Variability Of Summer Monsoon Rainfall Research Articles

Impact of sea surface temperature in the Arabian Sea on the variability of Summer Monsoon Rainfall over Pakistan Region

The seas and oceans are essential in preserving energy in the Earth, Ocean, and atmosphere system. Assessing past trends and expected sea surface temperature (SST) shifts is critical for future climate scenarios within this framework. Previous studies have emphasized the importance of SST in the emergence and intensification of heavy rainfall events in the South Asian basin and the development of heat waves in the coastal regions of South Asia. This study has focused to investigate the relationship between SST of the Arabian Sea and mean rainfall in South Asia using Singular Value Decomposition Analysis (SVDA) for the July, August, and September (JAS) season, as most of the region's rainfall is in this season. The first mode accounts for 69 % of the covariance between Arabian Sea SST and regional JAS rainfall, with three dominant SVDA modes explaining 96 % of the total squared covariance. The degree to which the connected fields are correlated has been investigated using Root Mean Squared Covariance. By heterogeneous correlation maps, it is concluded how significant is the impact of one field (SST) on the other (rainfall), which validates our hypothesis that the SST of the Arabian Sea affects variation in precipitation. The empirical results from the SVDA are consistent with those of the composite diagrams. Dry and wet years have been defined and analyzed to examine the impact of SST on regional JAS rainfall further. Vertically integrated moisture transport reveals a significant difference in moisture transport over the Arabian Sea between wet and dry years during the JAS season. Water vapor transport is much stronger during wet years compared to dry years.

Optimization of CMIP6 models for simulation of summer monsoon rainfall over India by analysis of variance

AbstractThe advent of weather and climate models has equipped us to forecast or project monsoon rainfall patterns over various spatiotemporal scales; however, utilizing a single model is not usually sufficient to yield accurate projection due to the inherent uncertainties associated with the individual models. An ensemble of models or model runs is often used for better projections as a multimodel ensemble (MME). This study analyzes the accuracy of MME in simulating the Indian summer monsoon rainfall (ISMR) variability using Coupled Model Intercomparison Project Phase 6 (CMIP6) simulations. The results highlighted that although the MME primarily reproduces the observed pattern and annual cycle of rainfall, significant biases are noted over homogeneous meteorological regions of India, except northeast India. To overcome this issue, an analysis of variance (ANOVA) and post hoc statistical tests are employed to identify a group of models for which the modified MME gives a better estimate of rainfall and reduces the bias significantly. Our findings underscore the potential of ANOVA and post hoc tests as a practical approach to enhancing the accuracy of multimodel ensemble rainfall for the assessment of model projections.

Unusual subseasonal variability of Indian summer monsoon rainfall in 2020

AbstractAbove‐normal all‐India summer monsoon (ISM) rainfall was received in 2020 with 109% of its long‐period average. According to the India Meteorological Department (IMD), ISM 2020 experienced robust month‐to‐month rainfall variations; in particular, the peak monsoon month of July 2020 witnessed deficit rainfall. The present study investigated the possible mechanisms that are responsible for the July 2020 deficit rainfall. Analysis revealed that the strong low‐level moisture divergence caused by the westward‐propagating atmospheric Rossby wave, induced by suppressed western North Pacific (WNP) convection, is primarily responsible for the July rainfall deficit. The WNP suppressed convection is linked to anomalous low‐level anticyclonic circulation. It is noted that the intense WNP anticyclone is maintained by the tropical Indian Ocean (TIO) warming‐induced atmospheric Kelvin waves and strong low‐level convergence over the Meiyu‐Baiu rainband. Unlike July, the strength of the WNP anticyclone and TIO warming are weaker in June and August. In addition to the observational analysis, the skill of the Climate Forecast System version‐2 (CFSv2) model in predicting the July rainfall at a lead of about two months is examined. Strong positive rainfall anomalies over India are predicted by the model in July, which is in contrast to the observations. Despite predicting the TIO warming, the model failed to capture the westward extension of the WNP anticyclone, which impacted the July rainfall prediction. To understand the importance of the WNP anticyclone on ISM rainfall, a CFSv2 sensitivity experiment is carried out by imposing strong negative sea surface temperature (SST) anomalies over the WNP region to excite the anticyclone. Both the westward extension of the WNP anticyclone and suppressed rainfall over the core monsoon region in July are captured by the model when low‐level circulation is imposed. The model sensitivity experiment strongly supports the role of the WNP anticyclone and its westward extension in inducing reduced rainfall in July 2020 over the monsoon trough region.

