Monsoon Region Of China Research Articles

Multi-Directional Rather Than Unidirectional Northward-Dominant Range Shifts Predicted under Climate Change for 99 Chinese Tree Species

Climate change has a profound impact on the distribution of species on Earth. At present, there are two contrasting views explaining the direction of species range shifts. One is a single poleward (northward in the Northern Hemisphere) view, while the other is a multi-directional view (e.g., westward, southward, and eastward). Exploring the universality of these two views has become a key focus in climate change ecology. Here, we study the habitat range shift velocity of 99 tree species in China under future climate change scenarios using a bioclimatic envelope model (also called species distribution model) and a climate velocity method. A Monte Carlo method is used to test the consistency between the range shift pattern and stochastic process, and confusion matrices and kappa values are calculated to evaluate the consistency between the bioclimatic envelope model and climate velocity method. The results indicate that the tree species in China are generally expected to shift northwards, with northwest and northeast directions accounting for a larger proportion. The northward-shifting species are mainly distributed in the east monsoon region of China, while the multi-directional shifting species are mainly distributed in the alpine and arid regions of China. The shift directions described by the bioclimatic envelope model are inconsistent with those described by the climate velocity method. The results imply that the tree species in China support the view of the northward shift pattern but, more specifically, should be considered in terms of a multi-directional northward shift pattern. The results also emphasize that the inter-species variation in climate tolerance has been largely ignored in physical-based climate velocity methods. The development of a biological and vector operation-based climate velocity indicator may be more useful in characterizing the range shifts of species, compared to existing physical and scalar operation-based climate velocity indicators. This study provides favorable evidence for the pattern of climate change-induced range shifts in China, as well as in Eastern Asia.

Reconstructed springtime (March–June) precipitation tracked by tree rings dating back to 1760 CE in the Qinling-Bashan mountainous area

In recent decades, considerable advances have been made in dendroclimatic reconstruction in the eastern monsoon region of China. However, understanding of long-term hydroclimatic changes has not been comprehensive due to the complexity of the regional geography in China's north-south transitional zone. Growth-climate response analysis indicated that springtime precipitation is the main factor limiting the radial growth of pine trees in the Qinling-Bashan mountainous area. Based on the three tree ring chronologies distributed in the southeast of Shaanxi Province, we developed a March–June precipitation reconstruction spanning 1760–2020 CE for the Qinling-Bashan mountainous area. Precipitation reconstruction accounts for 40.6% of the total precipitation variance during the instrumental period 1955–2016. Spatial correlation analysis indicated that the precipitation reconstruction recorded similar common precipitation signals for the eastern Qinling Mountains and the Yangtze-Huai River Basin. The results of the superposed epoch analysis (SEA) revealed that low precipitation was one of the main causes of severe drought and locust plague events. The preliminary synoptic climatology analysis showed that our reconstructed precipitation is closely linked to the El Niño-Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD) variability.

Simulating the water δ18O of a small open lake in the East Asian monsoon region based on hydrologic and isotope mass-balance models

Hydrologic and isotope mass-balance models (MBMs) are useful tools for the simulation and quantitative interpretation of lake water δ18O (δL). Such studies of small, open lakes are important because δL may show large responses to weather-driven hydrological variability. A δL sequence was simulated for three-year and five-day interval data from Taozi Lake, a small, open lake in Changsha, in the East Asian monsoon region of China. The MBMs performed well, with the optimal model explaining 90% of the observed δL variability. However, it was necessary to parameterize the precipitation input by increasing the lake water depth during heavy precipitation events to capture the observed sharp decreases in δL. We found that the MBMs using air temperature and the equilibrated atmospheric vapor δ18O (δA) produced a more negative δL compared to the model using the surface water temperature and the observed δA, and that the equilibrated δA was somewhat arbitrary, which introduced a large error in the model output. A sensitivity test highlighted the importance of the seasonal variability of hydrometeorological and isotopic variables to reproduce the observed δL variability. Additionally, the simulated average δL showed a similar pattern of variation to the meteorological variables shifted by different ratios, but for the relative humidity, there was only a narrow window within which a realistic δL series could be reproduced. Our results show that a realistic MBM can be established based on long-term observations, with implications for studies of hydrologic processes and paleoclimate reconstruction.

