Increase In Monsoon Precipitation Research Articles

Signals of Medieval Warm Period and Little Ice Age from southwestern Madhya Pradesh (India): A pollen-inferred Late-Holocene vegetation and climate change

Pollen analysis of a 2 m deep sediment core from Khedla Quila Lake, Betul District (southwestern Madhya Pradesh), India has demonstrated the vegetation succession and climate change since the Late-Holocene. The pollen sequences have revealed that between 1416 and 506 cal BP (AD 534–1444), open mixed tropical deciduous forest comprising Madhuca indica, Sapotaceae, Holoptelea, Acacia, and Schleichera occupied the region under a warm and moderately humid climate, corresponding, to a certain extent, with the Medieval Warm Period (MWP) that is known between AD 740 and 1150 worldwide. Between 506 and 120 cal BP (AD 1444–1830), the open mixed tropical deciduous forest was succeeded by dense mixed tropical deciduous forest due to the prevalence of a warm and humid climate, coinciding with the Little Ice Age (LIA) which falls within the temporal range of AD 1450 and 1850 at global level. Since 120 cal BP to Present (AD 1830 onwards), the open mixed tropical deciduous forest again came into existence owing to a warm and less humid climate. The cereal-based agriculture practice continued at almost the same pace, but the lake widened during the second phase, which could be attributed to increased monsoon precipitation.

Sensitivity of precipitation to sea surface temperature over the tropical summer monsoon region—and its quantification

Over the tropical oceans, higher sea surface temperatures (SST, above 26 °C) in summer are generally accompanied by increased precipitation. However, it has been argued for the last three decades that, any monotonic increase in precipitation with respect to SST is limited to an upper threshold of 28–29.5 °C, and beyond this, the relationship fails. Based on this assessment it has often been presumed that, since the mean SSTs over the Asian monsoon basins (Indian Ocean and north-west Pacific) are mostly above the threshold, SST does not play an active role on the summer monsoon variability. It also implies that increasing SSTs due to a changing climate need not result in increasing monsoon precipitation. The current study shows that the response of precipitation to SST has a time lag, that too with a spatial variability over the monsoon basins. Taking this lag into account, the results here show that enhanced convection occurs even up to the SST maxima of 31 °C averaged over these basins, challenging any claim of an upper threshold for the SST-convection variability. The study provides us with a novel method to quantify the SST-precipitation relationship. The rate of increase is similar across the basins, with precipitation increasing at ~2 mm day−1 for an increase of 1 °C in SST. This means that even the high SSTs over the monsoon basins do play an active role on the monsoon variability, challenging previous assumptions. Since the response of precipitation to SST variability is visible in a few days, it would also imply that including realistic ocean–atmosphere coupling is crucial even for short term monsoon weather forecasts. Though recent studies suggest a weakening of the monsoon circulation over the last few decades, results here suggest an increased precipitation over the tropical monsoon regions, in a global warming environment with increased SSTs. Thus the signature of SST is found to be significant for the Asian summer monsoon, in a quantifiable manner, seamlessly through all the timescales—from short-term intraseasonal to long-term climate scales.

Plant diversity of the Tianshui Basin in the western Loess Plateau during the mid-Holocene – Charcoal records from archaeological sites

Assessing the potential impact of increased temperature needs examination of robust palaeorecords that contain analogues. The fossil charcoal (anthracological) records from the mid-Holocene archaeological sites can provide palaeo-analogues on the impacts of climate change. The Xishanping and Dadiwan sites were continuously developed during the Neolithic Culture in the Tianshui Basin, western Loess Plateau. A total of 24 samples of fossil charcoal were recovered using a floatation method. At least 100 fragments were examined from each sample, and these fragments were identified following standard procedures, and the results were used to reconstruct the vegetation and plant diversity between 5200 and 4300 cal BP, which was a warm period for the region. The charcoal evidence from the Xishanping and Dadiwan sites confirm that woody plants were widely available, including temperate taxa such as Betula, Ulmus, Quercus, Carpinus, Acer, Corylus and Padus, and typical subtropical taxa such as Bambusoideae, Liquidambar formosana, Castanopsis, Pseudotsuga sinensis, and Eucommia ulmoides. The assemblages of fossil charcoal show that mixed forests of north-subtropical evergreen and deciduous broadleaved trees existed. This is a broader range of woody plants than at present in the Tianshui Basin. This leads to the conclusion that the warmer and increasing monsoon precipitation resulted in a northward shift in the southern vegetation zones. And that the natural botanical diversity between 5200 and 4300 cal BP was also greater than at present in the Tianshui Basin, western Loess Plateau.

