Search

Over the past 50 years, temperatures on the Qinghai-Tibet Plateau (QTP) have risen roughly twice as fast as the global average, making it the most unpredictable region of environmental change due to global warming. In this paper, an Environmental Area Index model was developed using data from the Coupled Model Intercomparison Project to assess the ecological risk faced by QTP ecosystems under the influence of climate factors. The results show that ecological risk gradually decreases from northwest to the southeast, and there are different trends in ecological risk for each class in areas with different elevation gradients. As elevation increased, the proportion of potential risk areas gradually decreased, and the proportion of high- and higher-risk areas gradually increased. We predict that in the period 2021–2100, the overall ecological risk change trend on the QTP will not be obvious, but there will be a more obvious change on the vertical gradient. In general, under the existing global climate change scenario, the ecological risk faced by the QTP show a decreasing trend under the influence of climate factors, and the decrease in ecological risks is much higher at higher elevations than at lower elevations. [ABSTRACT FROM AUTHOR]

The intensity and location of the westerly jet (WJ) in the mid-latitudes of the Northern Hemisphere has been closely related to weather and climate changes in Eurasia. In this paper, we analyzed the seasonal and inter-annual variations in the strength and position of the WJ, using the NCEP-DOE reanalysis II (NCEP) data. Spring is the period that the Tibetan Plateau (TP) transits from a cold to a warm condition, and at the same time the WJ weakens and moves northward. Correlation analysis showed that the westerly wind over the north (south) of the TP has a significant positive (negative) correlation with the TP surface temperature in spring during 1979-2013 (99.9% significance level). In spring, surface sensible heat release dominates thermal conditions of the TP, while the contribution of latent heat becomes important in summer. We conducted three numerical experiments to determine the effects of the TP surface sensible heat flux anomaly in spring on the intensity and location of the WJ using the community atmosphere model 5 (CAM5). Experimental results indicated that changing the TP surface sensible heat flux can produce changes in the TP heat sources. When the TP sensible heat flux is switched off (TPSHL), the TP surface has a lower temperature and no longer heats up the middle and upper troposphere, and leads to a maximum cooling of -1.2C at 200 hPa over the TP with a significance level of 95%. In spring, the abnormal low temperature over the TP caused the WJ to strengthen and move southward compared with the control experiment (CTL), and this results in a westerly (easterly) wind anomaly over the south (north) of the TP with a significance level of 95%. We obtained the opposite conclusion from the comparison of the enhanced TP surface sensible heat flux (TPSHH) with CTL test results. In TPSHL, the WJ is still steadily located near 30N in May as well as April, i.e., the first northward jump occurs from May to June which is a delay of one month compared to CTL. While in TPSHH, the WJ moves northward approximately 10 of latitude from April to May which is 5 larger than CTL. Thus, the strength and north-south migration of WJ is closely linked to the TP heat source, especially during the spring-summer seasonal transition period, while TP surface temperature increased significantly and showed early signal compared to the surroundings with the global warming. Therefore, considerable attention must be paid to the location and strength of the WJ with respect to the sensible heat flux over the TP. [ABSTRACT FROM AUTHOR]

The source region of the Yangtze River (SRYR) is located in the hinterland of the Tibetan Plateau (TP). Due to the harsh climate environment, there are few meteorological stations in its territory, and the measured meteorological data are also less. To overcome the impact of lack of measured meteorological data, the China Meteorological Forcing Dataset (CMFD) was used to couple with the meteorological data, to make the meteorological data more representative of the average climate state of the SRYR. Furthermore, we used the Soil and Water Assessment Tool (SWAT) to verify interpolation effect of meteorological data. Then the six global climate models (GCMs) were integrated through deep learning (DL) algorithm to make it closer to the changes in weather data after correction. The future water resource changes of SRYR were obtained by coupling the SWAT model with the integrated meteorological data. The results show that the CMFD dataset has a high precision in the SRYR, and that the average relative error (RE), coefficient of determination (R2), Nash–Sutcliffe efficiency (Ens) with the measured temperature and precipitation are 10.66%, 0.99, and 0.93, respectively. The CMFD dataset can be used for meteorological data integration. After the meteorological data integration, the Ens between simulated runoff and observed runoff increased from 0.64 to 0.70, and the RE reduced from 13.4 to 10.3%. Under the future climate scenario, the runoff in the SRYR shows a decreasing trend, the average annual runoff decreased by 11.89%, and the distribution of runoff during the year changes is even more dramatic. This shows that the SRYR faces the risk of water resources reduction, which will bring challenges to water resources management in the SRYR. This study provides a new idea for meteorological data correction. [ABSTRACT FROM AUTHOR]

