El Nino-Southern Oscillation Conditions Research Articles

Pacific climate reflected in Waipuna Cave drip water hydrochemistry

Abstract. Cave microclimate and geochemical monitoring is vitally important for correct interpretations of proxy time series from speleothems with regard to past climatic and environmental dynamics. We present results of a comprehensive cave-monitoring programme in Waipuna Cave in the North Island of New Zealand, a region that is strongly influenced by the Southern Westerlies and the El Niño–Southern Oscillation (ENSO). This study aims to characterise the response of the Waipuna Cave hydrological system to atmospheric circulation dynamics in the southwestern Pacific region in order to assure the quality of ongoing palaeo-environmental reconstructions from this cave. Drip water from 10 drip sites was collected at roughly monthly intervals for a period of ca. 3 years for isotopic (δ18O, δD, d-excess parameter, δ17O, and 17Oexcess) and elemental (Mg∕Ca and Sr∕Ca) analysis. The monitoring included spot measurements of drip rates and cave air CO2 concentration. Cave air temperature and drip rates were also continuously recorded by automatic loggers. These datasets were compared to surface air temperature, rainfall, and potential evaporation from nearby meteorological stations to test the degree of signal transfer and expression of surface environmental conditions in Waipuna Cave hydrochemistry. Based on the drip response dynamics to rainfall and other characteristics, we identified three types of discharge associated with hydrological routing in Waipuna Cave: (i) type 1 – diffuse flow, (ii) type 2 – fracture flow, and (iii) type 3 – combined flow. Drip water isotopes do not reflect seasonal variability but show higher values during severe drought. Drip water δ18O values are characterised by small variability and reflect the mean isotopic signature of precipitation, testifying to rapid and thorough homogenisation in the epikarst. Mg∕Ca and Sr∕Ca ratios in drip waters are predominantly controlled by prior calcite precipitation (PCP). Prior calcite precipitation is strongest during austral summer (December–February), reflecting drier conditions and a lack of effective infiltration, and is weakest during the wet austral winter (July–September). The Sr∕Ca ratio is particularly sensitive to ENSO conditions due to the interplay of congruent or incongruent host rock dissolution, which manifests itself in lower Sr∕Ca in above-average warmer and wetter (La Niña-like) conditions. Our microclimatic observations at Waipuna Cave provide a valuable baseline for the rigorous interpretation of speleothem proxy records aiming at reconstructing the past expression of Pacific climate modes.

Impact of ENSO on the South China Sea during ENSO decaying winter–spring modeled by a regional coupled model (a new mesoscale perspective)

Studies have suggested that the ocean dynamics in the South China Sea (SCS) play a crucial role in local air–sea processes and the regional weather or climate system. We used a high-resolution regional coupled model to investigate the impact of the El Niño Southern Oscillation (ENSO) on the atmospheric and oceanic processes in the SCS during ENSO decaying winter–spring. The coupled model demonstrates the important roles of mesoscale features in the regional air–sea interaction induced by the anomalous ENSO conditions. During El Niño, the Kuroshio intrusion into the SCS is enhanced which further modifies the upper and middle layer circulation of the SCS. The reduced planetary vorticity transport during El Niño results in a weakened cyclonic circulation and thinner mixed layer in the southern SCS. The modulations of the cyclonic circulation in the southern SCS, Vietnam offshore jet, and the coastal current during ENSO event enhance oceanic advection that favors an ocean-forcing energy exchange to the atmosphere across the air–sea interface. The relative importance of atmospheric and oceanic forcing on the SST change during the ENSO evolution is verified using a heat budget analysis for different regions of SCS. In the El Niño following spring, the advective term due to anomalous Ekman drift dominates the cooling process in the northern and eastern SCS. These thermal structure changes in the SCS are contributed by the wind–current–topography interactions.

