A 5200-year record of vegetation dynamics and variations in the Indian Summer Monsoon from the Garhwal Himalaya, India

Atmospheric transport and deposition of potentially toxic elements along a South-North altitudinal transect (2-3650m a.s.l.): Assessing spatiotemporal patterns, sources, orographic control, and public health implications.

The far eastern Himalayas, dominated by the Indian Summer Monsoon, receive some of the highest precipitation in High Mountain Asia, yet their glacial history remains poorly constrained. We present 63 new in situ cosmogenic 10 Be exposure ages from the Dri River catchment in Dibang Valley, Arunachal Pradesh, eastern Himalayas of India, providing the first directly dated Late Pleistocene glacial chronology along the southern slopes of the eastern Himalayas east of Mt. Everest. At its maximum, the Dri palaeoglacier extended ∼100 km, reaching one of the lowest toe altitudes in the Himalayas (1500–1300 m a.s.l.). This major advance occurred before mid-MIS 3 (∼44.8 ka), possibly as early as late-MIS 4 (≥58.5 ka). Glacial landforms further up valley dated to ∼19.6 ka indicate that the glacier had retreated by the end of the global Last Glacial Maximum, terminating at ∼1680 m a.s.l. By 12.6 ka the glacier had retreated to a length of ∼25 km to upland valleys, whilst cirques at ∼3700 m a.s.l. became ice-free by 13.3 ka. Glacial retreat coincided with regional warming, revealing a threshold-like response in which temperature increase enhanced melting and shifted monsoonal precipitation from snow to rain, reducing accumulation. Conversely, during colder phases, abundant monsoonal moisture coupled with lower temperatures enabled glacier expansion to considerable scales. This pattern demonstrates that glacier extent in the monsoon-dominated Himalayas was primarily temperature-driven, with precipitation acting as a secondary modulator, and highlights the climatic sensitivity of monsoonal glaciers to warming during deglacial transitions. The new chronology bridges a major spatial gap in Himalayan palaeoglaciology and provides critical constraints on how monsoon-dominated glaciers evolved across High Mountain Asia. • First 10 Be-dated Late Pleistocene glacial chronology from easternmost Himalayas. • At its maximum (≥58 ka), Dri palaeoglacier was ∼100 km in length reaching one of the lowest elevations in the Himalayas. • Cirques at 3700 m were ice-free by 14–13 ka; Dri palaeoglacier extent was only ∼25 km around 12.6 ka. • Glacier mass balance controlled mainly by temperature, not precipitation amount. • New record bridges major gap and refines monsoon-dominated glacier evolution.

Coupled role of Westerlies and Indian Summer Monsoon in the climatic variability of Kashmir Valley, NW India during the Late Quaternary

Different coercivity magnetic components in a lacustrine sequence from Heqing Basin and its linkage with millennial Indian summer monsoon variability since 52 ka

Heavy rainfall verification over Arunachal Pradesh during the Indian Summer Monsoon: a diagnostic study

Abstract The iconic Indian summer monsoon (ISM), that is often ascribed to the season of June–July–August–September (JJAS), is found to be changing in recent decades. An objective definition of the ISM season is used to diagnose the onset and retreat of the monsoon to the precision of a day in the year. This analysis provides compelling observational evidence that the ISM season has distinctly shortened in parts of northern, northeastern, and peninsular India in recent decades. This is caused by a late onset over northeastern India and an earlier retreat date of the ISM in all these regions in the recent decades, resulting in a reduction of 10 days to a month in the length of the ISM season over these regions. Our analysis reveals that in recent decades, the West Pacific High is further east at the time of the onset of the ISM over northeastern India, while at the time of retreat, the rainfall is much stronger in Southeast Asia with the West Pacific High shifted further west. Both these changes in recent decades reduce the moisture flux that is associated with a comparative reduction of the mean daily rain rate. This reduction of the mean daily rain rate then relates to the delay of the onset and the advance of the retreat of the ISM season in some of these regions over India that exhibit a shortened ISM season in recent decades.

