Onset Of El Research Articles

El Niño–Global Atmospheric Oscillation as the Main Mode of Interannual Climate Variability

The interannual variability of the global mean monthly anomalies of near-surface air temperature, sea-level pressure, wind speed near the surface, amount of precipitation and total cloudiness was investigated. The amplitudes of the anomalies of these hydrometeorological characteristics between opposite phases of the Global Atmospheric Oscillation (GAO) were calculated. The regional element of the GAO in the tropics of the Indian and Pacific Oceans is the Southern Oscillation. The results show that the oscillations of these characteristics are associated with the GAO not only in the tropical belt of the Earth but also in the middle and high latitudes, especially in the Arctic and northern Eurasia. The physical mechanism by which the transition of the GAO from the negative to the positive phase influences the weakening of the Pacific trade winds, and, as a consequence, the onset of El Niño is described.

The effect of the variability of wind forcing on ENSO simulation in an OGCM: case of canonical and protracted event

This study is an attempt to understand the onset and the evolution of canonical (typical length ~ 18–24 months; CE) and protracted El Niño (> greater than 3 years; PE) compared to the normal state (NS) in an ocean model. Indo-Pacific warm pool indicates higher sea surface temperature (SST) before the onset of strong CE compared to the NS and PE. The ocean model (MOM5.1.0) used in the study shows a systematic SST bias in the Indo-Pacific Ocean with warmer (cooler) temperatures in the western (eastern) Pacific during NS, CE, and PE exhibiting La Niña–like conditions. The model also exhibits deeper thermocline depth in the western equatorial Pacific Ocean during PE and CE than NS, indicating higher heat content values. Despite higher heat content in the western Pacific before the onset of El Niño, the difference in the variability of surface wind forcing during the preceding months determines the type of El Niño. The difference in surface wind forcing among the NS, PE, and CE states without altering the ocean state can modify the subsurface propagation in the equatorial Pacific Ocean. A change in longitudinal extent of upwelling Kelvin waves from western Pacific towards eastern Pacific along with the change in surface wind forcing decides the fate of El Niño. Based on the results of model experiments for 1948–2009, observed features of the recent protracted El Niño of 2014–2016 appear to be a blend of PE and CE in terms of ocean dynamics and surface wind forcing.

Impacts of Precipitation–Evaporation–Salinity coupling on upper ocean stratification and momentum over the tropical pacific prior to onset of the 2018 El Niño

Precipitation affects upper ocean salinity and temperature over a wide range of temporal and spatial scales. Although the effects of freshwater on the diurnal mixing and formation of barrier layer have been shown in previous studies, the impacts of freshwater from the large-scale precipitation associated with the Madden–Julian Oscillation (MJO) on the ocean from the western to central-eastern Pacific are not well understood. This study investigates the coupling of precipitation, evaporation, and salinity (P–E–S) and its impact on the upper ocean stratification and momentum on time scales from days to weeks (intraseasonal) and beyond. The Unified Wave INterface – Coupled Model (UWIN-CM) is used to simulate multiscale air–sea interactions during January–July 2018, including multiple MJO events leading up to the onset of the 2018–2019 El Niño. The atmospheric component of the UWIN-CM is constrained by reanalysis and reinitialized daily, while the ocean component evolves continuously and is fully coupled with the atmosphere. The initial and lateral boundary conditions for the atmosphere and ocean are from the ECMWF ERA5 and HYCOM global analysis, respectively. The UWIN-CM simulation captures the surface winds, rainfall, and the evolution of the upper ocean compared with in situ and satellite observations. To determine the effect of P–E–S coupling, the UWIN-CM simulation with full P–E–S coupling is compared with a model experiment in which the P–E input to the ocean is set to zero (NoPE). The difference between the two increases with time and becomes particularly large during the 3rd MJO event in April 2018. Two key results emerge. First, heavy precipitation and strong winds from the MJO events result in a locally fresher, warmer western Pacific warm pool with a shallower mixed layer and thicker barrier layer. Second, the fresh, warm water mass extends into the central-eastern Pacific from mid-April to late May with up to 0.5 m s−1 eastward currents. A well-defined salinity/density front, propagating eastward at about 0.3 m s−1, is located at the leading edge of the warm pool. The P–E–S coupling plays an important role in the eastward extension of the warm pool prior to the onset of El Niño in July 2018.