Climate on the Tibetan Plateau is often considered sensitive to global changes, yet the degree of sensitivity in different spaces and seasons prior to instrumental records is not clear. In this paper, we studied tree-ring maximum latewood density (MXD) to examine the late-summer (August–September) temperature variation over the past two and half centuries on the eastern Tibetan Plateau. The MXD regional chronology was established from 109 tree-ring samples of Balfour spruce [ Picea likiangensis var. balfouriana (Rehd. et Wils.)] at four high elevation sites. The chronology exhibited a high correlation ( r = 0.82, n = 56, p < 0.001) with the mean August–September temperature. Using the tree-ring data, we reconstructed the late-summer temperature for the period A.D. 1765–2009. The reconstruction accounted for 71.4% of the variance in instrumental temperature in the period 1954–2009. The reconstructed temperature did not show a warming trend in the past 250 years, suggesting a unique characteristic of late-summer temperature variability in the study region of the Tibetan Plateau. Our tree-ring data are useful for further understanding of the plateau's thermal condition in late summer and its role in regulating southward retreat of the Southwest Asian monsoon. [ABSTRACT FROM AUTHOR]

Data analysis indicates that the interannual variability of the spring atmospheric heat source over the Tibetan Plateau (TP) depends largely on the intensity of the overlying subtropical westerly jet (WJ), which is closely related to the early spring (February-March-April) sea surface temperature anomaly (SSTA) tripole pattern over the North Atlantic, i.e., the SSTA tripole pattern with a warm core to the southeast of Newfoundland and two cold cores to the south of Iceland and southeast of Bermuda, respectively. Such an SSTA pattern can be regarded as a response to the atmospheric forcing of the preceding January-February-March North Atlantic Oscillation. Numerical experiment results from both linear baroclinic model with an idealized diabatic heating profile and an atmospheric general circulation model with prescribed SSTA forcing demonstrate that the warm core alone of the tripole pattern can stimulate a steady downstream Rossby wave train, which further intensifies the spring WJ over the TP. As a result, a positive anomaly of surface sensible heating occurs over most parts of the TP, whereas the precipitation and corresponding latent heating is characterized by a seesaw pattern with a positive/negative anomaly over the northern/southern TP. Meanwhile, the air column radiation cooling effect is enhanced to a certain degree over the plateau. Further analysis suggests that the early spring SSTA over the North Atlantic may exert a seasonal-lagged impact upon the East Asian summer monsoon by modulating the thermal forcing over the TP. [ABSTRACT FROM AUTHOR]

The climate system is a prototypical nonlinear complex system exhibiting nonstationary temporal variation and complicated spatial patterns. One of the ideal locations for studying climate systems is the Qinghai-Tibet Plateau (QTP), which is considered an amplifier of global climate change. In this study, recurrence quantification analysis (RQA) was used to analyze the annual temperature series of 17 stations in different climate zones of the QTP, based on station observation data of daily temperature (minimum, maximum and mean) from 1961 to 2008. Spatial patterns and variation of RQA indices of Determinism (DET) and Kolmogorov (K2) entropy suggested that there are marked differences in temperature pattern in the QTP. Correlation analysis between RQA indices of temperature series and environmental factors, such as topographical variation and Normalized Difference Vegetation Index suggest that both the source and effect of climate complexity are nonlinear. Results of this study indicate that RQA measurement was indeed an efficient approach to analyze the dynamics of a climate system. [ABSTRACT FROM AUTHOR]