El Nino-Southern Oscillation Years Research Articles

Equatorial Western–Central Pacific SST Responsible for the North Pacific Oscillation–ENSO Sequence

Abstract El Niño–Southern Oscillation (ENSO), the dominant mode of interannual variability in the tropical Pacific, is well known to affect the extratropical climate via atmospheric teleconnections. Extratropical atmospheric variability may in turn influence the occurrence of ENSO events. The winter North Pacific Oscillation (NPO), as the secondary dominant mode of atmospheric variability over the North Pacific, has been recognized as a potential precursor for ENSO development. This study demonstrates that the preexisting winter NPO signal is primarily excited by sea surface temperature (SST) anomalies in the equatorial western–central Pacific. During ENSO years with a preceding winter NPO signal, which accounts for approximately 60% of ENSO events observed in 1979–2021, significant SST anomalies emerge in the equatorial western–central Pacific in the preceding autumn and winter. The concurrent presence of local convection anomalies can act as a catalyst for NPO-like atmospheric circulation anomalies. In contrast, during other ENSO years, significant SST anomalies are not observed in the equatorial western–central Pacific during the preceding winter, and correspondingly, the NPO signal is absent. Ensemble simulations using an atmospheric general circulation model driven by observed SST anomalies in the tropical western–central Pacific can well reproduce the interannual variability of observed NPO. Therefore, an alternative explanation for the observed NPO–ENSO relationship is that the preceding winter NPO is a companion to ENSO development, driven by the precursory SST signal in the equatorial western–central Pacific. Our results suggest that the lagged relationship between ENSO and the NPO involves a tropical–extratropical two-way coupling rather than a purely stochastic forcing of the extratropical atmosphere on ENSO.

Interannual Lightning Variability within the TRMM LIS Dataset Using an ENSO Perspective

Abstract The Tropical Rainfall Measuring Mission (TRMM) Lightning Imaging Sensor (LIS) was used to investigate interannual variability of lightning from 1998 to 2014 within the 38°S–38°N range. Previous studies have indicated that the El Niño–Southern Oscillation (ENSO) phenomenon is one significant contributor to interannual lightning variability, potentially the dominant mechanism on the global scale. This period of 16 years contained four warm- (El Niño), eight cold- (La Niña), and four neutral-phase ENSO years based on the oceanic Niño index. Large magnitude lightning anomalies were found during the warm phase of ENSO, with mean warm-phase anomalies of >10 flashes (1000 km)−2 min−1 in north-central Africa and Argentina. This includes a +35 flashes (1000 km)−2 min−1 anomaly in Argentina during the 2009 El Niño. In general, large-scale anomalies of thermodynamic properties and upper-atmospheric vertical motion coincided with the lightning anomalies observed in both Africa and South America. The anomaly over north-central Africa, however, was characterized by a 6-week shift in the annual lightning maximum with the warm phase, a result of the more complex environmental response to ENSO over the Sahel. The most consistent ENSO anomalies with appreciable lightning were found in southeastern Africa, northwestern Brazil, central Mexico, and the southern Red Sea. Of these, all but the Mexico region had enhanced lightning with the cold phase and suppressed lightning with the warm phase.

Interpreting Negative IOD Events Based on the Transfer Routes of Wave Energy in the Upper Ocean

