Increase In Monsoon Precipitation Research Articles

Impact of Climate Change and Adaptation Measures on Transhumance Herding System in Gatlang, Rasuwa

Climate change impact is global and Nepal is no exception, posing vulnerability for different communities and regions. Transhumance herding is the culture and identity of indigenous settlement in Himalayan region where herders follow vertical transhumance herding as a part of subsistence mixed agriculture system for their livelihood. It differs from nomadism in terms of its periodicity, regularity, and mobility. This study confers the impacts of climate change and adaptation on transhumance herders in Gatlang of Rasuwa District. Focus Group Discussion, Key Informant Interview, and Questionnaire survey were carried out covering herder’s perception toward climatic variability, changes in the biophysical indicator, its impact and adaptation strategies. Data were analyzed using descriptive statistics, weighted mean, and Index of Usefulness of Practice for Adaptation (IUPA) tools. This study showed increase in mean average temperature (0.0202°C), increase in monsoon precipitation (2.1 mm) and decrease in winter precipitation (0.5 mm). Seasonal movement of livestock was mainly guided for adjusting temperature. The observed changes in biophysical indicator were diverse with shrinking grazing lands as most agreed statements followed by low crop productivity and faster melting of snow in rangeland. Herders perceived different adaptation strategies where reserving some grazing areas scored highest IUPA ranking followed by seasonal movement, storage of grass/hay, and so on. Though transhumance itself is one of the adaptation strategy against climate change people were not aware about changing monsoon precipitation and following same seasonal calendar as before which have affected livestock. These observations suggested that herders were unaware of the underlying cause and its impacts on the system which needed to be monitored scientifically.

Phenomenon of the Asian Monsoon Penetrating to Northern Asia

It has been shown that the abnormal rainfall in the catchment of the Amur river in 2013 had a monsoon nature. The origin and evolution of the Asian monsoon (AM) from the region of its formation in the western Indian Ocean to the penetration to Northern Asia have been analyzed. It has been shown that the indices of the Indian Ocean dipole, El Nino, and the North Pacific indices were in phases that contributed not only to maximization of its intensity, but also to the fastest possible movement of the AM from the region of origin through the Indian subcontinent, Southeast Asia, and China to the Russian Far East. Due to the current composition of the climate indices in the Indian and Pacific oceans, the overwetted monsoon air mass brought the minimum possible loss of precipitation on its way to the final region. Increased monsoon precipitation in the vast catchment of the Amur river was facilitated by the fact that the Arctic Oscillation was in the negative phase, which led to the transfer of cold arctic air into the region. The latter circumstance influenced an increase in precipitation through the mechanism of accelerated condensation in humid air. Negative values of the North Pacific indices contributed to the development of blocking situations in the zonal current of temperate latitudes, which localized the zone of precipitation.

Global Monsoon Responses to Decadal Sea Surface Temperature Variations during the Twentieth Century: Evidence from AGCM Simulations

AbstractMultidecadal variations in the global land monsoon were observed during the twentieth century, with an overall increasing trend from 1901 to 1955 that was followed by a decreasing trend up to 1990, but the mechanisms governing the above changes remain inconclusive. Based on the outputs of two atmospheric general circulation models (AGCMs) forced by historical sea surface temperature (SST) covering the twentieth century, supplemented with AGCM simulations forced by idealized SST anomalies representing different conditions of the North Atlantic and tropical Pacific, evidence shows that the observed changes can be partly reproduced, particularly over the Northern Hemisphere summer monsoon (NHSM) domain, demonstrating the modulation of decadal SST changes on the long-term variations in monsoon precipitation. Moisture budget analysis is performed to understand the interdecadal changes in monsoon precipitation, and the dynamic term associated with atmospheric circulation changes is found to be prominent, while the contribution of the thermodynamic term associated with humidity changes can lead to coincident wetting over the NHSM domain. The increase (decrease) in NHSM land precipitation during 1901–55 (1956–90) is associated with the strengthening (weakening) of NHSM circulation and Walker circulation. The multidecadal scale changes in atmospheric circulation are driven by SST anomalies over the North Atlantic and the Pacific. A warmer North Atlantic together with a colder eastern tropical Pacific and a warmer western subtropical Pacific can lead to a strengthened meridional gradient in mid-to-upper-tropospheric thickness and strengthened trade winds, which transport more water vapor into monsoon regions, leading to an increase in monsoon precipitation.

