ENSO Events Research Articles

ENSO Forcing of Rainfall Erosivity in the Wuding River Basin

Rainfall erosivity (RE) is an important indicator of the ability of rainfall to cause soil erosion and is linked to ENSO through the transport of rainfall. Accurate assessment of RE and improved understanding of RE are essential for soil erosion prediction, optimization of soil and water conservation measures, and ecological management and restoration. Therefore, the Wuding River Basin, a typical ecologically fragile area, is selected as the research area. The erosivity model based on daily rainfall was first used to calculate RE, and the temporal and periodic characteristics of RE are studied. Then the effects of the Southern Oscillation Index (SOI), the Surface Temperature of the Central East Equatorial Pacific Ocean (SST), and the Multivariate ENSO Index (MEI) on RE are explored by using cross wavelet technique. Results indicated that: (1) the concentration of rainfall leads to the largest RE values in summer compared with other seasons, accumulating about 69% of the annual RE; (2) The overall trend of increasing RE in the Wuding River basin is not significant, but shows an abrupt change in 2015; (3) the influence of the SOI and SST indices of ENSO events on RE is significant, which is shown to be a statistically significant correlation (95% confidence level), indicating that ENSO has a strong influence on the changing pattern of RE. These findings are helpful in predicting soil erosion and are significant for developing further erosion control measures.

Taxonomical and functional diversity dynamics of conspicuous echinoderms in the northeastern tropical Pacific over a decade

Understanding what determines spatio-temporal changes in echinoderm assemblages from an integrative perspective that considers biodiversity, species evenness, and species’ niches could permit superior community-scale characterizations of habitat resilience to disturbance. Such an approach was taken herein by tracking a Central Mexican Pacific echinoderm assemblage between 2012 and 2021, and higher richness, diversity, evenness, and functional entity counts were associated with more heterogeneous benthic assemblages. Echinoderm taxonomic composition was influenced by ENSO events, with higher functional diversity found during La Niña events. Conservation strategies should focus on species with unique functional traits to maintain the balance of coral community functionality.

Responses of the Sea Surface Temperature and Suspended Matter Concentration to ENSO Events in the Bohai Sea

Responses of the Sea Surface Temperature and Suspended Matter Concentration to ENSO Events in the Bohai Sea

Estimating Probabilities of Extreme ENSO Events from Copernicus Seasonal Hindcasts

Multi-system seasonal hindcasts supporting operational seasonal forecasts of the Copernicus Climate Change Service (C3S) are examined to estimate probabilities that El Niño and La Niña episodes more extreme than any in the reliable observational record could occur in the current climate. With 184 total ensemble members initialized each month from 1993 to 2016, this dataset greatly multiplies the realizations of ENSO variability during this period beyond the single observed realization, potentially enabling a detailed assessment of the chances of extreme ENSO events. The validity of such an assessment is predicated on model fidelity, which is examined through two-sample Cramér–von Mises tests. These do not detect differences between observed and modeled distributions of the Niño 3.4 index once multiplicative adjustments are applied to the latter to match the observed variance, although differences too small to be detected cannot be excluded. Statistics of variance-adjusted hindcast Niño 3.4 values imply that El Niño and La Niña extremes exceeding any that have been instrumentally observed would be expected to occur with a > 3% chance per year on average across multiple realizations of the hindcast period. This estimation could also apply over the next several decades, provided ENSO variability remains statistically similar to the hindcast period.

