Asian Monsoon Area Research Articles

Atmospheric Blockings in Western Siberia. Part 2. Long-term Variations in Blocking Frequency and Their Relation with Climatic Variability over Asia

This paper studies the long-term variability of frequency of atmospheric blockings over Western Siberia in 1948–2015 based on the data of three reanalysis projects. We revealed a decreasing blocking frequency for eight of twelve months. However, since the estimated trends of blocking frequency are small comparing to the significant amplitude of interannual variations, we proposed to divide the entire studied period into several quasi-decadal intervals that differ both in the amplitude of interannual fluctuations of blocking frequency and in trends. The effect of Western Siberian blockings imposed on synoptic and climatic variability of meteorological parameters in Asia was studied. The study demonstrated that in summer teleconnection patterns in temperature and precipitation fields are of the close sign-alternating structure; this indirectly indicates that in Western Siberia the blocking is a part of a large-scale wave mechanism. Like the Ural blockings, the blockings occurring over Western Siberia affect meteorological characteristics within the East Asian monsoon area. In winter time they contribute to lower surface temperature and decreased precipitation in Southeast Asia. In summer during blocking events over Western Siberia, precipitation increases in the East Asian monsoon area.

Simulation Dataset on Daily Mean Temperature and Precipitation in East Asian Monsoon Area of China

Simulation Dataset on Daily Mean Temperature and Precipitation in East Asian Monsoon Area of China

Holocene moisture variations over the arid central Asia revealed by a comprehensive sand-dune record from the central Tian Shan, NW China

Arid central Asia (ACA) is one of the largest arid (desert) areas in the world, and its climate is dominated by the westerlies. In this study, we examined sand dune evolution from the Bayanbulak Basin in the Tian Shan (Xinjiang, NW China), aiming to infer the Holocene moisture history of the ACA. Combined with stratigraphic observation and environmental proxies analysis (grain size, magnetic susceptibility and total organic content), large numbers of luminescence ages from multiple sites (eight sections, 79 samples) were applied to reconstruct the evolution of the sand dune accumulation in the study basin. The overall results imply very dry conditions characterized by sand dune accumulation at ∼12–6.5 ka, a wet interval between ∼6.5 and 0.8 ka when soil formation occurred, and decreased moisture during the last 0.8 ka. This moisture variation pattern is generally consistent with that inferred from many lacustrine records in the core zone of ACA, suggesting a widespread dry period in the early-to-middle Holocene and relatively wet middle-to-late Holocene. Thus, the moisture history derived from the current sand dune system contrasts with that in Asian monsoon areas, which are characterized by a strong monsoon (high precipitation) in the early and mid-Holocene and a weak monsoon (low precipitation and dry climate) during the late Holocene. Our results strongly suggest that the winter solar insolation and the external boundary conditions such as atmospheric CO2 concentration, ice sheets, and meltwater fluxes, have been major influential factors triggering the Holocene moisture evolution in the core zone of ACA.

Sequence differences in the seed dormancy gene Qsd1 among various wheat genomes

BackgroundPre-harvest sprouting frequently occurs in Triticum aestivum (wheat) and Hordeum vulgare (barley) at the end of the maturity period due to high rainfall, particularly in Asian monsoon areas. Seed dormancy is a major mechanism preventing pre-harvest sprouting in these crops.ResultsWe identified orthologous sequences of the major Hordeum vulgare (barley) seed dormancy gene Qsd1 in hexaploid wheat cv. Chinese Spring by performing genomic clone sequencing, followed by transcript sequencing. We detected 13 non-synonymous amino acid substitutions among the three sub-genomes of wheat and found that the Qsd1 sequence in the B sub-genome is most similar to that in barley. The Qsd1 sequence in A genome diploid wheat is highly similar to that in the hexaploid A sub-genome. Wheat orthologs of Qsd1 showed closer similarities to barley Qsd1 than did those of other accessions in the DNA database. Like barley Qsd1, all three wheat Qsd1s showed embryo-specific gene expression patterns, indicating that barley and wheat Qsd1 share an orthologous origin. The alignment of four hexaploid wheat cultivars indicated that the amino acid sequences of three spring cultivars, Chinese Spring, Haruyo Koi, and Fielder, are exactly the same in each sub-genome. Only Kitahonami has three amino acid substitutions at the B sub-genome.ConclusionsKitahonami has a longer seed dormancy period than does Chinese Spring. Sequence polymorphisms between Chiniese Spring and Kitahonami in the B sub-genome may underlie the phenotypic differences in seed dormancy between these hexaploid wheat cultivars.