Intensification of Westerly Wind Bursts Caused by the Coupling of the Madden‐Julian Oscillation to SST During El Niño Onset and Development

AbstractThe Madden‐Julian Oscillation (MJO) plays an important role in El Niño dynamics in connection with westerly wind bursts (WWBs) that occur in the equatorial Pacific; however, our understanding of the relationship between these climate phenomena remains incomplete. Here, we use a Lagrangian Atmospheric Model (LAM) to examine the response of the MJO and resulting WWBs to sea surface temperature (SST) anomalies similar to those observed during the onset and development of El Niño. We find that when a localized SST anomaly (≤1°C) is imposed in the western‐central equatorial Pacific between December and April (mimicking El Niño onset), the MJO convective envelope shifts from the southern hemisphere toward the equator. When an SST anomaly (≤1.5°C) is imposed in the central‐eastern equatorial Pacific between May and November (mimicking El Niño development), the MJO weakens in the northwestern Pacific, but strengthens in the central equatorial Pacific. In both experiments, the ensuing changes enhance MJO activity along the equator, facilitating WWBs.

Unveiling the mysteries of SST evolutions in the equatorial Pacific at the onset of El Niño events

AbstractIt is generally accepted that the El Niño-Southern Oscillation (ENSO) dominates interannual climate variability. Yet its genesis and maintenance mechanisms are still under intense debate with no scientific consensus. Some authors argued that the westerly winds originating over the equatorial Indian Ocean significantly enhanced and extended eastward in the western and central equatorial Pacific during El Niño events, thus advecting the warm pool eastward along the equator and causing SST anomalies. However, this assertion is unlikely to be quantitatively supported by observational data. Here we present detailed observational data and modeling evidence to demonstrate that the westerly winds remained little changein intensity in the western equatorial Pacific, with a wider zonal extent only during most El Niño events, and with a slight increase even if in the most pronounced 1997 El Niño. Instead, an eastward equatorial current near the equator has been observed and considered to play a significant role in shifting the eastern edge of the warm pool eastward, elevating SSTs in the central and eastern equatorial Pacific and giving rise to El Niño, with the interactions between the eastward warm pool and the upwelling in the eastern cold tongue ascertaining the amplitudes of SST anomalies.

A brief massive aggregation of pelagic swimming crabs Euphylax dovii (Decapoda: Portunidae) at Cocos Island, Costa Rica coincides with onset of El Niño event

Introduction: Sporadic aggregations of decapod crustaceans can occur for various reasons and in some cases their drivers are poorly understood. Objective: Here, we present our observations of an apparently rare massive aggregation of pelagic swimming crabs, Euphylax dovi. Methods: During a research cruise at Cocos Island (5°32’34” N, 87°05’06” W), we encountered large numbers of E. dovii in surface waters in the evenings of May 6-7, 2015, some of which we collected for identification prior to returning to the water. Results: Crabs of both sexes were identified, yet no females were bearing eggs. Crabs aggregated around a small dinghy used for scientific surveying from 4pm through 8pm each evening, and around our research vessel throughout the night, presumably attracted by the lights. On both occasions, the aggregation dissipated around dawn. Crabs were not seen prior to or after the two nights. Conclusions: Sea surface temperatures at Cocos during this period were markedly warm, with no perceptible thermocline down to at least 40 m, coinciding with the onset of the 2015 El Niño event. It appears that the aggregation formed in response to El Niño conditions, yet the biological reason behind it remains unknown.

What is the El Niño–Southern Oscillation?

