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In this study, using the NCAR Community Earth System Model (CESM1.2.2), we investigate the changes in the characteristics of the summer monsoon low pressure systems (LPS) over India in a twenty-first century climate change simulation corresponding to the RCP8.5 scenario. A slight weakening in monsoon circulation and an increase in mean summer monsoon precipitation over India are simulated in a warmer climate, consistent with several previous studies. The weakening of the monsoon circulation is associated with a pair of anticyclonic anomalies straddling the equator in the low level, weakening the cross-equatorial monsoonal flow from the southern hemisphere. These low-level circulation anomalies appear to be robust features in the equatorial Indian Ocean under climate change. An increase in moisture flux is also simulated over the Indian subcontinent. However, we find no significant change in the number of LPS or their spatial distribution under the RCP8.5 scenario. This is attributed to a small but non-significant decrease in the low-level meridional cyclonic shear in zonal winds. An increase in the intensity and frequency of extreme precipitation over India in a warmer world is simulated and is likely associated with an increase in moisture content. Our study shows that the fractional contribution of LPS to mean and extreme precipitation over India in a warmer world is likely unchanged, but the frequency and intensity of extreme events are larger. Because of the diversity in the results from single model studies on LPS characteristics in a warmer world, a future study that uses CMIP6 multi-model data would be valuable to assess the robustness and the uncertainty in changes in LPS activities under climate change. [ABSTRACT FROM AUTHOR]

The Indian Ocean Dipole (IOD) can affect the El Niño-Southern Oscillation (ENSO) state of the following year, in addition to the well-known preconditioning by equatorial Pacific Warm Water Volume (WWV), as suggested by a study based on observations over the recent satellite era (1981-2009). The present paper explores the interdecadal robustness of this result over the 1872-2008 period. To this end, we develop a robust IOD index, which well exploits sparse historical observations in the tropical Indian Ocean, and an efficient proxy of WWV interannual variations based on the temporal integral of Pacific zonal wind stress (of a historical atmospheric reanalysis). A linear regression hindcast model based on these two indices in boreal fall explains 50 % of ENSO peak variance 14 months later, with significant contributions from both the IOD and WWV over most of the historical period and a similar skill for El Niño and La Niña events. Our results further reveal that, when combined with WWV, the IOD index provides a larger ENSO hindcast skill improvement than the Indian Ocean basin-wide mode, the Indian Monsoon or ENSO itself. Based on these results, we propose a revised scheme of Indo-Pacific interactions. In this scheme, the IOD-ENSO interactions favour a biennial timescale and interact with the slower recharge-discharge cycle intrinsic to the Pacific Ocean. [ABSTRACT FROM AUTHOR]

This article examines the structural aspects of climate vulnerabilities in the context of monsoon failures. The paper is based on a unique household survey, conducted in Tamil Nadu, India. The study uses a rural differentiation framework to interrogate unequal vulnerabilities to monsoon failures, based on measures such as Gini coefficients and Lorenz curves of monetary losses. Results show that negative consequences of climate change in general, and monsoon failures in particular, intensify pre-existing socio-economic disparities. When the rural differentiation theory is applied in a broader sense, the analysis shows that landed and farming households have greater exposure and losses. When we move beyond these aggregate categories, the revelation is that households with pre-existing disadvantages such as marginal landholders, subsistence farmers and agricultural workers are more vulnerable. • Global warming affects agriculture in South Asia in a major way through monsoon failures. • Vulnerability to monsoon failures can be measured by associated monetary losses. • These losses are highly unevenly distributed, pointing to significant inequality in impacts. • Landless households, marginal holders and subsistence farmers have higher losses. • Climate change intensifies existing structural disadvantages. [ABSTRACT FROM AUTHOR]

The Indian summer monsoon is an integral part of the global climate system. As its seasonal rainfall plays a crucial role in India's agriculture and shapes many other aspects of life, it affects the livelihood of a fifth of the world's population. It is therefore highly relevant to assess its change under potential future climate change. Global climate models within the Coupled Model Intercomparison Project Phase 5 (CMIP5) indicated a consistent increase in monsoon rainfall and its variability under global warming. Since the range of the results of CMIP5 was still large and the confidence in the models was limited due to partly poor representation of observed rainfall, the updates within the latest generation of climate models in CMIP6 are of interest. Here, we analyze 32 models of the latest CMIP6 exercise with regard to their annual mean monsoon rainfall and its variability. All of these models show a substantial increase in June-to-September (JJAS) mean rainfall under unabated climate change (SSP5-8.5) and most do also for the other three Shared Socioeconomic Pathways analyzed (SSP1-2.6, SSP2-4.5, SSP3-7.0). Moreover, the simulation ensemble indicates a linear dependence of rainfall on global mean temperature with a high agreement between the models independent of the SSP if global warming is the dominant forcing of the monsoon dynamics as it is in the 21st century; the multi-model mean for JJAS projects an increase of 0.33 mm d -1 and 5.3 % per kelvin of global warming. This is significantly higher than in the CMIP5 projections. Most models project that the increase will contribute to the precipitation especially in the Himalaya region and to the northeast of the Bay of Bengal, as well as the west coast of India. Interannual variability is found to be increasing in the higher-warming scenarios by almost all models. The CMIP6 simulations largely confirm the findings from CMIP5 models, but show an increased robustness across models with reduced uncertainties and updated magnitudes towards a stronger increase in monsoon rainfall. [ABSTRACT FROM AUTHOR]

