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This paper investigates the sensitivity of projected future climate changes over China to the horizontal resolution of a regional climate model RegCM4.4 (RegCM), using RCP8.5 as an example. Model validation shows that RegCM performs better in reproducing the spatial distribution and magnitude of present-day temperature, precipitation and climate extremes than the driving global climate model HadGEM2-ES (HadGEM, at 1.875° × 1.25° degree resolution), but little difference is found between the simulations at 50 and 25 km resolutions. Comparison with observational data at different resolutions confirmed the added value of the RCM and finer model resolutions in better capturing the probability distribution of precipitation. However, HadGEM and RegCM at both resolutions project a similar pattern of significant future warming during both winter and summer, and a similar pattern of winter precipitation changes including dominant increase in most areas of northern China and little change or decrease in the southern part. Projected precipitation changes in summer diverge among the three models, especially over eastern China, with a general increase in HadGEM, little change in RegCM at 50 km, and a mix of increase and decrease in RegCM at 25 km resolution. Changes of temperature-related extremes (annual total number of daily maximum temperature > 25 °C, the maximum value of daily maximum temperature, the minimum value of daily minimum temperature in the three simulations especially in the two RegCM simulations are very similar to each other; so are the precipitation-related extremes (maximum consecutive dry days, maximum consecutive 5-day precipitation and extremely wet days’ total amount). Overall, results from this study indicate a very low sensitivity of projected changes in this region to model resolution. While fine resolution is critical for capturing the spatial variability of the control climate, it may not be as important for capturing the climate response to homogeneous forcing (in this case greenhouse gas concentration changes). [ABSTRACT FROM AUTHOR]

The Three-River Headwater Region (TRHR) has undergone significant hydrological changes and affects the water resources security in the local and downstream areas. We use multiple observational precipitation product, as well as the ERA5 reanalysis dataset to investigate the precipitation variations over the TRHR during the rainy season from 1990 to 2020, and to analyze the contributions of local evaporation and remote water vapor transport to the precipitation and its variations. The precipitation shows a significant increasing trend (17.8 mm decade−1). The precipitation variability (PV) is larger at daily scale and smaller at interannual scale. The spatial distribution of PV varies on different timescales, which reflects the different dominant regimes driving the moisture transport. The mean precipitation in the TRHR is predominantly contributed by western and southern moisture influxes, and the increasing trend of these influxes (10.8 kg s−1 decade−1) determines the precipitation increase. Local evaporation provide about 6% of water vapor for the precipitation, while it has little influence on the precipitation change. The anomalous precipitation in wet and dry years is mainly controlled by the atmospheric circulation over the Tibetan Plateau, which regulates the southwestern moisture transport towards the TRHR. Additionally, the precipitation during 1990–2020 increases by about 3.9% compared to that during 1960–1989. It is related to the higher conversion ratio of water vapor influxes to precipitation and larger evaporation over the TRHR. These findings improve our understanding of the precipitation variations in the TRHR and provide insights for policy makers to optimize water resources management to cope with the global climate change. [ABSTRACT FROM AUTHOR]

In this paper we present results of a numerical study using the NASA finite-volume GCM to elucidate a plausible mechanism for aerosol impact on the Asian summer monsoon involving interaction with physical processes over the Tibetan Plateau (TP). During the pre-monsoon season of March–April, dusts from the deserts of western China, Afghanistan/Pakistan, and the Middle East are transported into and stacked up against the northern and southern slopes of the TP. The absorption of solar radiation by dust heats up the elevated surface air over the slopes. On the southern slopes, the atmospheric heating is reinforced by black carbon from local emission. The heated air rises via dry convection, creating a positive temperature anomaly in the mid-to-upper troposphere over the TP relative to the region to the south. In May through early June in a manner akin to an “elevated heat pump”, the rising hot air forced by the increasing heating in the upper troposphere, draws in warm and moist air over the Indian subcontinent, setting the stage for the onset of the South Asia summer monsoon. Our results suggest that increased dust loading coupled with black carbon emission from local sources in northern India during late spring may lead to an advance of the rainy periods and subsequently an intensification of the Indian summer monsoon. The enhanced rainfall over India is associated with the development of an aerosol-induced large-scale sea level pressure anomaly pattern, which causes the East Asia ( Mei-yu) rain belt to shift northwestward, suppressing rainfall over East Asia and the adjacent oceanic regions. [ABSTRACT FROM AUTHOR]