Downscaled climate change projections with uncertainty assessment over India using a high resolution multi-model approach

This study presents the possible regional climate change over South Asia with a focus over India as simulated by three very high resolution regional climate models (RCMs). One of the most striking results is a robust increase in monsoon precipitation by the end of the 21st century but regional differences in strength. First the ability of RCMs to simulate the monsoon climate is analyzed. For this purpose all three RCMs are forced with ECMWF reanalysis data for the period 1989–2008 at a horizontal resolution of ~25km. The results are compared against independent observations. In order to simulate future climate the models are driven by lateral boundary conditions from two global climate models (GCMs: ECHAM5-MPIOM and HadCM3) using the SRES A1B scenario, except for one RCM, which only used data from one GCM. The results are presented for the full transient simulation period 1970–2099 and also for several time slices. The analysis concentrates on precipitation and temperature over land. All models show a clear signal of gradually wide-spread warming throughout the 21st century. The ensemble-mean warming over India is 1.5°C at the end of 2050, whereas it is 3.9°C at the end of century with respect to 1970–1999. The pattern of projected precipitation changes shows considerable spatial variability, with an increase in precipitation over the peninsular of India and coastal areas and, either no change or decrease further inland. From the analysis of a larger ensemble of global climate models using the A1B scenario a wide spread warming (~3.2°C) and an overall increase (~8.5%) in mean monsoon precipitation by the end of the 21st century is very likely. The influence of the driving GCM on the projected precipitation change simulated with each RCM is as strong as the variability among the RCMs driven with one.

Spatial variability of Holocene changes in the annual precipitation pattern: a model-data synthesis for the Asian monsoon region

This study provides a detailed analysis of the mid-Holocene to present-day precipitation change in the Asian monsoon region. We compare for the first time results of high resolution climate model simulations with a standardised set of mid-Holocene moisture reconstructions. Changes in the simulated summer monsoon characteristics (onset, withdrawal, length and associated rainfall) and the mechanisms causing the Holocene precipitation changes are investigated. According to the model, most parts of the Indian subcontinent received more precipitation (up to 5 mm/day) at mid-Holocene than at present-day. This is related to a stronger Indian summer monsoon accompanied by an intensified vertically integrated moisture flux convergence. The East Asian monsoon region exhibits local inhomogeneities in the simulated annual precipitation signal. The sign of this signal depends on the balance of decreased pre-monsoon and increased monsoon precipitation at mid-Holocene compared to present-day. Hence, rainfall changes in the East Asian monsoon domain are not solely associated with modifications in the summer monsoon circulation but also depend on changes in the mid-latitudinal westerly wind system that dominates the circulation during the pre-monsoon season. The proxy-based climate reconstructions confirm the regional dissimilarities in the annual precipitation signal and agree well with the model results. Our results highlight the importance of including the pre-monsoon season in climate studies of the Asian monsoon system and point out the complex response of this system to the Holocene insolation forcing. The comparison with a coarse climate model simulation reveals that this complex response can only be resolved in high resolution simulations.