Regional and temporal variability of Indian summer monsoon rainfall in relation to El Niño southern oscillation

The Indian summer monsoon rainfall (ISMR) exhibits significant variability, affecting the food and water security of the densely populated Indian subcontinent. The two dominant spatial modes of ISMR variability are associated with the El Niño Southern Oscillation (ENSO) and the strength of the semi-permanent monsoon trough along with related variability in monsoon depressions, respectively. Although the robust teleconnection between ENSO and ISMR has been well established for several decades, the major drivers leading to the time-varying relationship between ENSO and ISMR patterns across different regions of the country are not well understood. Our analysis shows a consistent increase from a moderate to substantially strong teleconnection strength between ENSO and ISMR from 1901 to 1940. This strengthened relationship remained stable and strong between 1941 and 1980. However, in the recent period from 1981 to 2018 the teleconnection decreased consistently again to a moderate strength. We find that the ENSO–ISMR relationship exhibits distinct regional variability with time-varying relationship over the north, central, and south India. Specifically, the teleconnection displays an increasing relationship for north India, a decreasing relationship for central India and a consistent relationship for south India. Warm SST anomalies over the eastern Pacific Ocean correspond to an overall decrease in the ISMR, while warm SST anomalies over the Indian Ocean corresponds to a decrease in rainfall over the north and increase over the south of India. The central Indian region experienced the most substantial variation in the ENSO–ISMR relationship. This variation corresponds to the variability of the monsoon trough and depressions, strongly influenced by the Pacific Decadal Oscillation and North Atlantic Oscillation, which regulate the relative dominance of the two spatial modes of ISMR. By applying the PCA-Biplot technique, our study highlights the significant impacts of various climate drivers on the two dominant spatial modes of ISMR which account for the evolving nature of the ENSO–ISMR relationship.

Strengthening of Sri Lanka summer monsoon rainfall with rapid Arabian Sea warming

AbstractSeveral studies have shown that rapid sea surface temperature (SST) warming in the tropical Indian Ocean (IO) significantly modulates the summer monsoon rainfall (SMR) over India. However, it remains unclear how the IO SST warming affects the SMR in Sri Lanka (SL). Therefore, based on observations and reanalysis data, this study investigates the impact of IO warming on SMR variability in the wet‐zone of SL during 2001–2020. The results revealed that the SMR (May–September) in SL's wet zone is increasing and is associated with rapid SST warming in the Arabian Sea during the summer monsoon. Although it is reported that the SMR may decrease over India due to the weakening of land‐sea thermal gradient in summer associated with IO warming, the rapid warming of the AS appears to enhance the SMR in the wet zone of SL. The warming of the AS during summer strengthened the low‐level easterlies, favouring moisture convergence and convection over SL, which enhanced the SMR of the wet zone of SL.

Variations in Indian Summer Monsoon Rainfall patterns in Changing Climate

The Indian summer monsoon is a large scale synoptic and dominant circulation feature which is largely restricted to the summer months from June to September. The proper understanding of rainfall pattern and its trends may help water resources development, agriculture sector and to take decisions for developmental activities. The present study is an attempt to evaluate the spatial variability in Indian summer monsoon rainfall (ISMR) over the Indian subcontinent during the climatological period (1901-2010). The long-term annual, decadal and tricadal monsoon rainfall differences are considered for the period 1901-2010 during the monsoon (June-September) and peak monsoon month (July-August). The results show concern for the major areas of upper Himalaya, Western and peninsular India where positive rainfall difference/increase rainfall with 0.2 to 1 mm/day variation have been reported during the monsoon and peak monsoon months. Also, decrease in rainfall have been reported over Western Ghats, Indo-Gangetic Plain (IGP) and some central Indian regions in the range of -0.6 to -1.5 mm/day. Further, a broad overview of the study shows an enhancement of ISMR over Western India whereas a substantial decline over Northeast Indian regions which suggests the western shift of ISMR in changing climate.