The El Niño–Southern Oscillation (ENSO) is a large-scale climatic phenomenon that originates in the tropical Pacific but affects global climate patterns. The warm phase is known as El Niño, and the cold phase, La Niña. El Niño occurs irregularly every 2 to 7 years and generally peaks during Northern Hemisphere winter. In a normal year, when ENSO is inactive, the equatorial Pacific trade winds blow from east to west. The winds push the warmer surface water towards the west, and colder water rises up from deeper in the ocean to replace it. This creates an east–west difference in sea-surface temperature (SST) and hence an east–west difference in sea level air pressure that maintains the trade winds and so drives a positive feedback loop (Figure 1(a)). During an El Niño year, the east–west SST difference weakens, the air pressure difference weakens, and the trade winds and their effects on the ocean weaken, so the eastern Pacific warms (Figure 1(b)). During a La Niña year, the opposite ­happens: the east–west difference in temperature strengthens, the pressure difference strengthens, and the trade winds and their effects on the ocean strengthen, so the east Pacific cools further (Figure 1(c)). Such changes in sea-surface temperature affect the atmosphere over vast areas, with both local and global repercussions. Locally, during the El Niño phase, the associated atmospheric circulation changes drive increased atmospheric convection and precipitation over the central and eastern Pacific, while rainfall is reduced over the western Pacific. These changes have remote impacts throughout the tropics but also at higher latitudes via large-scale motion of the atmosphere, especially when ENSO is at its strongest in winter. A network of ocean buoys measure sea surface temperature, ocean currents and the wind. Satellites also provide surface temperature and ocean current data, providing the ability to monitor ENSO in real time. El Niño months can be predicted in advance by measuring the heat content of the upper ocean, one of the precursors for the onset of El Niño, and then using climate models to predict its evolution. Although various criteria exist, an El Niño event is normally said to be underway when the sea surface temperature in the equatorial Pacific (officially called the ‘Niño 3.4’ region) rises by +0.5 degC above the historical average for at least three months in a row. The strongest impacts are experienced by those countries near the tropical Pacific origin of ENSO. Changes in surface temperature, wind and moisture affect rainfall intensity and patterns, which can lead to extreme events such as flooding and drought. During an El Niño event, Peru, Ecuador and southeastern parts of South America receive heavy rainfall. In northern Brazil, drier conditions or even drought may result. Indonesia, South Asia and parts of Australia are also more likely to experience drought during the El Niño phase. The change in weather patterns associated with El Niño can greatly impact the economy, in particular agriculture, water resources, fisheries and public health. ENSO also has a strong influence on the occurrence and intensity of tropical cyclones, and Atlantic hurricane activity weakens during El Niño but strengthens during La Niña. In the UK we experience the socio-economic impacts of an El Niño event, partly through increased food prices, and there are effects on the jet stream and European weather, especially in late winter, when El Niño increases the chances of cold snaps and La Niña increases the chances of wet and stormy conditions. El Niño releases heat to the atmosphere and increases subsequent global temperatures. For example, global average temperatures for 2016 were around 1.1 degC above pre-industrial values, and the strong El Niño episode of 2015/2016 partly contributed to this rise. However, researchers have concluded that the warming from this El Niño accounted for only about 0.2 degC of this overall figure. Because of the large event-to-event variability of El Niño, we don't have enough past years of observations to show how climate change may impact it. There is now some evidence that rainfall may increase during El Niño events in the future and that we may even see more very strong ENSO events, but these remain active research questions. Real-time observational monitoring of the tropical ocean and El Niño are available from NOAA at: https://www.pmel.noaa.gov/tao/drupal/disdel/ Met Office Hadley Centre forecasts of El Niño and global temperature can be found here: https://www.metoffice.gov.uk/research/climate/seasonal-to-decadal/gpc-outlooks/el-nino-la-nina Forecasts from other prediction models provided by the International Research Institute for Climate and Society are available here: https://iri.columbia.edu/our-expertise/climate/forecasts/enso/current/

ENSO-Related Global Ocean Heat Content Variations

Abstract The modulation of the full-depth global integrated ocean heat content (GOHC) by El Niño–Southern Oscillation (ENSO) has been estimated in various studies. However, the quantitative results and the mechanisms at work remain uncertain. Here, a dynamically consistent ocean state estimate is utilized to study the large-scale integrated heat content variations during ENSO events for the global ocean. The full-depth GOHC exhibits a cooling tendency during the peak and decaying phases of El Niño, which is a result of the negative surface heat flux (SHF) anomaly in the tropics (30°S–30°N), partially offset by the positive SHF anomaly at higher latitudes. The tropical SHF anomaly acts as a lagged response to damp the convergence of oceanic heat transport, which redistributes heat from the extratropics and the subsurface layers (100–440 m) into the upper tropical oceans (0–100 m) during the onset and peak of El Niño. These results highlight the global nature of the oceanic heat redistribution during ENSO events, as well as how the redistribution process affects the full-depth GOHC. The meridional heat exchange across 30°S and 30°N is driven by ocean current anomalies, while multiple processes contribute to the vertical heat exchange across 100 m simultaneously. Heat advection due to unbalanced mass transport is distinguished from the mass balanced one, with significant contributions from the meridional and zonal overturning cells being identified for the latter in the vertical direction. Results presented here have implications for monitoring the planetary energy budget and evaluating ENSO’s global imprints on ocean heat content in different estimates.