Understanding the spatial–temporal changes in glacier mass balance and associated drivers on the Tibetan Plateau (TP) is important for predicting future water supplies and glacier-related hazards. However, the comparative study of changes in glacier mass balance in different regions of the same glacierized massif on the TP remains scarce. Combining the reconstructed detailed mass balance time-series from 1970 to 2015 for Ningchan No.1 Glacier in the eastern Qilian Mountains and Qiyi Glacier in the western Qilian Mountains using the energy and mass balance model in this work with the published mass balance data from different glaciers, we find that interannual changes in glacier mass balance are broadly similar in different regions of the Qilian Mountains. These interannual changes are primarily driven by variations in ablation-season (June–September) air temperature (Ta), which impact albedo and melt by changing snowfall and incoming longwave radiation (Lin). We link such interannual mass balance variability to the combination of changes in atmospheric circulation over Europe and changes in sea surface temperature (SST) in the Northwest Pacific during the ablation season which can cause the changes in Ta across the Qilian Mountains. In addition, we find a trend of increasingly negative glacier mass balance across the Qilian Mountains from 1970–1994 compared to 1995–2015. This interdecadal trend is driven by higher ablation-season Ta through increasing Lin and through increasing precipitation falling as rain. Lastly, higher glacier mass loss in the east than in the west Qilian Mountains from 1970–1994 and 1995–2015 was mainly caused by lower glacier area-altitude distribution, as well as a reduction in ablation-season precipitation in the eastern Qilian Mountains. [ABSTRACT FROM AUTHOR]

Precipitation changes over the Tibetan Plateau (TP), "Asian Water Tower", greatly affect water resources of the surrounding countries. A dipole pattern in summer precipitation trend over the TP is observed for 1961–2013, increasing over the north TP (NTP) and decreasing over the south TP (STP). Since the TP is one of the most vulnerable regions to climate change in the world, it is of great importance to investigate the role of anthropogenic forcing in the TP precipitation changes. Moisture budget analysis based on reanalysis reveals that the precipitation trends over NTP and STP are dominated by thermodynamic and dynamic terms of vertical moisture advection, respectively. Southward shift in the summer subtropical Asian westerly jet (AWJ) over the west of TP and northward shift in AWJ over the east of TP collaboratively result in the increase and decrease in dynamic component over NTP and STP, respectively. Here, we successfully detect the anthropogenic contribution to the NTP summer precipitation trends using the attribution experiments from the CLIVAR Climate of the 20th Century Plus Project (C20C+). The drying trends over STP are mainly controlled by internal variability, and the anthropogenic forcing is favorable for the drying trends. The impacts of anthropogenic forcing are twofold. First, human activity induced warming increases the specific humidity over TP, increasing the thermodynamic component of moisture budget. Second, the warming trend caused by anthropogenic forcing is unevenly distributed over the Eurasian continent, leading to the southward (northward) shift of AWJ over the west (east) of TP, favoring more precipitation over the NTP but less precipitation over the STP. This study provides evidence of the importance of anthropogenic forcing on the water cycle changes over the TP. [ABSTRACT FROM AUTHOR]

As the first purely multi-decadal satellite-based soil moisture product that spans over 35 years (from November 1978 to December 2013) on a daily basis designed for climate application, the applicability of the European Space Agency (ESA) soil moisture product, including the hydrological consistency between the product and the observed precipitation and the product continuity on the Tibetan Plateau (TP) were investigated. The results show that there is significant degree between the ESA soil moisture product and the observed precipitation. The positive anomaly of the ESA soil moisture product can reflect the occurrences of precipitation, but the precipitation may not definitely lead to soil moisture anomaly, which largely depends on the precipitation amounts. For climate application, large number of missing gaps was shown on the west of the TP, where it is considered that the retrieval algorithms are largely affected by the permafrost covered in this region, leaving the ESA soil moisture product for further improvement. In application, the ESA soil moisture product was used to study the response of surface soil moisture to climate change on the TP. With the rapid warming and the overall wetting of the TP, soil moisture increases on the central of the TP with the increase of precipitation, and decreases in the southeast TP with the precipitation deduction. However, it decreases in the west TP, where it was probably influenced by both the insignificant precipitation changes and the significant increase of evaporation. [ABSTRACT FROM AUTHOR]