Latitudinal variations of summer monsoon rainfall in different intensity classes over the Western Ghats

Latitudinal variations of summer monsoon rainfall in different intensity classes over the Western Ghats

Assessment of intraseasonal variability indices on identifying Indian summer monsoon rainfall variability

Assessment of intraseasonal variability indices on identifying Indian summer monsoon rainfall variability

Quantifying the role of antecedent Southwestern Indian Ocean capacitance on the summer monsoon rainfall variability over homogeneous regions of India

The role of ocean variability is at a focal point in improving the weather and climate forecasts at different spatial and temporal scales. We study the effect of antecedent southwestern Indian Ocean mean sea level anomaly (MSLA) and sea surface temperature anomalies (SSTA) as a proxy to upper ocean heat capacitance on all India summer monsoon rainfall (AISMR) during 1993–2019. SSTA and MSLA over the southwestern Indian Ocean (SWIO) have been influenced by El Niño-Southern Oscillation (ENSO), the impact of ENSO-induced SWIO variability was low on rainfall variability over several homogeneous regions. Rainfall over northeast (NE) and North India (EI) has been modulated by ENSO-induced SSTA and MSLA over SWIO, thus effecting the total AISMR magnitude. The ENSO-induced changes in heat capacitance (SSTA and MSLA) over SWIO during antecedent months has less impact on west coast of India, central India and North India (NI) rainfall variability. The long-term trend in pre-monsoonal SSTA and MSLA over SWIO shows decreasing rainfall trend over NI, NE, and EI in the recent time. Furthermore, the cooler (warmer) anomaly over the western Indian Ocean affects rainfall variability adversely (favourably) due to the reversal of the wind pattern during the pre-monsoon period. While SSTA and MSLA are increasing in the SWIO, large-scale variability of these parameters during preceding winter and pre-monsoon months combined with surface winds could impact the inter-annual AISMR variability over homogeneous regions of India. Similarly, from an oceanic perspective, the antecedent heat capacitance over SWIO on an inter-annual time scale has been the key to the extreme monsoon rainfall variability.

Chemical weathering evidence for East Asian Summer Monsoon rainfall variability in the upper reaches of the Yellow River since the Early Pleistocene

The East Asian Summer Monsoon (EASM) is critically important for determining the spatial variability of precipitation in the continental interior of East Asia. Hence, knowledge of past EASM variability may help predict the response of monsoon rainfall to ongoing global climate change, with important implications for the living environment of the large human population of East Asia. In this study, we obtained several geochemical records from the Hetao Basin in the upper reaches of the Yellow River (UYR), which we use to reconstruct variations in chemical weathering intensity since 1.68 Ma. Our results suggest that chemical weathering was significantly intensified during the interval of ∼0.47–0.18 Ma, evidenced by lower Rb/Sr and αAlSr values, and higher LEF Mg/Al values, within the lacustrine sediments during this period. This enhanced chemical weathering was closely linked to increased monsoon rainfall associated with a strong EASM. The long-term trends of EASM rainfall in the UYR were caused by variations in the atmospheric circulation over the Pacific Ocean, such as the ENSO cycle and the PDO phase transition, which may act as testable factors in the prediction of future EASM rainfall.

Variability and Trend in Summer Monsoon Rainfall and its Correlation with Crop Yield in the Districts of Andhra Pradesh During 2011-2020

In the context of climate change and its impact on agriculture, the paper analyses the trend of monsoon rainfall and its correlation with crop yield in Andhra Pradesh. The summer monsoon is the main rainy source of water for the state of Andhra Pradesh. The Kharif crops depend on the southwest monsoon rains to the extent that its adverse variability may lead to water stress and agrarian crisis. It has been observed from the study that in recent years the contribution of monsoon rainfall during September is increasing, and any harvest during the month is correspondingly affected, leading to a decline in the crop yield.

Different role of spring season Atlantic SST anomalies in indian summer monsoon rainfall (ISMR) variability before and after early 2000

