Increase In Monsoon Precipitation Research Articles

Diverse fluvial aggradation and incision response to interglacial—Glacial transitions in the headwaters of the Yangtze River, SE Tibetan Plateau

As a key geomorphic archive, staircase sequences of terraces and sediments record the history of fluvial aggradation and incision, which are related to tectonic activities, climatic fluctuations, and varying base levels. While numerous studies have investigated their influence on the formation of fluvial terraces, the manner in which rivers adapt to diverse climatic transitions (specifically, the shifts from warm to cold and from cold to warm) remains a subject of ongoing debate, particularly when considered within varying tectonic and climatic contexts. Here, we address this issue by reconstructing terrace distributions and identifying sedimentary features with OSL dating in the headwaters of the Yangtze River in the southeastern Tibetan Plateau. We discovered two distinct sets of thick valley-filling sequences at different elevations indicating two phases of aggradation during the penultimate and last glacial periods, when the Yangtze River was in a transport-limited condition. During the warmer interglacial and deglacial periods, increased monsoon precipitation led to higher discharge, causing the river to incise into these valley fills. In addition, superimposed tectonic activities produced diverse river response to the climatic transition from interglacial to glacial between the upstream shallow valley and the downstream deeply incised gorge. In the upper valley, stable tectonic conditions resulted in minimal incision, with younger deposits overlying older ones. Conversely, in the downstream gorge, with more intense tectonic activities, sediments only partially covered the riverbed. These sediments acted as abrasion tools, facilitating rapid incision during the warm-to-cold transition, thereby creating two separated valley fills. This finding enhances our understanding of how tectonic forces influence river responses to interglacial—glacial cycles.

Spatiotemporal variation and teleconnections of extreme precipitation in the Upper Indus Basin: insights for natural hazard assessment

ABSTRACT The study investigates trends and teleconnections of extreme precipitation events in the Upper Indus Basin (UIB) within the Indian region, part of the crucial geo-ecological Hindu Kush Himalayan Mountain system. Utilizing high-resolution (10 km × 10 km) HAR data from 2002 to 2013, we analyzed 11 indices established by the Expert Team on Climate Change Detection and Indices (ETCCDI) to observe variations in extreme precipitation at the monthly, seasonal, and annual time scale. The result shows an increase in dry and wet extreme precipitation frequency and intensity, increasing monsoon precipitation and a shift of winter precipitation, increasing continuous dry days. Using the APHRODITE daily (0.25° × 0.25°) data from 1952 to 2014, continuous wavelet transform and wavelet coherence analysis indicate significant periodicities and correlations with large-scale climate anomalies such as the El Niño-Southern Oscillation (ENSO) and North Atlantic Oscillation (NAO). Wavelet coherence analysis reveals that monthly extreme precipitation events significantly correlate with ENSO at a 3–5 years periodicity, while annual extremes show significant coherence with NAO at 8–10 years and over 16 years periodicities. The study highlights the impact of global climate change on regional precipitation and the need for adaptive water management policies to mitigate flood risks during the rainy season and address water scarcity in the dry season.

Increasing monsoon precipitation extremes in relation to large-scale climatic patterns in Pakistan