Abstract In this study, we examined the role of local land–atmosphere interactions during the onset of the Indian summer monsoon over Central India (CI; 16°N–26°N, 76°E–86°E), utilizing the composites of early- and late-onset years. Differences in surface and atmospheric processes between early- and late-onset years are examined using India Meteorological Department precipitation data and ERA5 reanalysis for the period 1948–2020. The analysis reveals that early-onset years are characterized by a pronounced pre-onset buildup of lower-tropospheric moisture and moist static energy (MSE), beginning nearly two to three weeks prior to onset and driven primarily by the moisture term. This early enhancement of lower-level MSE creates a progressively unstable atmospheric environment that is favorable for the initiation of moist convection. Consistent with this thermodynamic preconditioning, boundary-layer height (PBLH) becomes significantly shallower over CI during early-onset years, accompanied by enhanced surface latent heat flux and reduced sensible heat flux, reflecting a shift toward moisture-dominated surface energy partitioning. Granger causality analysis further demonstrates that lower-tropospheric moisture and MSE systematically precede and exert a strong causal influence on PBLH evolution, which successively influences surface fluxes. Precipitation emerge primarily as downstream responses to this sequence, with enhanced convective rainfall occurring once sufficient thermodynamic instability is established. Together, these results highlight that lower-tropospheric moisture and energy buildup, rather than surface heating alone, play a dominant role in accelerating the timing of MOCI.

ABSTRACT The Indian summer monsoon (ISM) governs the hydrological and agricultural foundation of South Asia, yet its response to anthropogenic warming remains uncertain and regionally diverse. Here we assess projected mean rainfall, variability and categorised monsoon extremes using six skill‐selected CMIP6 models (BCC‐CSM2‐MR, CMCC‐CM2‐SR5, FIO‐ESM‐2‐0, MCM‐UA‐1‐0, MIROC6, TaiESM1) evaluated against the high‐resolution IMD 0.25° dataset. Analyses are performed for the seasonal (JJAS) and monthly (June–September) scales under four Shared Socioeconomic Pathways (SSP1‐2.6, SSP2‐4.5, SSP3‐7.0, SSP5‐8.5). Century long observed records reveal a quasi‐stationary all‐India mean monsoon rainfall, accompanied by a marked increase in interannual variability consistent with progressive amplification of hydroclimatic extremes. The CMIP6 multi‐model ensemble (MME) reproduces this behaviour and projects a further 20%–35% rise in variability by the late 21st century. The coefficient of variation strengthens by 0.04–0.06 under high‐emission scenarios, with statistically significant regime shifts detected around 2040–2060. Enhanced seasonality is evident, with June and September exhibiting pronounced drying (≈−2 σ ) and July–August showing intensified wet excursions (≥ +3 σ ). Categorical analyses indicate a 40%–60% increase in moderate and extreme excess monsoon years and a 20%–30% rise in deficit years, while event intensities strengthen to +4 σ (wet) and –3 σ (dry). These concurrent amplifications of surplus and deficit rainfall define a hydroclimatic paradox: simultaneous amplification of mean rainfall and interannual variability, leading to heightened probabilities of both surplus and deficit extremes. The findings directly tangled with the reduced seasonal predictability and challenges for reservoir management and crop planning, as evidenced by projected increases in extreme excess years and intensified deficits. The warming climate is reorganising the ISM towards a high‐variance regime, challenging water security and adaptation planning across a region that depends critically on its seasonal rainfall predictability.

Abstract This study evaluates the ability of the Coupled Model Intercomparison Project phase 6 (CMIP6) climate models to simulate the observed effects of tropical Pacific and Indian Ocean sea surface temperature anomalies (SSTAs) on Indian summer monsoon rainfall (ISMR) variability. Using observational data and the large ensemble historical simulations of seven CMIP6 models from 1950 to 2014, we applied a cyclostationary linear inverse model (CS-LIM) to isolate the impacts of tropical Pacific SSTAs, Indian Ocean SSTAs, and their interaction on the interannual variability of ISMR. Overall, these CMIP6 models well reproduced the observed enhanced (reduced) ISMR variability from Pacific SSTAs (Indian Ocean SSTAs and the Indo-Pacific interaction), though with varying spatial patterns and magnitudes. Among them, CESM2 and Energy Exascale Earth System Model version 2.0 (E3SM-2-0) showed the best agreement with observations for the effects of Pacific SSTAs and the Indo-Pacific interaction, respectively. Composite analysis of ISMR anomalies during the developing phases of pure and co-occurring El Niño–Southern Oscillation (ENSO) and Indian Ocean dipole (IOD) events revealed that the impacts from Pacific SSTAs were captured reasonably well by E3SM-2-0, CESM2, MIROC6, and MPI-ESM1-2-LR, while E3SM-2-0 also showed the best agreement with observations for the effects from the Indo-Pacific interaction. However, all seven models exhibited substantial biases in simulating the Indian Ocean SSTA impacts on ISMR, particularly during pure El Niño events. Overall, this study provides new insights into how individual CMIP6 models simulate the isolated impacts from the tropical Pacific and Indian Oceans, which have important applications for improving ISMR predictions and interpreting ISMR future projections.