The present study shows that the weak (out-of-phase) correlation between the boreal spring Atlantic Meridional Mode (AMM) index and Indian summer monsoon rainfall (ISMR) during the 1990–2001 periods turned into a significant positive relationship after that. During the first period, boreal spring (MAM) season Atlantic SST variability is dominated by stronger cooling in the southeastern region. After 2002, the spring season SST pattern has north Atlantic warming extending to the equatorial region and continuing to summer (JJAS). The primary mode of the Atlantic SST co-occurred with a pre-existing El Nino during period 1 and the formation of La Nina by summer during period 2. During period 1, ENSO-induced anomalies dominated with weak divergence over India and the Atlantic region, while during period 2, the warm SST anomalies of north Atlantic-induced off-equatorial convection and associated circulation extended to the Indian Ocean and Indian land region resulting in increased monsoon rainfall during JJAS. The study further showed that during period 2, the increased correlation of ENSO and ISMR is also contributed by the Atlantic SST anomalies with additional off-equatorial wind anomalies and circulation from the north Atlantic extending to the Indian Ocean and monsoon region. Thus, MAM season Atlantic SST anomalies play a significant role in ENSO phase reversal and ISMR during the recent period. Many of the seasonal prediction models that participated in the NMME project capture the phase reversal of AMM-ISMR correlation when initialized during February. But models have more robust equatorial SST patterns during the summer season, and the north Atlantic SST anomalies are vital in the absence of ENSO. The study indicates that the spring season AMM index can provide a predictive signal for ISMR in seasonal prediction models. Still, they need to improve the simulation of the Atlantic basic state and its teleconnection with the tropical east Pacific.

Symmetric and asymmetric response of Indian Summer Monsoon rainfall to different ENSO decay phases in observations and CMIP6 models

The present study assesses the ability of the World Climate Research Programme's Coupled Model Intercomparison Project-6 (CMIP6) models in simulating the Indian Summer Monsoon (ISM) rainfall variability and its symmetric or asymmetric relationship with the El Niño–Southern Oscillation (ENSO) decay phase. The El Niño decays are classified into three categories based on their transition characteristics (rapid/slow) with respect to the subsequent boreal summer season, namely El Niño early-decay, El Niño mid-decay, and El Niño no-decay. Similarly, La Niña decays are also classified into the La Niña early-decay, La Niña mid-decay, and La Niña no-decay. In the case of El Niño and La Niña early-decay events, the observed summer rainfall anomalies over India are similar in spatial distribution and amplitude but opposite in sign, suggesting the symmetric rainfall response. This symmetric response is mainly due to the influence of the westward extension of western north Pacific (WNP) anomalous anticyclone/cyclone accompanied by tropical Indian Ocean (TIO) warming/cooling. In contrast to this, summers of El Niño and La Niña mid-decay events exhibited asymmetric rainfall anomaly pattern over India. This asymmetry in rainfall pattern between these two summers is attributed to differences mainly in the moisture divergence and low-level circulation over the Indo-Western Pacific region. Similar to El Niño and La Niña mid-decay cases, the summers of observed El Niño and La Niña no-decay events displayed ISM rainfall asymmetry. Differences in spatial distribution and magnitude of Sea surface temperature anomalies and related atmospheric circulation between these events mainly responsible for ISM rainfall asymmetry. Analysis of CMIP6 revealed that only ∼ 14% of selected CMIP6 models have simulated the rainfall anomalies somewhat correctly compared to observations during summers of different decay phases of ENSO. Further, symmetric/asymmetric response of summer rainfall anomalies over India between decay phases of El Niño and La Niña are not well captured by CMIP6 models. It is also noted that the CMIP6 models have displayed a tendency to simulate positive (negative) Indian Ocean Dipole conditions during the summers of El Niño no-decay (La Niña no-decay) events unlike in the observations.

Spatio-temporal analysis of rainfall in relation to monsoon teleconnections and agriculture at Regional Scale in Haryana, India.

This study examined the long-term (1980-2019) spatio-temporal trends, variability and teleconnections of Indian summer monsoon rainfall (ISMR) of all districts of Haryana, India and their impact on agricultural productivity. The gridded datasets of India Meteorological Department (IMD) were used to statistically analyse the rainfall distribution, trend, coefficient of variation and intensity of rainfall. The gridded datasets of European Centre for Medium-Range Weather Forecasts (ECMWF) atmospheric reanalysis V5 (ERA5) were examined for lower and upper tropospheric wind circulation (850hPa and 200hpa), vertically integrated moisture transport (VIMT) and surface moisture flux (SMF). The datasets of National Oceanic and Atmospheric Administration (NOAA) were correlated with ISMR and composite deviation of rainfall and rainfall intensity during El Niño and La Niña from neutral years was examined at district level. Our analysis revealed that districts lying in eastern agroclimatic zone (EAZ) of Haryana received more ISMR during each month of monsoon season as compared to the ones situated in western agroclimatic zone (WAZ). Trend-free pre-whitening Mann-Kendall (TFPW-MK) test revealed that Kurukshetra, Panipat, Ambala, Rohtak, Faridabad, Jhajjar, Sonipat, Fatehabad and Palwal have shown a decreasing trend while Mahendragarh and Panchkula have shown an increasing trend of rainfall. During the El Niño years, most of the locations in the state received deficient to large deficient category, whereas during the La Niña episodes, most of the locations received excess to large excess category of ISMR, which is indicative of the influence of El Niño-Southern Oscillation (ENSO) on the regional scale. The influence of ISMR on bajra productivity for the districts lying in WAZ and rice productivity for the districts lying in EAZ was undertaken. This study is beneficial for understanding the impacts of climate change and climate variability on ISMR dynamics in Haryana which may further guide the policy-makers and beneficiaries for optimising the use of hydrological resources.

