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Since the 1950s, divergence problems have reduced the temporal stability of tree rings in response to climate, shaken the foundations of dendroclimatology, and affected the reliability of reconstructed models based on tree rings and the accuracy of historical climate series. Therefore, it is of great importance to investigate divergence problems, which will help us to better understand the growth strategies of trees in response to climate warming and provide a scientific basis for accurate climate reconstruction and simulation of forest dynamics. This paper aims to elucidate the mechanism of divergent growth of Picea schrenkiana at high altitudes in the western Tianshan from three aspects: variations in atmospheric circulation, changes in climatic factors, and the coping strategy of trees with climate change. High spring temperatures accelerate the melting of snow cover. Large amounts of snowmelt initially replenish soil water, leading to the rapid growth of trees, but later, the continuous consumption of snowmelt reduces the available water capacity of soil, resulting in water stress on trees. The pattern of trees' response to changes in climate ranges from a pure temperature limitation to a collaborative temperature–moisture limitation. Since the 1990s, the weakening of the westerly circulation and the North Atlantic Oscillation has reduced their impacts on the hydroclimate in the Tianshan Mountains of Central Asia. The combination of heat-induced water deficit and a long-term weakening trend in atmospheric circulation has slowed tree growth over the past decade. [ABSTRACT FROM AUTHOR]

This paper presents a definition of bifurcation-type abrupt changes based on the bifurcation features of Lorenz trajectories. These abrupt changes are the result of the transition behavior of dynamical system trajectories among different equilibrium regions. We demonstrate that these bifurcation-type jumps can better reflect the nature of abrupt change. In analyzing the features of Lorenz equation trajectories, a dynamical method for detecting bifurcation-type abrupt changes is presented. A numerical solution of the Lorenz equation is adopted, using a curve integral or vector product to construct a time series of positive and negative values. Changes in the sign of this time series accurately determine whether the trajectory is in the right or left equilibrium region, and the points at which the time series is equal to zero are the times at which the trajectory jumps between different equilibrium regions, that is, the occurrence times of bifurcation-type abrupt changes. This method is completely dependent on the dynamical characteristics of the system. A theoretical approach for detecting abrupt climate changes based on the dynamical characteristics of the atmospheric model is described. Compared with the original method of identifying abrupt climate changes, this method has dynamic significance and can detect abrupt changes in multi-dimensional time series. Although this method can be applied theoretically, applications to real atmospheric data first require the data to be smoothed. [ABSTRACT FROM AUTHOR]

The conventional typical meteorological year (TMY) based on continuous-year original meteorological records without considering abrupt climate changes (ACC) may not be able to represent a real "typical" climate properly. Consequently, building performance analyses and simulations based on TMY may be not accurate. Current research rarely tackles this issue in TMY development. This paper presents an innovative TMY development with the consideration of ACC in the original meteorological records. It is based on the Chinese standard weather database method (CSWD) with the meteorological records of six Chinese cities in different climate zones. It applies the Moving t-test method to identify and exclude ACC points and to refine the timescales for TMY development. It also depicts the development of individual typical meteorological months again with the ACC impact to improve the accuracy of TMY. The method has been verified in several building energy consumption and thermal comfort analyses. The results demonstrate that the analysis based on the new TMY climate datasets when considering ACC will end up with less energy consumption and better thermal performance compared to the analyses based on the conversion dataset without considering ACC. This experimental research will refine TMY development, and further improve building energy performance analysis and design. [ABSTRACT FROM AUTHOR]

We combine our ice-sheet and climate models to formulate a deductive theory of abrupt climate changes pertaining to Heinrich/Dansgaard–Oeschger (H/DO) cycles and the last deglaciation punctuated by the Younger Dryas (YD). Since they are all accompanied by ice-rafted debris, we posit their common origin in the calving of the ice sheet due to a thermal switch at its bed, which naturally endows abruptness to these climate signals of the millennial timescale characteristics of the ice-mass balance. To distinguish the H/DO cycles, we differentiate the thermal triggers by geothermal-heat/surface-melt in the calving of inland/coastal ice, which provide their respective freshwater sources. Since surface-melt requires post-H warmth during the glacial, but is already operative in the Holocene, the DO cycles are encased within the H cycle during the glacial, but self-sustaining in the Holocene. They otherwise share the same time signature, thus resolving this seeming puzzle of commonality without invoking unknown climate forcing. The DO cycles transcend deglaciation to produce the observed sequence, but the calving-induced freshwater flux needs to be boosted by the rerouting of continental meltwater to cause YD. We discern a key process of an eddying ocean in its millennial adjustment toward maximum entropy production (MEP), which would melt the H-induced sea ice to cause an abrupt post-H warming followed by a gradual cooling that anchors the DO cycles to form the hierarchical Bond cycle. Since the modelled anatomies resemble the observed ones, our theory may provide a robust and unified account of abrupt climate changes. [ABSTRACT FROM AUTHOR]

