Monsoon Rainfall Research Articles

Unraveling the role of the western North Pacific circulation anomaly in modulating Indian summer monsoon rainfall variability beyond ENSO

The Indian summer monsoon (ISM) rainfall interannual variability is known to be strongly linked to the El-Niño–Southern Oscillation (ENSO). This linear relationship is the primary factor in controlling the interannual variation in ISM precipitation. However, there are many outlier cases, and such deviations pose significant challenges in seasonal prediction over this region. Here we show that such challenges can be attributed to anomalous atmospheric pressure patterns in the Western North Pacific (WNP) region. The anticyclonic circulation anomaly over WNP region causes the easterly wind toward the Indian subcontinent, leading to positive precipitation anomalies with stronger low-level moist convergence, while the cyclonic circulation decreases ISM precipitation. The linear baroclinic model simulation results further support that the WNP circulation pattern can serve as an independent factor for forecasting precipitation over India. The WNP circulation anomaly play the crucial role generating ISM precipitation particularly for July and September. Our study suggests that the role of the WNP circulation anomaly should be carefully considered as the secondary prevailing mechanism on the subseasonal timescale during the boreal summer in addition to the ENSO signal.

Assessment of Spatial Variation in Terrain Parameters Impacting Surface and Groundwater Quality for Sustainable Geo-Environmental Management

Soil and water conservation measures crucial for quality enhancement should focus on terrain-specific challenges. Evaluating groundwater resources from wells in the area is essential to ascertain their appropriateness for different applications. In semiarid tropical regions, the risk of inland salinity can escalate under extreme conditions like droughts and reduced monsoonal rainfall. During droughts, the groundwater table declines, leading to deterioration in groundwater quality, making it unsuitable for consumption, industrial processes, and arboriculture. In this scenario, analysing the spatial variation in water quality parameters becomes crucial for safeguarding environmental geology and effectively managing the geo-environment of impacted regions. Unfavourable geo-environmental conditions can be mitigated by reducing surface and groundwater pollution, sheet erosion, landslides, and land subsidence. Examining the variation in groundwater quality across both spatial and temporal dimensions is necessary to recommend treatments that make groundwater suitable for various uses, including potable purposes. The spatial as well as temporal variations of different water quality parameters, determined through a composite water quality index, can inform land use alterations, resource exploitation without unacceptable consequences, and artificial recharge measures that do not pollute the geo-environment. Enhancing the sustainability of the geo-environment can be achieved by investigating and prioritizing conservation measures and practices. Employing temporal remote sensing alongside related datasets facilitates the assessment of delineated watersheds within the region through the Analytical Hierarchy Process (AHP) Model. This approach is essential for prioritizing watersheds and formulating strategic action plans to sustain a balanced geo-environment.

Sustainable Water Resource Planning for Alanda Micro Watershed Using Geospatial Techniques

Groundwater is a vital natural resource, especially in areas lacking surface water bodies. About one-third of the global population relies on it for drinking, irrigation and industrial purposes. However, excessive and unregulated exploitation has led to a rapid decline in water tables, emphasizing the need for sustainable groundwater management. The Alanda micro watershed in Barshitakli Taluka, Akola District, Maharashtra, spans 11.39 km², with a sub-humid climate and uneven monsoon rainfall averaging 780 mm. The region faces high water stress in summer, with dried bore wells and farmers relying on rain and groundwater for irrigation. The water resource development plan for Alanda micro watersheds integrates GIS, remote sensing and AHP to identify groundwater potential zones. The Alanda micro watershed soil and water conservation plans were developed using GIS, remote sensing and the AHP method. Thematic maps were overlaid in ArcGIS, applying weighted factors from a pairwise comparison matrix to identify groundwater potential zones. These zones, categorised as high, moderate and low potential, highlight that the largest area has moderate potential, suggesting good opportunities for conservation measures. The survey of the study area identified existing soil and water conservation structures, including 3 farm ponds, 1 check dam and a contour bund. Additional recommendations include 5 farm ponds, 4 check dams, contour trenches and bunding measures, along with agronomic practices for effective surface and groundwater management.