On the connection between interannual variations of winter haze frequency over Beijing and different ENSO flavors

This study investigated the connection between interannual variations in winter haze frequency over Beijing and different flavors of the El Niño–Southern Oscillation (ENSO). The results showed that the haze frequency was highest during eastern-Pacific (EP) El Niño winters and lowest during EP La Niña winters. No below-normal winter haze frequency years were observed during EP El Niño winters, and no above-normal years were observed during EP La Niña winters. However, the relationship between winter haze frequency and central-Pacific (CP) ENSO conditions was more complex, i.e., both above- and below-normal haze frequency years were equally probable during CP El Niño and CP La Niña winters, and the difference in the number of mean haze days associated with these flavors was exceptionally small. The nearly opposite atmospheric circulation patterns between EP El Niño and EP La Niña winters were responsible for the substantial difference in local winter haze frequency, as these patterns established favorable and unfavorable local meteorological conditions for haze formation, respectively. However, the diverse in situ haze frequency situations during CP El Niño and CP La Niña winters and the small relative differences between such winters could reflect the complexity of the CP ENSO's impacts on haze-related circulation anomalies. The results of this study may help improve winter haze frequency forecasts for Beijing through more accurate climatic predictions.

A global analysis of austral summer ocean wave variability during SAM–ENSO phase combinations

Anticipating and mitigating wave-related hazards rely heavily on understanding wave variability drivers. Here, we describe wave conditions related to concurrent Southern Annular Mode (SAM) and El Nino–Southern Oscillation (ENSO) phases during the austral summer. To identify such conditions, significant wave height (Hs) and peak wave period (Tp) daily anomalies were composited during different SAM–ENSO phase combinations over the last four decades (1979–2018). Surface wind anomalies were also composited to assist in the interpretation of wave conditions. The composites show significant wave variability across all ocean basins and in several semi-enclosed seas throughout the different SAM–ENSO phase combinations. The Southern, Indian, and Pacific Oceans generally experience the strongest Tp anomalies during combinations of SAM phases with El Nino, and the weakest Tp anomalies during combinations of SAM phases with La Nina. The anomalously large waves observed in the south-western Pacific, Tasman Sea, and the Southern Ocean, previously ascribed to ENSO conditions, seem to be instead associated with the SAM variability. SAM-related atmospheric conditions are found to be able to modulate the intensity of ENSO-related winds over the South China Sea, which, in turn, alter the magnitude of waves in that region. These and other wave anomaly structures described here, especially those contrasting the behaviour expected for a given ENSO phase, such as the one found along the California coast, stress the importance of understanding relationships between wave parameters and climate patterns interactions.

Improved Predictability of the Indian Ocean Dipole Using a Stochastic Dynamical Model Compared to the North American Multimodel Ensemble Forecast

AbstractThis study assesses the predictive skill of eight North American Multimodel Ensemble (NMME) models in predicting the Indian Ocean dipole (IOD). We find that the forecasted ensemble-mean IOD–El Niño–Southern Oscillation (ENSO) relationship deteriorates away from the observed relationship with increasing lead time, which might be one reason that limits the IOD predictive skill in coupled models. We are able to improve the IOD predictive skill using a recently developed stochastic dynamical model (SDM) forced by forecasted ENSO conditions. The results are consistent with the previous result that operational IOD predictability beyond persistence at lead times beyond one season is mostly controlled by ENSO predictability and the signal-to-noise ratio of the Indo-Pacific climate system. The multimodel ensemble (MME) investigated here is found to be of superior skill compared to each individual model at most lead times. Importantly, the skill of the SDM IOD predictions forced with forecasted ENSO conditions were either similar or better than those of the MME IOD forecasts. Moreover, the SDM forced with observed ENSO conditions exhibits significantly higher IOD prediction skill than the MME at longer lead times, suggesting the large potential skill increase that could be achieved by improving operational ENSO forecasts. We find that both cold and warm biases of the predicted Niño-3.4 index may cause false alarms of negative and positive IOD events, respectively, in NMME models. Many false alarms for IOD forecasts at lead times longer than one season in the original forecasts disappear or are significantly reduced in the SDM forced by forecasted ENSO conditions.