Pollen Records of Vegetation and Inferred Climate Change in South-western Madhya Pradesh during the Last ca. 3800 Years

Abstract Pollen analysis of 1.5m deep sediment core from Sapna Lake, Betul District (M.P.) has demonstrated that between 3,800 and 2,700 yr BP, open Acacia-dominant scrub forests interspersed with stretches of herbaceous vegetation comprising grasses, sedges, Asteraceae, Cheno/Am, etc., occurred in the region under a regime of dry climate. A few trees of Madhuca indica, Holoptelea, Shorea robusta, Lagerstroemia parviflora, etc. were also sparingly distributed therein. The vicinity of the lake was under cereal-based agricultural practice as portrayed by the presence of Cerealia and other culture pollen taxa viz., Cheno/Am, Caryophyllaceae, Artemisia and Cannabis sativa. Around 2,700 to 1,260 yr BP the Acacia-dominant scrub forests were succeeded by the open mixed deciduous forests as evidenced from the improvement in frequencies of Madhuca indica, Sapotaceae, Holoptelea, Shorea robusta as well as sporadic invasion of Terminalia, Mitragyna, Flacourtia, Grewia, Lannea coromandelica, etc. This enhancement in the forest floristic reflects the initiation of a warm and humid climate possibly in response to increasing monsoon precipitation. Owing to the prevailing favourable climatic condition there was acceleration in the agricultural practice as indicated by the rising trend of Cerealia and other culture pollen taxa. Since 1,260 yr BP onwards the depletion in the prominent forest constituents such as Madhuca indica, Sapotaceae, Shorea robusta, Holoptelea and other associated trees implies that the forests turned more sparse and less diversified due to the inception of a warm and less humid climate, attributable to reduced monsoon precipitation. However, the agricultural practice continued with almost same intensity as before, because the Cerealia and other culture pollen taxa remain unchanged.

Pollen-inferred vegetation vis-á-vis climate dynamics since Late Quaternary from western Assam, Northeast India: Signal of global climatic events

Palynological observation of one 3.4 m deep sedimentary profile cored from Chayagaon swamp, Kamrup District, Western Brahmaputra flood plain of Assam, Northeast India, has revealed climate and vegetation succession since the Late Quaternary. The contemporary pollen/vegetation relationship in and around the swamp can be employed as background information for the palaeoclimate studies. Persistent fluvial activity during 14,895–12,450 cal BP may be responsible for the paucity of pollen and spores, with fluvial marker taxa such as Ludwigia octavalvis, Mimosa pudica, Pleospora, Glomus and Botryococcus along with frequent Pseudoschizia. Later, fluvial activity was succeeded by tropical tree savanna under cool and dry climate with weakened monsoon precipitation between 12,450–10,810 cal BP, corresponding to the Younger Dryas. Between 10,810–7680 cal BP, relatively less cool and dry climate prevailed with inception of tropical mixed deciduous arboreals including Syzygium cumini, Dillenia pentagyna and Lagerstroemia parviflora. Human activity was witnessed and some sort of incipient cereal-based pastoral practice commenced during this phase. This phase is followed by fluvial activity between 7680–6780 cal BP, as indicated by reduced frequency of pollen and spores along with frequent fluvial marker taxa. The fluvial activity was succeeded by enrichment of tropical mixed deciduous forest laden with the invasion of arboreal taxa including S. cumini, Terminalia bellirica, Mimusops elengi and D. pentagyna along with a relative increase of marshy and aquatic taxa. The warm and moderately humid climatic regime between 6780–1950 cal BP is well matched with the peak period of Holocene Climatic Optimum (7000 BP) signifying an increase in monsoon precipitation. The size of the swamp increased comparatively along with a relative decrease in agricultural practice. During 1950–989 cal BP, the establishment of tropical mixed deciduous forest occurred with further proliferation of deciduous tree taxa under increased warm and humid climate, corresponding to the Medieval Warm Period. The swamp level rose relatively, along with an abrupt decline in cereal and other cultivation taxa during this phase. Deterioration of the tropical mixed deciduous forest under a warm and relatively dry climatic regime since 989 cal BP was accompanied by accelerated human settlement, as shown by an abrupt increase in cereal pollen along with typical ruderal pollen taxa. Relative increases in Melastoma, Ziziphus and Areca catechu combined with decreased arboreal Shorea, Terminalia, Lagerstroemia, Dillenia and Emblica imply forest clearance in this phase.