The 9.2 ka event in Asian summer monsoon area: the strongest millennial scale collapse of the monsoon during the Holocene

Numerous Holocene paleo-proxy records exhibit a series of centennial-millennial scale rapid climatic events. Unlike the widely acknowledged 8.2 ka climate anomaly, the likelihood of a significant climate excursion at around 9.2 cal ka BP, which has been notably recognized in some studies, remains to be fully clarified in terms of its magnitude and intensity, as well as its characteristics and spatial distributions in a range of paleoclimatic records. In this study, a peat sediment profile from the Dajiuhu Basin in central China was collected with several geochemical proxies and a pollen analysis carried out to help improve understanding of the climate changes around 9.2 cal ka BP. The results show that the peat development was interrupted abruptly at around 9.2 cal ka BP, when the chemical weathering strength decreased and the tree-pollen declined. This suggests that a strong drier regional climatic event occurred at around 9.2 cal ka BP in central China, which was, in turn, probably connected to the rapid 9.2 ka climate event co-developing worldwide. In addition, based on the synthesis of our peat records and the other Holocene hydrological records from Asian summer monsoon (ASM) region, we further found that the 9.2 ka event probably constituted the strongest abrupt collapse of the Asian monsoon system during the full Holocene interval. The correlations between ASM and the atmospheric 14C production rate, the North Atlantic drift ice records and Greenland temperature indicated that the weakened ASM event at around 9.2 cal ka BP could be interpreted by the co-influence of external and internal factors, related to the changes of the solar activity and the Atlantic Meridional Overturning Circulation (AMOC).

Holocene ENSO-related cyclic storms recorded by magnetic minerals in speleothems of central China.

Extreme hydrologic events such as storms and floods have the potential to severely impact modern human society. However, the frequency of storms and their underlying mechanisms are limited by a paucity of suitable proxies, especially in inland areas. Here we present a record of speleothem magnetic minerals to reconstruct paleoprecipitation, including storms, in the eastern Asian monsoon area over the last 8.6 ky. The geophysical parameter IRMsoft-flux represents the flux of soil-derived magnetic minerals preserved in stalagmite HS4, which we correlate with rainfall amount and intensity. IRMsoft-flux exhibits relatively higher values before 6.7 ky and after 3.4 ky and lower values in the intervening period, consistent with regional hydrological changes observed in independent records. Abrupt enhancements in the flux of pedogenic magnetite in the stalagmite agree well with the timing of known regional paleofloods and with equatorial El Niño-Southern Oscillation (ENSO) patterns, documenting the occurrence of ENSO-related storms in the Holocene. Spectral power analyses reveal that the storms occur on a significant 500-y cycle, coincident with periodic solar activity and ENSO variance, showing that reinforced (subdued) storms in central China correspond to reduced (increased) solar activity and amplified (damped) ENSO. Thus, the magnetic minerals in speleothem HS4 preserve a record of the cyclic storms controlled by the coupled atmosphere-oceanic circulation driven by solar activity.

Hydroclimatic contrasts over Asian monsoon areas and linkages to tropical Pacific SSTs.

Knowledge of spatial and temporal hydroclimatic differences is critical in understanding climatic mechanisms. Here we show striking hydroclimatic contrasts between northern and southern parts of the eastern margin of the Tibetan Plateau (ETP), and those between East Asian summer monsoon (EASM) and Indian summer monsoon (ISM) areas during the past ~2,000 years. During the Medieval Period, and the last 100 to 200 years, the southern ETP (S-ETP) area was generally dry (on average), while the northern ETP (N-ETP) area was wet. During the Little Ice Age (LIA), hydroclimate over S-ETP areas was wet, while that over N-ETP area was dry (on average). Such hydroclimatic contrasts can be broadly extended to ISM and EASM areas. We contend that changes in sea surface temperatures (SSTs) of the tropical Pacific Ocean could have played important roles in producing these hydroclimatic contrasts, by forcing the north-south movement of the Intertropical Convergence Zone (ITCZ) and intensification/slowdown of Walker circulation. The results of sensitivity experiments also support such a proposition.

