Were merely storm-landslides driven by the 2015-2016 Niño in the Mendoza River valley?

Since Holocene time, above-mean precipitations recorded during the El Niño warm ENSO phase have been linked to the occurrence of severe debris flows in the arid Central Andes. The 2015–2016 El Niño, for its unusual strength, began driving huge and dangerous landslides in the Central Andes (32°) in the recent South Hemisphere summer. The resulting damages negatively impacted the regional economy. Despite this, causes of these dangerous events were ambiguously reported. For this reason, a multidisciplinary study was carried out in the Mendoza River valley. Firstly, a geomorphological analysis of affected basins was conducted, estimating morphometric parameters of recorded events such as velocity, stream flow, and volume. Atmospheric conditions during such events were analyzed, considering precipitations, snow cover, temperature range, and the elevation of the zero isotherm. Based on our findings, the role of El Niño on the slope instability in the Central Andes is more complex in the climate change scenario. Even though some events were effectively triggered by intense summer rainstorm following expectations, the most dangerous events were caused by the progressive uplifting of the zero isotherm in smaller basins where headwaters are occupied by debris rock glaciers. Our research findings give light to the dynamic coupled system ENSO–climate change–landslides (ECCL) at least in this particular case study of the Mendoza River valley. Landslide activity in this Andean region is driven by wetter conditions linked to the ENSO warm phase, but also to progressive warming since the twentieth century in the region. This fact emphasizes the future impact of the natural hazards on Andean mountain communities.     

Comparison of 1982–1983 and 1997–1998 El Niño effects on the shallow-water fish assemblage of the Patos Lagoon estuary (Brazil)

Meteorological impacts of El Niño events of 1982–1983 and 1997–1998 were observed in locations throughout the world. In southern Brazil, El Niño events are associated with increased rainfall and higher freshwater discharge into Patos Lagoon, a large coastal lagoon that empties into the Atlantic Ocean. Based on interdecadal meteorological and biological data sets encompassing the two strongest El Niño events of the last 50 yr, we evaluated the hypothesis that El Niño-induced hydrological changes are a major driving force controlling the interannual variation in the structure and dynamics of fishes in the Patos Lagoon estuary. High rainfall in the drainage basin of the lagoon coincided with low salinity in the estuarine area during both El Niño episodes. Total rainfall in the drainage basin was higher (767 versus 711 mm) and near-zero salinity conditions in the estuarine area lasted about 3 mo longer during the 1997–1998 El Niño event compared with the 1982–1983 event. Hydrological changes triggered by both El Niño events had similar relationships to fish species composition and diversity patterns, but the 1997–1998 event appeared to have stronger effects on the species assemblage. Although shifts in species composition were qualitatively similar during the two El Niño events, distance between El Niño and non-El Niño assemblage multivariate centroids was greater during the 1996–2000 sampling period compared with the 1979–1983 period. We provide a conceptual model of the principal mechanisms and processes connecting the atmospheric-oceanographic interactions triggered by the El Niño phenomena and their effect on the estuarine fish assemblage.     

Characteristics of tropical cyclones making landfall on the Pacific coast of Mexico: 1970-2010

This study evaluates impacts from tropical cyclone (TC) landfalls on populated areas located along the Pacific Ocean coast of Mexico. The period of interest is from 1970 through 2010 and an international disaster database is used to identify the impact from the landfalling TCs. More than 30 landfall events occurred during the period; we examined the top 25 TCs based on rainfall accumulation, as well as the top 10 TC-related disasters based on the affected population. Each event resulted in affected population from 20 000 to more than 800 000. Strong winds and heavy rainfall, during periods of one to three days, are associated with property damage and loss of lives. Our results indicate that excessive rainfall accumulations and daily rates, over highly populated areas, are important elements associated with the occurrence of disasters. Six of the top 10 TC-related disasters occurred during El Niño and three during neutral conditions; however, looking at the top 25 events, 10 occurred during El Niño and 10 during neutral conditions. Three case studies that occurred during El Niño events (Liza in 1976, Pauline in 1997, and Lane in 2006) are documented in more detail as they affected areas with different population densities in the southern and northwestern coasts of Mexico.     