Active restoration efforts in the Central Mexican Pacific as a strategy for coral reef recovery

Introduction: The 1997-98 El Niño event caused massive coral bleaching and mortality in the Central Mexican Pacific (CMP). Punta de Mita alone used to harbor more than 30 % of the coral coverage in this region, with a mono-specific Pocillopora coverage. The 1997-1998 ENSO event caused massive coral mortality reducing live coral coverage to < 5 %. Despite being considered a coral region unlikely to recover, recent restoration efforts have been implemented to rehabilitate the coral community.
 Objective: To assess coral recovery by analyzing the coral growth and survival rates of branching Pocillopora species at Punta de Mita.
 Methods: Healthy coral fragments of opportunity were re-attached to the natural substrata using zip ties and measured considering their growth in terms of maximum length and width (cm) to determine their annual extension rates.
 Results: After 50 weeks, corals duplicated their size, with a mean growth of ~ 4 cm year-1. After 100 weeks (2 years), corals triplicated their size, increasing on average 8–9 cm in each diameter.
 Conclusions: Successful coral reef restoration activities in the Central Mexican Pacific are the result of Pocillopora’s physiological processes, such as fast growth rates, and recent life-history traits, like the ability to cope with thermal anomalies, which enable them to thrive in a dynamic region severely affected by natural and anthropogenic perturbations. Indeed, a region considered unlikely to recover has regained its live coral cover from < 5 % in 1998 up to 15 % in 20 years. This demonstrates the importance of assisting natural coral recovery with restoration efforts, especially in coral locations that, despite environmental perturbations, have proven to be resilient and may become coral refugia areas under the current climate change scenario.

The Conservation of Endemic Species--Take Galapagos Penguins as an Example

Endemic species refers to the species that are distributes only in a certain region of the world. Galapagos penguins, well-known as one of the smallest penguins in size, can be used as a typical example of endemic species. Since the extinction of endemic species in one place may lead to the extinction of the whole population of the species, endemic species may need some special attentions from the public. Unfortunately, Galapagos penguins, as a kind of endemic species, after being severely affected by ENSO event and human activities such as bycatch, is at the brink of extinction at the moment. Given that climate change is making ENSO even more frequently in the future, it is highly possible that without further intervention, the species of Galapagos penguins will be lost forever.

Quantifying the Predictability of ENSO Complexity Using a Statistically Accurate Multiscale Stochastic Model and Information Theory

Abstract An information theory–based framework is developed to assess the predictability and quantify the forecast uncertainty of ENSO complexity, which includes different types of ENSO events with diverse characteristics. With the assistance of a recently developed multiscale stochastic conceptual model that successfully captures both the large-scale dynamics and many crucial statistical properties of the observed ENSO complexity, it is shown that different ENSO events possess distinct predictability limits. Beyond the ensemble mean value, the spread of the ensemble members also contains valuable information about predictability. First, La Niña events are most predictable at long lead times, especially as a subsequent transition after eastern Pacific (EP) El Niño events or during multiyear La Niña phases. Second, EP El Niños tend to be more predictable than the central Pacific (CP) El Niño events up to one year ahead due to a more favorable signal-to-noise ratio, even though their onset remains hard to predict. Third, 4 out of 6 CP El Niño events seem to be predictable up to 24 months ahead, where such strong predictability is often converted to skillful forecast. Fourth, strengthening/weakening the Walker circulation intensity increases/decreases CP predictability at long leads. Fifth, accounting for intraseasonal wind events in the initial condition strongly contributes to EP predictability at lead times of less than one year. Finally, it is shown that a Gaussian approximation of the information gain computation is accurate, making the information theory approach tractable for studying the predictability of more sophisticated models.

Extreme temperatures detection and attribution related to external forcing in Madagascar

AbstractIn this article, we use standard extreme temperature indices to detect and attribute external forcing in Madagascar. These indices are calculated from observations and multi‐model ensemble mean responses on anthropogenic‐plus‐natural (ALL), greenhouse gases (GHG), natural (NAT) and anthropogenic (ANT) which are subtracted from ALL and NAT forcings over 1950–2018. Correlation analysis emphasizes that the observed changes are more influenced by ENSO events, especially in minimum temperature. The observed changes are regressed or combined with model simulations from the sixth phase of the Coupled Model Inter‐comparison Project (CMIP6) to assess human impacts in indices. CMIP6 models with ALL, GHG and ANT forcings correspond well with the observations for the frequency indices than the intensity indices. Moreover, decadal trends indicate the existence of anthropogenic warming according to observations and multi‐model ensembles with ALL, GHG and ANT forcings. Detection and attribution parties identify and justify the causes of the observed changes. We do this by performing the single‐signal and two‐signal analysis using the Regularized Optimal Fingerprinting (ROF) method with Total Least Square (TLS) regression. We estimate internal climate variability by means of control model simulations. As a result, we note an inconsistency in the warming trend with the NAT forcing. The influence of ALL, GHG and ANT forcings is detectable for standard extreme temperature indices between 1950 and 2018. Nearly, observed changes are attributed to GHG and ANT forcings except for coldest night and warm nights in Madagascar.