Soil temperature changes in cold regions can have great impacts on the land surface energy and water balance, and hence changes in weather and climate, surface and subsurface hydrology and ecosystem. We investigate the spatiotemporal variations of annual soil temperature at depths of 0, 5, 10, 15, 20, and 40 cm during 1983-2013 using observations at 85 stations on the Tibetan Plateau (TP). Our results show that the climatological soil temperatures exhibit a similar spatial pattern among different depths and they are generally higher than surface air temperature at the individual stations. Spatially averaged soil temperature show that the TP has experienced significant warming trends at all six depths during 1983-2013, and the soil at 0-cm depth has the fastest warming rate among all the six layers and the surface air temperature. The first leading mode of joint empirical orthogonal function (EOF) analysis exhibits a spatially prevailing warming pattern across the six depths. This plateau-wide soil warming correlates very well with surface air temperature and sea surface temperature in response to increasing radiative forcing caused by greenhouse gases. The joint EOF2 displays a southeastern-northwestern dipole pattern on the TP in the interannual-decadal variability of soil temperature at all layers, which appears to be related to the warm season precipitation and anomalous atmospheric circulations. The spatial difference of soil warming rates across stations on the TP is associated primarily with the spatial distribution of precipitation (mainly rainfall), with vegetation, snowfall and elevation playing a rather limited role. [ABSTRACT FROM AUTHOR]

We conduct several experiments using a fully-coupled climate model to understand the role of Tibetan Plateau (TP) surface heating in the climate variations over West Asia, South Europe, North Africa, and the North Atlantic during summer. Emphasis has been placed on the physical processes and responsible mechanisms that involve the shift of the Hadley cell and the important features of rotational and divergent response of the atmosphere to the TP heating. The relative importance of the TP to the Asian continent is also analyzed. A heating of the TP surface leads to local increases in tropospheric temperature and the thickness of the air column due to the so-called air pumping effect. In the upper troposphere, the South Asian high intensifies and extends westward. To the west of TP, especially in West Asia, South Europe, North Africa, and the North Atlantic, distinguished Rossby wave responses to the TP heating occur with anomalous high pressure and uniform warming in the entire troposphere. Correspondingly, descending motions intensify and precipitation decreases. However, the tropical Sahel rainfall increases because of a northward shift of the Atlantic intertropical convergence zone and the anomalous westerlies due to the weakening of the southeastern portion of the Atlantic subtropical high. These effects of the TP heating explain a remarkable portion of the effects by the Asian continent heating. In addition, the impacts of different magnitudes of TP surface heating are also discussed. [ABSTRACT FROM AUTHOR]

Tibetan Plateau is the headwater region of many major Asian rivers and very susceptive to climate change. Therefore, knowledge about climate and its spatiotemporal variability in this area is very important for ecological conservation, water resource management and social development. The aim of this study was to reconstruct and analyze the hydroclimate variation on eastern Tibetan Plateau (ETP) over many centuries and explore possible forcing factors on regional hydroclimate variability. We used 118 tree-ring chronologies from ETP to reconstruct the gridded May-July Standardized Precipitation Evapotranspiration Index for the ETP over the last millennium. The reconstruction was developed using an ensemble point-by-point reconstruction method, and a searching region method was used to locate the candidate tree-ring chronologies. The reconstructions have nicely captured the spatial and temporal features of the regional drought variation. The drought variations in south and north of 32.5°N are notably different, which may be related to the divergence influence of North Atlantic Oscillation on the climate systems in the south and north, as well as differences in local climate. Spectral analysis and series comparison suggest that the drought variation in the northeastern Tibetan Plateau has been possibly influenced by solar activity on centurial and longer time scale. [ABSTRACT FROM AUTHOR]