A Tropical Stochastic Skeleton Model for the MJO, El Niño, and Dynamic Walker Circulation: A Simplified GCM

AbstractA simple dynamical stochastic model for the tropical ocean atmosphere is proposed that captures qualitatively major intraseasonal to interannual processes altogether including El Niño–Southern Oscillation (ENSO), the Madden–Julian oscillation (MJO), the associated wind bursts, and the background dynamic Walker circulation. Such a model serves as a prototype “skeleton” for general circulation models (GCMs) that solve similar dynamical interactions across several spatiotemporal scales but usually show common and systematic biases in representing tropical variability as a whole. The most salient features of ENSO, the wind bursts, and the MJO are captured altogether including their overall structure, evolution, and fundamental interactions in addition to their intermittency, diversity, and energy distribution across scales. Importantly, the intraseasonal wind bursts and the MJO are here solved dynamically, which provides their upscale contribution to the interannual flow as well as their modulation in return in a more explicit way. This includes a realistic onset of El Niño events with increased wind bursts and MJO activity starting in the Indian Ocean to the western Pacific and expanding eastward toward the central Pacific, as well as significant interannual modulation of the characteristics of intraseasonal variability. A hierarchy of cruder model versions is also analyzed in order to highlight fundamental concepts related to the treatment of multiple time scales, main convective nonlinearities, and the associated stochastic convective parameterizations. The model developed here also should be useful to diagnose, analyze, and help eliminate the strong tropical biases that exist in current operational models.

Impact of the 2015/2016 El Niño on the terrestrial carbon cycle constrained by bottom-up and top-down approaches

Evaluating the response of the land carbon sink to the anomalies in temperature and drought imposed by El Niño events provides insights into the present-day carbon cycle and its climate-driven variability. It is also a necessary step to build confidence in terrestrial ecosystems models' response to the warming and drying stresses expected in the future over many continents, and particularly in the tropics. Here we present an in-depth analysis of the response of the terrestrial carbon cycle to the 2015/2016 El Niño that imposed extreme warming and dry conditions in the tropics and other sensitive regions. First, we provide a synthesis of the spatio-temporal evolution of anomalies in net land–atmosphere CO2 fluxes estimated by two in situ measurements based on atmospheric inversions and 16 land-surface models (LSMs) from TRENDYv6. Simulated changes in ecosystem productivity, decomposition rates and fire emissions are also investigated. Inversions and LSMs generally agree on the decrease and subsequent recovery of the land sink in response to the onset, peak and demise of El Niño conditions and point to the decreased strength of the land carbon sink: by 0.4–0.7 PgC yr−1 (inversions) and by 1.0 PgC yr−1 (LSMs) during 2015/2016. LSM simulations indicate that a decrease in productivity, rather than increase in respiration, dominated the net biome productivity anomalies in response to ENSO throughout the tropics, mainly associated with prolonged drought conditions.This article is part of a discussion meeting issue ‘The impact of the 2015/2016 El Niño on the terrestrial tropical carbon cycle: patterns, mechanisms and implications’.

Sea surface temperature and rainfall anomaly over the Bay of Bengal during the El Niño-Southern Oscillation and the extreme Indian Ocean Dipole events between 2002 and 2016