Vegetation dynamics in response to climate change from the wetlands of Western Himalaya, India: Holocene Indian summer monsoon variability

India’s agricultural output, economy and societal well-being are strappingly dependent on the stability of the southwest summer monsoon precipitation, its variability and extremes. Deviations in the Indian summer monsoon (ISM) precipitation may profoundly impact the agricultural productivity and gross domestic product (GDP) of the country. Understanding the spatiotemporal dynamics of the ISM precipitation during the Holocene is significant in many respects, particularly in terms of human development and establishment of centres of civilisations. Here, pollen records of the variability in ISM precipitation and their interpretation in terms of vegetation and climate change from two wetlands (Gharana and Nanga; Ramsar sites) of the Western Himalaya (India) is presented. The results suggest that between ~8536 and 5296 cal yr BP, mixed conifer/broad-leaved forests occurred in the Jammu region (Gharana Wetland sediment profile) under a cool and dry climate, probably indicating decreased monsoon precipitation. Subsequently, they were succeeded by mixed broad-leaved/conifer forests between ~5296 and 2776 cal yr BP under a warm and humid climate with increased monsoon precipitation, partly corresponding to the Holocene Climate Optimum (HCO). Between ~2776 and 1376 cal yr BP, with more expansion of broad-leaved forest elements in response to a warm and more humid climate the dense mixed broad-leaved/conifer forests came into existence in the region, indicating a further increase in monsoon precipitation. From ~1376 cal yr BP to present, the climate deteriorated, as manifested by the replacement of dense mixed broad-leaved/conifer forests by mixed conifer/broad-leaved forests in the region. The palaeoclimatic inferences drawn from the Nanga Wetland sediment profile of Samba District match with the Gharana Wetland sediment profile of Jammu District for the late-Holocene. This study provides insights into the vegetation dynamics, associated climate change and the ISM variability from the poorly understood wetland ecosystems of Southeast Asia during the Holocene.

High resolution monsoon precipitation changes on southeastern Tibetan Plateau over the past 2300 years

Climate changes on Southeastern Tibetan Plateau have important impacts on social and economic development, as well as the ecosystem of southwestern China and Indo-China Peninsula. Here, we collected two stalagmites from Shenqi (Miraculous) cave in southern Sichuan, China. The stalagmite δ18O record shows good coherence with local instrumental rainfall record, as well as tree ring- and pollen-based moisture reconstructions from southeastern Tibetan Plateau during overlapped time periods. As a result, we reconstructed high-resolution (∼4.9 yrs) monsoon precipitation variations on southeastern Tibetan Plateau over the past 2300 years by using the combined stalagmite δ18O record.The result reveals an overall decreasing precipitation trend, with two most notable wet periods occurred in 60–280 AD and 370–510 AD. The most remarkably dry period is the recent 200 years. Some decadal scale wet and dry intervals were also identified. The abnormal drought during 1160–1245 AD might have accelerated Dali kingdom's demise at 1253 AD. Power spectrum analysis indicated significant 373-, 187-, 22-, 12- and 11- yr cycles in our stalagmite record, suggesting the impact of solar activity. Increased monsoon precipitation on southeastern TP was observed in solar activity minima during the last millennium. We further synthesized an integrated precipitation record for southwestern China and discussed spatial patterns of precipitation over China during the last two millennia. The comparisons confirm a "dry southern and wet northern" pattern in monsoonal China during the Medieval Warm Period and a "wet southern and dry northern" pattern during the Little Ice Age and Dark Age Cold Period. Solar activity, the strength of westerly jet and summer monsoon, as well as the SST of tropical Indo-Pacific might play important roles on the rainfall spatial patterns over monsoonal China during the last 2000 years.

South American monsoon response to iceberg discharge in the North Atlantic

Heinrich Stadials significantly affected tropical precipitation through changes in the interhemispheric temperature gradient as a result of abrupt cooling in the North Atlantic. Here, we focus on changes in South American monsoon precipitation during Heinrich Stadials using a suite of speleothem records covering the last 85 ky B.P. from eastern South America. We document the response of South American monsoon precipitation to episodes of extensive iceberg discharge, which is distinct from the response to the cooling episodes that precede the main phase of ice-rafted detritus deposition. Our results demonstrate that iceberg discharge in the western subtropical North Atlantic led to an abrupt increase in monsoon precipitation over eastern South America. Our findings of an enhanced Southern Hemisphere monsoon, coeval with the iceberg discharge into the North Atlantic, are consistent with the observed abrupt increase in atmospheric methane concentrations during Heinrich Stadials.