A New Paradigm for Active–Break Cycle in the Indian Summer Monsoon

Abstract A multichannel singular spectrum analysis of 121 years of daily rainfall over India and 43 years of outgoing longwave radiation and horizontal wind has revealed two dominant intraseasonal oscillations (ISOs) that describe the space–time variability of monsoon rainfall. The two nonlinear oscillations are not perfectly periodic but exhibit broadband spectra centered at 45 and 28 days. These modes have coherent and near-regular spatial structure and temporal variations. This study posits that the two nonlinear oscillations provide a consistent and comprehensive framework to study the variability and predictability of intraseasonal rainfall variations. The active and break cycles of monsoon rainfall over India have been traditionally defined by using an arbitrarily chosen duration of persistence of arbitrarily chosen amount of rainfall averaged over an arbitrarily chosen area. This study shows that the phases of the two objectively derived modes of variability provide an objective method for defining the active and break cycles. The two ISOs are further shown to make negligible contribution to the seasonal mean rainfall and its interannual variability. This study proposes that the investigations of the origins of these nonlinear modes, and modulations of their amplitudes and phases, provide a new paradigm for future research on validation and predictability of intraseasonal variations in climate models.

Interannual variation of summer southwest monsoon rainfall over the monsoon core regions of the eastern Bay of Bengal and its relationship with oceans

The study looked at how summer monsoon rainfall in the eastern Bay of Bengal area changes from year to year due to Indian Ocean Dipole (IOD) and El Niño Southern Oscillation (ENSO). Study used rainfall data and sea surface temperature data to see these variations. It's found that during ENSO positive phase, rainfall decreased in the eastern coastal region of the Bay of Bengal but increased in the northern Indo-Myanmar region. The opposite happened during ENSO negative phase. The study used a special analysis method called EOF and Morlet wavelet power-spectrum analysis to look for important patterns in the rainfall data and did correlation analysis to understand what causes abnormal rainfall in these regions. The study also found that the local convection and water vapor flux during ENSO positive phase are related to the anomalous rainfall in the Monsoon Core region. Rainfall is made stronger by the unusual anticyclone circulation in the upper troposphere. A strong/weak Mainland Indochina southwest monsoon (MSwM) in the positive or negative phase of ENSO can bring excess/less moisture to wet/dry the local southwest summer rainfall. In northern Indo-Myanmar, the anomalous rainfall is not only relied on the intensity of the MSwM but also the frequency of western disturbances also influences the regional rainfall, and further study need to develop.

Late Holocene vegetation history and monsoonal climate change from the Core Monsoon Zone of India

To understand the vegetation response to climate change and the Indian Summer Monsoon rainfall (ISMR) variability during the Late Holocene (approx. 2.5 ka), pollen analysis was conducted on a 1.2-m-long lacustrine sediment profile from the Korba District of Chhattisgarh, central India, within the core monsoon zone (CMZ). The pollen evidence suggest that between approx. 2500 and 1950 cal yr BP, open tropical deciduous forest vegetation occupied the landscape under a warm and relatively less humid climate, coupled with decreased ISMR. Between approx. 1950 and 1035 cal yr BP, a warm and relatively more humid climate prevailed, along with moderate ISMR, leading to the transition of the existing vegetation to an open mixed tropical deciduous forest. Between approx.1035 and 220 cal yr BP (CE 915–1730), the mixed tropical deciduous forest became established under a warm and humid climate with increased ISMR, coinciding globally with the Medieval Climatic Anomaly (MCA). Mixed tropical deciduous forest expanded and transformed into a dense mixed tropical deciduous forest between approx. 220 cal yr BP to the present (CE 1730 onwards). This transformation occurred under a warm and relatively more humid climate, accompanied by intensified ISMR, aligning with the Current Warm Period (CWP). Gradual forest transformation from open vegetation to dense mixed tropical deciduous forests, as well as in the ISMR has been observed since the last approx. 2.5 ka in central India. Cereal-based agricultural practices and other anthropogenic activities have been documented in the study area since approx. 2.5 ka, with an accelerated pace observed from 1035 cal yr BP to the present.