Richness, not evenness, of invasive plant species promotes invasion success into native plant communities via selection effects

Native plant communities are often invaded by multiple alien species. It is still unclear how increasing diversity of alien invasive species suppresses the growth of native species and thus contributes to invasion success. In the subtropical monsoon region of southeast China, we experimentally created a native plant community with 18 herbaceous species. One week later, we let it be invaded by either zero (controls without invasion), one, two, four or eight alien plant species, with either high or low species evenness. After a four‐month growth period we harvested the aboveground biomass of each species. We found that increasing invasive species richness significantly increased invasive plant biomass, the biomass of all invasive and native plant species within the community, and invasion success (the ratio of invasive plant biomass to the biomass of all native and invasive plants), but it did not significantly reduce native plant biomass. Experimentally manipulating invasive species evenness did not influence invasion success and did not show any differential suppression effects on native plants. One invasive species,Sesbania cannabina, became dominant in terms of plant biomass, irrespective of its proportion in the alien plant mixtures. Throughout this experiment, effects of invasive species richness on invasion success were mainly due to such selection effects among the invasive species. On the other hand, the unchanged biomass of native species under increasing invasive plant richness suggests the presence of at least partly complementary resource niches between invasive and native species.

Sources of Forecast Errors for Rainstorms in the South China Monsoon Region

The possible sources of forecast errors associated with rainstorms in the South China monsoon region were investigated based on Weather Research and Forecasting (WRF) model forecasts for 19 rainstorm cases that occurred in the past 13 years. Two datasets were separately selected as the initial fields of WRF with the same physical parameterization schemes. By investigating the improvement rate of the forecast when using one set of data rather than the other, the important degree of the initial conditions with respect to the forecasts for each case has been obtained. For those initial errors are the important sources of forecast errors, we further explored the source of the initial errors by comparing the two initial conditions. It was found that, interestingly, the significant differences between two initial conditions are all located upstream the rainfall area, with a distance of 5° of longitude away and an area of about 4° × 4°. Based on this, we developed a new method (which we refer to as the “guide flow method”) to identify the sensitive area for rainstorm forecasts in the South China monsoon region and then examined the efficiency of the sensitive areas. It was found that reducing the initial errors in the sensitive areas leads to better forecast results than doing the same in other areas. Thus, the sensitive areas are the source areas of forecast errors for rainstorms in the South China monsoon region.

Sulfur emissions from consumption by developed and developing countries produce comparable climate impacts

Regional consumption activities supported by domestic production and international trade have led to substantial aerosol-related emissions worldwide. Here we quantify sulfur dioxide emissions associated with consumption by developed and developing countries and assess the resulting climate impacts using an Earth system model. We find that although the consumption-associated emissions of developed countries are 40% less than those of developing countries, they lead to similar impacts on global mean surface air temperature and precipitation. This is because the effective radiative forcing induced per emission is greater for developed countries, which we attribute to the emissions being located at higher northern latitudes and being more evenly distributed zonally. Emissions from developing countries have a greater impact on temperature and precipitation over the tropical monsoon regions of China and India. Our results demonstrate the importance of trade and emission region in determining how consumption translates into global climate impact. Sulfur dioxide emissions due to consumption by developed and developing countries differ in magnitude but produce comparable climate impacts due to the regional distribution of emissions, according to simulations using an Earth system model.

CHARACTERISTICS AND IMPACTS OF EXTREME PRECIPITATION UNDER CLIMATE CHANGE: BASED ON CNKI LITERATURE INVESTIGATION

Extreme precipitation event is one of the most extensive and harmful meteorological disasters in China and even the world. Discussing the research situation of extreme precipitation under the background of climate change can grasp the research status and hot spots in this field from a macro perspective and provide a reference for in-depth understanding of the causes and trends of extreme precipitation. Since 1992, the research on extreme precipitation has been gradually carried out, so this study systematically counts and analyzes the scientific literature from the CNKI database from 1992 to 2022 by bibliometric. It shows that the frequency and intensity of extreme precipitation events increase in the China monsoon region, and the regional differences are obvious. It also has a great impact on agricultural production and vegetation coverage. In addition, in recent years, scholars have gradually carried out research on the relationship between extreme precipitation and atmospheric circulation, especially the relationship between the spatial and temporal characteristics of extreme precipitation and ENSO events, which has become a new research hotspot. It is suggested that future studies should comprehensively analyze various influencing factors, quantitatively analyze the impact of extreme precipitation on agricultural production and vegetation coverage, and put forward corresponding solutions.

