Asian Summer Monsoon Precipitation Research Articles

Climate sustained the evolution of a stable postglacial woody cover over the Tibetan Plateau

The Tibetan Plateau (TP) is referred to as the world's “Third Pole” and the “Asian Water Tower”. It is dominated by herbaceous plants, with sparse to no vegetation cover in its central and western parts. Only 12% of the TP land mass is covered by forest on its eastern edge where most of the human population is distributed. Understanding forest evolution and its driving forces in this region is essential to sustainable development in east, southeast, and south Asia. In this study, we built a database of 622 topsoil pollen samples and 24 fossil pollen sites, and reconstructed the postglacial evolution of woody and herbaceous cover using the modern analogy technique (MAT) and the random forest (RF) methods. We found that postglacial woody cover was sustained at ~17% (13–21%) on the eastern TP (ETP) and ~ 5% (3–9%) on the central and western TP (CWTP). The change in woody cover on the ETP was mainly driven by the East Asian summer monsoon (EASM) precipitation (42%) and summer temperature (30%), while the change in herbaceous cover on the CWTP was mainly driven by the summer temperature (54%) and moisture-laden westerlies (16%). Humans only slightly affected the woody cover after 3600 cal. yr BP, even when large populations started to settle on the TP. Future climate warming might be beneficial for increasing the forest cover on the TP.

Severe Drought Conditions in Northern East Asia During the Early Pliocene Caused by Weakened Pacific Meridional Temperature Gradient

AbstractThe evolution of hydroclimate in East Asia during the Pliocene—a potential analog of the future greenhouse climate—remains highly uncertain. Here we reconstruct changes in the hydroclimate of Northern China during this epoch. Our results reveal previously undocumented severe drought conditions that persisted through the early Pliocene with a significantly greater magnitude than suggested by other records. Using a broad hierarchy of climate simulations, we find that reduction in the Pacific meridional sea surface temperature (SST) gradient has particularly strong impacts on precipitation over Northern China, which suggests its key role in maintaining drought conditions during the early Pliocene. The weaker Pacific meridional SST gradient causes the weakening of the East Asian summer monsoon precipitation over this region via a reduction of atmospheric northward moisture transport from the ocean, which enhances aridity inland. Our results highlight the fundamental control of the tropical ocean on the extra‐tropical hydrological cycle.

Role of Asian Westerly Jet Core's Zonal Migration in Holocene East Asian Summer Monsoon Precipitation

AbstractPaleoclimatic records reveal spatially asynchronous changes of East Asian summer monsoon (EASM) precipitation during the Holocene, but the underlying mechanisms are not fully understood. This study explores the role of the zonal shift of the Asian westerly jet (AWJ) core on the spatial‐temporal variability of EASM precipitation based on Holocene climate simulations using the KCM and CESM forced by orbital variations. We analyzed the composite differences of summer precipitation and associated atmospheric circulations between the early (middle) and middle (late) Holocene. Simulations suggest a dipole pattern of summer precipitation with increasing (decreasing) precipitation in central (southern) China from the early to late Holocene, which was shaped by the eastward shift of the AWJ core. The eastward shift of the AWJ core and the accompanied eastward movement of the upper‐level convergence over the AWJ's right exit region weakened the low‐level downward motions over central China. Meanwhile, the low‐level upward motions over southern China were weakened by the concurrent eastward (westward) migration of the South Asian High (western Pacific subtropical High) during the Holocene. Consequently, summer precipitation increased (decreased) in central (southern) China from the early to late Holocene. The eastward shift of the AWJ core was primarily driven by amplified meridional insolation gradient at middle latitudes via strengthening upper‐level westerly intensity during the Holocene. In addition, land cover difference between East Asia and central Asia caused a greater enhancement of westerlies intensity in East Asia, further modulating the eastward movement of the AWJ core during the Holocene.