An alternative approach for quantitatively estimating climate variability over China under the effects of ENSO events

Abstract Previous studies generally use the traditional composite analysis to diagnose the physical interrelationships between the El Nino-Southern Oscillation (ENSO) and climate variables such as temperature and precipitation. This study presents a simple probabilistic tool for quantifying changes in precipitation and temperature in the wet season over China during either developing or decaying phases of El Nino and La Nina events with a particular focus on the extreme conditions. We first construct the joint dependence structure between each climate variable (e.g. precipitation and temperature) and ENSO using a variety of bivariate copulas. We then examine variations of climate variables related to ENSO conditions through the conditioning sets of bivariate copulas. This approach allows a quantitative estimation of precipitation and temperature anomalies and a delineation of their spatial pattern across the country under individual effects of the developing and decaying phases of ENSO events. Comparison of results produced by the conditional probabilistic approach with those by conventional composite analysis reveals large similarity, highlighting the robustness of the presented approach in examining the response of climate variations to ENSO phases and its potential for a broader application in other regional/global diagnoses. Of particular importance is that this approach offers a way to yield probabilistic predictive information on extreme climate anomalies conditioned by ENSO signals. Despite only ENSO's effect considered in the current study, the presented approach could also be used to detect the effect of other large-scale climate signals on regional or global climate variations.

Hydroclimatic teleconnections of large-scale oceanic-atmospheric circulations on hydrometeorological extremes of Tapi Basin, India

Abstract Current study presents an integrated approach to assess the hydroclimatic teleconnections of large-scale coupled oceanic-atmospheric circulations on basin-scale extreme rainfall and streamflow indices for climatologically sensitive Tapi basin, India. The trend analysis of rainfall extremes revealed spatial heterogeneity across the basin. The coastal and mountainous regions of Lower and Upper Tapi basins respectively experienced wet conditions, while the plains of Middle and Upper Tapi (Purna sub-catchment) basins exhibited drier conditions during the analysis. The decreasing trend in high streamflow indices (except for Burhanpur sub-catchment) and significant increasing trend in low flow days (except for Lower Tapi basin) are observed, indicating the dominance of drier and moisture deficient conditions across Tapi basin. The hydroclimatic teleconnections of large-scale oceanic-atmospheric circulations of tropical Pacific and equatorial Indian Ocean regions, i.e., El Nino-Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD) respectively, with hydrometeorological extremes in Tapi basin for the concurrent period are investigated. As Indian summer monsoon rainfall (ISMR) and Tapi basin monsoon rainfall (TBMR) shows explained variance of around 42%, the influences of ENSO and IOD circulations on TBMR may be asymmetric with ISMR. The anomalous warming of the Indian Ocean, i.e., positive IOD (pIOD), and co-occurrence of pIOD and weak El Nino conditions, are associated with higher flood risk across the basin vis-a-vis other ENSO and IOD conditions. On other hand, the effects of ENSO and IOD are not apparent on low flow days, as the anthropogenic changes in the basin including streamflow regulations have considerably influenced the low flow regimes. The time interlocking between ENSO-IOD conditions and streamflow extremes in Tapi basin is further envisaged by performing a lead-lag correlation analysis.

Analysis and quantification of ENSO-linked changes in the tropical Atlantic cloud vertical distribution using 14 years of MODIS observations

Abstract. A total of 14 years (September 2002 to September 2016) of Aqua Moderate Resolution Imaging Spectroradiometer (MODIS) monthly mean cloud data are used to quantify possible changes in the cloud vertical distribution over the tropical Atlantic. For the analysis multiple linear regression techniques are used. For the investigated time period significant linear changes were found in the domain-averaged cloud-top height (CTH) (−178 m per decade), the high-cloud fraction (HCF) (−0.0006 per decade), and the low-cloud amount (0.001 per decade). The interannual variability of the time series (especially CTH and HCF) is highly influenced by the El Niño–Southern Oscillation (ENSO). Separating the time series into two phases, we quantified the linear change associated with the transition from more La Niña-like conditions to a phase with El Niño conditions (Phase 2) and vice versa (Phase 1). The transition from negative to positive ENSO conditions was related to a decrease in total cloud fraction (TCF) (−0.018 per decade; not significant) due to a reduction in the high-cloud amount (−0.024 per decade; significant). Observed anomalies in the mean CTH were found to be mainly caused by changes in HCF rather than by anomalies in the height of cloud tops themselves. Using the large-scale vertical motion ω at 500 hPa (from ERA-Interim ECMWF reanalysis data), the observed anomalies were linked to ENSO-induced changes in the atmospheric large-scale dynamics. The most significant and largest changes were found in regions with strong large-scale upward movements near the Equator. Despite the fact that with passive imagers such as MODIS it is not possible to vertically resolve clouds, this study shows the great potential for large-scale analysis of possible changes in the cloud vertical distribution due to the changing climate by using vertically resolved cloud cover and linking those changes to large-scale dynamics using other observations or model data.