The Northern Hemisphere atmospheric blocking is a primary weather and climate system that accompanies extreme cold spells and heat waves. This study assesses effects of the Tibetan Plateau (TP), the largest continental mountain belt, on the blocking frequency (BF) and amplitude (BA) with progressive TP uplift experiments from 0 to 100 % using a coupled atmosphere-ocean general circulation model. The TP uplift increases the annual-mean BF by 3 and 21 % over the Pacific and Atlantic basins, respectively. A particular focus is placed on the seasonally distinct mechanism in the effects of TP uplift on the boreal winter and summer blockings. During winter, the TP uplift increases the BF over the active centers of both ocean basins via amplifying the eddy kinetic energy of stationary waves. On the other hand, in summer, the TP uplift tends to shift the location of BF northward due to notable poleward displacement of the jet stream and transient eddy activities, particularly over the Atlantic. Compared to the considerable BF increase in both seasons, the amplification of BA due to the TP uplift is much stronger in winter than in summer, reaffirming the seasonally varying TP effect on the blocking. Further analyses reveal that in summer, the TP uplift modulates more effectively the jet displacement than its strength, leading more linear northward shift of jet and BF, especially over the Atlantic. This study will contribute to advances in simulation and prediction of atmospheric blocking events. [ABSTRACT FROM AUTHOR]

Ice cores from the Tibetan Plateau provide high-resolution records of changes in the snow and ice isotopic composition. In the monsoon sector of southern Tibetan Plateau, their climatic interpretation has been controversial. Here, we present a new high-resolution δO record obtained from 2206 measurements performed at 2-3 cm depth resolution along a 55.1 m depth ice core retrieved from the Noijinkansang glacier (NK, 5950 m a.s.l.) that spans the period from 1864 to 2006 AD. The data are characterized by high δO values in the nineteenth century, 1910s and 1960s, followed by a drop in the late 1970s and a recent increasing trend. The comparison with regional meteorological data and with a simulation performed with the LMDZiso general circulation model leads to the attribution of the abrupt shift in the late 1970s predominantly to changes in regional atmospheric circulation, together with the impact of atmospheric temperature change. Correlation analyses suggest that the large-scale modes of variability (PDO and ENSO, i.e. Pacific Decadal Oscillation and El Nino-Southern Oscillation) play important roles in modulating NK δO changes. The NK δO minimum at the end of the 1970s coincides with a PDO phase shift, an inflexion point of the zonal index (representing the overall intensity of the surface westerly anomalies over middle latitudes) as well as ENSO, implying interdecadal modulation of the influence of the PDO/ENSO on the Indian monsoon on southern TP precipitation δO. While convective activity above North India controls the intra-seasonal variability of precipitation δO in southern TP, other processes associated with changes in large-scale atmospheric circulation act at the inter-annual scale. [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]

Data analysis based on station observations reveals that many meteorological variables averaged over the Tibetan Plateau (TP) are closely correlated, and their trends during the past decades are well correlated with the rainfall trend of the Asian summer monsoon. However, such correlation does not necessarily imply causality. Further diagnosis confirms the existence of a weakening trend in TP thermal forcing, characterized by weakened surface sensible heat flux in spring and summer during the past decades. This weakening trend is associated with decreasing summer precipitation over northern South Asia and North China and increasing precipitation over northwestern China, South China, and Korea. An atmospheric general circulation model, the HadAM3, is employed to elucidate the causality between the weakening TP forcing and the change in the Asian summer monsoon rainfall. Results demonstrate that a weakening in surface sensible heating over the TP results in reduced summer precipitation in the plateau region and a reduction in the associated latent heat release in summer. These changes in turn result in the weakening of the near-surface cyclonic circulation surrounding the plateau and the subtropical anticyclone over the subtropical western North Pacific, similar to the results obtained from the idealized TP experiment in Part I of this study. The southerly that normally dominates East Asia, ranging from the South China Sea to North China, weakens, resulting in a weaker equilibrated Sverdrup balance between positive vorticity generation and latent heat release. Consequently, the convergence of water vapor transport is confined to South China, forming a unique anomaly pattern in monsoon rainfall, the so-called 'south wet and north dry.' Because the weakening trend in TP thermal forcing is associated with global warming, the present results provide an effective means for assessing projections of regional climate over Asia in the context of global warming. [ABSTRACT FROM AUTHOR]