ENSO‐Like Modulated Tropical Pacific Climate Changes Since 2.36 Myr and Its Implication for the Middle Pleistocene Transition

AbstractEl Niño/Southern Oscillation (ENSO) activity and the Pacific Walker Circulation are controlled by the zonal sea surface temperature (SST) gradient between the western and Eastern Equatorial Pacific (EEP) and the corresponding barometric difference. Variations in the zonal SST gradient since the early Pleistocene have primarily been triggered by changes in the SST in the Eastern Equatorial Pacific. However, the response of the ENSO‐like long‐term state to the cooling of the EEP and its coupling role with tropical Pacific climate changes are still not well established. Here we present a high‐resolution grain‐size record spanning the last 2.36 Myr, obtained from marine core sediment located in the West Philippine Sea in order to decipher the tropical pacific climate changes and reveal its controlling mechanism. By combining our data with other long‐term climatic records from the Equatorial Pacific, we demonstrate that the cooling of SST and enhanced upwelling in the EEP resulted in the development of the Walker Circulation and increased monsoon precipitation in Luzon from 2.2 to 1.6 Myr, from 1.2 to 0.8 Myr, and since 0.2 Myr ago. The progressive cooling of the high‐latitudes in the Quaternary may be responsible for our observation here. A newly identified 100 kyr dominant period between 2.2 and 1.6 Myr in the ENSO‐like modulated Pacific climate records indicates that the ENSO‐like system may play a key role in facilitating or responding to the global climate changes.

Centennial- to decadal-scale monsoon precipitation variations in the upper Hanjiang River region, China over the past 6650 years

The upper Hanjiang River region is the recharge area of the middle route of South-to-North Water Transfer Project. The region is under construction of the Hanjiang-Weihe River Water Transfer Project in China. Monsoon precipitation variations in this region are critical to water resource and security of China. In this study, high-resolution monsoon precipitation variations were reconstructed in the upper Hanjiang River region over the past 6650 years from δ18O and δ13C records of four stalagmites in Xianglong cave. The long term increasing trend of stalagmite δ18O record since the middle Holocene is consistent with other speleothem records from monsoonal China. This trend follows the gradually decreasing Northern Hemisphere summer insolation, which indicates that solar insolation may control the orbital-scale East Asian summer monsoon (EASM) variations. Despite the declined EASM intensity since the middle Holocene, local precipitation may not have decreased remarkably, as revealed by the δ13C records. A series of centennial- to decadal-scale cyclicity was observed, with quasi-millennium-, quasi-century-, 57-, 36- and 22-year cycles by removing the long-term trend of stalagmite δ18O record. Increased monsoon precipitation during periods of 4390–3800 a BP, 3590–2960 a BP, 2050–1670 a BP and 1110–790 a BP had caused four super-floods in the upper reach of Hanjiang River. Dramatically dry climate existed in this region during the 5.0 ka and 2.8 ka events, coinciding with notable droughts in other regions of monsoonal China. Remarkably intensified and southward Westerly jet, together with weakened summer monsoon, may delay the onset of rainy seasons, resulting in synchronous decreasing of monsoon precipitation in China during the two events. During the 4.2 ka event and the Little Ice Age, the upper Hanjiang River region was wet, which was similar to the climate conditions in central and southern China, but was the opposite of drought observed in northern China. We propose that weakened summer monsoon and less strengthened or normal Westerly jet may cause rain belt stay longer in the southward region, which reduced rainfall in northern China but enhanced it in central and southern China.