Influences of Central and Eastern Atlantic Niño on the West African and South American summer monsoons

The rainfall variabilities of the West African and South American summer monsoons, pivotal for local and global climate systems, are strongly influenced by tropical Atlantic sea surface temperature anomalies. This study investigates the impacts of two recently identified Atlantic Niño types, central and eastern Atlantic Niño (CAN and EAN), on these monsoon systems using observational data and numerical experiments. During boreal summer, EAN events exhibit increased rainfall over West Africa compared to CAN events, indicating a strengthened West African summer monsoon. Enhanced moisture flux convergence from eastern Atlantic warming drives these wetting conditions during EAN events. Conversely, CAN events have a more pronounced influence on South American monsoon rainfall during austral summer, causing a rainfall anomaly dipole between the Amazon and eastern Brazil, suggesting an eastward shift in the South American summer monsoon rainfall belt. These rainfall changes are linked to cyclonic circulation anomalies over the southwest Atlantic Ocean, attributed to central Atlantic warming during CAN events. Furthermore, a statistical model assesses hindcast skills of rainfall variability in the two summer monsoon regions, affirming the benefits of separating Atlantic Niño into CAN and EAN events for improved seasonal climate predictions.

Wet and dry spell induced changes in the soil CO2 effluxes of Pine and Oak ecosystems of Central Himalaya: a comparative assessment for monsoon and winter seasons.

Soil efflux of CO2( ) is known to be dependent on natural drying and rewetting of the soil. Although the central Indian Himalayan region is predominantly occupied with two ecosystems, i. e. Pine (Pinus roxburghii) and Oak (Quercus leucotrichophora), differences in their dynamics and responses of to varying wet and dry spells were hardly known. To address this knowledge gap, this study provides a comparative assessment of variability from Pine and Oakecosystems of central Himalaya as a response to rainfall induced wet and dry spells of monsoon and winter seasons. The data presented in this study are collected for242 days of 2021-22 that include monsoon and winter seasons from a Pine and an Oak sites. The mean sof Pine and Oak sites are found to be 3.95(± 0.02) and 3.61(± 0.01) μmol.m-2.s-1, respectively. We find that the winter reduction in the in comparison to monsoon at the Pine site (78%) is more substantial than at Oak site (64.6%). The cross wavelet spectra of and monsoon rainfall amount at the Oak site, unlike the Pine site, indicate a negative relationship. The rainfall spell duration and amount of monsoon wet spells are noted to have an inverse relationship with at both sites, although, increasing rainfall spell duration in winter is noted to increase at Pine and Oak sites. Similarly, increasing is observed with increasingdry spells of monsoon at both sites. Results of this study indicate that in comparison to Oak, variability at Pine ecosystem is primarily driven by abiotic factors wherein wet spell is a major determinant.

Determining dengue infection risk in the Colombo district of Sri Lanka by inferencing the genetic parameters of Aedes mosquitoes

BackgroundFor decades, dengue has posed a significant threat as a viral infectious disease, affecting numerous human lives globally, particularly in tropical regions, yet no cure has been discovered. The genetic trait of vector competence in Aedes mosquitoes, which facilitates dengue transmission, is difficult to measure and highly sensitive to environmental changes.MethodsIn this study we attempt, for the first time in a non-laboratory setting, to quantify the vector competence of Aedes mosquitoes assuming its homogeneity across both species; aegypti and albopictus and across the four Dengue serotypes. Estimating vector competence in relation to varying rainfall patterns was focused in this study to showcase the changes in this vector trait with respect to environmental variables. We quantify it using an existing mathematical model originally developed for malaria in a Bayesian inferencing setup. We conducted this study in the Colombo district of Sri Lanka where the highest number of human populations are threatened with dengue. Colombo district experiences continuous favorable temperature and humidity levels throughout the year creating ideal conditions for Aedes mosquitoes to thrive and transmit the Dengue disease. Therefore we only used the highly variable and seasonal rainfall as the primary environmental variable as it significantly influences the number of breeding sites and thereby impacting the population dynamics of Aedes.ResultsOur research successfully deduced vector competence values for the four identified seasons based on Monsoon rainfalls experienced in Colombo within a year. We used dengue data from 2009 - 2022 to infer the estimates. These estimated values have been corroborated through experimental studies documented in the literature, thereby validating the malaria model to estimate vector competence for dengue disease.ConclusionOur research findings conclude that environmental conditions can amplify vector competence within specific seasons, categorized by their environmental attributes. Additionally, the deduced vector competence offers compelling evidence that it impacts disease transmission, irrespective of geographical location, climate, or environmental factors.

