Showing papers on "Monsoon published in 2022"

Intraseasonal variability of global land monsoon precipitation and its recent trend

Abstract: Abstract Accurate prediction of global land monsoon rainfall on a sub-seasonal (2–8 weeks) time scale has become a worldwide demand. Current forecasts of weekly-mean rainfall in most monsoon regions, however, have limited skills beyond two weeks, calling for a more profound understanding of monsoon intraseasonal variability (ISV). We show that the high-frequency (HF; 8–20 days) ISV, crucial for the Week 2 and Week 3 predictions, accounts for about 53–70% of the total (8–70 days) ISV, generally dominating the sub-seasonal predictability of various land monsoons, while the low-frequency (LF; 20–70 days)’s contribution is comparable to HF only over Australia (AU; 47%), South Asia (SA; 43%), and South America (SAM; 40%). The leading modes of HFISVs in Northern Hemisphere (NH) monsoons primarily originate from different convectively coupled equatorial waves, while from mid-latitude wave trains for Southern Hemisphere (SH) monsoons and East Asian (EA) monsoon. The Madden-Julian Oscillation (MJO) directly regulates LFISVs in Asian-Australian monsoon and affects American and African monsoons by exciting Kelvin waves and mid-latitude teleconnections. During the past four decades, the HF (LF) ISVs have considerably intensified over Asian (Asian-Australian) monsoon but weakened over American (SAM) monsoon. Sub-seasonal to seasonal (S2S) prediction models exhibit higher sub-seasonal prediction skills over AU, SA, and SAM monsoons that have larger LFISV contributions than other monsoons. These results suggest an urgent need to improve the simulation of convectively coupled equatorial waves and two-way interactions between regional monsoon ISVs and mid-latitude processes and between MJO and regional monsoons, especially under the global warming scenarios.

Provincial and seasonal influences on heavy metals in the Noyyal River of South India and their human health hazards

Abstract: This study was carried out to evaluate the heavy metals (Lead (Pb), Nickel (Ni), Chromium (Cr), Copper (Cu), Cadmium (Cd) and Zinc (Zn)) pollution in the Noyyal River of South India by collecting 130 river water samples (65 each in pre- and post-monsoon). The heavy metals were measured using Atomic Absorption Spectrophotometer (AAS). The data were used to calculate the associated health hazards for the inhabitants consume river water. Correlation analyses and average concentration of heavy metals denoted that post-monsoon metal concentrations were lesser compared to the pre-monsoon due to dilution effect. Modified Contamination Degree (MCD) indicated that 45% of pre-monsoon and 25% of post-monsoon samples were classified under extremely polluted category. Heavy metal pollution index (HPI) showed that all the regions fall under highly polluted category except 'Region I' where 20% of samples were under safe category during the pre-monsoon, whereas 9%,28%, 17% and 26% of samples in Regions I, II, III and IV were highly polluted during the post-monsoon season, respectively. Ecological Risk Index (ERI) revealed that high risks attained in Regions II (78%) and III (82%) during pre-monsoon, and reduced risks found in Regions II (28%) and III (45%) during post-monsoon season due to dilution by monsoon rainfall. Non-carcinogenic risks as inferred by the Hazard Index (HI) indicated that 78% and 52% of samples for infants, 75% and 49% of samples for teens and 71% and 45% of samples for adults exceeded the threshold limits of USEPA (HI > 1) and possessed risks during pre- and post-monsoon, respectively. The cancer risk assessment based on ingestion of heavy metals indicated that the order of risk is Ni > Cr > Cu. The HI for infants and teens was notably high to that of adults in both the seasons. This study will be useful to develop effective strategies for improving river water quality and to reduce human health hazards.

Monitoring the causes of pollution using groundwater quality and chemistry before and after the monsoon