Palaeoclimatic reconstruction by using the varvite sediments of Bharatpur, Upper Lahaul Valley, NW Himalaya, India

A 6 m thick varvite profile exposed at Bharatpur (77° 27′ E: 32° 48′ N, altitude 4692 m) in the NW Himalaya was investigated to understand the past climatic signatures during the Late Quaternary period. The radiocarbon chronology brackets the varvite sedimentation between ∼24.3 and 7.2 ka BP and the sedimentary sequence is bounded by river born gravel at the top and glacial outwash at the bottom. The proxies used were lithology, chronology (AMS/radiocarbon dating), geochemical analysis, loss on ignition (LOI), and mineral magnetism. Other parameters, e.g., Chemical Index of Alteration (CIA), Chemical Index of Weathering (CIW), Al2O3/SiO2, Fe2O3, CaO, MgO and Al/Na ratio were also used. Based on the combined data set, six phases of warm and cold climatic conditions are reconstructed. The mean CIA, CIW and Al/Na ratios reveal that the sediments were incorporated from sedimentary rocks by moderate silicate chemical weathering process. Based on the available chronology, the basal most glacial outwash event can be estimated as ca. 24.3 ka BP and the laminated section shows continuity of sedimentation from the Late Quaternary to Holocene. The period between ∼ ca. 24.3 and 22.6 ka can be regarded as an arid phase. From ∼ ca. 22.6–20.5 ka BP, a slight increase in monsoonal precipitation is observed, followed by decreased precipitation from ∼ca. 20.5 to 18 ka BP. The period from ca. ∼18 to 15.7 reveals warm and humid climatic conditions. We suggest that a cold event from ca. ∼15.7 to 11.5 may correspond to the Younger Dryas (YD) which in turn is followed by a phase of maximum moisture of the Holocene Climate Optimum (HCO) (ca. ∼11.5–7.2 ka BP) in the study area. The increased CIA during deglaciation and HCO suggest high chemical weathering, whereas, the LGM (Last Glacial Maximum) and YD are represented by the low CIA. The observed climatic phases/events are in agreement with the records from other parts of the Himalaya.

Vegetation and climate reconstruction based on a ∼4 ka pollen record from north Chhattisgarh, central India

ABSTRACTWe present pollen proxy records of the variability in the Indian Summer Monsoon (ISM) precipitation during the last ∼4ka (ka= thousand years ago; Late Holocene) from a lacustrine area of Koriya District in Chhattisgarh (C'garh), (central Indian core monsoon zone [CMZ]), India. The results show that open, mixed tropical, deciduous forest occupied the region under a warm and moderately humid climate probably indicative of moderate monsoon precipitation between ∼3796 and ∼2428 cal yr BP. Subsequently, between ∼2428 and ∼1431 cal yr BP, the forest became dense and succeeded the open, mixed tropical, deciduous forest owing to the prevalence of a warm and relatively more humid climate with increased monsoon precipitation. The forest became less diversified from ∼1431cal yr BP to Present under the regime of a warm and relatively less humid climate with decreased monsoon precipitation.

A late Quaternary record of monsoon variability in the northwest Kimberley, Australia

Understanding of the late Quaternary environment of Australia's vast Kimberley region has to date been hindered by the region's lack of classic palaeoenvironmental archives such as deep lake sediments. However, mound spring peat deposits in the region have been found to be a potentially rich archive of palaeoenvironmental data. Here we present a high resolution record from Black Springs mound spring in the Kimberley's northwest, filling some of the current gaps in knowledge of the region's environmental history. This builds on a ∼6000 year record developed from the same site and indicates that since the Last Glacial-Interglacial Transition the Australian summer monsoon has varied greatly in intensity, with an increase in monsoonal precipitation from ∼14,000 yr BP and pronounced drying in the late Holocene. Despite some chronological uncertainties thought to be due to the inclusion of younger, microscopic root fragments, changes in the record compare well with other records of climatic change from the Kimberley, and across tropical northern Australia.

Early Holocene groundwater table fluctuations in relation to rice domestication in the middle Yangtze River basin, China

Abstract The early Holocene environmental amelioration stimulated the trajectory of Neolithic farming cultures and specific geographic settings played a role in determining the nature of these cultures. Using microfossil evidence, the present study reveals that the fluctuations of the groundwater table substantially influenced rice domestication in the Dongting Lake area of the middle Yangtze River basin in the early Holocene. Our 14 C-dated sediment core taken from the Bashidang (BSD) Neolithic site contains evidence that the site was a floodplain prior to human occupation ca . 8600 years ago. Poaceae, which contained wild rice ( Oryza sp.) as indicated by combined pollen and phytolith evidence, and low counts of freshwater algae indicated a moist site condition. The area then gradually evolved into wetlands as the water table rose, in response to the increasing monsoon precipitation during the early Holocene. This favored rice domestication, assisted by firing and clearing, that continued to flourish for several hundred years. Finally, rice domestication declined during the late stage of the Pengtoushan culture, accompanied by evidence of the expansion of wetlands reflecting the effects of a rising groundwater table that had caused the cessation of rice farming at the Bashidang site after ca. 8000-7900 cal yr BP. This study shows that there are local effects at particular sites that may differ from the trend at the regional scale, necessitating a careful interpretation of the available evidence.