Revisiting the physical mechanisms of East Asian summer monsoon precipitation changes during the mid-Holocene: a data–model comparison

The mid-Holocene (MH; 6 ka) is one of the benchmark periods for the Paleoclimate Modeling Intercomparison Project (PMIP) and provides a unique opportunity to study monsoon dynamics and orbital forcing (i.e., mostly precession) that differ significantly from the present day. We conducted a data–model comparison along with a dynamic analysis to investigate monsoonal (i.e., East Asian summer monsoon; EASM) precipitation changes over East Asia during the MH. We used the three phases of the PMIP simulations for the MH, and quantitatively compare model results with pollen-based climate records. The data–model comparison shows an overall increase in the summer monsoon precipitation, except a local decrease during the MH. Decomposition of the moisture budget into thermodynamic and dynamic components allows us to assess their relative role in controlling EASM precipitation during the MH, and to investigate the precipitation changes obtained from pollen records in terms of physical processes. We show that the dynamic effect, rather than the thermodynamic effect, is the dominant control in increased EASM precipitation during the MH in both the proxy records and models. The dynamic increase in precipitation results mainly from the enhancement of horizontal monsoonal moisture transport that is caused by intensified stationary eddy horizontal circulation over East Asia. In addition, a cloud-related cooling effect reduced the thermodynamic contribution to the increase in EASM precipitation during the MH.

Extra predictability from a seamless approach for Asian summer monsoon precipitation from days to weeks

AbstractMultiple‐scale atmospheric or oceanic prediction has been a challenging issue due to the different dynamical and thermodynamic processes involved and the uncertainty inherent in highly nonlinear and stochastic forcing, such as the prediction of Asian summer monsoon (ASM) precipitation. Seamless prediction was proposed to address this issue. The idea behind this approach is that temporal averaging reduces the spread of the prediction ensemble but retains the approximate first moment, which effectively increases the signal‐to‐noise ratio of the prediction. In this study, the superiority of the seamless prediction was assessed for the ASM precipitation at time‐scales from days to weeks. The hindcasts from the European Centre for Medium‐Range Weather Forecasts in the Subseasonal to Seasonal ensemble dataset were used for the detailed assessment. Results show significant advantages of the seamless approach in evaluating the ASM precipitation prediction on time‐scales ranging from 2 days to 2 weeks. Furthermore, the source of the average window predictability was analysed for two lead times with significantly superior prediction accuracy: lead times of 4d4d and 3w3w. For 4d4d, the Madden–Julian Oscillation is dominant, while the role of the El Niño–Southern Oscillation phase becomes substantial for 3w3w. These results offer a detailed analysis for the prediction of ASM precipitation within a framework of seamless prediction, benefiting further interpretation of seamless prediction of ASM precipitation.

East Asian monsoon precipitation decrease during Plio-Pleistocene transition revealed by changes in the chemical weathering intensity of Red Clay and loess-paleosol

East Asian Monsoon variations during the Plio-Pleistocene transition have attracted much scientific interest, but they are still not well understood. We analysed the trace and major element concentrations of the Red Clay and loess-paleosol sequence of the XSC section, on the southern Chinese Loess Plateau (CLP), over the time interval of 4–2 Ma. From the results of geochemical and mineralogical analysis, we conclude that the Na/K ratio can be used to reflect the weathering intensity of plagioclase. Grain- size effects on the Na/K ratio were minimized based on the analysis of multiple size fractions. The Na/K ratios show similar trends between different grain-size fractions during the Pliocene-Pleistocene transition. Additionally, the Na/K ratio for various Holocene eolian sediments is well correlated with the regional mean annual precipitation (MAP). Based on this observation, we relate the Na/K ratio to East Asian Summer Monsoon (EASM) precipitation and propose that the EASM is the primary control of the post-depositional weathering intensity. The Na/K record of the EASM precipitation, as inferred from the Na/K record of the XSC section, progressively weakened and increased in amplitude between 4 and 2 Ma, indicating that the climate on the monsoonal margin evolved from warm and moist during the Late Pliocene to dry and cold during the Early Pleistocene. Our results support the hypothesis that global cooling was responsible for driving the decrease in EASM-derived rainfall via the migration of the intertropical convergence zone (ITCZ) and the associated monsoon precipitation belt during the Plio-Pleistocene transition.

Shifts in the silicate weathering regime in South China during the Meso-Cenozoic linked to Asian summer monsoon evolution

The scarcity of reliable and relatively continuous Meso-Cenozoic weathering records hinders the accurate temporal tracing of silicate weathering regimes and their possible shifts, which has resulted in a knowledge gap in our understanding of the interactions of the weathering-CO2-climate system on geological timescales. Here, we present a detailed compilation of Meso-Cenozoic silicate weathering records from South China. The results show that a trend of increasing weathering occurred in South China during the Meso-Cenozoic, coupled with increases in the average silicate weathering intensity (expressed by the chemical index of alteration (CIA) and the Kaolinite/(Illite+Chlorite) ratio), characterized by three stages. Comparison of silicate weathering regimes with the CIA reveals that expansions of a supply-limited weathering regime in the study region occurred at ~47 Ma and ~2.6 Ma, potentially caused by increases in Asian summer monsoon (ASM) precipitation. Also, we speculate that an increase in the land-sea thermal contrast induced by the global sea-level fall and the India-Asia suture and the initial retreat of the Neotethys Sea may have caused the initial strengthening of the ASM at ~47 Ma; and that the substantially increased cross-equatorial airflow may have contributed substantially to the increase in interglacial ASM precipitation since ~2.6 Ma. A significant implication of the two expansions is that the ASM may have prevailed over South China since at least 47 Ma.