Late Quaternary vegetation, climate as well as lake-level changes and human occupation from Nitaya area in Hoshangabad District, southwestern Madhya Pradesh (India), based on pollen evidence

The pollen record of a 2.4 m thick sediment profile from a lake deposit at Nitaya Village, which has been named as Nitaya Lake, Hoshangabad District, southwestern Madhya Pradesh (India), displays a chronological record of vegetation, climate and lake-level changes as well as anthropogenic activities as a consequence of fluctuating trend of monsoon during the last 12,700 years. The study revealed that between 12,700 and 7150 yr BP, tree savanna vegetation existed with the dominance of grasses, Cheno/Am, Asteraceae as well as scattered Acacia, Ailanthus excelsa, Madhuca indica, and Bombax ceiba under a cool and dry climate with reduced monsoonal precipitation. A moderate-sized lake existed in the region prior to the Holocene. Human activity in the form of incipient cereal-based agriculture practice was also present. Between 7150 and 4657 yr BP, the tree savanna vegetation was transformed into an open mixed tropical deciduous forest as a result of expansion of prominent deciduous trees under warm and moderately humid climate, which could be attributed to an increase in monsoon precipitation. The lake size increased comparatively, and acceleration in agriculture practice took place. Later, between 4657 and 2807 yr BP with more or less similar floristic composition, the open mixed tropical deciduous forest continued in the region under a warm and less humid climate owing to weak monsoon precipitation. The lake became smaller in size while agriculture practice continued at the same pace. Subsequently, between 2807 and 1125 yr BP, mixed deciduous forest succeeded the open mixed tropical deciduous forest, which is indicated by the enhancement of M. indica, Acacia, Grewia, Symplocos, Shorea robusta, etc. and the debut of Tectona grandis around 1965 yr BP under a warm and more humid climate owing to an increase in monsoon precipitation. The lake-level remained unchanged but agricultural practice intensified. From 1125 yr BP to the present day, the mixed tropical deciduous forest became sparser and less diversified in composition, and consequently was transformed into open vegetation under a warm and comparatively less humid climate, equivalent to present. The lake also became smaller, although agriculture increased.

Projected Changes in Asian Summer Monsoon in RCP Scenarios of CMIP5

Responses of the Asian Summer Monsoon (ASM) in future projections have been studied based on two core future projections of phase five of the Coupled Model Intercomparison Project (CMIP5) coordinated experiments with the IAP-coupled model FGOALS_s2 (the Flexible Global Ocean-Atmosphere-Land System Model). The projected changes of the ASM in climatological mean and interannual variability were respectively reported. Both the South Asian Summer Monsoon (SASM) and the East Asian Summer Monsoon (EASM) were intensified in their climatology, featuring increased monsoon precipitation and an enhanced monsoon lower-level westerly jet flow. Accordingly, the amplitude of the annual cycle of rainfall over East Asia (EA) is enhanced, thereby indicating a more abrupt monsoon onset. After the EA monsoon onset, the EASM marched farther northward in the future scenarios than in the historical runs. In the interannual variability, the leading pattern of the EASM, defined by the first multi-variable EOF analysis over EA, explains more of the total variances in the warmest future scenario, specifically, Representative Concentration Pathway (RCP8.5). Also, the correlation coefficients analysis suggests that the relationship between the EASM interannual variations and ENSO was significantly strengthened in the future projections, which may indicate improved predictability of the EASM interannual variations.

Late Holocene vegetation, climate change and human impact in southwestern Madhya Pradesh, India

Pollen analysis of a 2 m deep sediment profile from the dried Kachhar Lake, Sehore District, has demonstrated that between 2050 and 1610 yr BP, open Acacia-scrub forest constituted of Acacia cf. nilotica, Grewia, Mitragyna, Sapotaceae flourished in the region under relatively warm and humid climate with moderate monsoon precipitation, than that prevails today. The retrieval of fragmentary charcoals implies the repeated forest fire incidences. The presence of Cerealia and ruderal plant taxa, viz. Cannabis sativa, Cheno/Am, Caryophyllaceae, etc. suggests the agricultural practices in the region. Between 1610 and 600 yr BP, Acacia-scrub forest turned profuse with expansion of Acacia cf. nilotica and other arboreals, viz. Shorea robusta, Terminalia, Grewia and Madhuca indica in response to more-humid climate with the onset of increased monsoon precipitation. Agriculture practice continued with same intensity as before. Since 600 yr BP onwards, the climate changed to less-humid as indicated by decline in Acacia-scrub forest. The decline in Cerealia reflects the low pace of agriculture practice.