This study comprehensively evaluates monsoon variability and its large-scale drivers in Pakistan, a country often affected by extreme monsoon events leading to destructive flooding. Utilizing the Monotonic Mann-Kendall and Sen's Slope test, we analyzed trends in seven indicators of extreme precipitation events (EPEs) from 1961 to 2017 across Pakistan and its homogeneous climatic regions. The wavelet coherence method further allowed us to probe the connection between EPEs and key climate indices such as the Atlantic Multidecadal Oscillation (AMO), North Atlantic Oscillation (NAO), El Niño–Southern Oscillation (ENSO), Indian Ocean Dipole (IOD), Pacific Decadal Oscillation (PDO), Indian summer monsoon (ISM), and Southern Oscillation Index (SOI) in the time-frequency domain. Our findings indicate a significant increase in all EPEs across Pakistan, particularly in the monsoon region (R-II) from 1961 to 2017, with a noticeable decline post-1980s. The findings revealed a significant increase in EPEs in the whole country from 1961 to 1989 to 1990–2017, with a dominant change in the monsoon region during 1990–2017. In terms of climate indices combinations, IOD + ISM showed the highest coherences (>0.65), while ENSO+IOD + ISM and ENSO+IOD + PDO displayed coherences >0.81 and > 0.79, respectively, across the entire country. The multi-linear regression (MLR) model analysis drivers indicate that IOD and ENSO are the leading drivers of changes in monsoon EPEs in the whole country, whereas the core monsoon region of Pakistan also showed a strong influence from AMO and NAO in tandem with ENSO and IOD. The overall increase in EPEs over Pakistan are mainly associated with the indices from the Pacific Ocean, especially IOD, ENSO and PDO and with their various combinations. Our study reveals the variations in EPEs across Pakistan, yielding insights that could inform water resource management strategies and disaster prevention measures.

Changes in monsoon precipitation in East Asia under a 2°C interglacial warming.

Past intervals of warming provide the unique opportunity to observe how the East Asia monsoon precipitation response happened in a warming world. However, the available evaluations are primarily limited to the last glacial-to-interglacial warming, which has fundamental differences from the current interglacial warming, particularly in changes in ice volume. Comparative paleoclimate studies of earlier warm interglacial periods can provide more realistic analogs. Here, we present high-resolution quantitative reconstructions of temperature and precipitation from north-central China over the past 800 thousand years. We found that the average precipitation increase, estimated by the interglacial data, was only around one-half of that estimated for the glacial-to-interglacial data, which is attributed to the amplification of climate change by ice volume variations. Analysis of the interglacial data suggests an increase in monsoon precipitation of ~100 mm for a warming level of 2°C on the Chinese Loess Plateau.

Future projections of precipitation and temperature extremes at Sohra (Cherrapunji) using Statistical Downscaling Model

The Statistical Downscaling Model (SDSM 4.2) is used to project the future precipitation and maximum and minimum temperatures at Sohra, one of the extreme places on earth, using the predictors of the Second-Generation Canadian Earth System Model (CanESM2). The SDSM was calibrated with daily precipitation and temperature data from 1979 to 2005 and validated from 2006 to 2020. Future scenarios generated under the three Representative Concentration Pathways (RCP) 2.6, 4.5 and 8.5 are divided into three future periods, Near Future (2021-2040), Mid Future (2041-2071), and Far Future (2071-2100). It is found that the precipitation and maximum/minimum temperature at Sohra are influenced mainly by the major global predictors; specific humidity at 850 hPa height (s850) and mean temperature at 2 m (temp)/near surface specific humidity (shum), respectively. The downscaled result reveals an increase in Monsoon precipitation in the range of 266-1543 mm under various RCPs compared with the base periods 1985-2005 during the Near Future and 1979-2008 during the Mid and Far Future. Also, annual maximum and minimum temperature increases in the range of 1-2.8 °C and 1.2-3.6 °C for all RCPs in the future.

High-northern-latitude forcing modulated fluvial‒aeolian interplay during the Last Glacial Period in the Mu Us Desert, northern central China