Luminescence dating reveals a rapid response to climate change of fluvial terrace formation along the Ani River, northeastern Japan, during the last glacial period

Fluvial terraces along the middle reaches of many Japanese rivers were formed during the last glacial period as a result of changes in sediment discharge related to cooler temperatures and/or reduced water discharge because of lower precipitation. The influence of climate change on these fluvial terraces is not yet fully understood because most previous studies lacked detailed reconstructions of the chronology of terrace development. This study provides a detailed luminescence chronology of fluvial terrace deposits along the Ani River, northeastern Honshu, Japan, and compares that chronology to paleoclimatic records. Eight samples for luminescence dating were obtained from an outcrop of terrace deposits (∼10 m thick) in the Ani River valley. The fading-corrected infrared stimulated luminescence (IRSL) ages are consistent with the fading-corrected post-IR IRSL ages for some samples, which suggests that fading corrections were effective despite the higher fading rates of the IRSL signal. However, for the other samples, the post-IR IRSL ages are significantly older than the fading-corrected IRSL ages due to incomplete bleaching. The pulsed IRSL signals are close to field saturation for older samples, which might have resulted in a greater variation of the ages. Fading-corrected IRSL ages demonstrate periods of rapid aggradation during 105–90 ka and 75–60 ka. Comparison of terrace development with paleoclimatic records indicates that the two periods of fluvial deposition correspond to decreases in precipitation caused by weakened East Asian summer monsoon precipitation and possibly decreases in temperature. The results of this study show that the Ani River responded rapidly to climate change on a time scale of a few tens of thousands of years during the last glacial period.

A new stalagmite oxygen isotope record over the last 1350 years: Insights into spatial variation in Asian summer monsoon and temperature forcing

Climate reconstructions over the last millennium are essential to estimate natural and anthropogenic forcing. Here we present a stalagmite δ18O record from southwestern China, which characterizes changes in the Asian Summer Monsoon (ASM) precipitation over the past 1350 years. Wet climate is clearly identified during the Dark Age Cold Period (DACP) and Little Ice Age (LIA); dry climate is clearly identified during the Medieval Warm Period (MWP) and Current Warm Period (CWP). These precipitation oscillations, except that over the CWP, are remarkably similar to, but strongly antiphase with, those in northwestern China. Over the CWP, our δ18O record, similar to other stalagmite records in East Asia, also exhibits a gradually increasing trend. This trend has been assumed to be caused by anthropogenic temperature warming. Here a better correlation is identified between our record and atmospheric temperature change during the preindustrial and industrial eras. This correlation provides solid evidence for the consistent modulation of the temperature on the ASM precipitation without and with the human-induced forcing. However, this modulation may act in a different manner during the industrial era, which results in the same δ18O variation across East Asia. In sum, our record provides a clear spatial variation of the ASM precipitation and highlights persistent temperature modulation on the ASM without and with anthropogenic emissions.

Significant weak monsoon events during the early to middle Holocene transition: Pollen evidence from an alpine lake in North China

The response characteristics of East Asian summer monsoon (EASM) precipitation to abrupt climatic events during the early to middle Holocene transition may provide insights into the response of EASM precipitation to possible extreme climatic events under future global warming scenarios. We present a high-resolution (∼10 yr) pollen record from a hydrologically closed alpine lake (Yazihai Lake) in North China spanning the interval of 9000–7500 cal yr BP. The results reveal two significant weak monsoon events during 8830–8730 cal yr BP and 8100–8000 cal yr BP. Based on a comparison with the GRIP δ18O ice core record from Greenland and the stalagmite δ18O record from Dongge Cave in South China, we suggest that the second weak monsoon event (8100–8000 cal yr BP) recorded at Yazihai Lake corresponds to the 8.2 ka event that originated in the North Atlantic region, it is spatially and temporally synchronous between the northern and the southern parts of the EASM region and is characterized by a significant decrease in EASM precipitation. For the first weak monsoon event (8830–8730 cal yr BP) recorded at Yazihai Lake, it was also captured by pollen, stalagmite δ18O, and marine sedimentary records from middle to low latitudes of the Northern Hemisphere, and its nature and amplitude resemble the 8.2 ka event. We infer that the possible cause of these two significant weak monsoon events was related to the southward shift of the intertropical convergence zone (ITCZ) due to the collapse of the Atlantic Meridional Overturning Circulation (AMOC), triggered by meltwater influx to the North Atlantic Ocean, and that the abrupt climate signals were transmitted via the monsoon circulation from low latitudes to middle–high latitudes in the EASM region.