Towards Probabilistic Multivariate ENSO Monitoring

AbstractA probabilistic approach to describing El Niño–Southern Oscillation (ENSO), based on consideration of the signal‐to‐noise ratio for the coupled ocean‐atmosphere ENSO state, is presented. The ENSO signal is estimated using an ensemble of historical atmospheric model simulations forced by observed sea surface temperatures and sea ice during 1980–2016. The noise is estimated from departures of individual model realizations from their ensemble average when subjected to identical forcing. It is found that this atmospheric noise effect is substantial and yields considerable uncertainty in detecting the true coupled ENSO mode. This uncertainty exceeds analysis errors by an order of magnitude. Greater atmospheric noise is found to prevail during El Niño than La Niña, suggesting that the intensity of the monitored ENSO state during El Niño is prone to greater misattribution. Our results demonstrate that a deterministic state estimate of ENSO conditions may not be representative of the true real‐time coupled ENSO mode.

Modulation of boreal extended summer tropical cyclogenesis over the northwest Pacific by the quasi‐biweekly oscillation under different El Niño‐southern oscillation phases

AbstractThe study of the interannual and intraseasonal modulation of tropical cyclogenesis (TCG) in the northwest Pacific (NWP) basin has received significant attention in the past. Most previous studies have focused on the individual impact of El Niño‐southern oscillation (ENSO) or Madden–Julian Oscillation on TCG, whereas the combined effect of ENSO and another leading intraseasonal oscillation mode, quasi‐biweekly oscillation (QBWO), on NWP TCG has rarely been studied. Therefore, this study systemically investigates the modulation of NWP TCG by the QBWO under different ENSO phases. A significant modulation of TCG by QBWO in the ENSO neutral years is observed, with significantly increased (decreased) TCG over the NWP in QBWO active (inactive) phases. Moreover, during El Niño years and La Niña years, the modulation of TCG by QBWO is not significant and no distinctive difference in the TCG frequency can be detected. Further analyses show that the modulation of TCG by the QBWO is mainly related to the changes in large‐scale environment and energy that affect TCG associated with active or inactive phases of the QBWO under different ENSO phases. Large‐scale environmental factors and energy are more favourable for TCG during ENSO neutral years compared with El Niño and La Niña years. These results are associated with QBWO cycle under the impact of background (e.g., boundary layer moisture and zonal wind shear) which is determined by ENSO conditions.

Role of ENSO Conditions on Particulate Organic Matter Concentrations and Elemental Ratios in the Southern California Bight

El Niño Southern Oscillation (ENSO) influences multi-year variation in sea-surface temperature and the intensity of upwelling in many Pacific regions. However, it is currently unknown how El Niño conditions will affect the concentration and elemental ratios of particulate organic matter (POM). To test this, we have been quantifying POM weekly for six years (2012 to 2017) at the MICRO time-series station in the Southern California Bight. We found a strong influence of the 2015 El Niño on sea-surface temperature and phosphate concentration but to a lesser extent on nitrate availability. The 2015 El Niño also resulted in low POC and POP concentrations, whereas PON concentrations declined by 26% during the whole sampling period. The changes in POM concentrations led to high C:P and N:P ratios. Following the changes in PON, C:N continued to climb reaching ~9.4 at the end of the sampling. We suggest that an Eastern Pacific- vs. a Central Pacific-type El Niño as well as a switch in the Pacific Decadal Oscillation phase influenced the local response in POM concentrations and ratios.