Mid-Holocene pollen records from southwestern Madhya Pradesh, central India, and their palaeoclimatic significance

ABSTRACTA new pollen record from south western Madhya Pradesh, central India provides a palaeoenvironmental record for the core monsoon zone (CMZ) of India. The 2m deep lacustrine sediment profile demonstrates that between ∼5679 and ∼4939 cal yr BP, open vegetation occurred in the region, indicative of a dry climate with reduced monsoonal precipitation. This was replaced by a mixed tropical deciduous forest under a warm and humid climate with increased monsoonal precipitation between ∼4939 to ∼3762 cal yr BP. From ∼3762 cal yr BP to the present day, a dense mixed tropical deciduous forest has existed under a warm and relatively more humid climate indicating a further increase in monsoonal precipitation. Cereal-based agricultural practice is evident during the most recent two phases.

Mid- to late Holocene climate response from the Triloknath palaeolake, Lahaul Himalaya based on multiproxy data

A 2.13-m-thick palaeolake sequence deposited between the right lateral moraine and the valley wall of Triloknath glacier, has been studied at high resolution to understand the past climatic changes in Lahaul Himalaya. The OSL and AMS14C chronology suggests that the lake building activity was initiated post-cooling phase since ~6484cal.YBP. The combination of sedimentological, geochemical, and environmental magnetic parameters helped to infer five first-order climatic zones. The influx of magnetic minerals along with a notable increase in antiferromagnetic mineralogy (appearance of hematite) and higher chemical index of alteration (CIA) values during ~5925cal.YBP to 5676cal.YBP suggests warm and wet conditions owing to enhanced Indian Summer Monsoon (ISM) precipitation corresponding to the mid-Holocene warming. Further, reduction in the magnetic mineral concentration with few peaks of antiferromagnetic mineralogy and higher CIA values suggests warmer episodes within an overall cold climate, and the finer ferrimagnetic grain size suggests intermittent low energy and ponding conditions during ~3904cal.YBP to 2365cal.YBP. This was followed by fluctuating cold arid conditions in response to reduced ISM precipitation during ~2365cal.YBP and 1758cal.YBP. Further, between 1758cal.YBP to the present, episodic warming, pedogenic enhancement, and increased monsoon precipitation have been recorded. A major warm episode (Medieval warm period) as depicted from enhanced antiferromagnetic mineralogy and higher CIA values has been recorded between ~742cal.yrs. BP and 593cal.YBP. The sudden drop in the magnetic mineral concentration as well as the CIA value, around ~300cal.YBP (1650 CE) is likely because of colder conditions prevailing during the Little Ice Age (LIA). The study illustrates high sensitivity of the lake sediment sequence to witness the climatic episodes experienced in the glaciated regime of the Triloknath glacier.

Impact of Climate Change on River Discharge and Rainfall Pattern: A Case Study from Marshyangdi River basin, Nepal

Climate models have predicted increase in monsoon precipitation for Nepal and expected to enhance further in scenario of deforestation and global green house gas emission which induces extremes resulting risk of flood, landslide during monsoon while water shortage in dry season. In this study, the impact of climate change on water resource for glacierized Marshyangdi River is evaluated using HBV light hydrological model with available hydrological data (1988-2009) to predict the future water availability and change in rainfall pattern based on available rainfall data (1981-2009). The results for Marshyangdi basin with 4104.59km2 area with average discharge of 204.03 m3/s (1988-2009) suggested decrease in rainy days while increase in frequency of intense rainfall, and the projected rainfall based on downscaling showed increase in rainfall for 2050’s. The model performance is adequate and able to simulate accurate result with estimated average discharge of 224.82 m3/s (1988-2009). The simulated result provided good fit with model efficiency 0.86 for first calibration and 0.81 for second calibration, while total volume difference of 1.43% and Nash-Sutcliffe Efficiency of 0.80 between observed and simulated discharge.Journal of Hydrology and Meteorology, Vol. 9(1) 2015, p.60-73