About the variability in thunderstorm and rainfall activity over India and its association with El Niño and La Niña

Thunderstorms are of much importance in tropics, as this region is considered to have central role in the convective overturn of the atmosphere and play an important role in rainfall activity. It is well known that El Niño and La Niña are well associated with significant climate anomalies at many places around the globe. Therefore, an attempt is made in this study to analyze variability in thunderstorm days and rainfall activity over Indian region and its association with El Niño and La Niña using data of thunderstorm day’s for 64 stations well distributed all over India for the period 1981–2005 (25 years). It is seen that thunderstorm activity is higher and much variable during pre-monsoon (MAM) and southwest monsoon (JJAS) than the rest of the year. Positive correlation coefficients (CCs) are seen between thunderstorms and rainfall except for the month of June during which the onset of the southwest monsoon sets over the country. CCs during winter months are highly correlated. Composite anomalies in thunderstorms during El Niño and La Niña years suggest that ENSO conditions altered the patterns of thunderstorm activity over the country. Positive anomalies are seen during pre-monsoon (MAM) and southwest monsoon months (JAS) during La Niña years. Opposite features are seen in southwest monsoon during El Niño periods, but El Niño favors thunderstorm activity during pre-monsoon months. There is a clear contrast between the role of ENSO during southwest monsoon and post-monsoon on thunderstorm activity over the country. Time series of thunderstorms and precipitation show strong association with similarities in their year-to-year variation over the country.     

Recent catastrophic debris flows in Luding county, SW China: geological hazards, rainfall analysis and dynamic characteristics

About 127 debris flow gullies have been identified, and debris flows have been an important type of geological hazards in Luding County, affecting cities, towns, rural areas, scenic spots and human’s engineering projects, such as mining and waterpower utilizing equipments. In this summary paper, recent two catastrophic debris flow events occurred on June 30, 2005, in Chuni town, in the central of the county, and on August 11, 2005, in Hailuogou scenic spot, in the southwest of the county, respectively, are reviewed. The debris flow events are introduced on the basis of field investigation and RS interpretation and the triggering factors for flow occurrence are identified. Furthermore, the rainfall related to flow occurrence including antecedent rainfall and intraday rainfall is analyzed, and a power-law function which can be used as a basic warning line is established based on both antecedent effective rainfall and intraday rainfall. Then dynamic parameters such as flow velocity and flow discharge are calculated, respectively. Through comparison and discussion, some conclusions are made including (1) The antecedent rainfall played an important role for debris flows which generated predominately based on the slope-instability due to the saturated loose sediments; (2) Despite slower flow velocity and smaller magnitude, the slope-type debris flows just like 2005-6-30 debris flows usually lead to serious damages for the difficulty to forecast and to prevent; (3) The mistaken recognition on debris flow hazards and lack of prevention consciousness strengthen the hazard and damage degree. This research is of certain significance for the prevention and mitigation of debris flow hazards and for the planning of the town building and tourism development in the future.     

Relationships between landscape morphology,climate and surface erosion in northern Peru at 5°S latitude

The northern segment of the Peruvian Andes is affected by a twofold climate with measurable implications on landscapes and landscape dynamics. During ‘normal’ or ‘neutral’ years easterly winds bring rain from the Atlantic and the Amazon Basin to the Sierras, which results in a seasonal climate with rather low-intensity precipitations. In contrast, during the large-scale warm phase of the ENSO cycle, El Niños transfer moisture from the Pacific to the Peruvian coast by westerly winds and result in high-intensity precipitation. We investigate the effects of this twofold climate for the case of the Piura drainage basin at ca. 5°S latitude (northern Peru). In the headwaters that have been under the influence of the easterlies, the landscape is mantled by a thick regolith cover and dissected by a network of debris flow channels that are mostly covered by a thick layer of unconsolidated sediment. This implies that in the headwaters of the Piura River sediment discharge has been limited by the transport capacity of the sediment transfer system. In the lower segment that has been affected by high-intensity rainfall in relation to the westerlies (El Niños), the hillslopes are dissected by debris flow channels that expose the bedrock on the channel floor, implying a supply-limited sediment discharge. Interestingly, measurements at the Piura gauging station near the coast reveal that, during the last decades, sediment was transferred to the lower reaches only in response to the 1982–1983 and 1997–1998 El Niño periods. For the latter period, synthetic aperture radar (SAR) intensity images show that the locations of substantial erosion are mainly located in areas that were affected by higher-than-average precipitation rates. Most important, these locations are coupled with the network of debris flow channels. This implies that the seasonal easterlies are responsible for the production of sediment through weathering in the headwaters, and the highly episodic El Niños result in export of sediment through channelized sediment transport down to the coastal segment. Both systems overlap showing a partially coupled sediment production–delivery system.     