Improved El Niño Southern Oscillation signals extracted by principal component analysis of tree-ring oxygen isotope records from the East Asian monsoon region of China

There is a great need for the reconstruction of independent El Niño Southern Oscillation (ENSO) from different archives and locations to provide a robust understanding of its driving and feedback mechanisms on long time scales. Though tree-ring cellulose δ18O (δ18OTR) records from the East Asian monsoon (EAM) region of China have the potential to reconstruct ENSO on an annual time scale, δ18OTR ENSO signals may be masked by local climate effects since any individual δ18OTR record is influenced by both large-scale atmospheric circulation and local climate. Few attempts have been made to reduce the uncertainties of the reconstructed ENSO index by δ18OTR records from the EAM region of China by ensemble data analysis. In this study, twelve published δ18OTR records spanning over 100 years (1902–2003 CE) have been collected and processed using principal component analysis (PCA). The first principal component (PC1) extracted from the δ18OTR records shows a positive/negative relationship with the annual Niño 3.4 index/southern oscillation index (SOI), with correlation coefficients higher than those between single δ18OTR record and the Niño 3.4 index/SOI, suggesting the ENSO signal is improved by PCA. A 31-year running correlation on PC1- Niño 3.4 index/SOI reveals an increasingly stronger correlation between δ18OTR and ENSO since the last century, inferring that, in the EAM region, the δ18OTR-ENSO correlation may become much stronger under continuous global warming in the future. Spectrum and spatial correlation analysis further support the idea that PC1 responds to ENSO. The significant relationships between observational precipitation δ18O and Niño 3.4 SST anomaly and PC1 from 1973–2003 CE suggest that precipitation δ18O is a key link to connect δ18OTR with ENSO. This study shows the advantage of ensemble data analysis on δ18OTR records in EAM region of China, which could better extract ENSO signals and reduce the uncertainties of reconstructed ENSO variations by individual δ18OTR records from the EAM region of China. It provides an alternative independent annual indicator for ENSO reconstruction on long time scales when more δ18OTR records from this region are extended in the near future.

New Insights Into Error Decomposition for Precipitation Products

AbstractIt is very important to quantify errors of precipitation estimation products. However, the existing methods do not describe all error components and are therefore not comprehensive enough. In this study, we propose a four‐component error decomposition method (4CED) that decomposes the total errors of precipitation products into four independent parts: hit positive bias, hit negative bias, false bias, and missed bias. And we use it to evaluate the performance of the three latest satellite precipitation products in the eastern monsoon region of China. Our study reveals 4CED has apparent improvements compared with the previous method. Results also provide new insights for tracking error sources and quantifying the error magnitudes of precipitation products. Moreover, the proposed 4CED can be extended to different spatial and temporal scales. Our new method will not only contribute to product upgrades, but also provide guidance for potential applications.

Biofuels Reserve Controlled Wildfire Regimes Since the Last Deglaciation: A Record From Gonghai Lake, North China

AbstractWildfire activity is an important activity in evolution of vegetation and carbon cycling. Whether wet weather will suppress wildfire or promote them by increasing fuel reserves during the Holocene is not clear. We obtained a record of black carbon from a sediment core spanning the last 14.8 kyr from Gonghai Lake, in North China. There is a close relationship between the timing of wildfire activity and vegetation development driven by the East Asian summer monsoon intensity. On a millennial timescales, wet climatic conditions provide a sufficient biofuels reserve, in the same period wildfire increase; thus, the regional potential biofuels reserve is shown to be an important controlling of regional wildfire activity in the monsoon region of China, under natural conditions. We infer that with the strengthening of Asian summer monsoon caused by global warming, the wildfire carbon emission in Asian monsoon region may increase in the future.