Assessment of the Heavy Metal Contaminations of Roadside Soil in Aizawl, Mizoram (India): An In-Depth Analysis Utilising Advanced Scientific Methodologies

The study was conducted to evaluate the heavy metal contamination levels in the roadside soil of Aizawl, Mizoram (India). Twelve sites were sampled monthly from August 2020 to July 2021, and concentrations of copper (Cu), iron (Fe), manganese (Mn), nickel (Ni), lead (Pb), and zinc (Zn) were analyzed using atomic absorption spectrometer. The concentrations of heavy metals at the twelve studied sites varied widely from 0.43-1.06, 20.54-21.21, 2.69-3.41, 0.25-0.54, 0.31-0.49 and 1.35-1.77 for Cu, Fe, Mn, Ni, Pb, and Zn respectively. Pollution assessment tools such as the pollution load index, geo-accumulation index, and enrichment factor indicated moderate pollution levels. The study also observed fluctuations in the contamination levels due to the monsoon rainfall and the COVID-19 pandemic lockdown. Principal component analysis identified vehicular emissions, industrial activities, and atmospheric deposition as the potential sources of heavy metal contamination, with varying patterns observed at each site. While the observed heavy metal concentrations generally met permissible limits, the elevated levels suggested anthropogenic influences. It is crucial to continuously monitor and manage heavy metal contamination to mitigate potential health risks associated with heavy metal exposure.

Influence of weather research and forecasting model microphysics and cumulus schemes for forecasting monsoon rainfall over the Kelani River basin, Sri Lanka

ABSTRACT Creating precise quantitative precipitation forecasts is essential for reducing losses and damages. This study aimed to identify the best microphysics and cumulus schemes for forecasting monsoon rainfall over the Kelani River basin, Sri Lanka, using the WRF-ARW model. Four extreme rainfall events from the 2020 and 2021 monsoon seasons were simulated with various microphysics and cumulus parameterizations to find the optimal combinations. These combinations were then tested for their ability to forecast two monsoon events with a 24-h lead time. Simulated and forecasted rainfalls were compared with observations from 15 gauging stations. Results indicate that WSM3 and WSM6 microphysics schemes with the Betts–Miller–Janjic (BMJ) cumulus scheme are optimal for simulating rainfall, with WSM3_BMJ being the most suitable for forecasting. The findings of this study provide valuable initial data for research in regions with similar environmental conditions, offering insights into the suitability of various physics schemes for simulating and forecasting monsoon rainfall, particularly under extreme conditions. Furthermore, given the prevalence of monsoons in many tropical and subtropical climates, these results will be instrumental in enhancing the use of numerical weather prediction models for forecasting monsoon rainfall on a global scale.

Trend Analysis and Change Point Detection of Climatic Parameters in Ambedkar Nagar District of Uttar Pradesh, India

Climate change is one of the most serious challenges confronting humanity today, and its effects can be seen all over the world. The assessment of changes in the long-term weather trend is critical for developing water resource management strategies under climate change scenarios. Long-term trends for annual, monsoon, non-monsoon rainfall, rainy days, maximum temperature, and minimum temperature of Akbarpur, Allapur, Bhiti, Jalalpur, and Tanda stations in Uttar Pradesh's Ambedkar Nagar district were examined in this study. The Mann-Kendall test revealed a non-significant decreasing trend for annual and monsoon rainfall at Akbarpur, Bhiti, and Jalalpur stations with an average rate of 1.64 mm/year whereas, it shows a non-significant increasing trend for annual and monsoon rainfall at the Allapur and Tanda stations with an average rate of 3.168 mm/year. Non-monsoon rainfall showed an in-significant decreasing trend at Allapur and Jalalpur stations with an average rate of 0.415 mm/year, whereas a non-significant increasing trend was shown at Akbarpur, Bhiti, and Tanda stations with an average rate of 0.197 mm/year. Annual rainy days shows non-significant decreasing trend for all stations of Akbarpur district with an average rate of 0.117 day/year (one day decrease with in nine year). It indicates seasonal shift and increased possibility of high intensity rainfall. The impact of extreme events of rainfall on the trend was evaluated on the whole and partial series before and after the break point and it was observed that there was no significant climate change in Ambedkar Nagar district and non-significant changing year of precipitation data series was found in 1995. A significant increasing trend in maximum temperature was observed for all stations in the months of August and December, with an average rate of 0.02 0C per year, while Allapur station also shows a significant increasing trend in maximum temperature in September, with a rate of 0.012 0C per year. However, a significant decreasing trend was observed in minimum temperature in the month of May at Akbarpur, Allapur, Jalalpur, Tanda station with an average rate of 0.027 0C per year. Rainfall and temperature are a principal climatic parameter which regulates the environmental condition of a particular region by directly influencing the agricultural productivity and water resources.