High-Resolution Monsoon Records Since Last Glacial Maximum: A Comparison of Marine and Terrestrial Paleoarchives from South Asia

Agricultural production and the availability of fresh water in Indian subcontinent critically depend on the monsoon rains. Therefore it is vital to understand the causal mechanisms underlying the observed changes in the Indian monsoon in the past. Paleomonsoon reconstructions show that the water discharge from the Ganges-Brahmaputra River system to the Bay of Bengal was maximum in the early to mid-Holocene; data from the Western Arabian Sea and Omanian speleothems indicate declining monsoon winds during the Holocene, whereas records from the South West Monsoon (SWM) precipitation dominated eastern Arabian Sea show higher runoff from the Western Ghats indicating gradually increasing monsoon precipitation during the Holocene. Thus there exists considerable spatial variability in the monsoon in addition to the temporal variability that needs to be assessed systematically. Here we discuss the available high resolution marine and terrestrial paleomonsoon records such as speleothems and pollen records of the SWM from important climatic regimes such as Western Arabian Sea, Eastern Arabian Sea, Bay of Bengal to assess what we have learnt from the past and what can be said about the future of water resources of the subcontinent in the context of the observed changes.

Regional Differences in South American Monsoon Precipitation Inferred from the Growth and Isotopic Composition of Tropical Trees*

Abstract The authors present results on the relationship between tree-ring proxies and regional precipitation for several sites in tropical South America. The responsiveness of oxygen isotopes (δ18O) and seasonal growth as precipitation proxies was first validated by high-resolution sampling of a Tachigali myrmecophila from Manaus, Brazil (3.1°S, 60.0°W). Monthly growth of Tachigali spp. was significantly correlated with monthly precipitation. Intra-annual measurements of cellulose δ18O in Tachigali spp. were also significantly correlated with monthly precipitation at a lag of approximately one month. The annual ring widths of two tropical tree taxa, Cedrela odorata growing in the Amazon (12.6°S, 69.2°W) and Polylepis tarapacana growing in the Altiplano (22.0°S, 66.0°W), were validated using bomb-derived radiocarbon 14C. Estimated dates were within two to three years of bomb-inferred 14C dates, indicating that these species exhibit annual rings but uncertainties in our chronologies remain. A multiproxy record spanning 180 years from Cedrela spp. showed a significant negative relationship between cellulose δ18O and January precipitation. A 150-yr record obtained from Polylepis spp. also showed a significant negative relationship between δ18O and March precipitation, whereas annual ring width showed a significant positive correlation with December precipitation. These proxies were combined in a multivariate framework to reconstruct past precipitation, revealing a significant increase in monsoon precipitation at the Amazon site since 1890 and a significant decrease in monsoon precipitation at the Altiplano since 1880. Proxy time series also showed spatial and temporal coherence with precipitation variability due to El Niño forcing, suggesting that oxygen isotopes and ring widths in tropical trees may be important diagnostics for identifying regional differences in the response of the tropical hydrologic cycle to anthropogenic warming.

Projected changes in South Asian summer monsoon by multi-model global warming experiments

South Asian summer monsoon (June through September) rainfall simulation and its potential future changes are evaluated in a multi-model ensemble of global coupled climate models outputs under World Climate Research Program Coupled Model Intercomparison Project (WCRP CMIP3) dataset. The response of South Asian summer monsoon to a transient increase in future anthropogenic radiative forcing is investigated for two time slices, middle (2031–2050) and end of the twenty-first century (2081–2100), in the non-mitigated Special Report on Emission Scenarios B1, A1B and A2 .There is large inter-model variability in the simulation of spatial characteristics of seasonal monsoon precipitation. Ten out of the 25 models are able to simulate space–time characteristics of the South Asian monsoon precipitation reasonably well. The response of these selected ten models has been examined for projected changes in seasonal monsoon rainfall. The multi-model ensemble of these ten models projects a significant increase in monsoon precipitation with global warming. The substantial increase in precipitation is observed over western equatorial Indian Ocean and southern parts of India. However, the monsoon circulation weakens significantly under all the three climate change experiments. Possible mechanisms for the projected increase in precipitation and for precipitation–wind paradox have been discussed. The surface temperature over Asian landmass increases in pre-monsoon months due to global warming and heat low over northwest India intensifies. The dipole snow configuration over Eurasian continent strengthens in warmer atmosphere, which is conducive for the enhancement in precipitation over Indian landmass. No notable changes have been projected in the El Nino–Monsoon relationship, which is useful for predicting interannual variations of the monsoon.