Growth increment and stable isotope analysis of marine bivalves: Implications for the geoarchaeological record of El Niño

The 1982–1983 El Niño event afforded the opportunity to develop criteria for the recognition of ancient El Niños using mollusks from archaeological sites along coastal South America. A combination of growth increment and stable isotope analyses indicated that elevated sea surface temperatures during large scale El Niños leave a record decodable from the growth patterns of selected bivalve shells. The intertidal venerid Chione subrugosa displayed a pronounced break in the valve margin profile following the 1982-1983 event but provided an inconsistent stable isotope pattern. The subtidal carditid Trachycardium procerum, on the other hand, preserved a discernible and diagnostic growth interruption as well as an expected trend in stable isotope indicators of salinity and temperature change. We conclude that some of the major culturally disruptive El Niño events can be recognized in the geoarchaeological record by these techniques, especially if ancillary information, such as faunal distribution patterns, are also considered. Perhaps the most serious constraint upon application of this approach involves microstratigraphic resolution of shell midden deposits. Stratigraphic sampling of midden material should be accompanied, if possible, by sampling of proximal natural strata. The chances of discovery of major El Niño perturbations in the geoarchaeological record of shell middens is enhanced by the catastrophic nature of such events and by the indication that major El Niños have a high probability of being closely spaced in time.     

Debris flow hazards for mountain regions of Russia: regional features and key events

The total area of debris flow territories of the Russian Federation accounts for about 10% of the area of the country. The highest debris flow activity areas located in Kamchatka-Kuril, North Caucasus and Baikal debris flow provinces. The largest debris flow events connected with volcano eruptions. Maximum volume of debris flow deposits per one event reached 500 × 10⁶ m³ (lahar formed during the eruption of Bezymyanny volcano in Kamchatka in 1956). In the mountains of the Greater Caucasus, the maximum volume of transported debris material reached 3 × 10⁶ m³; the largest debris flows here had glacial reasons. In the Baikal debris flow province, the highest debris flow activity located in the ridges of the Baikal rift zone (the East Sayan Mountains, the Khamar-Daban Ridge and the ridges of the Stanovoye Highland). Spatial features of debris flow processes within the territory of Russia are analyzed, and the map of Debris Flow Hazard in Russia is presented. We classified the debris flow hazard areas into 2 zones, 6 regions and 15 provinces. Warm and cold zones are distinguished. The warm zone covers mountainous areas within the southern part of Russia with temperate climate; rain-induced debris flows are predominant there. The cold zone includes mountainous areas with subarctic and arctic climate; they are characterized by a short warm period, the occurrence of permafrost, as well as the predominance of slush flows. Debris flow events are described for each province. We collected a list of remarkable debris flow events with some parameters of their magnitude and impact. Due to climate change, the characteristics of debris flows will change in the future. Availability of maps and information from previous events will allow to analyze the new cases of debris flows.     

The beach ridges at Santa,Peru: El Niño,uplift, and prehistory

Recent work on the beach ridges at Santa, Peru (9° s latitude) upholds an earlier hypothesis, based on sedimentary evidence, that the ridges were formed by massive sediment pulses during rains associated with major incursions of the warm water El Niño countercurrent. The ridges can therefore be used to date major El Niño events. The alternate hypothesis for the Santa ridge origin cited minor sequential uplift as the causal factor; this hypothesis has been disproven, though one previously unreported uplift event at about 4200 years B.P. has been identified at Santa. In general, landscape alteration processes such as El Niño floods and tectonic uplift affect human populations, and accurate chronologies of these events are necessary to interpret the archaeological record. Geoarchaeological research offers the key to constructing landscape alteration chronologies, which are also of use to geologists for studies of earthquake prediction, sedimentation processes, and paleoclimatology.     