Substantial stratigraphic evidence from the Late Quaternary at orbital- and millennial‒scales indicates that the formation and evolution of aeolian‒sand landscapes results from the interaction between regional aeolian and fluvial‒lacustrine activity. In many deserts (sandy lands) across the planet, fluvial‒aeolian interplay at the glacial‒interglacial scale since the Late Quaternary has been responsive to monsoonal precipitation, and linked to atmospheric CO2 and periodic variations in insolation. However, the patterns of fluvial‒aeolian interplay and their relationship with climate change are not always consistent over a given timescale during the Late Pleistocene. The paucity of studies on fluvial‒aeolian interplay in the Mu Us Desert (MUD) during the Last Glacial Period (LGP) hinders our understanding of the relationships between the dynamics of aeolian and fluvial‒lacustrine landscapes and their drivers. Here, based on a comprehensive field survey and stratigraphic dating of a typical fluvial‒aeolian sequence in the MUD, we synthesized the chronology of fluvial‒lacustrine and aeolian strata during the LGP. Our results show that extensive development of a fluvial‒lacustrine environment in the MUD during the LG mainly occurred during the late Last Glacial Maximum (LGMa, 20.1–18.4 ka BP) and Bølling/Allerød interstadial (14.8–12.6 ka BP), while thicker aeolian sands extensively accumulated during the Heinrich Stadial 2, Heinrich Stadial 1, and Younger Dryas periods. However, the development of fluvial‒lacustrine environments showed considerable spatial heterogeneity, mainly occurring on the southern and eastern margins of the desert, while they were extremely rare in the central and western parts of the desert owing to strong wind erosion. Comparisons with other high-resolution geological records from the Asian monsoon region reveal that the fluvial‒aeolian interplay in the MUD during the LGP was highly consistent with the evolution pattern of the East Asian summer monsoon (EASM) on the millennial‒centennial scale, and indicate that the development of fluvial‒lacustrine environments was mainly controlled by an increase in monsoonal precipitation during strengthening of the EASM. Consistency with other broad changes at high latitudes in the Northern Hemisphere suggests that fluvial‒aeolian interplay during the LGP in northern Chinese deserts, as represented by the MUD, was mainly controlled by changes in high-northern-latitude ice volume and the Atlantic Meridional Overturning Circulation.

Lake level evidence for a mid-Holocene East Asian summer monsoon maximum and the impact of an abrupt late-Holocene drought event on prehistoric cultures in north-central China

Uncertainty regarding the timing of the highest Holocene water level of enclosed Dali Lake in northern China has led to controversy about whether the East Asian summer monsoon (EASM) peaked in the early Holocene or the mid-Holocene. Therefore, a record combining a reliable chronology with unambiguous lake level indicators is essential to resolve the issue. In this study, we established a temporal sequence of well-preserved paleolake shorelines at different elevations around Dali Lake using quartz optically stimulated luminescence (OSL) dating. Combining the new OSL-based chronological data with the previously published ages of beach ridges, we constructed an integrated lake level record for Dali Lake since the last deglaciation; the record is chronologically well-constrained and provides a clearer representation of lake level changes than previous studies. The main findings are as follows: (1) the level of Dali Lake rose gradually during 14.5–8.0 ka and reached a highest level during 8.0–6.0 ka that was ~61 m higher than today, before gradually declining after ~6.0 ka; (2) although the short-lived highstand of Dali Lake during the early Holocene was caused by both monsoon precipitation and snow/ice meltwater influx, the mid-Holocene lake level maximum was mainly the result of increased monsoon precipitation. These findings indicate that the EASM maximum in the region occurred during the mid-Holocene, which is supported by precipitation-proxy records from the EASM margin; (3) a major decline (~30 m) of the level of Dali Lake occurred at ~4.2 ka, reflecting a regional-scale drought event in northern China. Combined with near-contemporaneous frequent floods in the lower Yellow River, we propose that the pattern of “drought in northern China, flooding in central China” occurred during ~4.2–3.8 ka, triggering the migration of the prehistoric human population of the area to the central Plain of China. This population migration may have destabilized the existing social order and promoted the emergence of more complex societies, leading to the development of early civilization in north-central China.

Higher Sensitivity of Northern Hemisphere Monsoon to Anthropogenic Aerosol Than Greenhouse Gases

AbstractBecause increased greenhouse gas emissions considerably warm and moisten the Earth's atmosphere, one may expect an increase in monsoon precipitation during the historical period. However, we find the observed Northern Hemisphere land summer monsoon (NHLM) precipitation has significantly decreased since 1901. Simulations from Coupled Model Intercomparison Project Phase 6 (CMIP6) well reproduce global warming and the drying of NHLM since the industrial revolution when forced by observed external forcings. Result from single forcing experiment shows that the anthropogenic aerosol (AA) dominates the Northern Hemisphere (NH) monsoon precipitation drying, while the greenhouse gases (GHG) largely control surface warming. Thus, the NH monsoon precipitation responds to AA more sensitively than the GHG. The AA can more effectively modulate downward solar radiation reaching the surface, decreasing evaporation and weakening monsoon circulations by reducing the interhemispheric temperature difference and land‐ocean thermal contrast, albeit with the same efficiency of the thermodynamic effect in the two forcings. Our result indicates the future intensive reduction of aerosol emission may rapidly recover the NH monsoon precipitation.