Magnesium isotopic evidence for staged enhancement of the East Asian Summer Monsoon precipitation since the Miocene

Knowledge of the evolution of the East Asian Summer Monsoon (EASM) provides a valuable opportunity to uncover the dynamic interactions of land-ocean-atmosphere system in the late Cenozoic. However, the evolutionary history of EASM remains debatable, mainly due to the difficulty in separating EASM precipitation and temperature signals. In this study, precipitation proxies of Sr/Ca ratio and δ26Mg value in loess secondary calcite (carbonate nodule (NC) and fine carbonate (FC) (grain size < 4 μm)) are further verified, with high precipitation corresponding to high δ26MgFC but low δ26MgNC and Sr/CaNC ratio, and vice versa. Then, these proxies are investigated in well-researched Chinese loess eolian deposits since ∼22.5 Ma. Results suggests that the EASM precipitation was staged enhancement in the mid-Miocene (∼16.5–14.0 Ma) and the Quaternary (∼2.6–0 Ma). The mid-Miocene enhancement can be compared with the strong EASM intensity and the warmest global temperature since the Miocene. Global warming thus is considered as the dominant force for this enhancement via an expansion in the latitudinal extent of the Indo-Pacific Intertropical Convergence Zone (ITCZ). In contrast, the Quaternary enhancement was accompanied by decreases in global temperature. We propose their linkage via the reinforcement of the Pacific Walker Circulation and a northward shift of the subtropical ridge in the western Pacific. Our study provides a new insight into EASM evolution and its dynamic linkage with global climate changes.

Quantification of Seasonal and Interannual Variations of the Tibetan Plateau Surface Thermodynamic Forcing Based on the Potential Vorticity

AbstractIn this study, a new index based on the potential vorticity (PV) framework is proposed for the quantification of the Tibetan Plateau (TP) surface thermodynamic and dynamic forcing. The results show that the derived TP surface PV (SPV) includes the topographical effect, near‐surface absolute vorticity, and land–air potential temperature differences. The climatological annual cycle of the SPV suggests that the TP transitions from a cooling to a heating source in April. The SPV reaches a maximum from June to August, which is consistent with the evolution of the Asian summer monsoon precipitation. Further analysis suggests that the intensified SPV in the boreal summer results in a low‐level cyclonic circulation anomaly associated with increased precipitation over the southeastern slope of the TP and South China and decreased precipitation over the Indian Ocean. In winter, the intensified SPV is associated with local cold air and divergence at the TP surface.

East Asian summer monsoon precipitation response to variations in upstream westerly wind

From spring to summer, the East Asian summer monsoon (EASM) rainband migrates northwestward. During summer, East Asian countries experience extensive precipitation due to the EASM rainband, but the springtime monsoon rainband lies over the Pacific. The seasonal evolution of the EASM rainband is influenced by the mechanical effect of the Tibetan Plateau, and seasonal changes in the westerly wind speeds impinging on the Tibetan Plateau are a key driver of this process. In this study, using interannual variability of the upstream zonal wind speed, the dynamical mechanism for the interannual variations of the EASM precipitation is revealed based on the topographically forced stationary Rossby wave theory. The dynamical mechanism regulating interannual variability in the EASM rainband is essentially the same mechanism that drives the seasonal evolution of the climatological EASM rainband. If the westerly winds impinging on the Tibetan Plateau are stronger (weaker) than average, then the EASM rainband shifts eastward (westward). Large variations in the upstream westerly wind during May induced considerable interannual variation in the zonal location of the rainband (up to a 20°–30° shift). The westerly wind speed exhibited less variations in June and July, resulting in a smaller zonal shift of approximately 10°.