GDGTs-based quantitative reconstruction of water level changes and precipitation at Daye Lake, Qinling Mountains (central-east China), over the past 2000 years

Alpine lakes are natural rain gauges, and reconstructing changes in their water level is a key to understanding the regional hydrological environment, climate change and vegetation evolution. Precipitation in the northern and the southern parts of the eastern monsoon region of China exhibits a centennial-scale inverse relationship over the past 2000 years; however, there is substantial uncertainty regarding the temporal range of this dipolar pattern. In order to better understand this north-south pattern of precipitation variation and its driving mechanism, we analyzed isoGDGTs biomarker compounds in a sediment core from alpine Daye Lake, in the Qinling Mountains, in the north-south climatic transition zone of eastern China. Measurements of %Cren were used to reconstruct changes in lake level over the past 2000 years. The results show that, from 240 to 1300 CE, prior to the Little Ice Age, the lake-level changes were consistent with the precipitation record for the northern part of eastern China, with the lake reaching its highest level of 25 ± 7.17 m at 555 CE; subsequently, the lake fell to its lowest level of 12 ± 7.17 m at 1030 CE. During the Little Ice Age, the water level maintained an increasing trend, especially during the last three centuries, when it remained above 20 ± 7.17 m, which is consistent with the precipitation record from southern China. The results indicate that the climatically transitional Qinling region has a complex history of climate change. During the early part of the record (240–1300 CE), the level of Daye Lake and the East Asian summer monsoon precipitation were in phase, controlled mainly by the strength of the East Asian summer monsoon. In contrast, since the Little Ice Age (1300 CE to the present), under the influence of ENSO, the westward extension and southward retreat of the West Pacific Subtropical High caused the rain belt to shift southward, decreasing the water vapor supply to the Qinling Mountains. The ascent of moisture-bearing air over the Qinling Mountains resulted in orographic rainfall, while the weakening of evaporation during the Little Ice Age reduced the evaporation of water vapor and also contributed to the continued rise of the level of Daye Lake. The abundant precipitation in the Qinling region during the Little Ice Age provided water resources to sustain human activities in the downstream Weihe Plain, but was also a major cause of flooding.

Simulation study on the indirect effect of sulfate on the summer climate over the eastern China monsoon region

In this study, we designed a sensitivity test using the half number concentration of sulfate in the nucleation calculation process to study the aerosol-cloud interaction (ACI) of sulfate on clouds, precipitation, and monsoon intensity in the summer over the eastern China monsoon region (ECMR) with the National Center for Atmospheric Research Community Atmosphere Model version 5. Numerical experiments show that the ACI of sulfate led to an approximately 30% and 34% increase in the cloud condensation nuclei and cloud droplet number concentrations, respectively. Cloud droplet effective radius below 850 hPa decreased by approximately 4% in the southern ECMR, while the total liquid water path increased by 11%. The change in the indirect radiative forcing due to sulfate at the top of the atmosphere in the ECMR during summer was − 3.74 W·m−2. The decreased radiative forcing caused a surface cooling of 0.32 K and atmospheric cooling of approximately 0.3 K, as well as a 0.17 hPa increase in sea level pressure. These changes decreased the thermal difference between the land and sea and the gradient of the sea-land pressure, leading to a weakening in the East Asian summer monsoon (EASM) and a decrease in the total precipitation rate in the southern ECMR. The cloud lifetime effect has a relatively weaker contribution to summer precipitation, which is dominated by convection. The results show that the ACI of sulfate was one possible reason for the weakening of the EASM in the late 1970s.

Climate change in the monsoon region of eastern China since the Little Ice Age (LIA) recorded from Lacustrine sediments in Yandang Mountain

Climate change in the monsoon region of eastern China since the Little Ice Age (LIA) recorded from Lacustrine sediments in Yandang Mountain

Feasibility of Species Origin Traceability by Hydrogen Stable Isotopes: Sample Case of Lymantria dispar L. (Lepidoptera: Erebidae)