A Simple Multiscale Intermediate Coupled Stochastic Model for El Niño Diversity and Complexity

AbstractEl Niño‐Southern Oscillation (ENSO) is the most prominent interannual climate variability in the tropics and exhibits diverse features in spatiotemporal patterns. This paper develops a simple multiscale intermediate coupled stochastic model to capture the ENSO diversity and complexity. The model starts with a deterministic and linear coupled interannual atmosphere, ocean, and sea surface temperature (SST) system. It can generate two dominant linear solutions representing the eastern Pacific (EP) and the central Pacific (CP) El Niños, respectively. In addition to adopting a stochastic model for characterizing the intraseasonal wind bursts, another simple stochastic process is developed to describe the decadal variation of the background Walker circulation. The latter links the two dominant modes in a simple nonlinear fashion and advances the modulation of the strength and occurrence frequency of the EP and the CP events. Finally, cubic nonlinear damping is adopted to parameterize the relationship between subsurface temperatures and thermocline depth. The model succeeds in reproducing the spatiotemporal dynamical evolution of different types of ENSO events. It also accurately recovers the strongly non‐Gaussian probability density function, the seasonal phase locking, the power spectrum, and the temporal autocorrelation function of the SST anomalies in all the three Niño regions (3, 3.4, and 4) across the equatorial Pacific. Furthermore, both the composites of the SST anomalies for various ENSO events and the strength‐location bivariate distribution of equatorial Pacific SST maxima for the El Niño events from the model simulation highly resemble those from the observations.

Sedimentary Records of Phytoplankton Communities in Sanmen Bay in China: The Impacts of ENSO Events over the Past Two Centuries

Phytoplankton communities, showing significant spatiotemporal variation within bay areas, play an important role in the structure and function of nearshore marine ecosystems. However, the absence of long-term high-resolution datasets has hindered our understanding of the effect of ENSO-driven environmental changes on phytoplankton communities in coastal ecosystems. Herein, by performing biomarker inversion analyses on two centuries’ worth of sedimentary organisms in the Sanmen Bay area, we observed a marked El Niño/La Niña-related succession; specifically, that El Niño-induced warming had increased the biomass of phytoplankton by 57.89%, while also increasing the proportion of diatoms by 76.40%. In contrast, La Niña years exhibited a decrease in the biomass of phytoplankton by 54.23%. Further, over three decades of observational data from the Sanmen Bay suggest that La Niña years can promote occasional blooms through monsoonal mixing and land-based inputs. Consequently, the nearshore marine ecosystem of the bay area, being subject to intense anthropogenic activity and land–sea interactions, can be said to be influenced by global-scale ocean–atmosphere processes. Going forward, the connection between short-term extreme events and long-term changes in the nearshore marine ecosystem should receive greater attention.

