Search

Seasonal rainfall forecasts are an important tool for risk management across many sectors. However, significant challenges arise in the development of skilful and practically useful seasonal forecasts for regions where the temporal and spatial variability of rainfall is large and/or knowledge about what causes this variability is in its infancy. This is evident in the state of South Australia (SA), where seasonal rainfall currently has low predictive skill. The key climate processes have yet to be fully identified in SA and therefore may not be adequately represented in forecast models. The aim of this paper is to identify and quantify relationships between large-scale ocean-atmospheric processes and seasonal rainfall variability across SA. We identify two distinct climate zones: (1) the arid northern region, where rainfall is mostly influenced by climate processes stemming from the tropical Indian and/or Pacific Oceans and (2) southern SA, which is dominated by Southern Ocean processes. The average percent of variability of SA rainfall accounted for by any single large-scale climate process (i.e. linear regression using a single predictor) is 8% in summer, 19% in autumn, 33% in winter and 24% in spring. However, when two or more processes are considered in combination (through multiple linear regression), this rises to 13, 26, 46, and 33%, respectively, highlighting the importance of capturing the interaction among multiple climate processes. Importantly, the findings from this study provide a set of metrics against which existing statistical and dynamical forecasting schemes can be tested and highlight processes that should be focused on in order to improve (or develop new) forecasting schemes. The study also recommends the need for further investigations into non-linear relationships between rainfall and large-scale ocean-atmospheric processes and the development of more objective methods for determining which climate process, or combination of processes, are most important for a certain season or location. [ABSTRACT FROM AUTHOR]

This study investigates the impact of El Niño Southern Oscillation (ENSO) and ENSO Modoki on rainfall variability over Southeast Asia (SEA) with a focus on its twenty sub-regions. For the period 1979–2019, seven El Niño (EN), six La Niña (LN), five El Niño Modoki (EM), and five La Niña Modoki (LM) events were identified. In the boreal summer (JJA) and winter (DJF) of EN events, rainfall reduction occurred over the Maritime Continent and the Philippines except for West Philippines in JJA and West Kalimantan in DJF. Similar patterns but with enhanced drier/wetter conditions were detected during EM. During LN, rainfall increased in most sub-regions except for West Philippines and parts of mainland Indochina in JJA, and in DJF in some southern areas such as South Sumatra, West Kalimantan, and Papua. Compared to LN, LM generally exhibited less wet/drier conditions in JJA over most sub-regions and wetter conditions in DJF over a major part of the Maritime Continent. The decrease (increase) in rainfall over SEA during Modoki events compared to the canonical ENSO events was explained by a reduced (enhanced) moisture transport into the region and a weakening (strengthening) of the ascending branch of the Walker circulation. [ABSTRACT FROM AUTHOR]

ABSTRACT This paper analyses the influence of different types of El Niño-Southern Oscillation ( ENSO) events on South American precipitation under a climate change scenario. We use two sub-selections of Coupled Model Intercomparison Project Phase 5 (CMIP5) models that have a good representation of teleconnections to the region, albeit with reduced magnitude anomalies. Comparing historical simulations and the RCP 8.5 scenario experiments, after removing the trend in the mean due climate change, the sub-ensemble means show similar global sea surface temperature anomalies and South American precipitation anomaly patterns in the future. No robust changes in the pattern or magnitude of precipitation anomalies are found, despite significant ENSO-related shifts in the Pacific basin, as highlighted in other studies. However, if the models are analysed individually, some show relatively strong changes in ENSO-related precipitation anomalies for both canonical and Modoki events. We show that, in individual models, tropical teleconnection changes associated with ENSO are primarily driven by changes in the magnitude of ENSO-related circulation but with no agreement on the sign. Increases in background moisture, which have been hypothesized to drive an intensification of ENSO-related precipitation anomalies, are of secondary importance. [ABSTRACT FROM AUTHOR]

The interannual and interdecadal variabilities of Indonesian rainfall in dry seasons (June-November) are investigated by using rainfall data from the Climate Research Unit (CRU) from 1939 to 2016 and from the Global Precipitation Climatology Project (GPCP) from 1979 to 2016. The first principal component (PC1) of both the CRU and GPCP data shows that the canonical El Niño-Southern Oscillation (ENSO), ENSO Modoki, and Indian Ocean Dipole (IOD) are major climate modes influencing the interannual variability of rainfall in Indonesia, and the Interdecadal Pacific Oscillation (IPO) is the major decadal phenomenon affecting the decadal variability of the rainfall. Furthermore, the IPO modulates the influence of IOD on Indonesian rainfall, with a weaker influence during the positive IPO phase during 1979 - 1997 and a stronger influence during the negative IPO phases during 1939 - 1978 and 1998 - 2016. The dependency of Indonesian rainfall response to the canonical ENSO and ENSO Modoki on IPO phases is not significant, although the response to the ENSO Modoki (canonical ENSO) becomes significant (less significant) in the negative IPO phase during 1998 - 2016 when compared with earlier periods. [ABSTRACT FROM AUTHOR]