Lymantria dispar L. (Lepidoptera: Erebidae) is an international quarantine pest with many hosts, widely distributed in Asia, Europe, and America. L. dispar is distributed mainly in the Eastern Monsoon Region of China. Currently, the most effective means of prevention and control of this pest are timely monitoring and early warning. However, their implementation is usually hampered by the lack of feasible methods and tools for fast tracking and traceability. Stable isotope technology can be used for material traceability, but in China, it is rarely employed for insect traceability. Therefore, using L. dispar as an example, we conducted a case study to explore the feasibility of using hydrogen stable isotopes for pest-source traceability. The grid data of hydrogen stable isotopes of global precipitation were downloaded from the Online Isotopes in Precipitation Calculator (OIPC; Bowen and Revenaugh, 2003, Bowen, 2017), and then, a zoning map of hydrogen stable isotopes of precipitation in mainland China was constructed using ArcGIS 10.4.1 (Esri, Redlands, CA, USA). The wings of 284 L. dispar adults captured in five regions in China were selected as experimental samples. A Finnigan Delta V Advantage Isotope Ratio Mass Spectrometer (Thermo Fisher Scientific, Inc., Waltham, Massachusetts, U.S.) and a Flash 2000 HT Elemental Analyzer (Thermo Fisher Scientific, Inc., Waltham, Massachusetts, U.S.) were used to measure the hydrogen stable isotope (δ2H) value of the samples. Then, using the recorded local precipitation hydrogen stable isotope of the sampling site, we performed a data simulation using R software (v.3.2.1; R Development Core Team, Vienna, Austria). A linear regression equation was next established: y = 1.186x − 13.247, where x represents the hydrogen stable isotope ratio of precipitation and y denotes the hydrogen stable isotope ratio of L. dispar. The t-test, F-test, and R2 test results confirmed the high significance and matching with the simulation data used in the model. To further verify the accuracy of the model, L. dispar samples from Chengdu in Sichuan Province were collected for model back-testing. The verification results also evidenced that the actual source of the L. dispar sample can be obtained based on the method applied and the model developed in this paper.

Holocene East Asian Summer Monsoon Rainfall Variability in Taiwan

Characterizing the spatiotemporal variability of the East Asian summer monsoon (EASM) advances our understanding of its rhythm, dynamics, and future impacts. EASM variations during the Holocene have been reconstructed from a variety of geological archives and proxies. However, the spatiotemporal heterogeneity of EASM rainfall during the Holocene remains controversial. Taiwan is geographically suitable for studying the EASM history through its geological archives. Herein, we synthesize the reported lake and peat sedimentary records of the entire Holocene, in addition to the records of mass-wasting and on-land deposition from cores collected from Taiwan to illustrate the EASM induced hydroclimate changes in Taiwan throughout the Holocene. Records from Taiwan indicate that the EASM rainfall maximum occurred during the early Holocene, concurring with other EASM records from monsoon region of southern China. We suggest that the early Holocene EASM rainfall maximum in southern China was mainly forced by the higher Northern Hemisphere summer insolation and sea surface temperatures in the Western Pacific Warm Pool (WPWP). A synthesis of EASM rainfall records from across China shows that the timing of Holocene EASM rainfall maximum occurred progressively later from southern to northern China. This time-transgressive EASM rainfall maximum may be due to the latitudinal shift of the westerlies and Western Pacific subtropical high (WPSH) that induced by changes of interhemispheric temperature gradients (ΔTN‐S) and northern high latitude ice volume. Moreover, records from Taiwan suggest a significant collapse of the EASM in Taiwan at ~4–2 ka BP. Based on the records from Taiwan, coastal East Asian and Tropical Pacific, we propose that the sea surface temperatures (SSTs) of the WPWP and/or El Niño -Southern Oscillation (ENSO) activity may have exerted a strong influence on the EASM rainfall changes during the late Holocene. Moreover, increased EASM rainfall in southern China during the last 2 ka was likely caused by a southward shift of WPSH which was associated with gradual decreases in ΔTN‐S during the late Holocene.