A 2000-year record of polycyclic aromatic hydrocarbon deposition in Lake Basongcuo, southeast Tibet: Source apportionment and implications for human impacts.

Improvement of the regional climate model with soil moisture initialization on simulations of Indian summer monsoon.

Rainfall and temperature variability serve as crucial indicators of hydroclimatic hazards, including floods, droughts, heatwaves, and cold spells. While such events may arise from a single variable reaching extreme levels, they often result from the interplay of multiple climatic factors. This study examines the spatio-temporal variability of compound extreme events (CEEs) over the semi-arid Ken and Betwa River catchments in Central India. Although these regions primarily receive rainfall during the Indian Summer Monsoon (ISM) season, they have experienced a post-2000 drying trend along with rising temperatures. A significant negative correlation between rainfall and temperature indicates rainfall suppression under hotter conditions due to enhanced atmospheric stability and reduced moisture availability. The analysis further shows that extreme wet and dry events have declined in the Betwa basin, while the Ken basin exhibits an increase in extreme dry events and a decrease in wet extremes. Cold extremes (T10) have also shown a decreasing trend across both regions. Investigation of different combinations of rainfall and temperature extremes reveals that moderate and extreme warm-dry CEEs have intensified over the past four decades, emerging as the most dominant compound events. The persistence of these events is largely driven by wind patterns and convective inhibition energy (CIN) in the case of moderate events, and by moisture transport and divergence for extreme ones. The intensification of such CEEs poses substantial risks to regional agriculture, eco-hydrological systems, and socioeconomic stability. Composite Resilience Index (CRI) was developed at the district level, integrating indicators like the Human Development Index, Multidimensional Poverty Index, and literacy rates. Results reveal that Ashoknagar, Shivpuri, Lalitpur, and Chhatarpur are the relatively low-resilience districts, while Bhopal, Sagar, Jhansi, and Hamirpur exhibit higher resilience. Overall, the findings underscore the urgent need for climate-informed policies and adaptive strategies to ensure water sustainability and socio-economic stability in the Ken–Betwa river catchments under a warming climate.

This study deals with the isotopic composition of monsoon precipitation in Southern Oman, specifically in the Salalah coastal plain and the adjacent Dhofar Mountains. Monsoon variability on the southern Arabian Peninsula has been described based on the oxygen isotope composition of various terrestrial archives, often on the millennial scale. However, the factors influencing the spatio-temporal variability of the oxygen isotope composition of today's monsoon precipitation have not yet been described for this region. Here, we present stable isotope ratios of oxygen and hydrogen for the Indian Summer Monsoon in the greater Salalah area. The precipitation amount-weighted mean isotope values along an elevation transect show lighter signatures at higher elevation, but generally low deuterium excess values ( d <10 ‰). To trace the origin and (short-term) history of the precipitation system, we applied a 3-step model incorporating evaporation of seawater, condensation, and sub-cloud evaporation. Our modelling exercise indicates that the classic elevation effect is quasi-negligible, and that sub-cloud evaporation is likely to be the main driver behind the encountered isotope pattern. This pseudo-elevation effect implies that the precipitation is not depleted in heavy isotopes with increasing elevation, but rather enriched with decreasing elevation. This effect may prevail in other (semi-arid) areas as well. • Monsoon precipitation was sampled at six sites along an elevation gradient in S-Oman. • Precipitation is isotopically lighter at higher elevations. • A 3-step model shows that the pattern is not caused by the classic elevation effect. • The system is governed by sub-cloud evaporation, causing a pseudo-elevation effect. • This effect may occur in other (semi-arid) areas too.