The El Niño–Southern Oscillation (ENSO) Modoki phenomenon has a substantial influence on regional climate. In this study, the results derived from observational and reanalyzed datasets show that the boreal winter climate anomalies over the Pacific and its rim in the different phases of ENSO Modoki are asymmetric during 1979–2017. During El Niño Modoki, an upper-level zonal "convergence–divergence–convergence" anomaly occurred in the Walker circulation over the Pacific sector, associated with anomalous ascending (descending) in the central side (both sides), leading to a wet "boomerang" pattern of rainfall anomalies in the tropical Pacific Ocean. Consequently, a drier winter occurred in Philippines, and warming and drying occurred in western Australia and northern South America. Meanwhile, a dipolar pattern with the wet south and the dry north in the United States occurred, accompanied by a Pacific/North American-like teleconnection. During La Niña Modoki, a roughly reversed Walker circulation anomaly and deeper Hadley circulation anomalies were associated with the strong air–sea feedback, which caused stronger rainfall anomalies in the Pacific Ocean. On land, anomalies of surface temperature and rainfall over the tropical Pacific Rim were more intense compared with El Niño Modoki. However, owing to the lack of a Pacific/North American anomaly, fewer anomalies occurred over the mid-latitude North America. In numerical experiments, the response to the different phases of ENSO Modoki basically reproduces the asymmetric climate anomalies in boreal winter, further confirming that the asymmetry can be partly attributed to tropical sea surface temperature anomalies. [ABSTRACT FROM AUTHOR]

ENSO diversity refers to the appearance in recent decades of different El Niño types in the tropical Pacific: In addition to the canonical El Niño, the newly discovered type, called Central Pacific (CP) El Niño, has its center of warming shifted more to the central equatorial Pacific. Whether these ENSO types are really distinct or are different manifestations of a continuum is currently under debate. The mechanisms for the recent appearance of the additional type of ENSO have not been clarified. While previously it was claimed that the increased CP El Niño occurrence in recent decades were due to tropical trade winds weakened by global warming, the observed trade winds actually intensified. We systematically study the variability of the Pacific sea-surface temperature (SST) using the new method of Rotated Principal Component Analysis (RPCA). The essential statistical characteristics of these two El Niño types are found to be describable by only three fundamental modes of pan-Pacific SST with different proportions: the ENSO-cycle, the pan-Pacific counterpart of the regionally defined Pacific Decadal Oscillation (PDO), and a new climate mode we call the Central Pacific Variability (CPV). It is shown that CP El Niño can be described by the PDO and the CPV. The latter has a horseshoe-shaped warm SST pattern in the Central Pacific flanked by cold SST to the east, roughly similar to the original definition of ENSO Modoki by Ashok et al. (J Geophys Res Oceans 112:C11007, 2007) as the second Empirical Orthogonal Function in a narrow tropical domain decomposition. The Principal Component (PC) of this mode, called Modoki PC (MPC) was thought to characterize the occurrence of this new phenomenon, but it has been shown to be unable to separate it from the canonical ENSO. In contrast, we demonstrate that Central Pacific El Niño occurs when the CPV index is larger than 0.5. The intensity of the CPV mode has increased dramatically since 1970s, likely as a result of the intensification of the easterly trade winds in the tropical Pacific, which tilts the thermocline along the tropical Pacific and raises the SST in the central equatorial Pacific. Moderate El Niños are more prone to stalling in the Central Pacific, becoming CP El Niños. [ABSTRACT FROM AUTHOR]