Spatial patterns of Holocene glacier advance and retreat in Central Asia

Glaciers in the southern Himalayas advanced in the early Holocene despite an increase in incoming summer solar insolation at the top of the atmosphere. These glacier advances are in contrast to the smaller alpine glaciers in the western and northern regions of Central Asia. Two different glacier mass-balance models are used to reconcile this Holocene glacier history with climate by quantifying the change in equilibrium-line altitudes (ELA) for simulated changes in Holocene climate. Both ELA models clearly show that the lowering of ELAs in the southern Himalayas is largely due to a decrease in summer temperatures, and that an increase in monsoonal precipitation accounts for less than 30% of the total ELA changes. The decrease in summer temperatures is a dynamic response to the changes in solar insolation, resulting in both a decrease in incoming shortwave radiation at the surface due to an increase in cloudiness and an increase in evaporative cooling. In the western and northern zones of Central Asia, both ELA models show a rise in ELAs in response to a general increase in summer temperatures. This increase in temperatures in the more northern regions is a direct radiative response to the increase in summer solar insolation.

Effect of anomalous warming in the central Pacific on the Australian monsoon

The influence of sea surface temperature (SST) anomalies in the central Pacific Ocean on rainfall variability over Australia is investigated using observations and idealized simulations from an atmospheric general circulation model. We show that the SST warming centered at 180°W is associated with increased monsoon precipitation over northern Australia from January to February and a decrease in December and March over the same region, leading to a shorter and more intense monsoon period. In recent years SST anomalies commonly associated with El Niño events have often exhibited a peak signature in the central, not eastern, Pacific. These so‐called El Niño Modoki events are shown here to result in a markedly shorter and more intense Australian monsoon season.

Effects of the Tibetan Plateau on the Asian summer monsoon: a numerical case study using a regional climate model

AbstractTo understand impacts of the Tibetan Plateau (TP) upon the Asian summer monsoon (ASM), including both the Indian summer monsoons (ISM) and East Asian summer monsoons (EASM), a series of numerical experiments using the National Centers for Environmental Prediction (NCEP) regional spectral model (RSM) are conducted with various TP heights ranging from the flat surface (1.2 km) to 140% of the actual height. It was found that an increase in the TP height leads to an increase in the simulated ISM precipitation over northern India and conversely a decrease in the height leads to a decrease in precipitation. This sensitivity is associated with both the thermal and dynamical effects of the TP; however, although the ISM precipitation over India is affected by the changes in atmospheric circulation, it is not directly affected by the thermal effect. The thermal effect of surface heating plays a role in developing positive vorticity with a consequent increase in monsoon precipitation over northern India. The width of the plateau also seems to be associated with the intensity of the sensitivity for the ISM region. For the EASM region, the orographic effect caused by changes in the lower‐atmospheric circulation and its link with upper‐atmospheric circulation are crucial to the monsoon circulation and precipitation. With increased TP height, the monsoon precipitation moves inland in a northwestward direction, which qualitatively follows the previous findings based on general circulation models (GCMs), but with a detailed dynamical mechanism in linkage between the lower‐ and upper‐atmospheric circulation in the regional climate modelling (RCM) framework in this study. Copyright © 2009 Royal Meteorological Society