Abstract Monsoon Low-Pressure Systems (LPS) are significant rain-bearing storms during the Indian summer monsoon, yet their impact on the interannual variation of Indian Summer Monsoon Rainfall (ISMR) remains uncertain. This study revisits the relationship between LPS and ISMR variations and extreme rainfall events, emphasizing the role of LPS-generated rainfall. A strong correlation is observed between LPS-generated rainfall and ISMR variations; years with an excess of ISMR correspond to increased LPS-induced rainfall, whereas years with a decrease in ISMR show a decrease in LPS rainfall. The increase in LPS rainfall during excess years is primarily linked to higher rainfall rates, which arise from elevated background humidity and stronger vertical motions associated with LPS, thus making a substantial contribution to excess ISMR. Traditional LPS intensity indices indicate that the dynamical intensity exhibits only minor variation despite the higher rainfall rates, suggesting an apparent decoupling between precipitation rate and dynamical strength. In contrast, our analysis reveals that increased rain rates coincide with strengthened horizontal pressure gradients and higher wind speeds in the vicinity of the LPS vortex center. These conditions correspond to LPS that are more intense and spatially more confined during excess monsoon years than during drought years, pointing to a certain degree of coupling between the dynamical intensity of monsoon LPS and their rainfall rates.

Abstract Volcanic eruptions are known to modulate climate by introducing sulfate aerosols that cool the surface and warm the stratosphere. This study examines the Indian monsoon’s sensitivity to these contrasting mechanisms using the MIROC-ES2L model from the VolMIP-CMIP6 multi-model framework. While previous studies have shown complex interactions between surface cooling and stratospheric heating following volcanic eruptions, this study aims to decouple these processes and clarify their individual roles in modulating the Indian summer monsoon. By isolating surface dimming and stratospheric heating through controlled simulations, we aim to better understand how each radiative pathway influences monsoonal rainfall patterns and atmospheric circulation. Through targeted experiments emulating both the 1991 Pinatubo eruption and idealized tropical events, we isolate the roles of surface dimming and stratospheric radiative heating. We find that surface cooling significantly suppresses monsoonal rainfall by weakening the land-sea thermal contrast, while stratospheric warming exerts secondary dynamical effects. Additionally, the stratospheric aerosol forcing induces a pronounced zonal SST gradient in the Indian Ocean, resembling a positive Indian Ocean Dipole (IOD), which reinforces cross-equatorial flow and modulates regional circulation patterns. These findings underscore the importance of disentangling radiative pathways in understanding volcanic impacts on tropical rainfall systems. Our results have broader implications for decadal prediction, monsoon variability, and interpreting natural climate variability under anthropogenic warming.

Abstract The monsoon intraseasonal oscillation (MISO) modulates heavy precipitation during the Indian summer monsoon, but accurate rainfall simulation remains a challenge in state‐of‐the‐art models. Our analysis reveals a moisture bias in MISO using simulations from the sixth phase of the Coupled Model Intercomparison Project models. Despite an overestimated local moisture supply from the ocean in the Bay of Bengal (BoB), atmospheric moisture content before MISO‐induced heavy rainfall is underestimated. Model diagnoses reveal deficient zonal moisture advection in the low‐level troposphere as the primary constraint, attributable to a weaker intraseasonal Arabian Sea moisture source and a bias in the mean zonal winds. The latter inhibits the development of barotropic instability and the energy transfer to intraseasonal timescales. Consequently, the weakly simulated MISO leads to insufficient moisture supply over the BoB, resulting in failed simulation of heavy rainfall during MISO events. These findings highlight potential approaches for model improvements to enhance monsoon precipitation simulations.