A millennium ENSO-related droughts and floods occurrences documented by fossil phytoliths in core sediments of Poyang Lake, East China

Droughts and floods caused by extreme hydroclimatic events in East Asian monsoon area often have serious effects on human society. The Poyang Lake region has always been one of the most severe floods and droughts in East China. In order to explore the relationship between monsoon climate change and occurrence of drought/flood, this study rebuilt a high-resolution (~10 yr) of temperature and aridity change history of the past 1000 years. Phytolith assemblages together with the climatic indices revealed 3 phases of paleoenvironmental changes over the last millennium: (1) Medieval Warm Period (MWP) during 900–1370 AD witnessed increased monsoon precipitation and frequent floods corresponding to strong El Niño–like state; (2) Little Ice Age (LIA) during 1370–1800 AD experienced severe droughts coupling with decreased monsoon precipitation and intensive La Niña–like state; (3) Current Warm Period (CWP) during 1800–2003 AD encountered highly frequent floods related to the increased monsoon precipitation modulated by strong El Niño–like state. Our results confirmed that there is a connection between solar irradiance, ENSO activity and monsoon precipitation in the subtropical East China. On interannual-decadal timescales, due to the modulation of ENSO on the location of the Western Pacific Subtropical High (WPSH) and Meiyu Belt, the occurrences of droughts and floods affected by ENSO-related monsoon precipitation has significantly affected not only the sedimentary environment, but also human activities, which is significant for the prediction of future prevention of droughts and floods in the East Asian monsoon region against the background of global warming.

Late Holocene vegetation dynamics and monsoonal climatic changes in Jammu, India

Knowledge of the Holocene Indian Summer Monsoon (ISM) variability is important for understanding the spatio-temporal dynamics of the ISM precipitation. In this study, a Late Holocene pollen proxy record of the changes in the ISM intensity from a 1.8 m deep lacustrine sedimentary deposit in Jammu District (Jammu and Kashmir State) in India is presented. The results show that between ~3205 and 2485 cal yr BP, mixed broad-leaved/conifer forests occurred in the region under a warm and humid climate, probably indicating high monsoon precipitation. Subsequently, the conifers, such as Pinus sp., Cedrus sp., Abies sp., Picea sp. and Larix sp. increased comparatively and show dominance over the existing broad-leaved taxa between ~2485 and 1585 cal yr BP under a cool and dry climate with reduced monsoon precipitation. The climate further deteriorated (towards attaining aridity under reduced monsoon condition) during ~1585 to 865 cal yr BP, which coincides with the Dark Ages Cold Period (DACP: CE/AD 400–765; 1185–1550 cal yr BP). Since ~865 cal yr BP (CE/AD 1085 onwards) to Present, the broad-leaved taxa, such as Alnus sp., Betula sp., Ulmus sp., Carpinus sp., Corylus sp. and Quercus sp. started expanding and showed their dominance over the conifers, indicating a warm and humid climate in the region with increased monsoon precipitation. This phase partly corresponds with the Medieval Climatic Anomaly (MCA) between CE/AD 950 and 1300. Thus, the ISM rainfall intensity is linked with some of the global climatic trends in the present study.