Statistical downscaling of CMIP5 multi-model ensemble for projected changes of climate in the Indus River Basin

The simulation results of CMIP5 (Coupled Model Inter-comparison Project phase 5) multi-model ensemble in the Indus River Basin (IRB) are compared with the CRU (Climatic Research Unit) and APHRODITE (Asian Precipitation-Highly-Resolved Observational Data Integration Towards Evaluation) datasets. The systematic bias between simulations and observations is corrected by applying the equidistant Cumulative Distribution Functions matching method (EDCDFm) and high-resolution simulations are statistically downscaled. Then precipitation and temperature are projected for the IRB for the mid-21st century (2046–2065) and late 21st century (2081–2100).The results show that the CMIP5 ensemble captures the dominant features of annual and monthly mean temperature and precipitation in the IRB. Based on the downscaling results, it is projected that the annual mean temperature will increase over the entire basin, relative to the 1986–2005 reference period, with greatest changes in the Upper Indus Basin (UIB). Heat waves are more likely to occur. An increase in summer temperature is projected, particularly for regions of higher altitudes in the UIB. The persistent increase of summer temperature might accelerate the melting of glaciers, and has negative impact on the local freshwater availability. Projections under all RCP scenarios show an increase in monsoon precipitation, which will increase the possibility of flood disaster. A decreasing trend in winter and spring precipitation in the IRB is projected except for the RCP2.6 scenario which will cause a lower contribution of winter and spring precipitation to water resources in the mid and high altitude areas of the IRB.

Pollen records related to vegetation and climate change from northern Chhattisgarh, central India during the late Quaternary

Pollen records from a 1.8-m deep sediment profile from Lakadandh Swamp, Baikunthpur Forest Range of Koriya District, Chhattisgarh (C'garh, central India), show the late Quaternary vegetation and climate history. Lakadandh Swamp occurs in the core monsoon zone of India. The study revealed that between ∼12,785 and ∼9035 cal. yrs BP, tree savannah vegetation, – composed of Poaceae, Amaranthaceae, Tubuliflorae along with the tree taxa Holoptelea sp. and Sapotaceae; sparsely distributed Acacia sp., Emblica officinalis, Lagerstroemia sp., Madhuca indica and Syzygium sp., thickets of Ricinus and Zizyphus sp. – occurred in the region under a cool and dry climate probably indicative of reduced monsoon precipitation. The early part of this phase is comparable with the Younger Dryas (YD) cold event which occurred between ∼12,800 and ∼11,500 yrs BP. Between ∼9035 and ∼4535 cal. yrs BP, the expansion of existing taxa Holoptelea sp., Sapotaceae, Madhuca indica, Ailanthus excelsa and Lagerstroemia sp. as well as the appearance of Acacia, and Shorea robusta, Acanthaceae, Rungia sp., and Ricinus sp., shows the tree savannah vegetation was replaced by open mixed tropical deciduous forest under a regime of warm and moderately humid climate with increased monsoon precipitation. Since ∼4535 cal. yrs BP to Present, owing to the improvement of most of the forest constituents, particularly Madhuca indica, Holoptelea sp., Sapotaceae and Lannea coromandelica, and also with immigration of Terminalia sp., Diospyros sp., Butea sp. and Maytenus sp., mixed tropical deciduous forest has taken over the space covered by open mixed tropical deciduous forest under a warm and relatively more humid climate, with further increase in monsoon precipitation. The existing cereal-based agricultural practice increased during the latter two phases, which could be attributed to increased monsoon precipitation.

Vegetation and climatic variability in southeastern Madhya Pradesh, India since Mid-Holocene, based on pollen records