In this work we investigate interannual variations in lower stratospheric ozone from 1984 to 2016 based on a satellite‐derived data set and simulations from a chemical transport model. An empirical orthogonal function (EOF) analysis of ozone variations between 2000 and 2016 indicates that the first, second, and third EOF modes are related to the quasi‐biennial oscillation (QBO), canonical El Niño–Southern Oscillation (ENSO), and ENSO Modoki events, respectively; these three leading EOFs capture nearly 80% of the variance. However, for the period 1984–2000, the first, second, and third modes are related to the QBO, ENSO Modoki, and canonical ENSO events, respectively. The explained variance of the second mode in relation to ENSO Modoki is nearly twice that of the third mode for canonical ENSO. Since the frequency of ENSO Modoki events was higher from 1984 to 2000 than after 2000, the Brewer‐Dobson circulation anomalies related to ENSO Modoki were stronger during 1984–2000, which caused ENSO Modoki events to have a greater effect on lower stratospheric ozone before 2000 than after. Ozone anomalies associated with QBO, ENSO Modoki, and canonical ENSO events are largely caused by dynamic processes, and the effect of chemical processes on ozone anomalies is opposite to that of dynamic processes. Ozone anomalies related to dynamic processes are 3–4 times greater than those related to chemical processes. Key Points: The second and third EOFs of the interannual variations in lower stratospheric ozone during 2000‐2016 are related to canonical ENSO and ENSO Modoki, respectivelyFor the period 1984‐2000, the second EOF is related to ENSO Modoki and the third EOF to canonical ENSOThe higher frequency of occurrence of ENSO Modoki than canonical ENSO led to a stronger impact of ENSO Modoki on circulation and ozone anomalies between 1984 and 2000 [ABSTRACT FROM AUTHOR]

Precipitation is a significant parameter in many aspects such as agriculture, water management and climate variability. To characterize rainy season variations is important to understand precipitation variability under the effect of climate change. In this study, rainy season features (i.e., onset, retreat and rainy‐season precipitation) over the Huaihe River basin (HRB) and the response to different types of El Niño–Southern Oscillation (ENSO), that is, central Pacific warming (CPW), eastern Pacific warming (EPW), eastern Pacific cooling (EPC), conventional ENSO and ENSO Modoki in the developing and decaying phases are evaluated. The multi‐scale moving t test was used to capture onset and retreat of rainy season. The possible dynamic causes of ENSO‐induced precipitation over the HRB, such as monsoon and atmospheric circulation, were also explored. Results show that (a) onset (retreat) of rainy season progressed northwards (westwards), with rainy‐season precipitation increasing from north to south; (b) rainy‐season precipitation showed a strong correlation to Sea Surface Temperature (SST) in Niño regions. Dry and wet signals were identified in different regions of the HRB in the developing and decaying phases of CPW, EPC and EPW. Special attention should be paid on decaying EPW, where totally dry signals were found, which can reach down to 25% below average precipitation; (c) developing El Niño Modoki and decaying El Niño showed totally dry signals, with decaying El Niño Modoki and conventional La Niña demonstrating overall increasing precipitation; (d) different performances of ENSO‐induced precipitation during rainy season over the HRB are attributable to the combined influences of the monsoon from the India Ocean and the anticyclonic flow in the western North Pacific (WNP). Stronger anticyclone and monsoon are generally associated with increasing rainy‐season precipitation. These results can improve predictability of rainy season features and ENSO‐induced precipitation over the Huaihe River basin. The graphical abstract map for this research. [ABSTRACT FROM AUTHOR]

China has experienced alarming drought events during recent decades. In this study, we investigated monthly drought severity related to the eastern Pacific cooling (EPC), eastern Pacific warming (EPW), and central Pacific warming (CPW), and analysed the differential influence of canonical ENSO (c‐ENSO) and El Niño Modoki (ENSO_M) events on monthly droughts severity based on the SPEI at multiple timescales in China. The results show that (a) EPC episodes negatively affected 1‐ and 3‐month drought severity in southeast and northeast China with negative anomalies lower than −0.4 (<−0.4) during November–February the next year. EPW and CPW episodes significantly negatively affect drought severity in central north China (<−0.8) and the coastal areas of southeast China (<−0.6) during the most months, respectively. (b) La Niña negatively affected drought severity in the most parts of northeast China (<−0.2) and southeast China (<−0.4) during the most months, and La Niña Modoki caused dry conditions in the most parts of China (<−0.2) during a few months. Significant dry conditions were observed in central north China (<−0.8) in many months during El Niño, but dry conditions covered south China (<−0.4) in the most months during El Niño Modoki. (c) SST anomalies in Niño3 and ENSO_M regimes and wind anomalies might explain the spatial distribution of dry conditions across China during c‐ENSO and ENSO_M phases. The results could provide valuable information for predicting droughts associated with the c‐ENSO and ENSO Mokodi. Spatial distribution of meteorological stations in China. [ABSTRACT FROM AUTHOR]