Contrasting El Niño–La Niña Predictability and Prediction Skill in 2-Year Reforecasts of the Twentieth Century

Abstract Despite the growing demand for long-range ENSO predictions beyond 1 year, quantifying the skill at these lead times remains limited. This is partly due to inadequate long records of seasonal reforecasts that make skill estimates of irregular ENSO events quite challenging. Here, we investigate ENSO predictability and the dependency of prediction skill on the ENSO cycle using 110 years of 24-month-long 10-member ensemble reforecasts from ECMWF’s coupled model (SEAS5-20C) initialized on 1 November and 1 May during 1901–2010. Results show that Niño-3.4 SST can be skillfully predicted up to ∼18 lead months when initialized on 1 November, but skill drops at ∼12 lead months for May starts that encounter the boreal spring predictability barrier in year 2. The skill beyond the first year is highly conditioned to the phase of ENSO: Forecasts initialized at peak El Niño are more skillful in year 2 than those initialized at peak La Niña, with the transition to La Niña being more predictable than to El Niño. This asymmetry is related to the subsurface initial conditions in the western equatorial Pacific: peak El Niño states evolving into La Niña are associated with strong upper-ocean heat discharge of the western Pacific, the memory of which stays beyond 1 year. In contrast, the western Pacific recharged state associated with La Niña is usually weaker and shorter-lived, being a weaker preconditioner for subsequent El Niño, the year after. High prediction skill of ENSO events beyond 1 year provides motivation for extending the lead time of operational seasonal forecasts up to 2 years.

Interannual Variability of Regional Hadley Circulation and El Niño Interaction

AbstractEl Niño‐Southern Oscillation (ENSO) triggers variations of the global Hadley circulation (HC), while the latter may potentially feedback to ENSO events. Previous studies mainly investigated the interactions between ENSO and the global zonal‐mean HC. Here, we present a regional perspective of HC variability by introducing zonal variations. Results show that El Niño intensifies the regional HC over the central‐eastern Pacific, while weakening the regional HC over both the Indo‐Pacific warm pool and the tropical Atlantic. The background seasonal cycle modulates the equatorial‐asymmetric component of HC, with an anticlockwise (clockwise) asymmetric circulation over the central equatorial Pacific before (after) El Niño peaks. Remarkably, the asymmetric HC in boreal spring leads ENSO with a lead correlation of up to 0.68, mediated by the wind‐evaporation‐sea surface temperature (SST) feedback and other atmosphere‐ocean dynamics. The antecedent HC anomaly may contribute to ENSO predictability.

How climate change and climate variability affected trip distance of a commercial fishery

Changes in climate factors affect the distribution of various tuna species differently due to their unique physiological adaptations and preferred habitats. As the resulting spatial distributions of tunas alter in response to climate change and climate variability, the distribution of fishing effort will, in turn, be affected. This study uses a quantitative model to estimate the impacts of SST and ENSO events on trip distance of the Hawaii deep-set longline fleet between 1991 and 2020. The results show that the higher the SST of the fishing grounds of the Hawaii longline fleet, the longer trip distance; whereas ENSO events could result in shorter trip distance, possibly due to changes in catch rates of different tuna species through spatial redistribution during El Niño and La Niña events.

Influence of the AMO and its modulation of the ENSO effects on summer precipitation in Mexican coastal regions

Abstract Due to its geographical location and interaction with the two largest oceans, Mexico's climate is strongly influenced by various climatic oscillations. Therefore, association studies between climatic indices and Mexico's climate have scientific and practical importance. Teleconnection patterns have been reported between summer precipitation and various climate oscillations. For the AMO, results are not totally coincident, and modulation of ENSO effects has not been explored. Correlation analyses between AMO and ONI 3.4 with summer precipitation (June–September) at individual 203 weather stations in Mexican coastal zones were carried out, and average precipitation was compared according to AMO phases and their combinations with ENSO events. With AMO + , it tends to rain more in northern Yucatan Peninsula, from Chiapas to Jalisco, and in the southern California Peninsula; with AMO− in Tamaulipas, Sonora and northern California Peninsula. AMO modulates ENSO effects; ONI correlations pattern strengthens with AMO+. El Niño summers are less dry with AMO− on Atlantic coast, Sonora and northern California Peninsula; on Pacific coast, alternating bands are observed. With AMO − , La Niña summers tend to be wetter toward south with AMO+ and toward north with AMO−. These changes can be related to variations in the surface and low-level wind regimes previously reported in literature.