Abstract The present study adopts an energy-based approach to interpret the negative phase of Indian Ocean dipole (IOD) events. This is accomplished by diagnosing the output of hindcast experiments from 1958 to 2018 based on a linear ocean model. The authors have performed a composite analysis for a set of negative IOD (nIOD) events, distinguishing between independent nIOD events and concurrent nIOD events with El Niño–Southern Oscillation (ENSO). The focus is on investigating the mechanism of nIOD events in terms of wave energy transfer, employing a linear wave theory that considers the group velocity. The proposed diagnostic scheme offers a unified framework for studying the interaction between equatorial and off-equatorial waves. Both the first and third baroclinic modes exhibit interannual variations characterized by a distinct packet of eastward energy flux associated with equatorial Kelvin waves. During October–December, westerly wind anomalies induce the propagation of eastward-moving equatorial waves, leading to thermocline deepening in the central-eastern equatorial Indian Ocean, a feature absent during neutral IOD years. The development of wave energy demonstrates different patterns during nIOD events of various types. In concurrent nIOD–ENSO years, characterized by strong westerly winds, the intense eastward transfer of wave energy becomes prominent as early as October. This differs significantly from the situation manifested in independent nIOD years. The intensity of the energy-flux streamfunction/potential reaches its peak around November and then rapidly diminishes in December during both types of nIOD years. Significance Statement The present study provides an interpretation of wave energy transfer episodes in the upper ocean during the negative phase of the Indian Ocean dipole (IOD) based on the diagnosis of hindcast experiments. The results suggest that the reflection of Kelvin and Rossby waves at the eastern and western boundaries of the Indian Ocean (IO), respectively, accompanied by variations in thermocline depth, plays a crucial role in the development process of IOD events. Specifically, during the negative phase of the IOD, the tropical IO exhibits positive signals of energy-flux streamfunction in the Northern Hemisphere, along with positive signals of energy-flux potential associated with westerly wind anomalies occurring in October–December. These findings highlight the significance of these factors in shaping the characteristics of negative IOD events.

Effects of extreme phases of El Niño–Southern Oscillation on rainfall extremes in Alagoas, Brazil

AbstractThe Northeast of Brazil (NEB) is influenced by the phases of El Niño–Southern Oscillation (ENSO), which are associated with increased or decreased rainfall in the East NEB (ENEB). The study evaluated the effects of extreme ENSO phases on rainfall extremes in ENEB. Rainfall data from 54 stations in Alagoas were obtained from the National Water and Basic Sanitation Agency (ANA) and subjected to statistical analysis, with a data imputation method used to fill in gaps in the time series. The Inverse Distance Weighting (IDW) method was consistent and suitable for spatially representing rainfall data in the state of Alagoas, according to the adopted statistical indicators. Extreme, decadal and anomaly maps were interpolated using IDW method in Quantum GIS (QGIS), due to the positioning of the stations. The criteria for analysing extreme ENSO years were based on the Oceanic Niño Index (ONI) for region 3.4, between 1960 and 2016. The results show high interannual variability due to ENSO phases in the climatic mesoregions of Alagoas. In over 70% of extreme ENSO years, rainfall was below average (during strong and very strong El Niño) or above average (during strong La Niña). Some cities in the mesoregions of Alagoas experienced higher rainfall than others, even in extreme ENSO situations, suggesting the influence of physiography and multiscale meteorological systems. On a decadal scale, the East region recorded the highest rainfall accumulations, primarily due to decadal variability of two rainfall cores, corresponding to the Metropolitan Region of Maceió (MRM) and the northern part of the state. An exception is the Upper São Francisco region, which experiences dry decades. The East mesoregion (coast) had higher rainfall records compared to the more continental mesoregions (Hinterland and Arid), regardless of ENSO phases and interannual and decadal scales.

ENSO‐Related Fire Weather Changes in Southeast and Equatorial Asia: A Quantitative Evaluation Using Fire Weather Index

AbstractInterannual variability of tropical fire activity has been linked to the El Niño‐Southern Oscillation (ENSO). Here we analyze changes in fire and simultaneous fire weather related to ENSO over Southeast (SEAS) and Equatorial Asia (EQAS) and quantitively evaluate the contribution of key meteorological variables to the fire weather variations for the past decades. During the fire seasons, large increases in fires emerge in El Niño years, which greatly coincides with the more fire‐susceptible weather conditions compared to La Niña years. Moreover, the fires exhibit a more significant correlation with the ENSO index in El Niño years, mainly due to the influence of asymmetry response of the fire weather to ENSO. Composite analysis shows that it is the positive anomalous low‐level geopotential height and less water vapor transportation over SEAS (March–May) and EQAS (August–October) during El Niño that forms the fire‐favoring weather. By conducting tests in calculating fire weather index (FWI) under different ideal conditions, we identified the daily precipitation as the dominant driver of FWI variation, with the contribution reaching 65.5%–77.5% and 60.9%–90.5% for SEAS and EQAS respectively, while decreased relative humidity induces nearly a quarter of increases in FWI in El Niño years. Changes in temperature and wind speed, however, rarely perturb the fire weather for both SEAS and EQAS regions. The quantitative evaluations of individual meteorological variables in shaping fire weather as well as their asymmetrical response in ENSO years could support fire management during fire seasons in Tropical Asia.