Previous study detected an intensified impact of the El Niño‐Southern Oscillation (ENSO) Modoki sea surface temperature (SST) anomalies on the tropical cyclone (TC) activity over the western North Pacific (WNP) after the early 1990s and attributed it to an expansion in areal coverage of the equatorial central Pacific (ECP) SST anomalies. This study identifies the contribution of SST anomalies in several other regions to this inter‐decadal change in the relationship between ENSO Modoki SST and the WNP TC genesis. Before the early 1990s, the positive ECP SST anomalies induce an anomalous lower‐level cyclone and consequently an increase in the TC genesis frequency over the southern part of the WNP, and the positive ECP and tropical Indian Ocean SST anomalies together induce an anomalous lower‐level anticyclone and accordingly a decrease in the TC genesis frequency over the northern part of the WNP. As such, the relationship between the ECP SST and the WNP TC genesis frequency is weak. After the early 1990s, the positive ECP SST anomalies with a large areal coverage induce a large anomalous lower‐level cyclone covering most of the WNP and thus an increase in the TC genesis frequency over the WNP. Meantime, the tropical northern Atlantic and western South Pacific SST anomalies during spring enhance the succeeding summer–autumn WNP atmospheric circulation response to the ECP SST anomalies through an Atlantic–Pacific teleconnection and a wind‐evaporation positive feedback, respectively. This strengthens the relationship between the ECP SST and the WNP TC genesis frequency. [ABSTRACT FROM AUTHOR]

While the Indian agriculture has earlier been dependent on the Indian summer monsoon rainfall (ISMR), a multifold increase in irrigation and storage facilities raise a question whether the ISMR is still as relevant. We revisit this question using the latest observational climate datasets as well as the crop production data and find that the ISMR is still relevant for the Kharif crop production (KCP). In addition, in the recent changes in the tropical Indo-Pacific driver evolutions and frequency, particularly more frequent occurrence of the ENSO Modokis in place of the canonical ENSOs, we carry out a correlation analysis to estimate the impact of the various Indo-Pacific climate drivers on the rainfall of individual Indian states for the period 1998-2013, for which crop production data for the most productive Indian states, namely West Bengal, Odisha, United Andhra Pradesh (UAP), Haryana, Punjab, Karnataka, Kerala, Madhya Pradesh, Bihar and Uttar Pradesh are available. The results suggest that the KCP of the respective states are significantly correlated with the summer monsoon rainfall at the 95-99% confidence levels. Importantly, we find that the NINO 3.4 and ENSO Modoki indices have a statistically significant correlation with the KCP of most of the Indian states, particularly in states such as UAP and Karnataka, through induction of anomalous local convergence/divergence, well beyond the equatorial Indian Ocean. The KCP of districts in UAP also has a significant response to all the climate drivers, having implication for prediction of local crop yield. [ABSTRACT FROM AUTHOR]

Relationship between the Southern Annular Mode (SAM) and the India summer monsoon rainfall (ISMR) has been examined based on the data period 1949-2013. While the entire data period indicates a significant increasing trend in SAM, recent decades 1983-2013 indicate no trend. The relationship between the two strengthened considerably since 1983. Results reveal that the February-March SAM is significantly related with the subsequent ISMR. A positive (negative) SAM during February-March is favorable (unfavorable) for the ensuing summer monsoon rainfall over the Indian sub-continent. The delayed response is relayed through the central Pacific Ocean. We propose a hypothesis that states: when a negative (positive) phase of February-March SAM occurs, it gives rise to an anomalous meridional circulation in a longitudinally locked air-sea coupled system over the central Pacific that persists up to the subsequent boreal summer and propagates from the sub-polar latitudes to the equatorial latitudes inducing a warming (cooling) effect over the central equatorial Pacific region. In turn, this effect concomitantly weakens (strengthens) the monsoon rainfall over the Indian sub-continent. Thus, the February-March SAM could possibly serve as a new precursor to foreshadow the subsequent behavior of the Indian summer monsoon. [ABSTRACT FROM AUTHOR]

