levels must be prepared to react quickly to the changing impact of large reservoirs; and (3) the key to solving sedimentation in the LYR is not Xiaolangdi Reservoir but instead soil conservation in the middle reaches of the Yellow River basin. Proper assessment of the impacts of large reservoirs will help promote development strategies that enhance the long-term sustainability of dam projects.

Spatiotemporal variations in vegetation cover on the Loess Plateau, China, between 1982 and 2013: possible causes and potential impacts

Vegetation is a key component of the ecosystem and plays an important role in water retention and resistance to soil erosion. In this study, we used a multiyear normalized difference vegetation index (NDVI) dataset (1982–2013) and corresponding datasets for observed climatic variables to analyze changes in the NDVI at both temporal and spatial scales. The relationships between NDVI, climate change, and human activities were also investigated. The annual average NDVI showed an upward trend over the 32-year study period, especially in the center of the Loess Plateau. NDVI variations lagged behind monthly temperature changes by approximately 1xa0month. The contribution of human activities to variations in NDVI has become increasingly significant in recent years, with human activities responsible for 30.4% of the change in NDVI during the period 2001–2013. The increased vegetation coverage has reduced soil erosion on the Loess Plateau in recent years. It is suggested that natural restoration of vegetation is the most effective measure for control of erosion; engineering measures that promote this should feature in the future governance of the Loess Plateau.