Potential CO2 forcing and Asian summer monsoon precipitation trends during the last 2,000 years

Abstract Holocene records for the Asian Summer Monsoon (ASM) indicate that, apart for the last 2,000 years (“2 kyr shift”), solar insolation was the dominant factor controlling the monsoon climate. The aim of this review is to provide a synopsis of climate characteristics over the last 2 kyr, clarifying mechanisms for the diverse trend with Northern Hemisphere Summer Insolation (NHSI) records. Here, we initially review proxy-based climate reconstructions for the last 2 kyr, and then compare them with records from the last five interglacial periods. Finally, we examine potential physical mechanisms responsible for the “2 kyr shift.” Findings from this review indicate that the “2 kyr shift” is a representative pattern of Holocene climate change within the core area of the ASM, and the “2 kyr shift” could be mainly controlled by changes in atmospheric CO2 concentration. In addition, suggestions to address a more humid condition dominating the Asian monsoonal margin zones are offered.

Nonlinear response of Asian summer monsoon precipitation to emission reductions in South and East Asia

Anthropogenic aerosols over South and East Asia currently have a stronger impact on the Asian summer monsoon (ASM) than greenhouse gas emissions, yet projected aerosol emission changes in these regions are subject to considerable uncertainties such as timescale, location, or emission type. We use a circulation/climate model with idealised aerosol distributions to demonstrate that the sum of ASM responses to aerosol emission reductions in each region is very different to the response to simultaneous reductions in both regions, implying the ASM response to aerosol emissions reductions is highly nonlinear. The phenomenon is independent of whether aerosols are scattering or absorbing, and results from interaction of induced atmospheric circulation changes. The nonlinearity from interactions between aerosol forcing from different regions represents a new source of uncertainty in projections of ASM changes over the next 30–40 years, and may limit the utility of country-dependent aerosol trajectories when considering their Asia-wide effects, though we recommend further work to establish whether the nonlinearity is buffered by other drivers. To understand likely changes in the ASM due to aerosol reductions, countries will need to accurately take account of emissions reductions from across the wider region, rather than approximating them using simple scenarios and emulators. The nonlinearity in the response to forcing therefore presents a regional public goods issue for countries affected by the ASM, as the costs and benefits of aerosol emissions reductions are not internalised; in fact, forcings from different countries such as India and China work jointly to determine outcomes across the region.

Predictable Pattern of Precipitation Over Asian Summer Monsoon Regions

AbstractPrecipitation prediction has been a challenging issue. The predictable pattern of Asian summer monsoon (ASM) precipitation is identified by the average predictable time method and precipitation hindcasts from the European Centre For Medium Range Weather Forecasts. The leading predictable pattern is characterized by a dipole pattern with the first center spanning from the northeast Bay of Bengal eastward to the western North Pacific, and the opposite center mainly in the Maritime Continent. It provides skillful prediction up to 21–24 days, far exceeding the skill averaged over the ASM (less than 5 days). Empirical mode decomposition analysis shows that the intraseasonal component, contributing 55% of the total variance of predictable components, provides the most predictability for ASM precipitation. The intraseasonal component originates from the boreal summer intraseasonal oscillation, which is enhanced by local ocean‐atmosphere interactions. The interannual component originating from the El Niño‐Southern Oscillation strengthens the predictability.

Tracing the Origin of the South Asian Summer Monsoon Precipitation and Its Variability Using a Novel Lagrangian Framework

AbstractThe water sources and their variability responsible for the South Asian summer monsoon precipitation were analyzed using Lagrangian atmospheric water-mass trajectories. The results indicated that evaporated waters from the central and south Indian Ocean are the major contributors to the South Asian summer monsoon rainfall, followed by the contribution from the local recycling (precipitated water that evapotranspirated from the South Asian landmass), the Arabian Sea, remote sources, and the Bay of Bengal. It was also found that although the direct contribution originating from the Bay of Bengal is small, it still provides a pathway for the atmospheric water that comes from other regions. This pathway is hence only crossing over the Bay of Bengal. The outcomes further revealed that the evaporated waters originating from the central and south Indian Ocean are responsible for the net precipitation over the coastal regions of the Ganges–Brahmaputra–Meghna Delta, northeast India, Myanmar, the foothills of the Himalayas, and central-east India. Evaporated waters from the Arabian Sea are mainly contributing to the rainfall over the western coast and west-central India. Summer monsoon precipitation due to the local recycling is primarily restricted to the Indo-Gangetic plain. No recycled precipitation was observed over the mountain chain along the west coast of India (Western Ghats). The month-to-month precipitation variation over South Asia was analyzed to be linked with the Somali low-level jet variability. The interannual variability of the South Asian summer monsoon precipitation was found to be mainly controlled by the atmospheric waters that were sourced and traveled from the central and south Indian Ocean.