Using CMIP5 model outputs in different El Niño-Southern Oscillation (ENSO) phases, this work investigates the indicator that could be used as an Index to characterise regional Indian Summer Monsoon (ISM) precipitation. Dividing the Indian subcontinent into five arbitrarily chosen regions, viz. Central North East (CNE) (18|N-31|N, 86|E-75|E), Hilly (H) (28°N-38°N, 85°E-70°E), North West (NW) (21°N-31°N, 79°E-67°E), North East (NE) (21°N-31°N, 86°E-97°E) and Southern India (S) (18°N-7°N, 73°E-85°E), local wind field and remote influences from the tropical Pacific are considered to improve understanding of regional monsoon rainfall. Results are also compared with observations/reanalysis data to pinpoint areas of shortcomings and agreements. Model results suggest that regional wind velocity, viz. meridional wind component (V) at 850 mb level (V850) and zonal component at 200 mb (U200) and 850 mb (U850) can yield better estimation of local precipitation in regions CNE, H and NW, agreeing well with earlier proposed monsoon Indices. Such observations are independent of different subcategories of ENSO phases and models show good correspondence with observations. Analyses with V at 200 mb (V200) indicate circulation of the upper branch of Hadley cells in regions CNE and S, though suggest the best agreement among models in comparison with other fields, but there are some deviations from observations, indicating a missing mechanism in the models. Using models, this study identified the best parameter in different regions that could be used for the regional monsoon Index, irrespective of various ENSO subcategories; for CNE it is the U200, for H it is U200 and U850, and forNWit is U850. The current analysis, however, fails to indicate anything clearly about the NE region. When focusing on the remote influence from the eastern Pacific region, it is found that atmospheric contribution to regional ISM precipitation fails to indicate consistent roles among models, but sea surface temperature suggests strong connection. However, remote influence from the Central Pacific is captured uniformly in models via zonal components of wind in the H and NW regions. [ABSTRACT FROM AUTHOR]

This study evaluates the forecast skill of the fourth version of the Canadian coupled ocean-atmosphere general circulation model (CanCM4) and its model output statistics (MOS) to forecast the seasonal rainfall in Malaysia, particularly during early (October-November-December) and late (January-February-March) winter monsoon periods. CanCM4 is the latest component of the Canadian Seasonal to Inter-annual Prediction System (CanSIPS), which is a multi-seasonal climate prediction system developed particularly for Canada but applicable globally. Generally, CanCM4's skill in reproducing the climatology during winter is not as good as in other seasons because of the model's inability to simulate the regional synoptic circulations over the western Maritime Continent. In particular, the model fails to forecast the cold surges and Borneo vortex circulations that play critical roles in moisture horizontal advection. Moreover, its forecast skill during the early winter monsoon period is poorer than during the late period. Interestingly, forecast skill is enhanced when MOS models are applied as the MOS utilizes the predictive signals in the quasi-global predictors from the CanCM4 forecast system. The predictability can be traced to the conventional El Niño--Southern Oscillation (ENSO) and ENSO Modoki signals that are present in the CanCM4 forecast MOS predictor fields. The quasi-global sea-surface temperature and quasi-global sea-level pressure fields are found to be the most useful predictors. Interestingly, CanCM4 forecast signals associated with the Indian Ocean Dipole also contribute to the skill. Skill enhancement is particularly significant for northern Borneo during early monsoon periods in medium- and long-lead forecasts when the CanCM4 has minimal direct skill in the region. [ABSTRACT FROM AUTHOR]

This study examines the modulation of tropical cyclogenesis over the South China Sea (SCS) by the El Niño-Southern Oscillation (ENSO) Modoki during the boreal summer. Results reveal that there were more tropical cyclones (TCs) formed over the SCS during central Pacific warming years and less TC frequency during central Pacific cooling years. How different environmental factors (including low-level relative vorticity, mid-level relative humidity, vertical wind shear, and potential intensity) contribute to this influence is investigated, using a genesis potential (GP) index developed by Emanuel and Nolan. Composite anomalies of the GP index are produced for central Pacific warming and cooling years separately, which could account for the changes of TC frequency over the SCS in different ENSO Modoki phases. The degree of contribution by each factor is determined quantitatively by producing composites of modified indices in which only one of the contributing factors varies, with the others set to climatology. The results suggest that the vertical wind shear and low-level relative vorticity, which are associated with the ENSO Modoki-induced anomalous circulations in Matsuno-Gill patterns, make the largest contributions to the ENSO Modoki modulation of tropical cyclogenesis over the SCS as implied by the GP index. These results highlight the important roles of dynamic factors in the modulation of TC frequency over the SCS by the ENSO Modoki during the boreal summer. [ABSTRACT FROM AUTHOR]