Phenomena like the El Niño-Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD) regulate the climate of several nations situated around the Indian Ocean rim as well as the entire globe. The present study focused on the Bay of Bengal (BoB) in the northern Indian Ocean, which is known for its crucial role in the Indian summer monsoon. The sea surface temperature (SST) and rainfall (RF) anomalies in the central, eastern, western and northern BoB were thoroughly analyzed with respect to all the El Niño, La Niña and extreme IOD events between the years 2002 and 2016. Most of the El Niño (La Niña) phases were accompanied by a positive (negative) SST anomaly and a negative (positive) RF anomaly. However, the magnitude of the SST and the RF anomalies did not co-vary with Oceanic Niño index observed in the Niño 3.4 region. The SST and RF anomalies in the BoB lagged the onset of El Niño by 1–7 months and 3 months, respectively. During La Niña, a negative SST anomaly was accompanied by a positive RF anomaly; however, the magnitude of the anomaly in case of both parameters was larger during El Niño phases when compared to the La Niña phases. Longer El Niño periods corresponded to larger reductions in rainfall in BoB. In general, El Niño is accompanied by positive IOD phase and La Niña by negative IOD phase. We observed a negative rainfall anomaly in the BoB during a positive IOD and vice versa. However, this trend reversed whenever El Niño coincided with negative IOD and La Niña with positive IOD. This showed that whenever an El Niño or La Niña coincided with the conventionally opposite IODMI phases, the effect of ENSO phases overruled the IODMI phases in BoB. Many previous studies have documented that SST and RF anomalies can potentially regulate as well as helps to forecast both droughts and floods in landmasses, not only in the vicinity to oceans but also inner continental regions. Since BoB plays a crucial role in regulating the monsoon and India being a monsoon dependent agricultural nation, the present observations may be of help to climate modelers to study the effect of SST anomalies in BoB (with respect to synoptic scale events like ENSO or IOD) upon the regional climate of India.

Forecasting the magnitude and onset of El Niño based on climate network

El Niño is probably the most influential climate phenomenon on inter-annual time scales. It affects the global climate system and is associated with natural disasters; it has serious consequences in many aspects of human life. However, the forecasting of the onset and in particular the magnitude of El Niño are still not accurate enough, at least more than half a year ahead. Here, we introduce a new forecasting index based on climate network links representing the similarity of low frequency temporal temperature anomaly variations between different sites in the Niño 3.4 region. We find that significant upward trends in our index forecast the onset of El Niño approximately 1 year ahead, and the highest peak since the end of last El Niño in our index forecasts the magnitude of the following event. We study the forecasting capability of the proposed index on several datasets, including, ERA-Interim, NCEP Reanalysis I, PCMDI-AMIP 1.1.3 and ERSST.v5.

Changes in phytoplankton vertical distribution during an El Niño event

The west coast of South America is a very productive oceanic region due to cold, nutrient-rich upwelled waters. This region experiences periodic El Niño events that cause a deepening of the thermocline along with the prevalence of warm nutrient-poor superficial water. Sampling conducted during a weak El Niño event in 2014 allowed us to identify changes in phytoplankton vertical distribution at superficial waters along 8 miles offshore the Ecuadorian coast. As such, it was found that phytoplankton mainly occurred at near-surface waters rather than at 10 m depth after the onset of El Niño in terms of both abundance and species richness. The shift in vertical distribution was interpreted as a result of the trapping of cells in a surface layer formed by the stratification of the water column associated with El Niño events. This finding opens the possibility of developing a potential new El Niño indicator.

Resource acquisition and reproductive strategies of tropical forest in response to the El Ni\xf1o\u2013Southern Oscillation

The El Niño–Southern Oscillation (ENSO) is the largest source of interannual climate variability in much of the tropics. We hypothesize that tropical plants exhibit interannual variation in reproduction and resource acquisition strategies driven by ENSO that mirrors their seasonal responses. We analyze the relationship of leaf and seed fall to climate variation over 30 years in a seasonally dry tropical forest in Panama where El Niño brings warm, dry, and sunny conditions. Elevated leaf fall precedes the onset of El Niño, and elevated seed production follows, paralleling associations with dry seasons. Our results provide evidence of a shift in allocation from leafing to fruiting in response to a warming phase of ENSO. This shift may enable plants to take advantage of higher light availability, while coping with higher atmospheric water demand and lower water supply. These findings might be an indicator of adaptive strategies to optimize reproduction and resource acquisition.

Large-scale climatic effects on traditional Hawaiian fishpond aquaculture.