Quantification of southwest China rainfall during the 8.2 ka BP event with response to North Atlantic cooling

Abstract. The 8.2 ka BP event could provide important information for predicting abrupt climate change in the future. Although published records show that the East Asian monsoon area responded to the 8.2 ka BP event, there is no high-resolution quantitative reconstructed climate record in this area. In this study, a reconstructed 10-year moving average annual rainfall record in southwest China during the 8.2 ka BP event is presented by comparing two high-resolution stalagmite δ18O records from Dongge cave and Heshang cave. This decade-scale rainfall reconstruction is based on a central-scale model and is confirmed by inter-annual monitoring records, which show a significant positive correlation between the regional mean annual rainfall and the drip water annual average δ18O difference from two caves along the same monsoon moisture transport pathway from May 2011 to April 2014. Similar trends between the reconstructed rainfall and the stalagmite Mg ∕ Ca record, another proxy of rainfall, during the 8.2 ka BP period further increase the confidence of the quantification of the rainfall record. The reconstructed record shows that the mean annual rainfall in southwest China during the central 8.2 ka BP event is less than that of present (1950–1990) by ∼ 200 mm and decreased by ∼ 350 mm in ∼ 70 years experiencing an extreme drying period lasting for ∼ 50 years. Comparison of the reconstructed rainfall record in southwest China with Greenland ice core δ18O and δ15N records suggests that the reduced rainfall in southwest China during the 8.2 ka BP period was coupled with Greenland cooling with a possible response rate of 110 ± 30 mm °C−1.

Investigation into pluvial flooding hazards caused by heavy rain and protection measures in Shanghai, China

Flooding hazards caused by heavy rainfall in Shanghai have been reported extensively in the last 15 years. Geologically, Shanghai is sensitive to flooding hazards due to low-lying ground caused by land subsidence. Climatically, Shanghai is in the East Asia monsoon area and frequently experiences torrential rains. In this study, data from fifty-four pluvial flooding events between 2001 and 2015 were collected and analysed. The influence factors contributing to pluvial flooding are evaluated, and recommendations for protective measures are presented. The pluvial flooding prevention capacity in Shanghai is controlled by rain water storage and discharge capacity, which is associated with the sewer network, pumping stations and its sluice and pumping gates. Within the last three decades, the number of local torrential rainfall events and short-duration torrential rains has increased annually. However, the rain water storage capacity has decreased dramatically and the rain water discharge capacity has become limited during this period. In an extreme case, the discharge function of the sewer network was even temporarily lost because of flooding of the distributaries of the Huangpu River. Thus, in order to prevent flooding hazards caused by heavy rain, it is suggested that a large sluice and pumping station between the Huangpu River and the Yangtze River estuary is constructed in the near future, considering the continuous subsidence of the city and the ongoing rising sea levels.

The climate reconstruction in Shandong Peninsula, northern China, during the last millennium based on stalagmite laminae together with a comparison to <i>δ</i><sup>18</sup>O

Abstract. Stalagmite ky1, with a length of 75 mm and the upper part (from top to 42.769 mm depth) consisting of 678 laminae, was collected from Kaiyuan Cave in the coastal area of Shandong Peninsula, northern China, located in a warm temperate zone in the East Asia monsoon area. Based on high-precision dating with the U–230Th technique and continuous counting of laminae, the 1st and 678th laminae have been confirmed to be AD 1894 ± 20 and 1217 ± 20 from top to bottom, respectively. By the measurement of laminae thickness and δ18O ratios, we haved obtained the time series data of thickness of laminae and δ18O ratios from AD 1217 ± 20 to 1894 ± 20, analyzed the climatic–environmental meaning of variations in the thickness of laminae, which have a good correspondence with the cumulative departure curve of the drought–waterlog index in the historical period. The results show that, in the ∼ 678 years from AD 1217 ± 20 to 1894 ± 20, both the thickness of the laminae and the degree of fluctuation in the thickness of the laminae of stalagmite ky1 have obvious stages of variation and are completely synchronized with the contemporaneous intensity of the summer monsoons and precipitation as time changed. There is a negative correlation between the thickness of the laminae and the summer monsoon intensity and precipitation. There is a positive correlation between the degree of fluctuation in the thickness of the laminae and both the intensity of the summer monsoons and the precipitation. Therefore, for the Kaiyuan Cave in the coastal area of both the warm temperate zone and the East Asia monsoon area, the variations in the thickness of the laminae are not only related to the change in the climatic factors themselves but also related to the degree of climatic stability. In the coastal area belonging to the warm temperate zone and the East Asia monsoon area, the climate change between the LIA (Little Ice Age) and the MWP (Medieval Warm Period), in addition to less precipitation and low temperatures (a type of dry and cold climate), also shows an obviously decreasing trend in the degree of climatic stability.