Amplified Asymmetric Impact of ENSO Events on the Wintertime Pacific‐North American Teleconnection Pattern

AbstractEl Niño/Southern Oscillation (ENSO) as the strongest tropical interannual signature has the most prominent impact on wintertime Pacific‐North American (PNA) teleconnection pattern. ENSO exhibits an increasing asymmetry in recent decades. This study quantifies its extratropical asymmetric impact on the amplitude of the PNA pattern, using a normalized asymmetry index defined as a ratio of asymmetric versus symmetric anomalies for El Niño and La Niña. Relative to the ENSO asymmetry, the extratropical asymmetric impact is largely amplified especially downstream by up to 82%. Such an amplification is attributed to noticeable increases, 83.6% (68.9%), in asymmetry of Rossby wave source (RWS) anomalies over two key regions of North Pacific, in which anomalous divergence induced by nonlinear condensational heating feedback and anomalous synoptic eddy forcing are two major contributors. The former contributes 39.3% (47.5%) over the western (eastern) North Pacific through increasing asymmetric RWS anomalies, while the latter contributes 29.5% (21.3%) through decreasing symmetric RWS anomalies.

Relationship between the hadley circulation and tropical SST meridional structures under different thermal conditions in the indo-pacific warm pool

The Hadley circulation (HC), as a thermally driven large-scale meridional circulation, acts a significant role in the changes of global climate. The modulation of Indo-Pacific warm pool (IPWP) thermal conditions on the relationship between the HC and different tropical sea surface temperature (SST) meridional structures was investigated. Based on the two components of HC and SST, one equatorially asymmetric component (HEA for HC, SEA for SST) and one equatorially symmetric component (HES for HC, SES for SST), the connections of HC to different SST variations in the warm and cold IPWP are explored. The result demonstrates that the relationship of the HC to tropical SST is suppressed in the cold IPWP conditions, whereas it is equivalent to the climatology in the warm IPWP conditions. The plausible mechanism is that the cold (warm) IPWP events are in concordance with the La Niña (El Niño) decay phase. The La Niña decay phase are associated with significant equatorially asymmetric SST anomalies within the IPWP, generating an anomalous meridional circulation and favoring a strengthened equatorially asymmetric anomalous meridional circulation. By contrast, the SST anomalies associated with El Niño decay phase are insignificant. The role of La Niña decay conditions in determining the suppressed connection between SST and HC is further verified by exploring the result after 1979. A similar suppressed response contrast has been detected. Therefore, the results demonstrate that warm and cold ENSO events have impacts on the interannual thermal conditions of IPWP, whereby it plays considerable role in impacting the relationship between the HC and tropical SST. Particularly, with the rapid warming, the interconnection between ENSO events and thermal conditions of IPWP under different timescales could be altered, the influence of which on the responses of the HC to tropical SST remains uncertain and is worthy further researching.

Spatiotemporal variation of daily precipitation concentration and its potential relationship with climatic factors and land use types in the Haihe River basin, China

AbstractPrecipitation concentration is a key climatic factor in the hydrologic system. The purpose of this study was to explore the spatiotemporal variation in precipitation concentration and its possible relationship with large‐scale atmospheric circulation and land use types. Based on daily precipitation recorded at 254 stations during 1961–2019 throughout the Haihe River basin (HRB), linear slope and Manner–Kendall trend analysis were used to analyse the spatial variations and trends of the annual daily precipitation concentration index (CI). The Pearson correlation coefficient and cross wavelet analysis were used to evaluate potential correlations between CI and eight climatic factors. Meteorological stations were classified into three land use types: urban type (UT), farmland type (FT), and natural type (NT) using hierarchical clustering, and the impacts of land use types on CI variations and trends were investigated. Annual CI in HRB showed a significant downward trend with a linear rate of −0.0058/decade, and about 210 of the 254 stations had a downtrend, in which 42 stations were at the significance level of 0.05 but did not reach the significance level of 0.01, and 52 stations are at the 0.01 significance level. The East Asian monsoon index (EASMI), South Asian monsoon index (SASMI), South China Sea monsoon index (SCSMI), and Southern Oscillation Index (SOI) were positively correlated with CI, whereas the Pacific Decadal Oscillation (PDO), Multivariate ENSO index (MEI), and Western Pacific index (WP) were negatively correlated. The Sunspot index (SS) had a significant resonance period of 9–14‐year with CI. EASMI and ENSO events were the dominant factors driving CI trends. The negative CI trends of UT were more significant than those of FT and NT, with linear slope gaps of −0.0041/decade (UT versus FT) and −0.0064/decade (UT vs. NT), respectively.