Abstract: The present study aims to assess the causes of pollution in groundwater before and after the monsoon in relation to water types, chemical elements, and their statistical variation in a rural region of Wanaparthy district, Telangana, India. Groundwater samples collected in both seasons were analyzed. Results indicated that pH, TDS, Ca2+, Mg2+, K+, Cl-, SO42−, and NO3− values were higher after the monsoon. The Overall Water Quality Index indicated that moderate (53.86%) and very low (20.18%) groundwater quality zones increased spatially during post-monsoon compared to pre-monsoon (35.22% and 4.77%, respctively). Piper's diagram showed that the transition from freshwater to mixed water type (70%) predominates in post-monsoon. Gibbs diagrams indicated 93.33% and 80% of groundwater samples had lithological influence before and after the monsoon, respectively. Genetic water quality classification revealed that 53% and 87% of groundwater samples showed Cl−−HCO3− type before and after the monsoon, respectively. The ionic ratios indicated the dominance of mineral weathering and dissolution, ion exchange, and evaporation in pre-monsoon, but they also indicated that anthropogenic pollution activities prevailed in post-monsoon, as confirmed by the high correlations between Cl-, SO42−, and NO3− ions and supported by land use practice. Principal component (PC) analysis captured three and four PCs with 80.795% and 78.532% of the total variance and eigenvalue greater than one (1.020–5.748) before and after the monsoon, respectively, which also supported human induced contamination in post-monsoon groundwater. PC scores (>1) identified index-wells for regularly monitoring groundwater quality and also assessed pollution causes for proper management planning to reduce cost and protect the aquifer system.

Investigating the contrast diurnal relationship of land surface temperatures with various surface parameters represent vegetation, soil, water, and urbanization over Ahmedabad city in India

Abstract: Many climatic problems have arisen due to congested and inefficient planning, reduced vegetation cover, and increased pollution from factories and vehicles. One such primary concern is increased land surface temperature (LST) contributes to the urban heat island (UHI) occurrence. This research aims to understand better the UHI effect in the region neighbouring the Indian city of Ahmedabad. MODIS sensor data (onboard Aqua and Terra platforms) and Landsat data were used for the study. The research was done for the summer, monsoon, and winter seasons in the research region, using data from thirteen years between 2003 and 2015. The current study looked at LSTs' spatial and temporal differences to assess the SUHI effect over Ahmedabad city. The association between diurnal LST and various surface variables such as vegetation, built-up, soil, water, and so on has also been examined. A variety of land surfaces influences the diurnal variations of LSTs. The diurnal associations of LST with vegetation, urbanization, soil, and water factors have been studied. The overall study of LST' relationship with all of the various parameters reveals a very significant dynamic relationship.

Genesis and Trends in Marine Heatwaves Over the Tropical Indian Ocean and Their Interaction With the Indian Summer Monsoon

Abstract: Marine heatwaves (MHWs) are extreme oceanic warm water events (above 90th percentile threshold) that significantly impact the marine environment. Recent studies have explored the genesis and impacts of MHWs in the global oceans though they are least understood in the tropical Indian Ocean. Here we investigate the genesis and trend of MHWs in the Indian Ocean during 1982–2018 and their role in modulating the Indian summer monsoon. We find that the rapid warming in the Indian Ocean plays a critical role in increasing the number of MHWs. Meanwhile, the El Niño has a prominent influence on the occurrence of MHWs during the monsoon. The Indian Ocean warming and the El Niño variability have synergistically resulted in some of the strongest and long-lasting MHWs in the Indian Ocean. The western Indian Ocean region experienced the largest increase in MHWs at a rate of 1.2–1.5 events per decade, followed by the north Bay of Bengal at a rate of 0.4–0.5 events per decade. Locally, the MHWs are induced by increased solar radiation, relaxation of winds, and reduced evaporative cooling. In the western Indian Ocean, the decreased winds further restrict the heat transport by ocean currents from the near-equatorial regions toward the north. Our analysis indicates that the MHWs in the western Indian Ocean and the north Bay of Bengal lead to a reduction in monsoon rainfall over the central Indian subcontinent. On the other hand, there is an enhancement of monsoon rainfall over southwest India due to the MHWs in the Bay of Bengal.

Warming-induced monsoon precipitation phase change intensifies glacier mass loss in the southeastern Tibetan Plateau

Abstract: Significance Rapid mass loss of glaciers in High Mountain Asia has large consequences for downstream water supply and glacier-related hazards. Glaciers in the southeastern Tibetan Plateau are experiencing the highest mass loss rates within Asia, despite the limited impact of recent warming on their spring accumulation regime. Based on model simulations reconstructing the climate and glacier evolution of the last 45 y, we show that the recent acceleration in observed glacier mass loss was effected by a warming-induced shift from snowfall to rainfall during the monsoon months, exacerbated by decreasing monsoon precipitation since the 2000s and only partly mitigated by increasing spring precipitation. Our results reveal the processes behind the high sensitivity to climate warming for glaciers in this region.