Early–middle Holocene hydroclimate changes in the Asian monsoon margin of northwest China inferred from Huahai terminal lake records

In the Asian monsoon margin of northwest China, millennial-scale precipitation and effective moisture changes during the Holocene differ from those observed in the primary monsoon area. Whether these differences were caused by a change in precipitation or other hydroclimate factors remains controversial. We selected Huahai Lake, located in the western portion of the Hexi Corridor, at the northwest margin of the Asian monsoon area, to address this question. Using paleoclimate proxies (mineralogical assemblages and immobile elements) and results from a previous study, we inferred hydroclimate changes in this area during the early and middle Holocene (10.5–5.5 cal ka BP). Heavy precipitation and abundant runoff occurred during the early Holocene (10.5–8.8 cal ka BP). Proxies (carbonate content, total organic carbon and C/N) for precipitation minus evaporation (P − E) in the same section, however, revealed low P − E during the early Holocene and highest P − E in the middle Holocene (8.8–5.5 cal ka BP). Therefore, on a millennial timescale, precipitation amount and effective moisture changes were asynchronous during the early and middle Holocene. The precipitation and effective moisture pattern in the study area during that time span was different from patterns in both the Asian monsoon and westerly wind-influenced areas, suggesting an interplay between the two climate features. High precipitation during the early Holocene corresponded to a strengthened Asian monsoon. Highest P − E in the study area occurred during the middle Holocene and may have been caused by low evaporation, rather than high precipitation.

Speleothem records of Asian paleomonsoon variability and mechanisms

In the last 20 years, speleothems have been increasingly applied in paleoclimate studies, and become one of the most important geologic records like oceanic sediments, loess deposits, and ice cores. Critically, the stalagmite archives from Asian monsoon (AM) area provide an insight into the mechanisms behind low-latitude precessional hydroclimate and abrupt AM changes in line with millennial-scale Greenland temperature variability. These climate records from the Asian continent interiors, well-duplicated over broad regions, extend back to 600 ka BP, and have been widely accepted as a North Hemisphere template for synchronizing global climate records. Here we review these independently- and precisely-dated stalagmite records from those climatically- and environmentally-sensitive locations and discuss various climate factors that control AM variability from annual to orbital time scales. As the speleothems are often annually laminated that extend back into a long growth history, it is possible to understand mechanisms of millennial- to annual-scale climate changes under different Earth’s climatic boundaries. By nature, these calcite records are instrumental in resolving the climate background for natural variability of current climate, abrupt climate changes in the distant time, and even a prediction for future climate.

Characteristics of the Yangtze River incised valley in the last glacial maximum in Nanjing–Haimen reach, China