Reasons for 2022 deficient Indian summer monsoon rainfall over Gangetic Plain

Reasons for 2022 deficient Indian summer monsoon rainfall over Gangetic Plain

Opposing Changes in Indian Summer Monsoon Rainfall Variability Produced by Orbital and Anthropogenic Forcing

AbstractFuture projections indicate that Indian Summer Monsoon Rainfall (ISMR) faces a “wetter and more variable” climate. However, the reasons remain uncertain. The Last Interglacial (LIG) climate provides a potential analog for future warming. Investigating ISMR responses to these two warming scenarios could help understand the causes of ISMR changes. Using PMIP4 simulations, we find that ISMR became “wetter and more stable” during the LIG, contrasting the future climate. The opposing changes in ISMR variability are related to divergent changes in the El Niño‐Southern Oscillation (ENSO) amplitudes, ENSO‐ISMR relationships, and ENSO‐induced large‐scale atmospheric circulation anomalies. During the LIG, orbital forcing weakened ENSO variability and its impacts on ISMR. A westward positioning of ENSO shifted the atmospheric circulation anomalies westward, suppressing extreme ISMR anomalies. These processes are supported by atmospheric model simulations. Our results suggest that different warming patterns (dynamic effects) are more critical than moisture‐increasing effects in controlling regional climate variability.

Formation mechanisms and biogeochemical response of coastal salinity front in the central eastern Arabian Sea

This study investigates the formation mechanisms and impact of a coastal salinity front observed in the central eastern Arabian Sea (EAS) coast, particularly off Mangalore (∼13°N), during the peak summer monsoon in August 2018. The interplay of intense monsoon rainfall, river runoff and coastal upwelling created a dynamic frontal zone characterised by distinct physical and biogeochemical properties in the central EAS. The study revealed that observed salinity fronts are formed due to the breaking of freshwater lenses by strong upwelled waters and the subsequent offshore transport of low-salinity plumes by prevailing current and Ekman transport. The high nutrient concentrations enhanced the chlorophyll a concentration 15–20 times higher (10.12 mg/m3) in the frontal zone compared to the non-frontal station. The dominance of diatoms in the frontal zone indicates herbivorous control in the coastal food web. Accumulation of plastic debris and foam-like particles in the frontal zone poses ecological risks and threatens aquatic life.

Grand dipole response of Asian summer monsoon to orbital forcing

The coherent continental-wide speleothem water isotope records are accompanied by regionally inconsistent moisture patterns within the Asian summer monsoon (ASM) region, leaving a disputed explanation of monsoonal hydroclimate variability at the orbital timescale. Here, the transient simulation forced by orbital parameters during the past 300,000 years in an isotope-enabled fully coupled model shows that the complex ASM response can be understood as a grand dipole pattern of oxygen isotope and rainfall between South Asia and Japan, with South China lying in a hybrid transition region. While the dipole monsoon rainfall change between South Asia and Japan is related to the large-scale circulation adjustment in response to Northern Hemisphere summer insolation, the dipole oxygen isotope pattern is associated with the changing contribution of moisture sources. Our results provide new clues to reconcile ASM hydroclimate patterns at orbital timescale as revealed by the water isotope records and other hydrological proxies.