It is well recognized that the global climate has been warming and it can have adverse regional impacts in the future. Besides producing changes in mean climate, global warming can also substantially alters the weather and climate extremes. Considering the impact of weather extremes on agriculture as well as water resource management in an agrarian country like India, present study aims to characterize future changes in precipitation extremes in northeast monsoon season (October–November–December) over south peninsular India based on statistically downscaled high-resolution NASA Earth Exchange Global Daily Downscaled Projections (NEX-GDDP) datasets. This NEX-GDDP dataset simulates the mean rainfall reasonably well. There may be an increase in precipitation in near (5% under RCP 4.5 and 11% under RCP 8.5) and far future (21% and 38% under RCP4.5 and RCP 8.5 respectively). Future climate projections indicate that both the intensity and frequency of precipitation extremes in most parts of the south peninsular India may increase under both the warming scenarios during northeast monsoon season. [ABSTRACT FROM AUTHOR]

The main source of sea surface temperature (SST) variability in the Tropical Atlantic at interannual time scales is the Equatorial Mode or Atlantic El Niño. It has been shown to affect the adjacent continents and also remote regions, leading to a weakened Indian Monsoon and promoting La Niña-type anomalies over the Pacific. However, its effects in a warmer climate are unknown. This work analyses the impact of the Equatorial Mode at the end of the twenty first century by means of sensitivity experiments with an atmosphere general circulation model. The prescribed boundary conditions for the future climate are based on the outputs from models participating in the coupled model intercomparison project-phase V. Our results suggest that even if the characteristics of the Equatorial Mode at the end of the twenty first century remained equal to those of the twentieth century, there will be an eastward shift of the main rainfall positive anomalies in the Tropical Atlantic and a weakening of the negative rainfall anomalies over the Asian monsoon due to the change in climatological SSTs. We also show that extratropical surface temperature anomalies over land related to the mode will change in regions like Southwestern Europe, East Australia, Asia or North America due to the eastward shift of the sea level pressure systems and related surface winds. [ABSTRACT FROM AUTHOR]

This study examines the Indian summer monsoon hydroclimate in the National Centers for Environmental Prediction (NCEP)-Department of Energy (DOE) Reanalysis (R2), the Climate Forecast System Reanalysis (CFSR), and the Modern Era Retrospective-Analysis for Research and Applications (MERRA). The three reanalyses show significant differences in the climatology of evaporation, low-level winds, and precipitable water fields over India. For example, the continental evaporation is significantly less in CFSR compared to R2 and MERRA. Likewise the mean boreal summer 925 hPa westerly winds in the northern Indian Ocean are stronger in R2. Similarly the continental precipitable water in R2 is much less while it is higher and comparable in MERRA and CFSR. Despite these climatological differences between the reanalyses, the climatological evaporative sources for rain events over central India show some qualitative similarities. Major differences however appear when interannual variations of the Indian summer monsoon are analyzed. The anomalous oceanic sources of moisture from the adjacent Bay of Bengal and Arabian Sea play a significant role in determining the wet or dry year of the Indian monsoon in CFSR. However in R2 the local evaporative sources from the continental region play a more significant role. We also find that the interannual variability of the evaporative sources in the break spells of the intraseasonal variations of the Indian monsoon is stronger than in the wet spells. We therefore claim that instead of rainfall, evaporative sources may be a more appropriate metric to observe the relationship between the seasonal monsoon strength and intraseasonal activity. These findings are consistent across the reanalyses and provide a basis to improve the predictability of intraseasonal variability of the Indian monsoon. This study also has a bearing on improving weather prediction for tropical cyclones in that we suggest targeting enhanced observations in the Bay of Bengal (where it is drawing the most moisture from) for improved analysis during active spells of the intraseasonal variability of the Indian monsoon. The analysis suggests that the land-atmosphere interactions contribute significant uncertainty to the Indian monsoon in the reanalyses, which is consistent with the fact that most of the global reanalyses do not assimilate any land-surface data because the data are not available. Therefore, the land-atmosphere interaction in the reanalyses is highly dependent on the land-surface model and it's coupling with the atmospheric model. [ABSTRACT FROM AUTHOR]

The onset of the Indian summer monsoon (ISM) over the southern tip of the Indian peninsula [also known as monsoon onset over Kerala (MOK)] has been considered the beginning of India’s rainy season. The Indian Meteorological Department (IMD) makes an official prediction of ISM onset every year using a subjective method. Based on an analysis of the past 60-yr (1948–2007) record, the authors show that the onset date can be objectively determined by the beginning of the sustained 850-hPa zonal wind averaged over the southern Arabian Sea (SAS) from 5° to 15°N, and from 40° to 80°E. The rapid establishment of a steady SAS westerly is in excellent agreement with the abrupt commencement of the rainy season over the southern tip of the Indian peninsula. In 90% of the years analyzed, this simple and objective index has excellent agreement with the onset dates that are subjectively defined by the IMD. There are only 3 yr of the past 60 yr during which the two onset dates differ by more than 10 days, and none of them perfectly reflects the MOK. A prominent onset precursor on the biweekly time scale is the westward extension of the convection center from the equatorial eastern Indian Ocean toward the southeast Arabian Sea. On the intraseasonal time scale, the onset tends to be led by northeastward propagation of an intraseasonal convective anomaly from the western equatorial Indian Ocean. The objective determination of the onset based on the SAS low-level westerly is a characteristic representation of the complex process of the ISM onset. Given its objectiveness and its representation of the large-scale circulation, the proposed new onset definition provides a useful metric for verifying numerical model performance in simulating and predicting the ISM onset and for studying predictability of interannual variations of the onset. [ABSTRACT FROM AUTHOR]