The Yangtze River is the largest river in the Asian monsoon region, research on the Yangtze River’s paleochannel in the last glacial maximum (LGM) will provide an important basis for an in-depth understanding of the hydrological characteristics and processes of large rivers in the Asian monsoon area during the last glacial period. The Nanjing–Haimen reach of the Yangtze River in Jiangsu Province was selected as the research subject. Five cross sections of incised valley depositional sequences were established on a section of the Yangtze River in the Nanjing–Haimen reach, with 173 bore data and eight documents from the references. The cross sections came from the following Yangtze River Bridges: Nanjing No. 4, Runyang, Yangzhong, Jiangyin, and Sutong. In the analysis of seven drilling core samples near the Nanjing No. 4 and the Yangzhong Bridges, carbon-14(14C) dating was used for eight age results and electron spin resonance for one age result. The results indicate that in the LGM the incised valley was cut down into bedrock at the upper reach of the Zhenjiang, and the paleochannel of the Yangtze River flowed through old riverbed sedimentary facies at the lower reach of the Zhenjiang. The Nanjing reach during the LGM had a deep incised valley at a depth of −63 to −94 m. The deep incised valley was relatively narrow and steep with a smaller width–depth ratio (B 1/2/H). At the Zhenjiang reach, the ratio of width to depth increased. At the lower reach of the Yangzhong, the incised valley became wider and a bifurcated incised valley system of the Yangtze River was formed. From the Nanjing reach to Haimen near eastern China region, the sediment of the ancient riverbed of the Yangtze River is mainly coarse sand and gravel that gradually tapers from upstream to downstream. Sediment of the incised valley displays a clear pattern, from pebble gravel and coarse sand to fine sand, from bottom to top.

Further Understanding of the Impacts of Rainfall and Agricultural Management Practices on Nutrient Loss from Rice Paddies in a Monsoon Area

As rice paddies are widespread sources of water pollution in the agricultural regions of the Asian monsoon area, a mechanistic understanding of nutrient loss from paddies is critical for water quality management. A 2-year experiment was conducted in a typical monsoon-affected rice field to improve our understanding of the impacts of rainfall and agricultural management practice on nitrogen (N) and phosphorus (P) loss. Samples of paddy drainage water were collected during rainfall events (n = 25) and analyzed for total N (T-N) and total P (T-P) concentrations. The impacts of rainfall (amount, duration, and intensity) and agricultural management practice (transplanting and fertilization) on the event mean concentration (EMC) and loss of nutrient were assessed using regression analyses. The results showed that T-N and T-P concentrations were affected by agricultural practice; meanwhile, loss of T-N and T-P was correlated with rainfall characteristics. Specifically, the EMC of T-N but T-P was negatively (p < 0.001) correlated with the number of days after agricultural practice in both years, which likely represents a decrease in nutrient availability in paddy water over time. Loss of T-N and T-P was positively (p < 0.01) correlated with rainfall amount, and this suggests that the rainfall-runoff process is a key driver of nutrient loss in the study area. Our results suggest that rainfall amount and days after transplanting need to be taken into account when estimating nutrient loss from rice paddies in monsoon regions.

Effects of Climate Change on the Movement of Turbidity Flow in a Stratified Reservoir

In this study, we investigated the effects of climate change on the movement of the turbidity flow in a stratified reservoir. Reservoir turbidity is primarily caused by the concentration of suspended solids in a watershed. Under the effects of climate change, which increases the frequency and intensity of extreme weather events in the Asian monsoon area, turbidity can be considered to be an essential water quality variable in a reservoir that supplies drinking water. We adopted a two-dimensional hydrodynamic water quality model coupled to a watershed model and used a future climate scenario applied to the Yongdam Reservoir in South Korea. To account for the uncertainty of climate change scenarios and the extent of the variation of both temperature and precipitation, three cases each from the 2050’s and 2090’s were selected for simulation. The simulations predicted that the significance of the summer stratification would produce a vertical circulation lower than 8 m in the warming reservoir of the 2090 scenario in comparison to 15 m in the 2050 scenario. The limited vertical circulation caused the density plume to spread within a depth of 8 m of the reservoir, isolating the upper water with high suspended solid concentrations from the hypolimnetic water. The results of this study provide the optimum horizontal and vertical location of the intake aqueducts to obtain drinking water with low turbidity during extremely heavy rainfall.