Simulated range of mid-Holocene precipitation changes from extended lakes and wetlands over North Africa

Abstract. Enhanced summer insolation over North Africa induced a monsoon precipitation increase during the mid-Holocene, about 6000 years ago, and led to a widespread expansion of lakes and wetlands in the present-day Sahara. This expansion of lakes and wetlands is documented in paleoenvironmental sediment records, but the spatially sparse and often discontinuous sediment records provide only a fragmentary picture. Previous simulation studies prescribed either a small lake and wetland extent from reconstructions or focused on documented mega-lakes only to investigate their effect on the mid-Holocene climate. In contrast to these studies, we investigate the possible range of mid-Holocene precipitation changes in response to a small-lake extent and a potential maximum lake and wetland extent. Our study shows that during the summer monsoon season, the African rain belt is shifted about 2 to 7∘ farther north in simulations with a maximum lake or wetland extent than in simulations with a small lake extent. This northward extent is caused by a stronger and prolonged monsoon rainfall season over North Africa which is associated with an increased monsoon precipitation over the southern Sahara and an increased precipitation from tropical plumes over the northwestern Sahara. Replacing lakes with vegetated wetlands causes an enhanced precipitation increase, which is likely due to the high surface roughness of the wetlands. A moisture budget analysis reveals that both lakes and wetlands cause a local precipitation increase not only by enhanced evaporation but also by a stronger inland moisture transport and local moisture recycling to the south of Lake Chad and the west Saharan lakes. Analysis of the dynamic response shows that lakes and wetlands cause a circulation response inverse to the one associated with the Saharan heat low. Depending on the latitudinal position of the lakes and wetlands, they predominantly cause a northward shift or a decay of the African Easterly Jet. These results indicate that the latitudinal position of the lakes and wetlands strongly affects the northward extension of the African summer monsoon.

ENSO effect on hydroclimate changes in southeastern China over the past two millennia

Meteorological observations indicate that both natural and anthropogenic forcing contribute to regional drought/flood in the East Asian summer monsoon (EASM) domain. However, spatiotemporal rainfall pattern and its dynamics during natural climatic variability remains unclear. Here we reconstruct a ∼3 year-resolution EASM precipitation record over the past two millennia, based on 13 230Th dates and 600 δ18O in a stalagmite from Songya Cave, southeastern China. The δ18O sequence shows a long-term decreasing trend, indicating an increasing monsoon precipitation over the past two millennia. A series of centennial-scale fluctuations are superimposed on the long-term trend, with a wetter Little Ice Age than the Medieval Warm Period. The long-term trend and centennial-scale oscillations in EASM rainfall are broadly related to El Niño-Southern Oscillation (ENSO) and Pacific decadal oscillation (PDO) variations, with an increased (decreased) EASM rainfall corresponding to El Niño-like (La Niña-like) conditions and positive (negative) phase of PDO. Comparison of δ18O records from Songya and Wanxiang Cave shows an anti-phased spatial rainfall pattern between southeastern and northwestern China. This spatiotemporal rainfall pattern, consistent with the modern observations, is possibly regulated by the ENSO, through changes in the location and strength of the Western Pacific Subtropical High (WPSH).

Pollen evidence of vegetation succession, climatic changes and human impact in southern Madhya Pradesh during last ca 6,700 years