Coherent Indian Summer Monsoon and Sahel Rainfall Variability Revealed by Ethiopian Rainfall δ18O

AbstractCoherent fluctuations in Sahel and Indian summer monsoon (ISM) rainfall influence the socio‐economic welfare of several densely populated regions. Here we identify a common mode of interannual rainfall variability over the Sahel and Indian regions and demonstrate the influence of both Pacific and Atlantic sea surface temperatures (SST) in inducing such a large‐scale response. The principal component of the leading mode of precipitation variability (PC1) over these regions correlates independently well with both ISM and Sahel rainfall indices. Here we show that this global SST‐driven dominant mode of Indo‐Sahel rainfall variability is well captured in present‐day rainfall δ18O and speleothem δ18O of the Ethiopian region. We use a ∼40‐year‐long monthly observational record of precipitation stable isotopes at Addis Ababa, Ethiopia to show that episodic isotopic depletions in rainfall at this site occur during the wet phases of PC1. These isotopic anomalies are associated with eastward intrusions of moisture initiating from the tropical Atlantic Ocean. Finally, we demonstrate decadal‐scale co‐variability between PC‐1 and a century‐long δ18O record from an actively growing Ethiopian speleothem to highlight the potential of rainfall isotopic records from this region to capture fluctuations in the coupled variability of the Indo‐African boreal monsoons.

Climate warming and summer monsoon breaks drive compound dry and hot extremes in India

Considering the severe impacts of compound dry and hot extremes, we examine the primary drivers of CDHEs during the summer monsoon in India. Using ERA5 reanalysis, we show that most of the CDHEs in India occur during the droughts caused by the summer monsoon rainfall deficit. Despite a decline in the frequency of summer monsoon droughts in recent decades, increased CDHEs are mainly driven by warming and dry spells during the summer monsoon particularly in the Northeast, central northeast, and west central regions. A strong land-atmospheric coupling during droughts in the summer monsoon season leads to frequent CDHEs in the Northwest and southern peninsular regions. Furthermore, regional variations in land-atmospheric coupling cause substantial differences in the CDHE occurrence in different parts of the country. Summer monsoon rainfall variability and increased warming can pose a greater risk of compound dry and hot extremes with severe impacts on various sectors in India.

The mechanism linking the variability of the Antarctic sea ice extent in the Indian Ocean sector to Indian summer monsoon rainfall.

The study investigates the mechanism of teleconnection between the variability of sea ice extent (SIE) in the Indian Ocean sector of the Southern Ocean and the variability of Indian summer monsoon rainfall. We utilized reanalysis, satellite, in-situ observation data, and model output from the coupled model intercomparison project phase 5 (CMIP5) from 1979 to 2013. The empirical orthogonal function (EOF) and correlation analysis show that the first and third modes of principal component (PC1 and PC3) of SIE in the Indian Ocean sector during April–May–June (AMJ) are significantly correlated with the second mode of principal component (PC2) of Indian summer monsoon rainfall. The reanalysis data revealed that the changes in the SIE in the Indian Ocean sector excite meridional wave train responses along the Indian Ocean for both principal component modes. Positive (negative) SIE anomalies based on first and third EOFs (EOF1 and EOF3), contribute to the strengthening (weakening) of the Polar, Ferrel, and Hadley cells, inducing stronger (weaker) convective activity over the Indian latitudes. The stronger (weaker) convective activity over the Indian region leads to more (less) rainfall over the region during high (low) ice phase years. Furthermore, a stronger (weaker) polar jet during the high (low) ice phase is also noted. The selected CMIP5 models captured certain atmospheric teleconnection features found in the reanalysis. During AMJ, the SIE simulated by the NorESM1-M model was significantly positively correlated with Indian summer monsoon rainfall, whereas the IPSL-CM54-LR model showed a negative correlation.