Abstract Extreme glacier mass loss on the Tibetan Plateau (TP) has seldom been investigated, limiting our knowledge of regional water availability and glacier‐related natural hazards. Here we present glacier mass balance estimates for the south–central TP based on glacio‐meteorological observations and geodetic data from 1960 to 2019. The results show that the frequency, intensity, and variability of extreme glacier mass loss events have increased and shifted in recent decades. The extreme mass loss events are mainly attributed to the extremely high air temperature ( T a ) during the ablation season (June–September), which generates exceptionally high incoming longwave radiation and sensible heat fluxes that greatly reduce albedo and enhance melting. The high T a on the south–central TP is linked to that over the northeastern Indian subcontinent by enhanced southerly wind, which, as a component of the Indian summer monsoon, transports heat northward from the Indian subcontinent to the TP. The enhanced T a in both regions is further associated with European geopotential heights, western tropical Indian Ocean sea surface temperatures, and regional warming trends. This study demonstrates that glacier and climate changes on the TP are influenced by heat variations in the surrounding lowlands, where dominant winds associated with large‐scale atmospheric circulation transport the heat into the TP. Thus, further research on identifying key regions of surrounding lowlands that contribute to the climate changes on the TP, and mitigating climate warming in key heat‐source regions (e.g., Indian subcontinent), are crucial for the preservation of glaciers on the TP.

Abstract Over the past half-century, evolving Indian Summer Monsoon environment has led to an east-west asymmetric rainfall trend over the subcontinent. This emerging asymmetry is shaped by a marked rise in heavy rainfall events across western India. However, the mechanisms underlying this prominent signal of the changing regional hydroclimate are not well understood. Using Self-Organizing Maps, this study identifies two dominant atmospheric circulation patterns linked to a significant increase in the frequency of these extreme events over western India during 1970–2022. The first pattern is marked by a large-scale mid-level cyclonic vortex spanning the subcontinent and strong easterly anomalies over the Equatorial Indian Ocean. The pattern results from extensive synoptic low-pressure activity across central monsoon zone of India, reinforced by zonal sea surface temperature gradient at the Equatorial Indian Ocean and associated dynamic forcing. In contrast, the other pattern is manifested as a localized cyclonic vortex centred over western India, featured by an isolated synoptic low-pressure system. Moisture recycling from antecedent wet soil in Northwest India catalyses this local pattern during periods of subdued remote forcing. Our analyses link the rising frequency of heavy rains over western India to the combined effects of zonally differential warming across the Equatorial Indian Ocean and progressive soil moistening in semi-arid northwest India. Examining the complex interactions among extreme weather patterns, large-scale oceanic forcings, and local land-atmosphere coupling, this study highlights the need for an improved understanding of multi-scale interactions that reshape monsoon hydrological extremes in a changing climate.

ABSTRACT Reconstructing the hydroclimatic history of the karst region in southwestern China (SWC) since the last deglaciation is crucial for understanding the dynamics and evolution of the Asian monsoon and its influence on the chemical weathering of carbonate rocks. Numerous studies have reconstructed paleoenvironmental variability in this region using archives such as lacustrine sediments and stalagmites. However, studies utilizing peat archives that span this period remain limited, and the use of geochemical elements in such settings is underutilized. This study presents a comprehensive element dataset derived from non‐destructive X‐ray fluorescence core scanning of a 650‐cm‐long peat core collected from the southwestern Guizhou Plateau in SWC. Based on an age‐depth model established with 12 AMS 14 C dates, our findings indicate that geochemical proxies, including the Si/Ti, Ti/K, Zr/Rb, and Rb/Sr ratios, reflected in principal component 1 (PC1), primarily reflect exogenous elemental influx. Furthermore, arboreal pollen percentage correlates positively with PC1, suggesting that PC1 serves as a proxy for precipitation and associated catchment weathering processes. In contrast, the PC2 score covaries with yellowness (b*), tracking the growth and accumulation of peatland vegetation. These findings demonstrate the utility of elements and chroma from peat archives for interpreting environmental shifts in this karst region. The record reveals three distinct intervals since 14 000 cal. a BP: (i) from 14 000 to 4500 cal. a BP, generally humid punctuated by intermittent millennial‐scale dry events; (ii) from 4500 to 3600 cal. a BP, there was a shift in sedimentation patterns and a transition towards a drier climate marked by high instability; and (iii) from 3600 to 1400 cal. a BP, was a dry period characterized by minimal exogenous input but enhanced peatland vegetation biomass. Comparisons with regional and global records suggest that these hydroclimatic shifts in SWC were primarily modulated by Indian Summer Monsoon intensity, driven by the meridional migration of the Intertropical Convergence Zone (ITCZ) and El Niño–Southern Oscillation (ENSO) variability. This study provides valuable insights into the climatic and vegetation history of SWC, enhancing our understanding of the paleoenvironmental significance of elemental compositions in karst peat archives.