Dominant modes of winter precipitation variability over Central Southwest Asia and inter-decadal change in the ENSO teleconnection

This study contributes to an improved understanding of Central Southwest Asia (CSWA) wintertime (November–April) precipitation by analyzing the dominant spatial–temporal modes of the regional winter precipitation and examining their relationship with global sea surface temperature (SST) and large-scale atmospheric circulation fields, for 1950/51–2014/15. Empirical orthogonal function (EOF) analysis results show that the first mode (EOF-1) of winter precipitation is characterized by a mono-sign pattern, with significant links to El Nino-Southern Oscillation (ENSO). EOF-2 displays a north–south dipole related to the latitudinal shift in the jet stream position, while the west–east dipole in EOF-3 appears to be influenced by the thermal contrast between the equatorial regions and higher latitudes. Further, we focus on the interdecadal change of connection between wintertime ENSO and EOF-1 observed around the early 1980s. The relationship is weak during 1950/51–1983/84 (P1), but strong and statistically significant in 1984/85–2014/15 (P2). In P1, without the ENSO signal, EOF-1 related atmospheric circulation anomalies are confined mainly over the mid- to high-latitudes of the Northern Hemisphere, associated with the extratropical East Atlantic–Western Russia (EA–WR) teleconnection. In P2, however, a close connection to the tropical Pacific is observed that includes a pronounced SST expression similar to that of ENSO. As a result of the increased relationship between ENSO and EOF-1 in P2, the regional impact of EA–WR observed over CSWA in P1 is linearly superimposed by the anomalous hemispheric–wide atmospheric response forced by the ENSO conditions in the Pacific.

Evaluation of summer monsoon climate predictions over the Indochina Peninsula using regional spectral model

Monsoons are a major component of the global climate system affecting floods, droughts and other climate extremes. In this study, we investigated the performance of RSM (Regional Spectral Model) for predicting the summer monsoon over the Indochina Peninsula (ICP) region from 1982 to 2010. The NCEP - Climate Forecast System Reforecast (CFS-reforecast) was used to provide initial and boundary forcing for the RSM configured with an approximately 26 km grid over the ICP. The large-scale fields as well as surface temperature and rainfall of RSM have been evaluated for differing El Niño-Southern Oscillation (ENSO) years. The factors affecting changes in the rainfall patterns in ENSO years were determined using the empirical orthogonal function method. In addition, the ability of forecasting onset of summer monsoon was assessed based on the changes in outgoing longwave radiation, rainfall and average zonal wind at 850 hPa. The RSM is satisfactory in terms of forecasting large-scale features in different ENSO conditions. It produces well the interaction between Southwest and Southeast airflow, which are the main characteristics of summer monsoon throughout the study area. The RSM reforecasts are compared to CRU (Climatic Research Unit) data for the distribution of temperature and precipitation; however, their changes due to ENSO condition is inconsistent with CRU data. The extremes maximum and minimum temperatures have reverse signals with ENSO conditions. The extremes maximum 1-day rainfall have a significant change over the gulf of Tonkin and western ICP area due to ENSO condition. RSM results have indicated the effects of terrain and the reverse effects of ENSO condition over ICP area. The onset of summer monsoon is later in summer of El Niño year when compared with the other conditions.

Effects of large-scale oceanic phenomena on non-cholera vibriosis incidence in the United States: implications for climate change.

Non-cholera Vibrio (NCV) species are important causes of disease. These pathogens are thermophilic and climate change could increase the risk of NCV infection. The El Niño Southern Oscillation (ENSO) is a 'natural experiment' that may presage ocean warming effects on disease incidence. In order to evaluate possible climatic contributions to observed increases in NCV infection, we obtained NCV case counts for the United States from publicly available surveillance data. Trends and impacts of large-scale oceanic phenomena, including ENSO, were evaluated using negative binomial and distributed non-linear lag models (DNLM). Associations between latitude and changing risk were evaluated with meta-regression. Trend models demonstrated expected seasonality (P < 0.001) and a 7% (6.1%-8.1%) annual increase in incidence from 1999 to 2014. DNLM demonstrated increased vibriosis risk following ENSO conditions over the subsequent 12 months (relative risk 1.940, 95% confidence interval (CI) 1.298-2.901). The 'relative-relative risk' (RRR) of annual disease incidence increased with latitude (RRR per 10° increase 1.066, 95% CI 1.027-1.107). We conclude that NCV risk in the United States is impacted by ocean warming, which is likely to intensify with climate change, increasing NCV risk in vulnerable populations.