Determing the effects of El Niño-Southern Oscillation events on coastal water quality

The importance of the El Niño-Southern Oscillation (ENSO) on regional-scale climate variability is well recognized although the associated effects on local weather patterns are poorly understood. Little work has addressed the ancillary impacts of climate variability at the community level, which require analysis at a local scale. In coastal communities water quality and public health effects are of particular interest. Here we describe the historical influence of ENSO events on coastal water quality in Tampa Bay, Florida (USA) as a test case. Using approximate randomized statistics, we show significant ENSO influences on water quality particularly during winter months, with significantly greater fecal pollution levels during strong El Niño winters and significantly lower levels during strong La Niña winters as compared to neutral conditions. Similar significant patterns were also noted for El Niño and La Niña fall periods. The success of the analysis demonstrates the feasibility of assessing local effects associated with large-scale climate variability. It also highlights the possibility of using ENSO forecasts to predict periods of poor coastal water quality in urban region which local agencies may use to make appropriate prepations.     

Trends and extreme value analysis of rainfall pattern over homogeneous monsoon regions of India

Trends of pre-monsoon, monsoon and post-monsoon rainfall pattern were studied on decadal basis over different homogeneous monsoon regions in India for the period 1871–2008. It is attempted to understand the relation of monsoon rainfall with the global teleconnections of El Niño and La Niña, for which the correlation analysis has been carried out with Darwin pressure and Niño 3.4 sea surface temperature (Niño 3.4 SST). The correlation analysis inferred that the significant correlations were observed when monsoon rainfall is related to ENSO indices on decadal scale than on annual ones. The study also found that the north-west region is more affected by the moderate El Niño years compared to strong El Niño years. The regions Central North-East and North-East could not make any difference among weak, moderate and strong La Niña events. The authors also have carried out the extreme value analysis over different homogeneous monsoon regions of India as well as for whole India. The results show that the return values of rainfall are increasing with the return periods for the forthcoming 10, 20, 50 and 100 years. The heterogeneity in number of threshold years that were recorded for the extreme rainfall over north-east (humid climatic type) and north-west (arid climatic type) described the climate variability. The results of the present study may be useful for the policy makers in understanding the rainfall exceedance in different return periods for planning the risk management strategies.     

Landslide susceptibility and hazard assessment in San Ramón Ravine, Santiago de Chile, from an engineering geological approach

Debris flows and soil and rock slides are among the main geological hazards in the mountain foothills of Central Chile. Geological risk associated with the development of landslides, especially debris flows triggered in the basins of ravines that drain into the capital city, Santiago, has increased in time due to accelerated urban expansion. A landslide hazard evaluation in the San Ramón Ravine, located within the foothills of Santiago is presented. Hazard evaluation is based on a methodology that combines the determination of landslide susceptibility calculated by integration of conditioning factors, with the assessment of slope failure and runout probabilities incorporating geotechnical engineering approaches. The methodology is appropriate for medium or subregional scale studies with limited data. The results show that in San Ramón Ravine the landslide hazard consists mainly of debris flows, rock block slides, rock falls and shallow soil slides. Among these, debris flows are the most important due to the urban area that can be affected. Other case studies show that the method can be used in other regions with minor adaptations for territorial planning or for engineering and environmental purposes.     

Short- and Long-Term Vegetative Propagation of Two <Emphasis Type="Italic">Spartina</Emphasis> Species on a Salt Marsh in Southern Brazil