Spatiotemporal Dynamics of Nitrogen Transport in the Qiandao Lake Basin, a Large Hilly Monsoon Basin of Southeastern China

The Qiandao Lake Basin (QLB), which occupies low hilly terrain in the monsoon region of southeastern China, is facing serious environmental challenges due to human activities and climate change. Here, we investigated source attribution, transport processes, and the spatiotemporal dynamics of nitrogen (N) movement in the QLB using the Soil and Water Assessment Tool (SWAT), a physical-based model. The goal was to generate key localized vegetative parameters and agronomic variables to serve as credible information on N sources and as a reference for basin management. The simulation indicated that the basin’s annual average total nitrogen (TN) load between 2007 and 2016 was 11,474 tons. Steep slopes with low vegetation coverage significantly influenced the spatiotemporal distribution of N and its transport process. Monthly average TN loads peaked in June due to intensive fertilization of tea plantations and other agricultural areas and then dropped rapidly in July. Subsurface flow is the key transport pathway, with approximately 70% of N loads originating within Anhui Province, which occupies just 58% of the basin area. The TN yields of sub-basins vary considerably and have strong spatial effects on incremental loads entering the basin’ major stream, the Xin’anjiang River. The largest contributor to N loads was domestic sewage (21.8%), followed by livestock production (20.8%), cropland (18.6%), tea land (15.5%), forest land (10.9%), atmospheric deposition (5.6%), orchards (4.6%), industry (1.4%), and other land (0.8%). Our simulation underscores the urgency of increasing the efficiency of the wastewater treatment, conserving slope land, and optimizing agricultural management as components of a comprehensive policy to control N pollution in the basin.

Simulating the change of precipitation-runoff relationship during drought years in the eastern monsoon region of China

Most hydrological simulation and prediction methods assume that the precipitation-runoff relationship was stationary. However, this assumption was found to be questionable during drought years: the annual runoff coefficients (the ratio of annual runoff to annual precipitation) during drought years tend to be smaller than those during non-drought years. However, little is known about the spatial distribution of the magnitude of runoff coefficient change (RCchange) during drought years, and which factors dominate the spatial pattern of RCchange over a large spatial scale. To answer these questions, this study investigated the RCchange in 265 catchments in China that cover a broad range of climate and landscape conditions. We identified the significant factors affecting RCchange from ten catchment characteristics and developed a multivariate generalized additive model to simulate the spatial pattern of RCchange across the eastern monsoon region of China. Results indicated that the RCchange showed an increasing trend from north to south of China, with values ranging from −67.1% to −0.3%, with the average being −26.4%. The lower RCchange (corresponding to more significant runoff reduction) in drought years was more likely to occur in catchments with dryer climate and lower elevation. The simulated RCchange by the multivariate generalized additive model demonstrated a good agreement with observed RCchange, and the values of Nash-Sutcliffe efficiency between observed and simulated RCchange were 0.77 for training catchments and 0.72 for testing catchments. Finally, we applied the model to extrapolate RCchange to the entire eastern monsoon region of China. The result would benefit water resources management during drought years.

Variation of summer monsoon intensity in the North China Plain and its response to abrupt climatic events during the early-middle Holocene

Ningjinpo paleolake was the largest lake in the North China Plain during the Holocene, and its continuous sedimentary record has the potential to reconstruct the summer monsoon intensity and determine the limnological response to abrupt climatic events at a high resolution. Here we use AMS 14C dating and analyses of grain-size and major element contents, and the results show that: (1) During 11.5–10.0 cal kyr BP, the geochemical climate change index (C) (1.16), sediment accumulation rate (SAR) (0.007 cm/yr) and median particle diameter (Md) (20.6 μm) are the lowest within the section, while the geochemical drought index (0.0323), Fe/Mn ratio (0.0088) and clay content (17.3%) are the highest, which indicate that the North China Plain received less precipitation, and chemical weathering and erosional intensity in the Ningjinpo paleolake catchment were weak. (2) During 10.0–7.7 cal kyr BP, the C index (1.36), content of sand (19.1%) and silt (68.0%), Md (27.2 μm) and SAR (0.019 cm/yr) increase significantly. These characteristics indicate that the climate gradually became wetter, chemical weathering and erosion intensity increased, and there was increased runoff to the lake, which raised the lake level. (3) During 7.7–5.5 cal kyr BP, the C index (1.56), silt content (71.8%) and SAR (0.030 cm/yr) increase to the highest, while the Fe/Mn ratio (0.0068), sand content (14.4%) and Md (21.4 μm) decrease to their lowest levels. These suggest the climate was warm and humid, the runoff to the lake was large, chemical weathering in the catchment was strong, and the water level of the lake reached the maximum for the Holocene. (4) During 5.5–3.3 cal kyr BP, the C index (1.26) and SAR (0.011 cm/yr) decrease substantially, whereas the sand content (28.2%) and Md (18.3 μm) increase to the highest levels. These characteristics demonstrate that the climate gradually became arid, the runoff to Ningjinpo paleolake was reduced, the intensity of chemical weathering and erosion in the catchment weakened, and the lake level decreased, although the high frequency of floods in this period. (5) In addition to the globally-recorded abrupt climatic events at ~8.2 cal kyr BP, ~5.3 cal kyr BP and ~4.2 cal kyr BP, which were recorded in the northern monsoon region of China, an abrupt climatic event in the middle Holocene, at ~7.2 cal kyr BP, was also recorded. In the northern monsoon region of China, these events may have been amplified by unusually active ENSO since the middle Holocene.