The El Niño–Southern Oscillation’s effect on summer heatwave development mechanisms in Australia

We investigate how the El Nino–Southern Oscillation (ENSO) affects the mechanisms and development of heatwaves in Australia. There are three fundamental mechanisms through which heat can accumulate in the atmosphere to generate temperatures high enough, and long-lasting enough to cause a heatwave. First, heat is advected, usually from lower latitudes, via a slow moving synoptic high pressure system; second, via diabatic heating of the boundary layer by the land surface; and third, via the subsidence of high potential temperature air which warms adiabatically as it approaches the heatwave affected region. Using an atmospheric model, we examine how ENSO affects these three mechanisms using prescribed sea surface temperatures characteristic of El Nino and La Nina conditions. By generating multiple ensembles of the same ENSO conditions, we can generate many ENSO realisations and examine how this large-scale mode of variability influences Australian heatwaves. We find that heatwave frequency and duration in the north and northeast are primarily affected by ENSO through land surface processes, soil moisture and changes in the surface energy balance. The importance of atmosphere–land coupling in ENSO related heatwave variability may help explain El Nino events with unusually few heatwaves and improve seasonal heatwave predictions. Other heatwave development mechanisms, such as the advection of heat and the subsidence of adiabatically warming air, are more important for the southern regions of Australia, but the influence of ENSO is weaker. The southeast tends to receive little influence from ENSO.

CFSv2 Monthly Forecasts of Tornado and Hail Activity

AbstractClimate Forecast System, version 2, predictions of monthly U.S. severe thunderstorm activity are analyzed for the period 1982–2016. Forecasts are based on a tornado environmental index and a hail environmental index, which are functions of monthly averaged storm relative helicity (SRH), convective precipitation (cPrcp), and convective available potential energy (CAPE). Overall, forecast indices reproduce well the annual cycle of tornado and hail events. Forecast index biases are mostly negative and caused by environment values that are low east of the Rockies, although forecast CAPE is higher than the reanalysis values over the High Plains. Skill is diagnosed spatially for the indices and their constituents separately. SRH is more skillfully forecast than cPrcp and CAPE, especially during December–June. The spatial patterns of forecast skill for CAPE and cPrcp are similar, with higher skill for CAPE and less spatial coherence for cPrcp. The indices are forecast with substantially less skill than the environmental parameters. Numbers of tornado and hail events are forecast with modest but statistically significant skill in some NOAA regions and months of the year. Skill tends to be relatively higher for hail events and in climatologically active seasons and regions. Much of the monthly skill appears to be derived from the first 2 weeks of the forecast. El Niño–Southern Oscillation (ENSO) modulates forecasts and, to a lesser extent, forecast skill, during March–May, with more activity and higher skill during cool ENSO conditions.

Diversity of ENSO Events Unified by Convective Threshold Sea Surface Temperature: A Nonlinear ENSO Index

AbstractWe show that the well‐known failure of any single index to capture the diversity and extremes of El Niño‐Southern Oscillation (ENSO) results from the inability of existing indices to uniquely characterize the average longitude of deep convection in the Walker Circulation. We present a simple sea surface temperature (SST)‐based index of this longitude that compactly characterizes the different spatial patterns, or flavors of observed and projected ENSO events. It recovers the familiar global responses of temperature, precipitation, and tropical cyclones to ENSO and identifies historical extreme El Niño events. Despite its simplicity, the new longitude index describes the nonlinear relationship between the first two principal components of SST, and unlike previous indices, accounts for background SST changes associated with the seasonal cycle and climate change. The index reveals that extreme El Niño, El Niño Modoki, and La Niña events are projected to become more frequent in the future at the expense of neutral ENSO conditions.