Aquaculture accounts for almost one-half of global fish consumption. Understanding the regional impact of climate fluctuations on aquaculture production thus is critical for the sustainability of this crucial food resource. The objective of this work was to understand the role of climate fluctuations and climate change in subtropical coastal estuarine environments within the context of aquaculture practices in Heʻeia Fishpond, Oʻahu Island, Hawaiʻi. To the best of our knowledge, this was the first study of climate effects on traditional aquaculture systems in the Hawaiian Islands. Data from adjacent weather stations were analyzed together with in situ water quality instrument deployments spanning a 12-year period (November 2004 –November 2016). We found correlations between two periods with extremely high fish mortality at Heʻeia Fishpond (May and October 2009) and slackening trade winds in the week preceding each mortality event, as well as surface water temperatures elevated 2–3°C higher than the background periods (March-December 2009). We posit that the lack of trade wind-driven surface water mixing enhanced surface heating and stratification of the water column, leading to hypoxic conditions and stress on fish populations, which had limited ability to move within net pen enclosures. Elevated water temperature and interruption of trade winds previously have been linked to the onset of El Niño in Hawaiʻi. Our results provide empirical evidence regarding El Niño effects on the coastal ocean, which can inform resource management efforts about potential impact of climate variation on aquaculture production. Finally, we provide recommendations for reducing the impact of warming events on fishponds, as these events are predicted to increase in magnitude and frequency as a consequence of global warming.

Why 2015 was a strong El Niño and 2014 was not

AbstractAnomalous oceanic and atmospheric conditions in the tropical Pacific were similar in the early months of 2014 and 2015, both apparently favoring onset of El Niño. Despite high expectations, the 2014 event did not truly take hold, but the 2015 event developed into a very strong El Niño. Here we argue that mean state differences played important roles in promoting El Niño in 2015 and not favoring growth in 2014. We show that the mean state difference in the Pacific between 2015 and 2014 was similar to the shift from cold phase to warm phase of the Interdecadal Pacific Oscillation (IPO). We demonstrate that this mean state change affected El Niño development between the two years using a forecast sensitivity experiment. The cold IPO‐like mean state during 2014 acted to reduce the coupled feedbacks, while the warm IPO‐like mean state of 2015 acted to enhance the coupled feedbacks.

Identifying Droughts Affecting Agriculture in Africa Based on Remote Sensing Time Series between 2000–2016: Rainfall Anomalies and Vegetation Condition in the Context of ENSO

Droughts are amongst the most destructive natural disasters in the world. In large regions of Africa, where water is a limiting factor and people strongly rely on rain-fed agriculture, droughts have frequently led to crop failure, food shortages and even humanitarian crises. In eastern and southern Africa, major drought episodes have been linked to El Niño-Southern Oscillation (ENSO) events. In this context and with limited in-situ data available, remote sensing provides valuable opportunities for continent-wide assessment of droughts with high spatial and temporal resolutions. This study aimed to monitor agriculturally relevant droughts over Africa between 2000–2016 with a specific focus on growing seasons using remote sensing-based drought indices. Special attention was paid to the observation of drought dynamics during major ENSO episodes to illuminate the connection between ENSO and droughts in eastern and southern Africa. We utilized Tropical Rainfall Measuring Mission (TRMM)-based Standardized Precipitation Index (SPI) with 0 . 25 ∘ resolution and Moderate-resolution Imaging Spectroradiometer (MODIS)-derived Vegetation Condition Index (VCI) with 500 m resolution as indices for analysing the spatio-temporal patterns of droughts. We combined the drought indices with information on the timing of site-specific growing seasons derived from MODIS-based multi-annual average of Normalized Difference Vegetation Index (NDVI). We proved the applicability of SPI-3 and VCI as indices for a comprehensive continental-scale monitoring of agriculturally relevant droughts. The years 2009 and 2011 could be revealed as major drought years in eastern Africa, whereas southern Africa was affected by severe droughts in 2003 and 2015/2016. Drought episodes occurred over large parts of southern Africa during strong El Niño events. We observed a mixed drought pattern in eastern Africa, where areas with two growing seasons were frequently affected by droughts during La Niña and zones of unimodal rainfall regimes showed droughts during the onset of El Niño. During La Niña 2010/2011, large parts of cropland areas in Somalia (88%), Sudan (64%) and South Sudan (51%) were affected by severe to extreme droughts during the growing seasons. However, no universal El Niño- or La Niña-related response pattern of droughts could be deduced for the observation period of 16 years. In this regard, we discussed multi-year atmospheric fluctuations and characteristics of ENSO variants as further influences on the interconnection between ENSO and droughts. By utilizing remote sensing-based drought indices focussed on agricultural zones and periods, this study attempts to contribute to a better understanding of spatio-temporal patterns of droughts affecting agriculture in Africa, which can be essential for implementing strategies of drought hazard mitigation.