Lakes in the Hindu Kush-Himalaya-Tibetan (HKHT) regions are crucial indicators for the combined impacts of regional climate change and resultant glacier retreat. However, they lack long-term systematic monitoring and thus their responses to recent climatic change still remain only partially understood. This study investigated lake extent fluctuations in the HKHT regions over the past 40 years using Landsat (MSS/TM/ETM+/OLI) images obtained from the 1970s to 2014. Influenced by different regional atmospheric circulation systems, our results show that lake changing patterns are distinct from region to region, with the most intensive lake shrinking observed in northeastern HKHT (HKHT Interior, Tarim, Yellow, Yangtze), while the most extensive expansion was observed in the western and southwestern HKHT (Amu Darya, Ganges Indus and Brahmaputra), largely caused by the proliferation of small lakes in high-altitude regions during 1970s–1995. In the past 20 years, extensive lake expansions (~39.6% in area and ~119.1% in quantity) were observed in all HKHT regions. Climate change, especially precipitation change, is the major driving force to the changing dynamics of the lake fluctuations; however, effects from the glacier melting were also significant, which contributed approximately 31.9–40.5%, 16.5–39.3%, 12.8–29.0%, and 3.3–6.1% of runoff to lakes in the headwaters of the Tarim, Amu Darya, Indus, and Ganges, respectively. We consider that the findings in this paper could have both immediate and long-term implications for dealing with water-related hazards, controlling glacial lake outburst floods, and securing water resources in the HKHT regions, which contain the headwater sources for some of the largest rivers in Asia that sustain 1.3 billion people. [ABSTRACT FROM AUTHOR]

We address the quantisation of a model that induces the Little Sibling of the Big Rip (LSBR) abrupt event, where the dark energy content is described by means of a phantom-like fluid or a phantom scalar field. The quantisation is done in the framework of the Wheeler-DeWitt (WDW) equation and imposing the DeWitt boundary condition; i.e., the wave function vanishes close to the abrupt event. We analyse the WDW equation within two descriptions: First, when the dark energy content is described with a perfect fluid. This leaves the problem with the scale factor as the single degree of freedom. Second, when the dark energy content is described with a phantom scalar field in such a way that an additional degree of freedom is incorporated. Here, we have applied the Born-Oppenheimer (BO) approximation in order to simplify the WDW equation. In all cases, the obtained wave function vanishes when the LSBR takes place, thus fulfilling the DeWitt boundary condition. [ABSTRACT FROM AUTHOR]

As a mountainous country, Nepal is most susceptible to precipitation extremes and related hazards, including severe floods, landslides and droughts that cause huge losses of life and property, impact the Himalayan environment, and hinder the socioeconomic development of the country. Given that the countrywide assessment of such extremes is still lacking, we present a comprehensive picture of prevailing precipitation extremes observed across Nepal. First, we present the spatial distribution of daily extreme precipitation indices as defined by the Expert Team on Climate Change Detection, Monitoring and Indices (ETCCDMI) from 210 stations over the period of 1981-2010. Then, we analyze the temporal changes in the computed extremes from 76 stations, featuring long-term continuous records for the period of 1970-2012, by applying a non-parametric Mann-Kendall test to identify the existence of a trend and Sen's slope method to calculate the true magnitude of this trend. Further, the local trends in precipitation extremes have been tested for their field significance over the distinct physio-geographical regions of Nepal, such as the lowlands, middle mountains and hills and high mountains in the west (WL, WM and WH, respectively), and likewise, in central (CL, CM and CH) and eastern (EL, EM and EH) Nepal. Our results suggest that the spatial patterns of high-intensity precipitation extremes are quite different to that of annual or monsoonal precipitation. Lowlands (Terai and Siwaliks) that feature relatively low precipitation and less wet days (rainy days) are exposed to high-intensity precipitation extremes. Our trend analysis suggests that the pre-monsoonal precipitation is significantly increasing over the lowlands and CH, while monsoonal precipitation is increasing inWMand CH and decreasing in CM, CL and EL. On the other hand, post-monsoonal precipitation is significantly decreasing across all of Nepal while winter precipitation is decreasing only over the WM region. Both high-intensity precipitation extremes and annual precipitation trends feature east-west contrast, suggesting significant increase over the WM and CH region but decrease over the EM and CM regions. Further, a significant positive trend in the number of consecutive dry days but significant negative trend in the number of wet (rainy) days are observed over the whole of Nepal, implying the prolongation of the dry spell across the country. Overall, the intensification of different precipitation indices over distinct parts of the country indicates region-specific risks of floods, landslides and droughts. The presented findings, in combination with population and environmental pressures, can support in devising the adequate region-specific adaptation strategies for different sectors and in improving the livelihood of the rural communities in Nepal. [ABSTRACT FROM AUTHOR]