Numerical experiments with different idealized land and mountain distributions are carried out to study the formation of the Asian monsoon and related coupling processes. Results demonstrate that when there is only extratropical continent located between 0 and 120°E and between 20/30°N and the North Pole, a rather weak monsoon rainband appears along the southern border of the continent, coexisting with an intense intertropical convergence zone (ITCZ). The continuous ITCZ surrounds the whole globe, prohibits the development of near-surface cross-equatorial flow, and collects water vapor from tropical oceans, resulting in very weak monsoon rainfall. When tropical lands are integrated, the ITCZ over the longitude domain where the extratropical continent exists disappears as a consequence of the development of a strong surface cross-equatorial flow from the winter hemisphere to the summer hemisphere. In addition, an intense interaction between the two hemispheres develops, tropical water vapor is transported to the subtropics by the enhanced poleward flow, and a prototype of the Asian monsoon appears. The Tibetan Plateau acts to enhance the coupling between the lower and upper tropospheric circulations and between the subtropical and tropical monsoon circulations, resulting in an intensification of the East Asian summer monsoon and a weakening of the South Asian summer monsoon. Linking the Iranian Plateau to the Tibetan Plateau substantially reduces the precipitation over Africa and increases the precipitation over the Arabian Sea and the northern Indian subcontinent, effectively contributing to the development of the South Asian summer monsoon. [ABSTRACT FROM AUTHOR]

We present a Palmer Drought Severity Index reconstruction ( r = 0.61, P < 0.01) from 1440 to 2007 for the southeastern Tibetan Plateau, based on tree rings of the forest fir ( Abies forrestii). Persistent decadal dry intervals were found in the 1440s–1460s, 1560s–1580s, 1700s, 1770s, 1810s, 1860s and 1980s, and the extreme wet epochs were the 1480s–1490s, 1510s–1520s, 1590s, 1610s–1630s, 1720s–1730s, 1800s, 1830s, 1870s, 1930s, 1950s and after the 1990s. Comparisons of our record with those identified in other moisture related reconstructions for nearby regions showed that our reconstructed droughts were relatively consistent with those found in other regions of Indochina, suggesting similar drought regimes. Spectral peaks of 2.3–5.5 years may be indicative of ENSO activity, as also suggested by negative correlations with SSTs in the eastern equatorial and southeastern Pacific Ocean. Significant multidecadal spectral peaks of 29.2–40.9 and 56.8–60.2 years were identified. As indicated by the spatial correlation patterns, the decadal-scale variability may be linked to SST variations in the northern Pacific and Atlantic Oceans. [ABSTRACT FROM AUTHOR]

We examine trends in climate variables and their interrelationships over the Tibetan Plateau using global climate model simulations to elucidate the mechanisms for the pattern of warming observed over the plateau during the latter half of the twentieth century and to investigate the warming trend during the twenty-first century under the SRES A1B scenario. Our analysis suggests a 4°C warming over the plateau between 1950 and 2100. The largest warming rates occur during winter and spring. For the 1961–2000 period, the simulated warming is similar to the observed trend over the plateau. Moreover, the largest warming occurs at the highest elevation sites between 1950 and 2100. We find that increases in (1) downward longwave radiation (DLR) influenced by increases in surface specific humidity ( q), and (2) absorbed solar radiation (ASR) influenced by decreases in snow cover extent are, in part, the reason for a large warming trend over the plateau, particularly during winter and spring. Furthermore, elevation-based increases in DLR (influenced by q) and ASR (influenced by snow cover and atmospheric aerosols) appear to affect the elevation dependent warming trend simulated in the model. [ABSTRACT FROM AUTHOR]

A modelling experiment with changes in vegetation types at the Last Glacial Maximum (21 ka BP) is performed by using an AGCM coupled with a simplified simple biosphere model (AGCM+SSiB). The results show that the decrease in temperature is large in Tibet and Eastern Asia at 21 ka. The amplitudes of the decrease vary with seasons and locations. Annual mean temperature decreases between 13 °C and 2 °C. Summer and annual precipitation in eastern China at 21 ka is only about 50% of that at present; while little more or unchanged precipitation appears in northwest, west and southwest of China. The effective precipitation (P–E) shows much drier conditions in eastern and southeastern China than today. A comparison with geological evidences of lake-status and pollen-based vegetation shows that this simulation is in broad scale agreement with the geological records. The changes by using palaeo-vegetation data to prescribe land surface show improved signals in the 21 ka climate simulations in East Asia. This result encourages us to study the potential causes, feedbacks and mechanisms of palaeoclimate changes using the AGCM+SSiB modelling approach continuously. [ABSTRACT FROM AUTHOR]