Seasonal Dependence of the Pacific–North American Teleconnection Associated with ENSO and Its Interaction with the Annual Cycle

Abstract The Pacific–North American (PNA) teleconnection pattern is one of the prominent atmospheric circulation modes in the extratropical Northern Hemisphere, and its seasonal to interannual predictability is suggested to originate from El Niño–Southern Oscillation (ENSO). Intriguingly, the PNA teleconnection pattern exhibits variance at near-annual frequencies, which is related to a rapid phase reversal of the PNA pattern during ENSO years, whereas the ENSO sea surface temperature (SST) anomalies in the tropical Pacific are evolving much slower in time. This distinct seasonal feature of the PNA pattern can be explained by an amplitude modulation of the interannual ENSO signal by the annual cycle (i.e., the ENSO combination mode). The ENSO-related seasonal phase transition of the PNA pattern is reproduced well in an atmospheric general circulation model when both the background SST annual cycle and ENSO SST anomalies are prescribed. In contrast, this characteristic seasonal evolution of the PNA pattern is absent when the tropical Pacific background SST annual cycle is not considered in the modeling experiments. The background SST annual cycle in the tropical Pacific modulates the ENSO-associated tropical Pacific convection response, leading to a rapid enhancement of convection anomalies in winter. The enhanced convection results in a fast establishment of the large-scale PNA teleconnection during ENSO years. The dynamics of this ENSO–annual cycle interaction fills an important gap in our understanding of the seasonally modulated PNA teleconnection pattern during ENSO years.

Revisiting the effect of increasing horizontal resolution on the evolution of El Niño in a coupled model

The ENSO (El Niño southern oscillation) in the tropical Pacific plays a crucial role in regulating the Indian summer monsoon. Many mechanisms have been proposed to explain the positive and negative feedback associated with the ENSO through air-sea interaction in the tropical Pacific. Historical run data at varying oceanic and atmospheric resolutions from the MPI-ESM model is analyzed and compared with observations to determine the possible reasons for the much earlier onset and delayed withdrawal of ENSO in the coupled model. Increasing the resolution of the oceanic and atmospheric components of the coupled model helps in well-resolving the annual cycle of sea surface temperature in the tropical Pacific. There is a significant improvement in the early onset and late withdrawal of El Niño in the coupled model with increasing horizontal resolution of the model components. The weak subsurface propagation along the 20 °C isotherm in the equatorial Pacific improves on increasing the horizontal resolution of the coupled model. Similar to observations, there is a clear eastward extension of convection, 20° east of the dateline, in the equatorial tropical Pacific in the coupled model during ENSO years. Increasing the resolution of the oceanic and atmospheric components of the coupled model improves the simulation of convective activity over the western Pacific along with the improved magnitude of anomalous zonal wind strength during El Niño years. However, the presentation of convective activity over the equatorial Pacific deteriorated on increasing atmospheric resolution further to T255 due to the enhanced value of the interannual amplitude of intraseasonal zonal wind around the international dateline. Also, the coupled model does not capture the accurate eastward propagation of the Madden Julian Oscillation envelope over the western Pacific. While higher resolutions showed improvement in the representation of El Niño events in terms of their number and duration, challenges persisted in accurately capturing the frequency of these events and their related triggering mechanisms. Understanding the intricate interplay of factors influencing the evolution of El Niño requires further research and progress in modeling strategies.