Pollen records of a 2.0 m deep sediment profile from Barehata Tal portray the vegetation scenarios and contemporaneous climatic events of southern Madhya Pradesh prior to Mid–Holocene. Between 6,700 and 6,015 cal yr BP, the region supported open mixed tropical deciduous forests comprising sparingly distributed trees, viz. Moringa oleifera, Acacia, Trewia nudiflora, Madhuca indica, Terminalia and Aegle marmelos under a warm and less–humid climate than today. The record of Cerealia pollen from the beginning of the pollen sequence denotes the cereal–based arable crop economy in the region. The lake did exist, but it was of small expanse as depicted by the deficient aquatic element, Potamogeton. Around 6,015 to 4,848 cal yr BP, the enhancement in Acacia, Moringa oleifera, Trewia nudiflora, Madhuca indica coupled with moderate increase in Terminalia, Aegle marmelos, Holoptelea, etc. suggest the proliferation of mixed deciduous forests with the arrival of a warm very humid climate attributed to active SW monsoon. The agrarian activities also intensified with the initiation of favourable climatic condition as testified by the increase in Cerealia and cropland weeds. The lake turned bigger in stretch as documented by the improvement in Potamogeton and Typha along with sporadic appearance of Zygnema. The abrupt decline in the number as well as frequencies of the trees existing earlier implies that the forest became sparse around 4,848 to 3,671 cal yr BP with the onset of a warm and dry climate, most likely due to weak SW monsoon. Between 3,671 and 2,450 cal yr BP, the expansion forests took place with the substantial rise of Acacia, Madhuca indica and Holoptelea and re–incursion of Tectona grandis, Buchanania lanzan, Schleichera oleosa, Schrebera, Aegle marmelos, Grewia, etc. This diversification of the forests signifies the advent of a warm and moderately–humid climate. There was augmentation in the agricultural practice and other human activities as evidenced from the consistent encounter of Cerealia and culture pollen. The lake attained a wider spread as a result of increased monsoon precipitation. Around 2,450 to 1,230 cal yr BP, the forests declined, which is manifested by the depletion in the prominent ingredients, excepting Grewia, Schleichera oleosa, Tectona grandis and Aegle marmelos. This change in the vegetation scenario reflects the prevalence of a warm and less–humid climate again. However, from 1,230 cal yr BP onwards, the enrichment of forests elucidates that a warm and humid climate prevailed in response to increased monsoon precipitation.

Provenance versus weathering control on sediment composition in tropical monsoonal climate (South China) - 1. Geochemistry and clay mineralogy

This study presents an integrated mineralogical and geochemical database on mud and sand transported by the Pearl River (Zhujiang) and coastal rivers of SE China. Clay mineralogy and bulk-geochemistry of fluvial sediments are used to trace changes in weathering intensity across South China, a vast tropical to subtropical region characterized by a strong longitudinal rainfall gradient. The control of climate-induced weathering is manifest in the mineralogy and geochemistry of Pearl River mud, although mud and, to a greater extent, sand composition are also largely affected by the lithology of parent rocks. The depletion in mobile alkali and alkaline-earth metals increases steadily from the drier western part of the Pearl River catchment to the wetter eastern part and is most marked in easternmost tributaries of the Pearl River and in southern coastal rivers. Na and Ca are the most strongly depleted elements in Pearl River sediments, whereas the low concentration of Ca and Mg in river sand of coastal SE China also reflects the felsic character of parent rocks in the Cathaysia block. Eastward-increasing weathering conditions are most clearly highlighted by the progressive eastward increase in kaolinite across the Pearl River catchment, whereas the weathering effect in sand is blurred by quartz addition owing to widespread recycling of quartz-rich siliciclastic source rocks.This actualistic case study from a region characterized by monsoonal climate underscores the care that should be taken while inferring climatic conditions from the geochemical composition of sediments and sedimentary rocks, which is controlled by multiple geological factors including the felsic versus mafic character of parent rocks and the presence of extensive carbonate or siliciclastic covers in source areas. Most reliable indications are provided by the kaolinite/(illite+chlorite) ratio and by αAl indices for Na, Ca, Mg and Sr, which consistently increase eastward across South China thus paralleling the marked eastward increase in monsoonal precipitation towards the coast.

Temperature Control on Silicate Weathering Intensity and Evolution of the Neogene East Asian Summer Monsoon

AbstractAccurately reconstructing the evolution of the Asian monsoon is predicated on understanding the impact of temperature, precipitation, and tectonic paleogeography on silicate weathering proxies over million year timescales. We find that decreasing trends in chemical weathering proxies in both the northern and southern Tibetan Plateau match those from benthic oxygen isotope and sea surface temperature stacks since the late Miocene. In contrast, a synthesis of magnetic parameter‐based records and marine clastic flux records reveals stronger monsoon precipitation during both the warm middle Miocene and cool late Miocene, supporting model simulations showing that both paleogeography and atmospheric CO2 content are important in controlling the summer monsoon. This trend of increasing monsoon precipitation contrasts with the record of decreasing chemical weathering, suggesting that chemical weathering proxies are mainly regulated by temperature at million year timescales, rather than precipitation. These findings clarify reconstructions of the Cenozoic evolution of the East Asian summer monsoon.