The local response of El Niño events and changing disease distribution in Tanzania

Climate is a key determinant of a number of disease pathogen lifecycles and disease transmission processes, particularly within tropical climates such as that experienced in Tanzania. Over recent decades, climate‐related diseases such as malaria, chikungunya and bacterial meningitis have shown notable changes in their spatial distribution, with instances of both re‐emergence and expansion beyond previously known boundaries being recorded. The unpredicted change in disease distribution already experienced in Tanzania has placed a significant burden on health systems and available resources, and whilst a number of factors are involved, climate remains the least understood aspect within epidemiological changes. Here we examine how climate extremes – particularly El Niño events – influence key environmental and climatic elements which promote epidemiological expansion.This study investigates the baseline climatology in five of Tanzania’s varying climatological regions using the Met Office MIDAS dataset for the period 1985–1995. Its aim is to characterise the average climate and investigate the impacts of El Niño on the climatology of these regions, and to explore associated changes in disease distribution to allow identification, in the present, of changes which are anticipated to occur in the future to be put into context. The years 1997 and 2015 are used to examine the climate extremes imposed by El Niño events through statistical comparison methods. The results demonstrate that average climate conditions vary beyond previously documented observations, with each region of Tanzania responding differently to the onset of El Niño, thus potentially promoting a spatially variable disease response. These results are particularly marked for areas of greater climatic and environmental sensitivity within Tanzania. Once further understood, knowledge of this relationship could be applied to more local analysis and aid in predicting future outbreaks within Tanzania.

A 7000‐year high‐resolution lake sediment record from coastal central Chile (Lago Vichuquén, 34°S): implications for past sea level and environmental variability

ABSTRACTWe present a 7‐ka environmental reconstruction based on sedimentological and geochemical data from Lago Vichuquén, a coastal eutrophic lake in central Chile (34°48′S, 72°03′ W, 4 m a.s.l.). A relatively shallow and restricted marine environment with low productivity, high detrital input and dominant anoxic conditions in the Vichuquén Basin occurred from 7.0 to 6.5 cal ka BP. Rapid onset of a Holocene marine transgression at 6.5 cal ka BP favoured deeper and more biologically productive environments that existed until 2.8 cal ka BP. Bioproductivity changes during the mid‐Holocene (6.5–4.2 cal ka BP) were related to upwelling dynamics controlled by the intensity of the South‐east Pacific Anticyclone (SPA). Periods with lower organic productivity and dominant anoxic conditions reflect an increased intensity of SPA (increased upwelling) and decreased precipitation. A shift at ∼4.0 cal ka BP reflects the onset of modern Southern Westerly Winds and El Niño‐Southern Oscillation patterns. Tectonic uplifting and geormorphological activity (dune advancement) are possible reasons behind the Vichuquén Basin closure at ∼1.2 cal ka BP, leading to a low bioproductivity lacustrine environment which has developed until the present. Copyright © 2017 John Wiley & Sons, Ltd.

Impact of Warmer Eastern Tropical Pacific SST on the March 2015 Atacama Floods

AbstractNorthern Chile hosts the driest place on Earth in the Atacama Desert. Nonetheless, an extreme precipitation event affected the region on 24–26 March 2015 with 1-day accumulated precipitation exceeding 40 mm in several locations and hourly mean rainfall rates higher than 10 mm h−1, producing floods and resulting in casualties and significant damage. The event is analyzed using ERA-Interim, surface station data, sounding observations, and satellite-based radar. Two main conditions favorable for precipitation were present at the time of the event: (i) a cutoff low (COL) off the coast of northern Chile and (ii) positive sea surface temperature (SST) anomalies over the eastern tropical Pacific. The circulation driven by the COL was strong but not extraordinary. Regional Climate Model, version 4 (RegCM4), is used to test the sensitivity of precipitation to SST anomalies by removing the warm SST anomaly in the eastern tropical Pacific. The cooler simulation produced very similar COL dry dynamics to that simulated in a control run (with observed SST), but suppressed the precipitation by 60%–80% over northern Chile and 100% in parts of the Atacama Desert due to the decreased availability of precipitable water. The results indicate that the warm SST anomaly over the eastern Pacific, favored by the onset of El Niño 2015/16, was instrumental to the extreme precipitation event by providing an anomalous source of water vapor transported to Atacama by the circulation ahead of the COL.