Spartina alterniflora and Spartina densiflora are native salt marsh plants from the Atlantic coast; their habitats in Patos Lagoon estuary (southern Brazil) are characterized by a microtidal regime (<0.5 m) and, during El Niño events, high estuarine water levels and prolonged flooding due to elevated freshwater discharge from a 200,000-km² watershed. During and between El Niño events, the vegetative propagation of these two Spartina species in the largest estuary of southern Brazil (Patos Lagoon) was evaluated by monitoring transplanted plants for 10 years (short-term study) and interpreting aerial photos of natural stands for 56 years (long-term study). During the short-term study, S. alterniflora quickly occupied mud flats (up to 208 cm year^?1) by elongation of rhizomes, whereas S. densiflora showed a modest lateral spread (up to 13 cm year^?1) and generated dense circular-shaped stands. However, moderate and strong El Niño events can promote excessive flooding and positive anomalies in the estuarine water level that reduce the lateral spread and competitive ability of S. densiflora. During the long-term study, natural stands of S. alterniflora and S. densiflora had steady lateral spread rates of 152 and 5.2 cm year^?1, respectively, over mud flats. In the microtidal marshes of the southwest Atlantic, the continuous long-term lateral expansion of both Spartina species embodies periods of intense flooding stress (moderate and strong El Niños), when there is a decrease of vegetative propagation and less stressful low water periods of fast spread over mud flats (non-El Niño periods and weak intensity El Niños).     

The characteristics of the Mocoa compound disaster event,Colombia

A rainfall-induced compound disaster happened in Mocoa in the pre-dawn hours of 1 April 2017. More than 300 people were killed, and a large number of houses and roads were destroyed in the worst catastrophe in the history of Mocoa. To investigate this disaster, a detailed interpretation was carried out using high-resolution images. Analysis of disaster characteristics based on satellite image revealed that the disaster could be identified as a consequence of compound mountain hazards including landslides, debris flows, and mountain torrents. The mountain hazards converged in the mountain watershed, which amplified the disaster’s effects. Analysis considers that this disaster is the result of heavy rainfalls. Moreover, in-depth interpretation of rainfall data and satellite images spanning over 16 years reveals that the previous El Niño event (2014–2016) also played an important role, which caused reduced rainfall and vegetation coverage. The long period of drought brought by El Niño affected the growth of vegetation and reduced the ability of vegetation to cope with heavy rainfalls. The results reveal that both antecedent rainfalls and climate impact need to be taken into consideration for mountain hazard analysis.     

ENSO impacts on salinity in Tampa Bay, Florida

Estuarine salinity distributions reflect a dynamic balance between the processes that control estuarine circulation. At seasonal and longer time scales, freshwater inputs into estuaries represent the primary control on salinity distribution and estuarine circulation. El Niño-Southern Oscillation (ENSO) conditions influence seasonal rainfall and stream discharge patterns in the Tampa Bay, Florida region. The resulting variability in freshwater input to Tampa Bay influences its seasonal salinity distribution. During El Niño events, ENSO sea surface temperature anomalies (SSTAs) are significantly and inversely correlated with salinity in the bay during winter and spring. These patterns reflect the elevated rainfall over the drainage basin and the resulting elevated stream discharge and runoff, which depress salinity levels. Spatially, the correlations are strongest at the head of the bay, especially in bay sections with long residence times. During La Niña conditions, significant inverse correlations between ENSO SSTAs and salinity occur during spring. Dry conditions and depressed stream discharge characterize La Niña winters and springs, and the higher salinity levels during La Niña springs reflect the lower freshwater input levels.     

Meteotsunamis in the northeastern Gulf of Mexico and their possible link to El Niño Southern Oscillation

Analysis of 20-year time series of water levels in the northeastern Gulf of Mexico has revealed that meteotsunamis are ubiquitous in this region. On average, 1–3 meteotsunamis with wave heights >0.5 m occur each year in this area. The probability of meteotsunami occurrence is highest during March–April and June–August. Meteotsunamis in the northeastern Gulf of Mexico can be triggered by winter and summer extra-tropical storms and by tropical cyclones. In northwestern Florida most of the events are triggered by winter storms, while in west and southwest Florida they appear both in winter and summer. Atmospheric pressure and wind anomalies (periods <6 h) associated with the passage of squalls originated the majority of the observed meteotsunami events. The most intense meteotsunamigenic periods took place during El Niño periods (1997–1998, 2009–2010 and 2015–2016). Meteotsunamis were also active in 2005, a year characterized by exceptionally intense tropical cyclone activity. Meteotsunami incidence varied yearly and at periods between 2 and 5 years. Results from cross-wavelet analysis suggested that El Niño and meteotsunami activity are correlated at annual and longer-period bands.     