Hydrological recurrence as a measure for large river basin classification and process understanding

Abstract. Hydrological functions of river basins are summarized as collection, storage and discharge, which can be characterized by the dynamics of hydrological variables including precipitation, evaporation, storage and runoff. The temporal patterns of each variable can be indicators of the functionality of a basin. In this paper we introduce a measure to quantify the degree of similarity in intra-annual variations at monthly scale at different years for the four main variables. We introduce this measure under the term of recurrence and define it as the degree to which a monthly hydrological variable returns to the same state in subsequent years. The degree of recurrence in runoff is important not only for the management of water resources but also for the understanding of hydrologic processes, especially in terms of how the other three variables determine the recurrence in runoff. The main objective of this paper is to propose a simple hydrologic classification framework applicable to large basins at global scale based on the combinations of recurrence in the four variables using a monthly scale time series. We evaluate it with lagged autocorrelation (AC), fast Fourier transforms (FFT) and Colwell's indices of variables obtained from the EU-WATCH data set, which is composed of eight global hydrologic model (GHM) and land surface model (LSM) outputs. By setting a threshold to define high or low recurrence in the four variables, we classify each river basin into 16 possible classes. The overview of recurrence patterns at global scale suggested that precipitation is recurrent mainly in the humid tropics, Asian monsoon area and part of higher latitudes with an oceanic influence. Recurrence in evaporation was mainly dependent on the seasonality of energy availability, typically high in the tropics, temperate and sub-arctic regions. Recurrence in storage at higher latitudes depends on energy/water balances and snow, while that in runoff is mostly affected by the different combinations of these three variables. According to the river basin classification, 10 out of the 16 possible classes were present in the 35 largest river basins in the world. In the humid tropic region, the basins belong to a class with high recurrence in all the variables, while in the subtropical region many of the river basins have low recurrence. In the temperate region, the energy limited or water limited in summer characterizes the recurrence in storage, but runoff exhibits generally low recurrence due to the low recurrence in precipitation. In the sub-arctic and arctic regions, the amount of snow also influences the classes; more snow yields higher recurrence in storage and runoff. Our proposed framework follows a simple methodology that can aid in grouping river basins with similar characteristics of water, energy and storage cycles. The framework is applicable at different scales with different data sets to provide useful insights into the understanding of hydrologic regimes based on the classification.

The mechanism and scenarios of how mean annual runoff varies with climate change in Asian monsoon areas

Understanding the effects of climate change on runoff is important for the sustainable management of water resources. However, the mechanism of such effects in the Asian monsoon region remains unclear. This study revisits Fu's two-parameter climate elasticity index and enhances it by using the Gardner function to strengthen the former's prediction reliability when the future climate condition is beyond the historical range. Then the improved method was applied to study the elasticity change with temperature and precipitation in the eastern monsoon basins of China, whereas to explore the mechanism of climate change on runoff. Furthermore, the runoff change and the elasticity of the study area from 2020 to 2050 under representative concentration pathways (RCPs) were predicted. Results show that the trend of elasticity change assumes a centrosymmetric picture with the symmetric point (0,0). Different catchments respond differently to the same climate change scenario: the sensitivity of the Haihe Basin is the highest; those of Yellow, Huaihe, Liaohe, Songhua, Pearl, Yangtze, and Southeast Rivers are lower, in descending order. The changing mode of precipitation and temperature differs greatly to keep the runoff unchanged. For semi-humid regions in which the mean annual temperature ranges from 0.71 degrees C to 9.0 degrees C, such as the basins of Songhua, Liaohe, Haihe, and Yellow, a 1 degrees C increase in temperature requires a corresponding 3.2-4.0% increase in precipitation to keep the runoff unchanged. However, in wet regions, such as the basins of Yangtze, Southeast Rivers, and Pearl, the same change in temperature requires a less than 2.8% increase in precipitation to keep the runoff unchanged. In the future, the runoff in most basins may decrease in different degrees. The decreasing velocity of the runoff is the fastest in the RCP8.5 scenario and the decreasing trend of the runoff slows down under the RCP4.5 and RCP2.6 scenarios. The proposed method can be applied to other basins to assess potential climate change effects on annual runoff. The results of the basins studies can inform planning of long-term basin water management strategies taking into account global change scenarios. (C) 2014 Elsevier B.V. All rights reserved.