Sea surface temperature (SST) anomalies in the Pacific Ocean during El Niño-Southern Oscillation (ENSO) episodes exhibit different spatial patterns from year to year. In most ENSO studies, SST anomalies have been analysed in the 3.4 or 3.0 El Niño regions. Recent analyses have considered different SST anomalies areas in the Pacific, such as ENSO Modoki, which takes into account anomalies in the central Pacific which are bounded by opposite anomalies in the eastern and western Pacific. In order to analyse the influence of different Pacific spatial patterns on South American precipitation and on the Southern Hemisphere atmospheric circulation, composites obtained from Canonical ENSO were compared with those from ENSO Modoki in cases when strong anomalies were present in the Central Pacific. During the Canonical El Niño (La Niña), there tends to be a precipitation increase (decrease) in the La Plata Basin (LPB, 45°W-65°W, 15°S-35°S) and a decrease (increase) over northern South America during all seasons. In ENSO Modoki exhibiting strong anomalies in the Central Pacific, these typical patterns are not observed, and in some regions the anomalies even show opposite signs. Precipitation anomaly differences or similarities over South America between the two cases occur in different areas and different seasons. In both cases, differences in tropical South American precipitation during both ENSO types are related to differences in the Walker circulation. In extra-tropical South America, the precipitation differences are due to differences in the Pacific wavetrains and differences in moisture flux intensity over the continent. Copyright © 2012 Royal Meteorological Society [ABSTRACT FROM AUTHOR]

Interannual variability of landfalling tropical cyclones (TCs) in China during 1960-2010 is investigated. By using the method of partial least squares regression (PLS-regression), canonical ENSO and ENSO Modoki are identified to be the factors that contribute to the interannual variability of landfalling TCs. El Niño Modoki years are associated with a greater-than-average frequency of landfalling TCs in China, but reversed in canonical El Niño years. Significant difference in genesis locations of landfalling TCs in China for the two kinds of El Niño phases occurs dominantly in the northern tropical western North Pacific (WNP). The patterns of low-level circulation anomalies and outgoing longwave radiation (OLR) anomalies associated with landfalling TC genesis with different types of El Niño phases are examined. During canonical El Niño years, a broad zonal band of positive OLR anomalies dominates the tropical WNP, while the circulation anomalies exhibit a meridionally symmetrical dipole pattern with an anticyclonic anomaly in the subtropics and a cyclonic anomaly near the tropics. In El Niño Modoki years, a vast region of negative OLR anomalies, roughly to the south of 25°N with a strong large-scale cyclonic anomaly over the tropical WNP, provides a more favorable condition for landfalling TC genesis compared to its counterpart during canonical El Niño years. For more landfalling TCs formed in the northern tropical WNP in El Niño Modoki years, there are more TCs making landfall on the northern coast of China in El Niño Modoki years than in canonical El Niño years. The number of landfalling TCs is slightly above normal in canonical La Niña years. Enhanced convection is found in the South China Sea (SCS) and the west of the tropical WNP, which results in landfalling TCs forming more westward in canonical La Niña years. During La Niña Modoki years, the landfalling TC frequency are below normal, owing to an unfavorable condition for TC genesis persisting in a broad zonal band from 5°N to 25°N. Since the western North Pacific subtropical high (WNPSH) in La Niña Modoki years is located in the westernmost region, TCs mainly make landfall on the south coast of China. [ABSTRACT FROM AUTHOR]

Extreme stream-flow events of Citarum River are derived from the daily stream-flows at the Nanjung gauge station. Those events are identified based on their persistently extreme flows for 6 or more days during boreal fall when the seasonal mean stream-flow starts peaking-up from the lowest seasonal flows of June-August. Most of the extreme events of high-streamflows were related to La Niña conditions of tropical Pacific. A few of them were also associated with the negative phases of IOD and the newly identified El Niño Modoki. Unlike the cases of extreme high streamflows, extreme low streamflow events are seen to be associated with the positive IODs. Nevertheless, it was also found that the low-stream-flow events related to positive IOD events were also associated with El Niño events except for one independent event of 1977. Because the occurrence season coincides the peak season of IOD, not only the picked extreme events are seen to fall under the IOD seasons but also there exists a statistically significant correlation of 0.51 between the seasonal IOD index and the seasonal streamflows. There also exists a significant lag correlation when IOD of June-August season leads the streamflows of September-November. A significant but lower correlation coefficient (0.39) is also found between the seasonal streamflow and El Niño for September-November season only. [ABSTRACT FROM AUTHOR]