Transition from debris flow to hyperconcentrated flow in a submarine channel (the Cretaceous Cerro Toro Formation, southern Chile)

ABSTRACT It is important to understand the exact process whereby very large amounts of sediment are transported. This paper reports peculiar conglomerate beds reflecting the transition of submarine debris flows into hyperconcentrated flows, something that has been well documented only in subaerial debris-flow events until now. Voluminous debris flows generated along a Cretaceous submarine channel, southern Chile, transformed immediately into multiphase flows. Their deposits overlie fluted or grooved surfaces and comprise a lower division of clast-supported and imbricated pebble–cobble conglomerate with basal inverse grading and an upper division of clast- to matrix-supported, disorganized conglomerate with abundant intraformational clasts. The conglomerate beds suggest temporal succession of turbidity current, gravelly hyperconcentrated flow, and mud-rich debris flow phases. The multiphase flows resulted from progressive dilution of gravelly but cohesive debris flows that could hydroplane, in contrast to the flow transitions in subaerial environments, which involve mostly non-cohesive debris flows. This finding has significant implications for the definition, classification, and hazard assessment of submarine mass-movement processes and characterization of submarine reservoir rocks.     

Interannual variations in length of day with respect to El Niño - Southern Oscillation’s impact (1962–2015)

The objective of research done in this study is to examine the variability of the length of day (LOD) and to investigate its correlation with ENSO (El Niño-Southern oscillation) episodes. For this purpose, the LOD time series (1962–2015), from the International Earth Rotation and Reference Systems Service (IERS), is investigated using the Singular Spectrum Analysis (SSA) technique. The results show that the LOD time series is very complex and is composed of several components: the long-term trend explains 95.97% of the original series, the annual harmonic 1.76% and the semi-annual 1.35%. Considering sea surface temperature anomalies (SSTA) index over the Niño3, Niño4 and Niño3.4 regions, Southern Oscillation Index (SOI) and Multivariate ENSO Index (MEI), the residuals signal, that represents only 0.92% of the initial LOD series, indicate a significant correlation with ENSO occurred during 1965–66, 1972–73, 1982–83 and 1997–98 El Niño events and 1970–71, 1973–74, 1988–89, 2007–08, 2010–11 La Niña ones. This is a pertinent result that suggests that LOD variability is at least partly related to ENSO phenomena.     

Deterministic strong ground motion study for the Sitamarhi area near Bihar–Nepal region

We explore the challenges of avalanche and debris flow hazard assessment for urban areas exposed in the Sakhalin region. Avalanches are a threat to more than 60 settlements in the region and debris flows to more than 30. Data are provided for avalanche and debris flow events that occurred in the Sakhalin region between 1928 and 2015. In this paper, the method for the design of hazard maps for snow avalanches and debris flows is described, providing the starting point for any planning constraints in general settlement planning schemes. These maps further allow conducting an assessment of avalanche and debris flow risk within a short time period for a larger territory and at minimum cost.     

Change of the ENSO-related δ18O–SST correlation from coral skeletons in northern South China Sea: A possible influence from the Kuroshio Current

Chemical proxies are useful analogs for reconstructing physical properties of sea water, such as sea surface temperature (SST) and sea surface salinity (SSS). Time series of these inferred properties would allow for reconstructions of past El Niño–Southern Oscillation (ENSO) events, where no instrumental records exist. In this study, a monthly oxygen isotope record from a Porites coral is used to explain how past ENSO events are recorded in the coral skeletons. The sample covers a 12 year period and was collected from Nanwan Bay, Taiwan. During El Niño events the coral skeleton is shown to produce a δ¹⁸O–SST correlation with a slope of −0.12 ± 0.04‰ °C⁻¹. During other times, this value is significantly different, with a slope of −0.21 ± 0.04‰ °C⁻¹. Coral that grew during El Niño summers have δ¹⁸O values which are enriched by ∼0.2‰, relative to other times. A possible mechanism to explain this difference may be enhanced penetration of Kuroshio Current waters into the South China Sea during summer. The observed contrast in the correlation of δ¹⁸O–SST variability in this sample supports the influence of El Niño in eastern Asia.