Heavy metal pollution in groundwater of urban Delhi environs: Pollution indices and health risk assessment

Abstract: The excess presence of heavy metals in water resources deteriorates the quality and has a high potential for bioaccumulation and environmental contamination. The study of heavy metals in water is essential because of their integration in the food chain and the potential for sublethal effects on aquatic and human life. To understand the extent of heavy metal pollution, a total of 64 groundwater samples (32 in each pre-and post-monsoon season) were collected around the Yamuna River's flood plains in the Delhi region. In this study, pollution indices and health risk assessment methodologies were used to estimate the significant threat to humans. In examined seasons, the sequence of heavy metal content in groundwater is Fe > Mn > Zn > B > As>Ni > Pb. The heavy metal pollution index (HPI) revealed that in the pre-and post-monsoon seasons, 53% and 44% (HPI >100), of groundwater samples are at high-risk zone respectively. 53% of pre-monsoon and 56% of post-monsoon samples were found highly polluted, according to the degree of contamination (Cd). Moreover, health risk assessment shows that hazard index (HI) values for heavy metals were found significantly high (HI >1) in groundwater samples inferring increased non-cancerous risk to the local community. The results imply that continuous exposure can lead to chronic diseases in the population residing in the study region. In both carcinogenic and non-carcinogenic assessments, children's hazard index and carcinogenic risk assessment (CR) scores were found higher. As a result, compared to adults in the study region, children are more vulnerable to potential health threats. The principal component analysis (PCA) method was used to figure out the origin of heavy metals, and it was found that As, Fe, Mn, and Zn come from non-anthropogenic sources, whereas mixed sources (natural and anthropogenic) may be responsible for B, Ni, and Pb presence. The results of the study will help to develop an effective strategy for environmental assessment and monitoring to control groundwater pollution of the Delhi urban environs.

Effects of anthropogenic aerosol and greenhouse gas emissions on Northern Hemisphere monsoon precipitation: mechanisms and uncertainty

Abstract: Northern Hemisphere Land monsoon precipitation (NHLM) exhibits multidecadal variability, decreasing over the second half of the 20st century and increasing after the 1980s. We use a novel combination of CMIP6 simulations and several large ensembles to assess the relative roles of drivers of monsoon precipitation trends, analyzing the effects of anthropogenic aerosol (AA), greenhouse gas (GHG) emissions and natural forcing. We decomposed summer global monsoon precipitation anomalies into dynamic and thermodynamic terms to assess the drivers of precipitation trends. We show that the drying trends are likely to be mainly due to increased AA emissions, which cause shifts of the atmospheric circulation and a decrease in moisture advection. Increases in GHG emissions cause monsoon precipitation to increase due to strengthened moisture advection. The uncertainty in summer monsoon precipitation trends is explored using three initial condition large ensembles. AA emissions have strong controls on monsoon precipitation trends, exceeding the effects of internal climate variability. However, uncertainties in the effects of external forcings on monsoon precipitation are high for specific periods and monsoon domains, and due to differences in how models simulate shifts in atmospheric circulation. The effect of AA emissions is uncertain over the northern African monsoon domain, due to differences among climate models in simulating the effects of AA emissions on net shortwave radiation over the North Atlantic Ocean.

Geochemical characterization, deciphering groundwater quality using pollution index of groundwater (PIG), water quality index (WQI) and geographical information system (GIS) in hard rock aquifer, South India

Abstract: Abstract Fifty groundwater samples were obtained pre and post-monsoon seasons in parts of hard rock terrain in Andhra Pradesh, South India, in order to assess the drinking water quality. PIG values of groundwater samples ranged from 0.95–1.53 and 0.83–1.28 during pre and post-monsoon seasons. PIG values are slightly higher in the pre-monsoon season when compared to the post-monsoon season. In the pre monsoon season, 96% of the groundwater samples showed insignificant pollution class (< 1), 4% of the groundwater samples are low pollution (1–1.5). 82% of the groundwater samples showed insignificant pollution status (< 1), 18% of the groundwater samples fall under the low pollution (1–1.5), is noticed in post-monsoon season, respectively. WQI values of groundwater samples ranged from 108.5–204 mg/L and 112.6–170 mg/L during pre and post-monsoon seasons; its shows that 100% are very poor for drinking purpose. Piper diagram reveals that groundwater is majorly mixed Ca 2+ -Mg 2+ -Cl − , Ca 2+ -Mg 2+ -Cl − -SO 4 2− , Na + -K + -Cl − - SO 4 2− type in this region. The Gibbs plot indicates that groundwater samples fall within the field of rock dominance. Through applying GIS techniques, the spatial distribution of groundwater quality analysis reveals that most of the groundwater samples do not comply drinking water quality standards and water needs to be prior treatment before consumption.