Quaternary glaciation of Mount Everest

The Quaternary glacial history of the Rongbuk valley on the northern slopes of Mount Everest is examined using field mapping, geomorphic and sedimentological methods, and optically stimulated luminescence (OSL) and 10Be terrestrial cosmogenic nuclide (TCN) dating. Six major sets of moraines are present representing significant glacier advances or still-stands. These date to >330 ka (Tingri moraine), >41 ka (Dzakar moraine), 24–27 ka (Jilong moraine), 14–17 ka (Rongbuk moraine), 8–2 ka (Samdupo moraines) and ∼1.6 ka (Xarlungnama moraine), and each is assigned to a distinct glacial stage named after the moraine. The Samdupo glacial stage is subdivided into Samdupo I (6.8–7.7 ka) and Samdupo II (∼2.4 ka). Comparison with OSL and TCN defined ages on moraines on the southern slopes of Mount Everest in the Khumbu Himal show that glaciations across the Everest massif were broadly synchronous. However, unlike the Khumbu Himal, no early Holocene glacier advance is recognized in the Rongbuk valley. This suggests that the Khumbu Himal may have received increased monsoon precipitation in the early Holocene to help increase positive glacier mass balances, while the Rongbuk valley was too sheltered to receive monsoon moisture during this time and glaciers could not advance. Comparison of equilibrium-line altitude depressions for glacial stages across Mount Everest reveals asymmetric patterns of glacier retreat that likely reflects greater glacier sensitivity to climate change on the northern slopes, possibly due to precipitation starvation.

Climate changes in East China since the Late-glacial inferred from high-resolution mountain peat humification records

High-resolution peat humification records were obtained from Dajiuhu of the Shennongjia Mountains and Qianmutian of the Tianmu Mountains to study climate changes in East China. The analyses of pollen, organic matters, TOC, and Rb/Sr indicate a high degree of peat humification and thus strong decomposition of organic matter when climate was dry. Conversely, when climate was humid, the degree of humification is low because peat was preserved in a waterlogged condition. Peat humification from Dajiuhu occurred not only during the Younger Dryas (about 11.4–12.6 cal ka BP), the Bolling-Allerod Warm Period (12.6–15.2 cal ka BP), and the Oldest Dryas (about 15.2–16.0 cal ka BP), but also during the early Holocene (about 11.4–9.4 cal ka BP), the 8.2 cal ka BP cold event, and the Holocene Optimum (about 7.0–4.2 cal ka BP). Both peat humification records since nearly 5 ka BP are consistent, showing that mountain peatland has synchronous responses to the East Asia monsoon-induced precipitation. The LOI data confirm the above observation. The monsoon precipitation since nearly 5 ka BP recorded in these two peat profiles can be divided into three phases. During 4.9–3.5 ka BP, precipitation amount was high but fluctuated greatly. During 3.5–0.9 ka BP, precipitation amount was low. During 0.9–0 ka BP, degree of humification reduced gradually, indicating the increase of monsoon precipitation. Contrast to other high-resolution records from East China monsoon region shows that the monsoon precipitation records of the two peat profiles since nearly 16 ka BP are controlled by a common forcing mechanism of summer solar radicalization in the Northern Hemisphere.

Holocene vegetation, climate and human habitation in the Central Ganga Plain, based on pollen records from the lake deposits