El Niño–Southern Oscillation and its impact in the changing climate

AbstractExtensive research has improved our understanding and forecast of the occurrence, evolution and global impacts of the El Niño–Southern Oscillation (ENSO). However, ENSO changes as the global climate warms up and it exhibits different characteristics and climate impacts in the twenty-first century from the twentieth century. Climate models project that ENSO will also change in the warming future and have not reached an agreement about the flavor, as to the intensity and the frequency, of future ENSO conditions. This article presents the conventional view of ENSO properties, dynamics and teleconnections, and reviews the emerging understanding of the diversity and associated climate impacts of ENSO. It also reviews the results from investigations into the possible changes in ENSO under the future global-warming scenarios.

Effects of Large-Scale Oceanic Phenomena on Non-Cholera Vibriosis Incidence in the United States: Implications for Climate Change

Purpose: Epidemics of diarrhea caused by toxigenic strains of Vibrio cholerae are of global public health concern, but non-cholera Vibrio (NCV) species are also important causes of disease. These pathogens are thermophilic, and climate change could increase the risk of NCV infection. The El Nino Southern Oscillation (ENSO) is a natural experiment that may presage the effects of ocean warming on disease incidence. Method: We obtained United States vibriosis case counts by digitizing annual reports from the U.S. Cholera and Other Vibrio Illness Surveillance surveillance system. Trends and environmental impacts (of ENSO and the North Atlantic Oscillation) were evaluated using negative binomial and distributed nonlinear lag models. Associations between latitude and changing risk were evaluated with meta-regression. Results: Trend models demonstrated significant seasonality (P < 0.001) and a 7% annual increase in disease risk from 1999 to 2014 (annual IRR 1.071, 95% CI 1.061 to 1.081). Distributed lag models demonstrated increased vibriosis risk following ENSO conditions over the subsequent 12 months (integrated RR 1.940, 95% CI 1.298 to 2.901). The rate of increase in vibriosis risk increased with state latitude (RR per 10° increase 1.066, 95% CI 1.027 to 1.107 ). Conclusion: We find that vibriosis risk in the United States is impacted by irregular large-scale ocean warming, and exhibits a north-south gradient in rate of change as would be expected if changing disease incidence is attributable to ocean warming, suggesting increasing, climate-change-related risk of this disease in vulnerable populations, even in high income countries with well-developed public health systems. Funding: Unfunded Declaration of Interest: No author had a competing interest to declare. Ethical Approval: The study was performed using aggregate, publicly available case data from public documents, and so research ethics approval was waived.

Opportunities for Joint Water–Energy Management: Sensitivity of the 2010 Western U.S. Electricity Grid Operations to Climate Oscillations

Abstract The increasing interconnectedness of energy and water systems makes it important to understand how interannual variations in water availability—and climate oscillations—could potentially impact the electric grid operations. The authors assess the vulnerability of the current western U.S. grid to historical climate variability using multiple energy and water system models. A 55-yr-long natural water availability benchmark is combined with the 2010 level of water demand from an integrated assessment model to drive a large-scale water management model over the western United States. The regulated flow at hydropower and thermoelectric power plants is then translated into boundary conditions for electricity generation in a production cost model. This analysis focuses on assessing regional interdependencies and the impact of interannual changes in water availability on power system operations, including reliability, cost, and carbon emissions. Results for August grid operations—when stress on the grid is often highest—show a range of sensitivity in production cost (–8% to +11%) and carbon emissions (–7% to +11%), as well as a 1-in-10 chance that electricity demand will exceed estimated supply. The authors also show that operating costs are lower under neutral El Niño–Southern Oscillation (ENSO) conditions than under other ENSO phases; carbon emissions are highest under La Niña conditions, especially in California; and the risk of brownouts may be higher under neutral and negative ENSO conditions. These results help characterize the grid’s performance under historical climate variations, are useful for seasonal and multiyear planning of joint water–electricity management, and can be used to support impact, adaptation, and vulnerability analyses.