Classifying floods by quantifying driver contributions in the Eastern Monsoon Region of China

Understanding the generation mechanisms of floods is important to estimating future flood hazards by improving flood frequency analysis and flood trend interpretation. From the hydrological perspective of flood classification, flood types are determined by the seasonality or magnitudes of hydrological drivers (e.g., rainfall, snowmelt, catchment wetness). Few studies attribute floods to the causative drivers by quantifying the contributions of each driver to the flood peaks. Therefore, we propose the Quantification of Driver Contributions for Flood Classification (QDC-FC) method, which combines a data-driven hydrological model, the Shapley value, which quantifies driver contributions to flood peaks, and a classification tree for dividing floods into five types: long-rain floods (>1 day), rain-on-snow floods, snowmelt floods, short-rain floods (≤1 day), and antecedent-wet floods. In the Eastern Monsoon Region (EMR) of China, the method is applied in 225 catchments where the data-driven model has high Nash–Sutcliffe efficiency (NSE > 0.6) in daily runoff simulation and a high R-squared value (R2>0.6) in flood peak simulation. Under the impact of the eastern monsoon, short-rain floods and long-rain floods are the most frequent types in 143 and 69 catchments, respectively. In 213 catchments, all extreme floods (with return periods larger than 10 years) are caused by short rain or long rain. Antecedent wetness causes more than 20% of floods in 26 out of 66 catchments in northeastern China and northern China with cumulative catchment wetness in summer. Although snowmelt-induced floods occur in April in some catchments of northeastern China, only one catchment has more than 20% of floods caused by snowmelt. As a new method for flood classification, the QDC-FC sheds light on the mixed generation mechanisms of floods and possible drivers of flood trends in the EMR of China.

Late Holocene monsoon precipitation changes in southern China and their linkage to Northern Hemisphere temperature

Observations and models suggest a latitudinal redistribution of precipitation as a result of ongoing global climatic warming. However, the dynamic link between temperature and regional precipitation in the course of natural climatic variability during the current interglacial period remains unclear, especially in the monsoon regions of China. Here we present a reconstruction of a ∼5 year-resolution summer monsoon rainfall record for the past 3200 years, based on 622 pairs of δ18O and δ13C and 29 230Th dates from a stalagmite (Wu37) from Wulu Cave in southern China. A close similarity between the δ18O and δ13C records on centennial to decadal timescales suggests that calcite δ18O is most likely a proxy associated with monsoon precipitation. The record reveals that the Little Ice Age (650 - 100 yr B.P.) was a relatively humid period, with two centennial-scale wet events, compared with the Medieval Warm Period (1050 - 650 yr B.P.). In contrast with previous observations in India and northern China, monsoon precipitation variations indicated by our record and other cave records nearby were inversely related to changes in Northern Hemisphere (NH) temperature over the past two millennia, in particular to variations in the thermal gradient between the Northern and Southern hemispheres. This suggests that NH temperature has an important influence on summer precipitation in southern China, via the interhemispheric thermal gradient and land-ocean thermal contrast. In addition, we find that variations of monsoon rainfall in southern China on multi-centennial to centennial timescales are inversely correlated with observed rainfall in the core monsoon region of India and in the northern fringe of the Asian summer monsoon region in China. This spatial pattern of rainfall variability can be interpreted as a result of the migration of the intertropical convergence zone that is likely dominated by the interhemispheric thermal gradient via cross-equatorial airflows.