The paper encompasses the Quaternary vegetation and climatic inferences drawn through the investigations on three lakes, viz. Lahuradewa, Sant Kabir Nagar District; Basaha, Unnao District and Misa Tal, Lucknow District, all located close to settlements in the Central Ganga Plain. The pollen sequence from Lahuradewa Lake has revealed that between 10600 and 9250 yr BP, open vegetation largely comprising grasses, Cheno/Am, Artemisia, etc. together with scanty trees of Aegle marmelos, Holoptelea, Terminalia, etc. grew in the region under a cool and dry climate. The record of aquatic taxa indicates the existence of lake. Between 9250 and 6400 yr BP, with the amelioration of climate a few more trees, viz. Bombax, Emblica officinalis, Syzygium, Lagerstroemia, etc. also invaded the region. The increase in aquatic taxa implies that the lake turned wider owing to improved monsoon rain. The appearance of Cerealia pollen around 7000 yr BP depicts the initiation of agricultural practices. During 6400 to 4050 yr BP, the much expansion of Bombax, Madhuca indica, Holoptelea, etc. suggests the establishment of forest groves with the further increase in monsoon precipitation. The expansion of agricultural practices is reflected by steady presence of Cerealia and other culture pollen. Between 4050 and 1300 yr BP, the enrichment of forest groves denotes the further enhancement in monsoon rainfall. The more frequent record of culture pollen portrays the acceleration in agriculture. Since 1300 yr BP onwards, the climate turned dry as indicated by sparse presence of trees in the forest groves. However, the agricultural practices continued with same intensity as before.
 The studies on two other lakes, viz. Basaha Jheel and Misa Tal in the region of Unnao and Lucknow, respectively have deciphered the short-term climatic variability and vegetation in the much later phases during 3300 yr BP to present. At Basaha Jheel, open vegetation dominated by grasses with sprinkled trees of Bauhinia, Holoptelea, Sapotaceae, etc. occupied the region under a semi-humid climate around 3300 yr BP. The record of Cerealia and other culture pollen is indicative of moderate agricultural practices. During 3200 to 2800 yr BP, the climate changed to humid as inferred by the improvement in the arboreals. Between 2800 and 2200 yr BP the decline in trees and culture pollen taxa suggests the onset of dry climate and depletion in agricultural practices. From 2200 yr BP onwards, the further decline in trees and lack of Cerealia pollen imply the reduced precipitation and desertion of settlement by the inhabitants. Pollen data from Misa Tal has deduced the scanty vegetation indicative of low rainfall and the occupancy of agriculture during 2000 to 1850 yr BP. This time is marked by the ruling of Kushanas. The rulings of Gupta, Turkic and Mughal dynasties spanning from 1850 to 300 yr BP, are manifested by the climatic improvement and prosperity in agriculture as reflected by the rise of trees and aquatics as well as better representation of Cerealia and other culture pollen taxa. The British Period faced the decline in rainfall and agricultural prosperity.

Climatic patterns in equatorial and southern Africa from 30,000 to 10,000 years ago reconstructed from terrestrial and near-shore proxy data

As part of a wider study of last glacial and deglacial climates in the Southern Hemisphere continents, we here review terrestrial and near-shore marine records from equatorial and southern Africa between 30,000 and 10,000 years ago (30–10 ka). This time interval covers the lead-up to the Last Glacial Maximum (LGM; 21 ± 2 ka), the LGM proper, and the ensuing deglacial. Records selected for review needed to meet three requirements: continuity or near continuity over the period; a well-established chronology; and at least one but preferably several unambiguous proxy(ies). We aim to show how regional climates of the sub-continent have responded to orbital forcing as opposed to other global glacial-interglacial boundary conditions, and how they are related to high latitude climates, sea and land surface conditions, positions of the Intertropical Convergence Zone (ITCZ) and of the westerly belt. Evidence of past climates derived from many independent proxies is given from west to southwest Africa (moisture from the Atlantic Ocean), then from equatorial East Africa to the southern subtropical summer rainfall domain (moisture mainly from the Indian Ocean). The LGM was cooler than today, and generally drier in the tropics. North of 8–9°S, glacial to Holocene increase in monsoonal precipitation, primarily related to orbitally-induced summer insolation in the northern hemisphere, occurred by steps of increasing amplitude (∼17–16, 14.5, 11.5 ka). Major wet–dry spells coincide with abrupt warm–cold events in high northern latitudes and related ITCZ migrations. In the southern tropics, the main post-glacial increase in tropical rainfall generally appears more gradual and in phase with Antarctic warming. Data suggest a restricted northward migration of the ITCZ and concentration of tropical rainfall well south of the Equator during the LGM and the Younger Dryas. Drier glacial conditions prevailed in southeastern Africa, while parts of southwestern Africa point to enhanced humidity during the LGM, suggesting that the winter westerly belt was either stronger than today or displaced further north possibly as a result of more extensive Antarctic sea-ice. Inferred African climatic fluctuations show the competing influences of tropical and high latitude climates of both hemispheres, and suggest changes in both meridional and zonal circulation modes. This review also reveals major geographical and methodological gaps, and a number of unresolved issues providing pointers for future research.