Tropical volcanism enhanced the East Asian summer monsoon during the last millennium

Abstract: Abstract Extreme East Asian summer monsoon (EASM) rainfall frequently induces floods that threaten millions of people, and has been generally attributed to internal climate variability. In contrast to the hydrological weakening theory of volcanic eruptions, here we present convergent empirical and modeling evidence for significant intensification of EASM rainfall in response to strong tropical volcanic eruptions. Our multi-proxy analyses show a significantly increased EASM in the first summer after tropical eruptions from 1470 AD to the present, and the more frequent occurrence of El Niños in the first boreal winter after eruptions is necessary for the enhanced EASM. Model simulation ensembles show that a volcano-induced El Niño and the associated stronger than non-volcanic El Niño warm pool air-sea interaction intensify EASM precipitation, overwhelming volcanic-induced moisture deficiency. This work sheds light on the intertwined relationship between external forcing and internal climate variability and potential flood disasters resulting from tropical volcanic eruptions.

Runoff and sediment response to deforestation in a large Southeast Asian monsoon watershed

Abstract: • Hydrological and sedimentary changes from 1981 to 2015 in the UCPRB of Thailand are analyzed. • The hydrological and sedimentary responses to deforestation are quantified. • Precipitation increase and deforestation dominated the runoff increase, and deforestation dominated the sediment increase. Deforestation has been reported to increase annual streamflow, baseflow, and sediment load in many parts of the world. However, studies about the hydrological effects of deforestation are scant in the tropical monsoon region. In this study, these effects were examined in the Upper Chao Phraya River basin (UCPRB) which is a typical tropical monsoon basin and is an important area of water resources in Thailand. A significant breakpoint for annual streamflow and annual precipitation in the entire UCPRB is identified as 1993, and this breakpoint is also identified for annual baseflow in most upstream sub-basins during the past decades (1981–2015). Significant increasing trend is detected in the annual suspended sediment load of the Wang River sub-basin. Land use maps generated by a CA-Markov model suggest that continuous deforestation occurred during the study period. The contributions of climate change and deforestation to the hydrological and sedimentary changes are then attributed within the Budyko Framework. Precipitation increment dominates the annual streamflow increment in the entire UCPRB and the annual baseflow increment in the Ping River sub-basin, and deforestation dominates the annual streamflow increment in the upstream sub-basins, the annual baseflow increment in most of the upstream sub-basins, and the increasing suspended sediment load in the Wang River sub-basin. The hydrological and sedimentary response to deforestation is then quantified. In the entire UCPRB, one percent reduction of the forest cover can increase the annual streamflow by 1.9%. In the upstream sub-basins, one percent reduction of the forest cover can increase the annual streamflow and annual baseflow by 2.5%–5.4% and 2.6%–6.7%, respectively. One percent reduction of the forest cover can increase the annual suspended sediment load by 8.7%. These findings will help develop better understanding of land use management in the UCPRB for water-soil conservation.

Observationally constrained projection of Afro-Asian monsoon precipitation

Abstract: Abstract The Afro-Asian summer monsoon (AfroASM) sustains billions of people living in many developing countries covering West Africa and Asia, vulnerable to climate change. Future increase in AfroASM precipitation has been projected by current state-of-the-art climate models, but large inter-model spread exists. Here we show that the projection spread is related to present-day interhemispheric thermal contrast (ITC). Based on 30 models from the Coupled Model Intercomparison Project Phase 6, we find models with a larger ITC trend during 1981–2014 tend to project a greater precipitation increase. Since most models overestimate present-day ITC trends, emergent constraint indicates precipitation increase in constrained projection is reduced to 70% of the raw projection, with the largest reduction in West Africa (49%). The land area experiencing significant increases of precipitation (runoff) is 57% (66%) of the raw projection. Smaller increases of precipitation will likely reduce flooding risk, while posing a challenge to future water resources management.