Variable monsoons and human adaptations: Archaeological and palaeoenvironmental records during the last 1400 years in north-western India

We present the first systematic evaluation of the relationship between the archaeological and palaeoclimatic record from north-western India during the past millennium, from the urban site of Chandravati. The rarity of Medieval sites, systematic excavations and multi-disciplinary work in the subcontinent obscure the impact of two distinct climate anomalies − the ‘Medieval Warm Period’ (‘MWP’, 740 − 1150 CE), followed by the ‘Little Ice Age’ (‘LIA’, 1350 − 1850 CE). The finds from the archaeological site indicate the presence of winter and summer crops, suggesting the region was likely warm and mild humid during pre-Medieval period (ca. 600 − 800 CE). During Medieval times (between ca. 800 − 1300 CE), a diversification of the crop assemblage suggests that the region was under a warm and humid climate, corresponding to the ‘MWP’, driving increased monsoon precipitation. During the post-Medieval period (ca. 1350 − 1800 CE), drought-resistant millets and other summer pulse crops indicate the region probably experienced weak SW monsoon precipitation coinciding with globally recognised ‘LIA’. These interpretations are supported through phytolith data from the archaeological deposit broadly indicating two phases, the first being a period of diversified agricultural/anthropogenic activity (ca. 600 − 1350 CE), followed by a period dominated by drought-resistant crops (ca. 1350 − 1800 CE). Pollen data from a proximal lake corroborate the warm and humid phase ca. 800 − 1400 CE, with strong representation of warm−humid favouring tropical forest taxa, followed by non-arboreal indicators of a drier more open landscape ca. 1500 − 1800 CE. These environmental changes may have combined with other historic and institutional factors that led to the ultimate abandonment of the city. These changing cropping patterns, vegetation and cultural developments provide insight into past human response to climate change as well as important lessons for modern societies in exploring sustainable agricultural strategies to future climate change.

Monsoon rainfall and contrasting source rocks influenced sediment composition of peninsular basins along the east coast of India (western Bay of Bengal)

The peninsular India is characterized by remarkable variation in lithological composition as well as contrasting rainfall distribution patterns. The erosional and weathering history of these source rocks along with monsoonal changes are archived in sediments deposited in the basins along the east of coast of India. Here, we present a 60 ky record of Sr-Nd isotope ratios coupled with major elemental compositions of a sediment core off Krishna-Godavari (K-G) basin, western Bay of Bengal. The marked temporal variation in 87Sr/86Sr, εNd, and Mg/Al ratios are attributed to the changes in relative contribution of sediments from the Deccan Basalts (DcB) and Archean-Proterozoic gneissic complexes (APGC). The enhanced contribution of APGC associated with an increase in monsoon precipitation may be attributed to heightened erosion of the granitic gneissic rocks. On the other hand, a close correlation of 87Sr/86Sr ratios with Rb/Sr ratio, δ18OG-ruber, and CIA profiles indicate the possible influence of weathering intensity on the sediment composition.

Pollen records of vegetation dynamics, climate change and ISM variability since the LGM from Chhattisgarh State, central India