Aerosol distribution during spring and summer and its relationship with Inter-Annual variability of summer monsoon rainfall over Indian region

The inter-annual variability of aerosol over Indian region and its possible implications on the Indian summer monsoon is investigated using Aerosol Optical Depth (AOD) data from Moderate Resolution Imaging Spectrometer (MODIS) during the period 2001 to 2016. An attempt has been made to link the seasonal aerosol distribution over South Asia during spring and summer season to Indian Summer Monsoon Rainfall (ISMR) distribution. AOD derived from MODIS Terra observations shows large spatial inhomogeneity and characteristic variability with distinct temporal distributions. The pre-monsoon (spring) seasons (March-April-May; MAM) is characterized by high aerosol concentration over north-west part of India along with IGP region. During the south-west monsoon (summer) seasons (June-July-August-September; JJAS), wide area of high aerosol loading along Indo Gangetic plains extending from North Arabian sea through north-west India and up to Himalayan foothills. The regional rainfall distribution and its relationship with spatial and temporal aerosol distribution are then evaluated. Further, distinct variability in the aerosol distribution with respect to excess, deficit and normal monsoon years are analysed to understand the role of aerosols on the inter-annual variability of ISMR. Monthly aerosol distribution over Central India [CI;15°-25oN;75°-88oE] and Indo Gangetic plain [IGP;25°- 350N;70°- 900E] shows increased aerosol loading during deficit rainfall years and corresponding delay in the monthly rainfall peak. This study emphasises the active role of regional aerosol loading on regulating the inter-annual variability of regional Indian summer monsoon rainfall.

Interannual crisscross pattern observed in South Asian monsoon rainfall and its relationship with aerosols

This study examines the interannual variability of South Asian summer monsoon rainfall (SAMR) using a linear trend analysis for the recent 17-year period from 2000 to 2016. The trends in SAMR analyzed from multiple rainfall datasets show a unique crisscross like pattern over South Asia and its surrounding oceans. Significant positive trends in SAMR occur over the middle and south Bay of Bengal (BOB) and North-West India (NWI) aligned in SE-NW direction. Similarly, significant negative trends are observed over North-East India and head Bay of Bengal (NEI) as well as over the middle and south Arabian Sea (AS) oriented in SW-NE direction. Western Ghats make an exception to this pattern, where significant positive trends have been observed. Interestingly, the trends in aerosol optical depth (AOD) for the same period closely follow the trends in SAMR. The relationship of AOD averaged over each of the significant aerosol trend regions with the SAMR suggest aerosol induced suppression in moisture transport from a region covering Southern Arabian Sea and Bay of Bengal played a dominant role over the negative trend regions. However, the decreased aerosols over the Northwest India due to significant positive trends in rainfall reduced dust transport from the Arabian Peninsula towards eastern parts of South Asia resulting in an increase in anthropogenic aerosols from local sources. This caused significant drying over the NEI and AS regions through aerosol indirect effects. Further, Aerosol direct radiative effects due to natural and anthropogenic sources inferred from the climate forcing estimates confirmed their role in positive trends and the indirect effects inferred from satellite cloud products depicted a strong association with negative trends, thus maintaining the observed crisscross pattern.

Dynamical and moist thermodynamical processes associated with Western Ghats rainfall decadal variability

The Western Ghats (WG) is a vast montane forest ecosystem known for its biodiversity and endemism. The decadal variability of WG summer monsoon rainfall is higher than most of the other regions of India. Spectrum and wavelet analysis of century-long rainfall observation confirm significant decadal variability (at 90% confidence level) in WG rainfall, with amplification of magnitude (about 1.5–2 times) in the recent years compared to the previous half-century. Correlation analysis of WG rainfall with Indian (Pacific) Ocean sea surface temperature (SST) shows a significant relationship during 1901–1942 (1943–1977 and 1978–2010). The analysis associated with decadal rainfall variability reveals the dominance of dynamical processes during 1901–1942 and moist thermodynamical processes during 1943–1977 and 1978–2010. The study concludes that decadal variability of WG rainfall is robust and the forcing mechanisms are essentially maintained by the Indian and Pacific Oceans variability, adding value in developing decadal prediction systems and may also contribute towards understanding the evolution of WG ecosystem.