Spatial and seasonal isotope variability in precipitation across China: Monthly isoscapes based on regionalized fuzzy clustering

Abstract: The spatial patterns of stable hydrogen and oxygen isotopes in precipitation (precipitation isoscapes) provide a geographic perspective to understand the atmospheric processes in modern environment and paleoclimate records. Here we compiled stable isotope data in modern precipitation at 223 sites across China and 48 in surrounding countries, and used regionalized fuzzy clustering to create monthly precipitation isoscapes for China (C-Isoscape). Based on regressions using spatial and climatic parameters for twelve months, the best-fitting equations were chosen for four climate clusters, and then the four layers were weighted using fuzzy membership. The moisture transportation path, controlled by the westerlies and the monsoon, results in different spatial and seasonal diversity of precipitation isotopes. Based on C-Isoscape, we determined a nationwide meteoric water line as δ2H = 7.4δ18O + 5.5 using least squares regression or δ2H = 8.0δ18O + 10.2 using precipitation weighted reduced major axis regression. Compared with previous global products, the C-Isoscape usually shows precipitation more enriched in 18O and 2H in summer and more depleted in winter for northwest China, while the C-Isoscape values are more enriched in heavy isotopes in most months for southwest China. The new monthly precipitation isoscapes provide an accurate and high-resolution mapping for Chinese precipitation isotopes, allowing for future intra-annual atmospheric process diagnostics using stable hydrogen and oxygen isotope in precipitation in the region.

Black carbon-climate interactions regulate dust burdens over India revealed during COVID-19

Abstract: Abstract India as a hotspot for air pollution has heavy black carbon (BC) and dust (DU) loadings. BC has been identified to significantly impact the Indian climate. However, whether BC-climate interactions regulate Indian DU during the premonsoon season is unclear. Here, using long-term Reanalysis data, we show that Indian DU is positively correlated to northern Indian BC while negatively correlated to southern Indian BC. We further identify the mechanism of BC-dust-climate interactions revealed during COVID-19. BC reduction in northern India due to lockdown decreases solar heating in the atmosphere and increases surface albedo of the Tibetan Plateau (TP), inducing a descending atmospheric motion. Colder air from the TP together with warmer southern Indian air heated by biomass burning BC results in easterly wind anomalies, which reduces dust transport from the Middle East and Sahara and local dust emissions. The premonsoon aerosol-climate interactions delay the outbreak of the subsequent Indian summer monsoon.

Limited influence of irrigation on pre-monsoon heat stress in the Indo-Gangetic Plain

Abstract: Abstract Hot extremes are anticipated to be more frequent and more intense under climate change, making the Indo-Gangetic Plain of India, with a 400 million population, vulnerable to heat stress. Recent studies suggest that irrigation has significant cooling and moistening effects over this region. While large-scale irrigation is prevalent in the Indo-Gangetic Plain during the two major cropping seasons, Kharif (Jun-Sep) and Rabi (Nov-Feb), hot extremes are reported in the pre-monsoon months (Apr-May) when irrigation activities are minimal. Here, using observed irrigation data and regional climate model simulations, we show that irrigation effects on heat stress during pre-monsoon are 4.9 times overestimated with model-simulated irrigation as prescribed in previous studies. We find that irrigation increases relative humidity by only 2.5%, indicating that irrigation is a non-crucial factor enhancing the moist heat stress. On the other hand, we detect causal effects of aerosol abundance on the daytime land surface temperature. Our study highlights the need to consider actual irrigation data in testing model-driven hypotheses related to the land-atmosphere feedback driven by human water management.

Neogene South Asian monsoon rainfall and wind histories diverged due to topographic effects

Abstract: The drivers of the evolution of the South Asian Monsoon remain widely debated. An intensification of monsoonal rainfall recorded in terrestrial and marine sediment archives from the earliest Miocene (23–20 million years ago (Ma)) is generally attributed to Himalayan uplift. However, Indian Ocean palaeorecords place the onset of a strong monsoon around 13 Ma, linked to strengthening of the southwesterly winds of the Somali Jet that also force Arabian Sea upwelling. Here we reconcile these divergent records using Earth system model simulations to evaluate the interactions between palaeogeography and ocean–atmosphere dynamics. We show that factors forcing the South Asian Monsoon circulation versus rainfall are decoupled and diachronous. Himalayan and Tibetan Plateau topography predominantly controlled early Miocene rainfall patterns, with limited impact on ocean–atmosphere circulation. The uplift of the East African and Middle Eastern topography played a pivotal role in the establishment of the modern Somali Jet structure above the western Indian Ocean, while strong upwelling initiated as a direct consequence of the emergence of the Arabian Peninsula and the onset of modern-like atmospheric circulation. Our results emphasize that although elevated rainfall seasonality was probably a persistent feature since the India–Asia collision in the Paleogene, modern-like monsoonal atmospheric circulation only emerged in the late Neogene. A modern-like South Asian Monsoon only appeared when East African and Middle Eastern uplift led to the establishment of the Somali Jet around 13 million years ago, according to Earth system modelling using a range of regional palaeogeographies.