Projection and uncertainty analysis of global precipitation-related extremes using CMIP5 models

Climate change is expected to influence the occurrence and magnitude of precipitation-related extremes and to increase drought and flood risk. Thus, future changes in dryness and wetness over global land areas are analysed using future climate simulations from the World Climate Research Programme's (WCRP) Coupled Model Intercomparison Project Phase 5 (CMIP5) under RCP4.5 forcing scenario. Model reproducibility is evaluated first, and it is shown that high performance can be achieved in present-day climate simulations by models, particularly in multi-model ensemble (MME) results. For future climate simulations, the highest reliability regarding changes in precipitation and its related extremes is found over Northern high latitudes, while the lowest confidence levels are mainly localized over the tropics. The projections indicate a high likelihood that there will be a shift to fewer dryness but to more extreme precipitation events or/and flood events in future over Northern high latitudes. Among populated areas, Mediterranean basin is highlighted as displaying a relatively high reliability of increases in both dryness and wetness indicators, implying increased probabilities of both drought and flood events, despite the fact that there would be less precipitation. In North America and Asian monsoon areas, dryness indictors show no obvious changes, while markedly increases are found in wetness indicators, concurrent with a high model agreement. In contrast, southern Africa, Australia, and the Amazon basin show relatively high reliability regarding increases in dryness, but a low confidence level in wetness. The severity of these changes is not uniform across annual and seasonal scales and is region dependent. Two sources of uncertainty in projections are investigated in this study: internal and inter-model variability. The analysis indicates that internal and inter-model variability are the dominant sources of uncertainty in extreme climate projections, and inter-model variability is much larger and increases with time. Further analysis shows that both sources of uncertainty generally perform lower on annual and global scales than on seasonal and regional ones.

Mid‐Holocene Asian summer climate and its responses to cold ocean surface simulated in the PMIP2 OAGCMs experiments

AbstractIn this study, the outputs from four Ocean‐Atmosphere Coupled General Circulation Model experiments within the Paleoclimate Modelling Intercomparison Project phase 2 and four sets of Atmospheric General Circulation Model experiments were used to analyze the Asian summer climate during the mid‐Holocene (6 ka, about 6000 years ago). Additionally, the role of the orbital forcings and the effects of a cold ocean surface for the 6 ka were investigated by comparing the Atmospheric General Circulation Model simulations forced by different combinations of forcing parameters. The results indicated that in the 6 ka summer, the orbital forcings were the prime drivers of the increased temperature and precipitation and the strengthened summer monsoon over the Asian continent. On the other hand, these different orbital forcings also resulted in a colder Indian Ocean‐northwestern Pacific during this period. Our results suggested that this cold ocean surface could reduce the warming amplitude and precipitation enhancement over the Asian monsoon area in the 6 ka summer. The changes caused by the different ocean surface conditions were comparable with simulated 6 ka climate changes. The cold ocean surface also suppressed the Asian summer monsoon circulations. Therefore, the influences from anomalous ocean surface conditions played an important role on regulating the Asian summer climate during the 6 ka. In addition, it was found that the summer climate in the South Asian monsoon area was more sensitive to the changes in the orbital forcings and ocean surface conditions than that in the East Asian monsoon area.

Decreasing intensity of the last glacial stadials in low latitude terrestrial East Asia inferred by a new observation of pollen records in central Taiwan

The cold intensity of the last glacial stadials corresponding to marine isotope stage (MIS) 5d (or 5b), MIS 4 and MIS 2 in terrestrial East Asia monsoon area is not discussed much due to the paucity of long continuous pollen records. A palynological study of drilling cores from three closely-linked intramontane basins (Toushe, Sun-moon Lake and Yuchi) in central Taiwan provides a history of shifting altitudinal vegetation zones in surrounding mountains during late Quaternary climate changes. By integrating these records, we found that the alpine conifer forest approached its lowest altitude, about 614m, during the earliest stadial (≒MIS 5d or 5b), and 745m during the early stadial (≒MIS 4) based on records of Yuchi Basin and Sun-moon Lake. In addition, the pollen records of Toushe Basin and Sun-moon Lake show more temperate conditions for the late stadial (≒MIS 2) than the early stadial (≒MIS 4). This leads to an interpretation of a decreasing intensity of stadials during the last glaciation, which might follow the regional insolation amplitude. Such a decreasing trend in coldness during the last glacial stadials does not exist in the record for the South China Sea which reflects a different sensitivity and response to climatic forcings between terrestrial and marine.