Analysing Spatial Variability of Monsoon Rainfall over West Africa

Climate variability and changes have become a topic of increasing importance in recent decades due to extreme climate events such as floods and droughts, which profoundly impact socioecological systems across West Africa during the monsoon months. This study analyses and updates rainfall variability and spatial trends during these crucial months using monthly gridded rainfall data from 1950 to 2022. We applied the ordinary least square regression test, Buishand's, Standard normal homogeneity and Pettitt's tests for trend and change point detection analyses at a 5% significant level. The spatial variability and trends in rainfall were examined across three time periods: 1950-2022, 1963-1992, and 1993-2022. Change-point detection analysis revealed that there had been significant changes in the monsoon months' rainfall variability within the study period except in August. The detection of both positive and negative trends, representing trends toward wetter and drier conditions respectively, provides valuable insights for understanding and managing the impacts of climate variability and change for the most vulnerable areas.

Increased Summer Monsoon Rainfall Over Northwest India Caused by Hadley Cell Expansion and Indian Ocean Warming

AbstractFrom 1979 to 2022, the summer monsoon precipitation has increased by a substantial 40% over Northwest India compared to the 1980s. This wetting trend aligns with the future projections of the Coupled Model Intercomparison Project 6 (CMIP6). The observationally constrained reanalysis data indicates that significant sea surface warming in the western equatorial Indian Ocean and the Arabian Sea is likely driving this increase in rainfall by enhancing the cross‐equatorial monsoonal flow and associated evaporation. We demonstrate that the strengthening of the cross‐equatorial monsoon winds is due to the rapid warming of the Indian Ocean and the enhanced Pacific Ocean trade winds, which result from the poleward shift and expansion of the Hadley cell. These strengthened winds boost the latent heat flux (evaporation), leading to increased moisture transport to Northwest India.

Impact of Enso on Indian Monsoon and Food Production

El Nino is a big ocean-atmosphere climate interaction It happens when Sea Temperatures (SST) warm up in central and eastern parts of the Equatorial Pacific. Whereas La Nina is the opposite event of it, when ocean SST cools down in those same areas. Together, El Nino and La Nina are known as the El Nino Southern Oscillation Index (O). Usually, El Nino brings warm and dry weather to southern & eastern inland regions of India, Australia, Indonesia, Philippines, Malaysia, and the central Pacific islands. The variations of Indian summer monsoon Rainfall (ISMR) are linked to changes in sea surface temperatures over the equatorial Pacific & Indian Oceans. ENSO events really affect summer rainfall in India and major droughts have faced during El Nino events. When El Nino kicks in, it often leads to weak monsoons & higher temperatures in India. This raises the chances of droughts, which could upset crop production & water supply in India. The lack of rain because of El Nino causes crop production to drop, especially short-duration Kharif crops. This situation can lead to higher inflation rates & slower GDP growth, since agriculture is such a huge part of India’s economy. Therefore, this paper provide information about how El Nino affects climate throughout various regions of India, especially regarding monsoons and growing food.

Moisture dynamic processes of the westward propagation of quasi-biweekly oscillation in Asian tropical summer monsoon rainfall

The quasi-biweekly oscillation (QBWO) is an important component of tropical monsoon variations. In this study, the QBWO rainfall demonstrates a westward propagation across the tropical Asian monsoon region, originating from the western North Pacific, passing through the South China Sea and the Bay of Bengal, and ultimately reaching the northwestern Indian Peninsula. Notably, the rainfall anomalies over the South China Sea precede those over the Bay of Bengal by one quarter of the QBWO life cycle. Enhanced (suppressed) rainfall is closely associated with significant positive (negative) specific humidity anomalies, primarily induced by meridional moisture transport at the lower levels, as revealed by a moisture budget analysis. Specifically, the alternating presence and westward movement of northerly anomalies on the eastern (western) flank of anticyclonic (cyclonic) circulation anomalies are responsible for transporting low-frequency moisture across tropical Asia, thereby instigating the westward propagation of QBWO rainfall. Thus, the multiscale interactions between atmospheric circulation and moisture play a pivotal role in the development of QBWO monsoon rainfall, and understanding the moisture dynamics of this rainfall development would provide useful information for subseasonal rainfall prediction in tropical Asia.