Influences of strong and moderate ENSO events on the Maranhão precipitation from the western equatorial Atlantic SST anomalies

Influences of strong and moderate ENSO events on the Maranhão precipitation from the western equatorial Atlantic SST anomalies

Effects of ENSO events on the intensity, seasonality, and diversity of reproductive phenology of Miconia (Melastomataceae) species in tropical rainforest.

We evaluated the phenology and reproductive phenological diversity of three sympatric species of Miconia in a gallery forest in the Chapada Diamantina mountains, Bahia, Brazil. The reproductive phenophases (bud, flower, immature fruit, and mature fruit) of M. alborufescens (N=38), M. holosericea (N=46), and M. prasina (N=44) were evaluated monthly, between June/2008 and June/2015. The Fournier index was used to assess the intensities of the reproductive phenophases; synchrony and seasonality were analyzed using circular statistics and the Rayleigh (Z) test. The Frideman and Wilcoxon tests were used to verify interannual variations in phenological patterns. Reproductive phenological diversity was measured by calculating the Shannon-Wiener index; ANOVA tested possible differences in the means of diversity among the different years. The reproductive phenophases of the studied Miconia species occurred sequentially (M. alborufescens, then M. holoserica, followed by M. prasina), in the transition between the dry and rainy seasons, with little overlap between them. In general, the species showed seasonal and synchronic phenological patterns, with some variations that coincided with El Niño and/or La Niña events, e.g., demonstrating changes in the periodicity, synchrony, and intensity of their phenophases. The intensity of fruiting, for example, showed increases during La Niña years. Reproductive phenological diversity appears to respond to climate changes resulting from El Niño events and periods of prolonged drought, with high Shannon-Wiener index values. The results also suggest that the effects of global climatic phenomena (El Niño and La Niña) that alter regional climatic seasonality can also cause variations in the reproductive phenological rhythms of the Miconia species studied.

An evaluation of high-resolution ocean reanalyses in the California current system

Sparse and inconsistent coverage of ocean observations makes analysis of climate impacts on ocean physics and marine ecosystems challenging. As a result, ocean reanalyses (i.e., ocean models constrained by observations through data assimilation) were developed to provide historical ocean state estimates that are spatially and temporally uniform. Recent advances in high performance computing and the number and quality of observations have led to the development of high-resolution ocean reanalyses, which offer an opportunity to investigate coastal ocean variability with enhanced fidelity. In this study, we evaluate the ability of three high-resolution ocean reanalyses, including the Global Ocean Reanalysis and Simulations (GLORYS), the Ocean Reanalysis System version 5 (ORAS5), and the California Current System Reanalysis (CCSRA), to accurately represent ocean temperature and salinity (from the surface to the bottom), sea surface height, and mesoscale activity in the California Current Large Marine Ecosystem (CCLME). Specifically, we compare these reanalyses to a variety of assimilated and independent in situ and satellite derived observations along the U.S. west coast. We find that the reanalyses generally reproduce large-scale variability in temperature and sea surface height within the CCLME, including effects of major ENSO events and recent marine heatwaves. We also show that GLORYS and CCSRA, with their finer horizontal resolution, have enhanced fidelity in simulating nearshore ocean parameters such as coastal sea level and bottom temperature along the continental shelf. Our results suggest that these tools can be used to study the fine-scale features of the California Current System over the past several decades.