Pollen records of a lacustrine sedimentary profile from the Chhattisgarh State, central India revealed that between ~22,200 and 18,658 cal yr BP, open vegetation occupied the landscape under a cool and dry climate, probably indicating a reduced monsoon precipitation. This cool and dry climate, influenced by weakening of the Indian Summer Monsoon (ISM), globally matches with the Last Glacial Maximum (LGM). Between ~18,658 and 7340 cal yr BP, under the influence of a warm and moderately humid climate with increased monsoon precipitation, the open vegetation was succeeded by open, mixed tropical deciduous forest. This open, mixed tropical deciduous forest continued to grow in the region, with an increase in the frequency of some of the tree taxa especially, between ~7340 and 1961cal yr BP under a warm and relatively more humid climate with increased monsoon precipitation, correlatable with the Holocene Climatic Optimum (HCO)/Holocene Thermal Maximum (HTM). Between ~1961 cal yr BP and the Present, dense, mixed tropical deciduous forest came into existence under a warm and relatively more humid climate with further increase in monsoon precipitation. The present study provides an unprecedented record of the vegetation dynamics, climate change and the ISM variability since the LGM from one of the poorly understood areas of the tropics where rainfall is essentially controlled by the monsoon (ISM) variability.

Western Pacific Ocean influences on monsoon precipitation in the southwestern Chinese Loess Plateau since the mid-Holocene

Numerous paleoclimate records on reconstructed monsoon precipitation isotopes (δDp and δ18Op) have been published to infer past hydroclimate changes in Asian monsoon region. However, there are still debates on whether or not these reconstructed δDp or δ18Op can represent changes of monsoon precipitation. In this study, we report a ~ 5000 year record of leafwax hydrogen isotope (δDwax) from a 6.67-m-long sediment core collected in Beilianchi (BLC) Lake in the southwestern Chinese Loess Plateau. Based on analyses of the instrumental precipitation isotopes, precipitation amounts, and moisture sources, we find that δDp in the southwestern Chinese Loess Plateau shows distinct negative correlation with amounts of summer (from April to September) monsoon precipitation at inter-annual scales. This is further supported by the observed negative relation between precipitation amounts and regional lake-sediments and speleothems inferred δDp (or δ18Op) values at decadal scales over the past 60 years. Therefore, our reconstructed ~ 35-year resolution monsoon precipitation, inferred from δDwax, reveals a long-term decrease since the mid-Holocene. Superimposed on this trend, there are several multi-centennial to millennial-scale fluctuations for increased monsoon precipitation at 4500–4000 years BP, 2900–2400 years BP and 1200–700 years BP and decreased precipitation at 3900–3000 years BP, 2200–1300 years BP, and 500–0 years BP. Reanalyses of instrumental data and Kiel Climate Model on regional atmosphere circulations show that moisture of this region is mainly derived from the western Pacific Ocean through the East Asian summer monsoon circulation at inter-annual to inter-decadal, and millennial timescales. We conclude that monsoon rainfall in the southwestern Chinese Loess Plateau is likely connected with changes in sea surface temperatures and migrations of the ITCZ in the western Pacific Ocean.

Prolonged warming over the last ca. 11,700 cal years from the central Indian Core Monsoon Zone: Pollen evidence and a synoptic overview

Paleopalynological records of 1.1 m deep lacustrine sediment profile from the central Indian Core Monsoon Zone (CMZ) have provided a prolonged warming trend over the last ca. 11,700 years. Palynological evidence suggests that between ca. 11,700 and 8500 cal yr BP, a mixed tropical deciduous forest occurred in the region under a warm and humid climate with good monsoon precipitation. The forest expanded into a dense mixed tropical deciduous forest since ca. 8500 cal yr BP to the present, under warm and relatively more humid climatic conditions with further increase in monsoon precipitation. This warm climatic phase represents the Holocene Climate Optimum (HCO) or Holocene Thermal Maximum (HTM). Prior to the initiation of the long warm period, an open vegetation occurred in the region between ca.14,100 and 11,700 cal yr BP, under a cool and dry climate, probably indicating reduced monsoon precipitation, and partially matching with the Older Dryas stadial. The present study provides insights into the vegetation dynamics and associated climatic changes in response to the Indian Summer Monsoon (ISM) variability over the last ~14.1 ka from a poorly understood area of the tropics in South Asia, where rainfall is essentially controlled by the ISM. In addition, an account of the asynchronous warming during the Holocene from the central Indian CMZ, as well as other tropical regions of the Indian sub-continent, has been presented here. Global contextualization of the Holocene warming has also been summarized in this communication.