Tree-ring oxygen isotope across monsoon Asia: Common signal and local influence

Tree-ring cellulose oxygen isotope (δ18O) in monsoon Asia (MA) is affected collectively by local hydroclimate and remote oceanic-atmospheric variations. Variations of tree-ring δ18O have been widely used for quantitative reconstructions of monsoon-season precipitation, relative humidity and drought severity. However, local hydroclimate and remote large-scale circulation's influences on tree-ring δ18O has not been fully resolved. Here, we collected 24 tree-ring δ18O chronologies covering the period of 1884–1999 across a wide range of MA and investigated the common signals of these chronologies using principal component analysis. The first principal component (PC1) of the 24 tree-ring δ18O chronologies explained 25.2% of the total variances and showed significant positive correlations with the observed Asian summer monsoon oxygen isotope index (r = 0.69) during the period of 1978–1999, suggesting that a common signal of precipitation δ18O does exist in MA and that it is highly correlated with El Niño–Southern Oscillation (ENSO) (r = 0.72) and the South Asian summer monsoon precipitation (r = −0.66). South Asian summer monsoon precipitation and ENSO are the main factors controlling this common signal of tree-ring δ18O across MA. PC1 of tree-ring δ18O chronologies in MA also depicted a negative (positive) correlation with the Atlantic Multidecadal Oscillation (Pacific Decadal Oscillation), indicating the large-scale circulation influences. After removing the large-scale circulation influences on tree-ring δ18O chronologies, however, the residual tree-ring δ18O chronologies exhibit negative correlations with the regional hydroclimate, highlighting the role local hydroclimate on the individual tree-ring δ18O variations.

Sensitivity of East Asian summer monsoon precipitation to the location of the Tibetan Plateau

AbstractRecent studies have highlighted that a primary mechanism of the East Asian summer monsoon (EASM) is the fluid dynamical response to the Tibetan Plateau (TP), that is, orographically forced Rossby waves. With this mechanism in mind, this study explores how changes in the location of the TP affect the EASM precipitation. Specifically, the TP is moved in the four cardinal directions using idealized general circulation model experiments. The results show that the monsoon aspects are entirely determined by the location of the TP. Interestingly, the strongest EASM precipitation occurs when the TP is situated near its current location, a situation in which downstream southerlies are well developed from the surface to aloft. However, southerlies into the EASM region weaken as the TP moves, which in turn reduces the precipitation. Nevertheless, as long as it moves in the east–west direction, the TP is likely to force the stationary waves that induce precipitation over the mid-latitudes (not necessarily over East Asia). In contrast, moving the TP well north of its original location does not induce strong monsoon flows over the EASM region, resulting in the driest case. Meanwhile, although the southward movement of the TP triggers downstream southerlies to some extent, it does not lead to an increase in the precipitation. Overall, these results show that the location of the TP is crucial in determining the EASM precipitation, and the latter is much more sensitive to the displacement of the TP in the meridional direction than in the zonal direction.

Miocene East Asia summer monsoon precipitation variability and its possible driving forces

The East Asian summer monsoon (EASM) precipitation is vital to hydrology, ecology and societal activities in the densely populated region of East Asia. However, its long-term evolution history and driving forces during the relatively warm Miocene remain unclear, even conflicting in some intervals. Here, we present a new, and quantitative record of EASM precipitation during Miocene using the Bayesian approach of Climate Reconstruction Software (CREST) based on pollen flora from the Tianshui Basin located on the northwestern Tibetan Plateau (TP). The results demonstrate that a strong and relatively stable EASM precipitation period occurred during the Neogene in northern China at ~17.1–13.6 Ma, which was followed by a strong and gradual decreasing period between ~13.6 and 7.4 Ma. This trend was abruptly stopped at ~7.4 Ma with the beginning of a period of large amplitude precipitation increase. The comparison analysis reveals that the gradual decrease of EASM precipitation during the period of ~17.1–7.4 Ma was primarily controlled by the global cooling, whereas the significant increase period after ~7.4 Ma was mainly related to the late Miocene uplift of the TP, supporting climate model simulations, in which both the global temperature and palaeogeography play important roles in regulating the long-term evolution of EASM precipitation.