Pollen analysis of 1.75 m deep sediment core from Tula-Jalda (Amarkantak) in Anuppur district, Madhya Pradesh unravels that around 4500–3600 cal years BP, this region supported open mixed tropical deciduous forests comprising chiefly Madhuca indica followed by Terminalia, Mitragyna parvifolia, Haldina cordifolia, Emblica officinalis and Acacia, under a warm and relatively less humid climate. The retrieval of Cerealia and other cultural plants, viz. Artemisia, Cheno/Am and Caryophyllaceae signifies that the region was under cereal-based agricultural practice. The open mixed deciduous forests got enriched and dense around 3600–2761 cal years BP with the expansion of trees that already existed coupled with invasion of Symplocos, Diospyros, Lannea coromandelica and Radermachera with the inception of a warm and moderately humid climate in response to increased monsoon precipitation. Around 2761–2200 cal years BP, much expansion of the forests took place owing toinitiation of a warm and more humid climate, attributed to intensification of the southwest (SW) monsoon. The modern Sal (Shorea robusta) forests were established around 2200 cal years BP, as clearly deciphered by the steady presence of S. robusta along with close allies such as M. indica, Terminalia, H. cordifolia, E. officinalis, etc. This change in the vegetation scenario implies that a warm and relatively more humid climate prevailed with timely arrival of the more active SW monsoon.

Late Quaternary vegetation history, climatic variability and human activity in the Central Ganga Plain, deduced by pollen proxy records from Karela Jheel, India

Pollen analysis of a 2.6 m thick sediment profile from Karela Jheel has indicated that between 14,000 and 12,500 cal BP, open grassland with sparingly distributed trees such as Holoptelea integrifolia and Oroxylum occurred in the region under a cool and dry climate. The meager presence of aquatic elements viz., Potamogeton, Typha and fresh-water alga Botryococcus suggests the existence of the lake. Around 12,500 to 8700 cal BP, the forest groves dominated by Oroxylum together with H. integrifolia, and Madhuca indica were established, interspersed with open grasslands under a warm and humid climate in response to increased monsoon precipitation. The debut of Cerealia ∼9000 cal BP along with cropland weeds viz., Cheno/Am, Artemisia and Rumex implies the initiation of cereal-based agrarian practice. However, an abrupt decline in Oroxylum and other associated trees, except for M. indica and Acacia, which increased slightly, ∼8700 to 4800 cal BP, indicates that the forest groves became less varied in response to a warm and less humid climate, because of decreased monsoon precipitation. Between 4800 and 2000 cal BP, maximum expansion of forest groves occurred as evident by the improvement in M. indica, Acacia, H. integrifolia, etc. and invasion of more trees. The proliferation of the overall vegetation envisages the onset of a warm and more humid climate, attributed to intensification of SW monsoon. The augmentation of agricultural practice is confirmed by the steady presence of Cerealia and other cropland weeds. Since 2000 cal BP, the depletion in the arboreals suggests that the region supported open grasslands with scattered trees, depicting the deterioration of climate due to reduced monsoon precipitation.

Vegetation and climate change during mid and late Holocene in northern Chhattisgarh (central India) inferred from pollen records

Pollen analysis of a 1.8 m deep sediment core from Matijharia Lake, Baikunthpur Forest Range of Koriya District in Chhattisgarh state (C'garh), central India, has been carried out with the principal aim of investigating the vegetation and climate history from mid- to late-Holocene. The study has demonstrated that between 6410 and 4250 cal. BP, tree savannah vegetation, which is largely constituted of grasses, Cerealia, Chenopodiaceae/Amaranthaceae, Tubuliflorae, together with sparsely distributed tree taxa Madhuca indica, Sapotaceae, and Lannea coromandelica occupied the region under a cool and dry climate with reduced monsoon precipitation. Between 4250 and 1000 cal. BP, with the enhancement of M. indica, Sapotaceae, L. coromandelica, Acacia, Holoptelea as well as the incursion of Diospyros melanoxylon, Emblica officinalis, Shorea robusta, Syzygium, Grewia, Ailanthus excelsa and others along with shrubby Rungia, the tree savannah vegetation was transformed into a mixed tropical deciduous forest. The overall enrichment in the vegetation mosaic, particularly arboreals, indicates that the region experienced a warm and humid climate with increased monsoon precipitation. Since 1000 cal. BP to Present, dense mixed tropical deciduous forest succeeded the mixed tropical deciduous forest with forest constituents particularly M. indica, Sapotaceae, L. coromandelica, S. robusta, E. officinalis, D. melanoxylon, Syzygium, and also with the immigration of some more arboreal taxa such as Terminalia, Grewia, Annona, Lagerstroemia, and others (though meagerly). From this proliferation of forest elements, it is surmised that a warm and relatively more humid climate prevailed in the region with further increase in monsoon precipitation. The region was under cereal-based agricultural practice, accelerated during the second phase (between 4250 and 1000 cal. BP) due to prevalence of the active SW monsoon.