Key to ENSO phase-locking simulation: effects of sea surface temperature diurnal amplitude

The tendency of El Niño/Southern Oscillation (ENSO) events to peak during boreal winter is known as ENSO phase-locking, whose accurate simulation is essential for ENSO prediction. However, the simulated peaks of ENSO events usually occur outside boreal winter in state-of-the-art climate models. Based on the Coupled Model Intercomparison Project Phase 6 (CMIP6) models, the model with a more reasonable diurnal amplitude (DA) in the sea surface temperature (SST) had a better simulation ability for ENSO phase-locking compared with other models. Further experiments based on the earth system model revealed that the DA is vital for ENSO phase-locking simulation primarily due to the spatial inhomogeneities in seasonal DA anomaly variations in ENSO years with positive/negative DA anomalies in the central equatorial Pacific and negative/positive in the western or eastern Pacific during El Niño/La Niña. Our findings indicate that DA simulation in climate models is crucial for resolving the long-standing failure associated with the ENSO phase-locking simulation accuracy.

On the Decadal Changes of the Interannual Relationship Between ENSO and Tropical South Atlantic SST in Boreal Summer

AbstractThis study aims to investigate the underlying mechanisms driving changes in the contemporaneous relationship between El Niño–Southern Oscillation (ENSO) and tropical South Atlantic (TSA) sea surface temperatures (SST) during boreal summer over the past century. Our findings indicate that the negative TSA–ENSO relationship is primarily attributed to persistent ENSO years rather than ENSO transition or development years. This is because of the distinct anomalies observed in both spring ENSO and the tropical North Atlantic (TNA) during ENSO persistent years, whose impacts on summer TSA are of the same sign. Thus, their combined effects lead to a strong TSA anomaly that is opposite to that of ENSO. On a decadal timescale, the frequency of persistent ENSO occurrence can explain the fluctuation of the ENSO–TSA relationship over the past century. These findings enhance our comprehension of the relationship between summer ENSO and the tropical Atlantic SST.

Influence of “El Niño Southern Oscillation” periods on plant density of Hoffmannseggia aphylla (Fabaceae) an endangered species

Backgrounds and aims: Studies on the natural regeneration of plant species under hyperaridity conditions have been scarce, mainly because of the low germination percentage of the species under these conditions. Presumably, sporadic phenomena such as the El Niño Southern Oscillation (ENSO) could have a positive effect on the natural germination of these species, although this effect has not yet been satisfactorily explored. M&M: To test the crucial assumption of our statement, a hyperarid region (average rainfall below 5 mm/year) was used as a model to determine the effect of ENSO years on the natural regeneration rate of adult individuals of the endemic legume Hoffmannseggia aphylla (retama) in the Atacama Desert, northern Chile. Thus, the vegetation density of an endemic leguminous species in a sector of the Pampa del Tamarugal, Tarapacá Region, northern Chile, was analyzed for six years. Results: The density of this species increased during ENSO years, mainly due to water flows from the highest sectors of the Tamarugal pampas, such as the town of Pica, in addition to the increase in humidity and summer rainfall. Conclusion: Our results highlight the transcendence of the ENSO in the regeneration of leguminous plants.

Keterkaitan Antara El Niño-Southern Oscillation (ENSO) Dengan Variabilitas Curah Hujan Bojonegoro

Indonesian climate, especially Java Island have been associated with El Niño-Southern Oscillation (ENSO). The research using rainfall station at Bojonegoro District from 1979 – 2009 to detect rainfall variability and its linkages with ENSO phenomenom. ENSO’s indexes then used to predict rainfall in Bojonegoro. Rainfall station was clustered using cluster analysis and then Mann-Kendall test used to predict rainfall trend of each cluster. There are 16 rainfall station that passed the rainfall test that can be conduct in the rainfall anomaly analysis. All stations have experienced both dry and wet anomalies during observation. Positive ENSO years have associated with more stations experienced dry anomalies; in other hand wet anomalies occurred more when negative ENSO. The stronger ENSO caused more extrem anomalies. There are obtained 5 clusters rainfall area over Bojonegoro District used HCA Ward method. Largest rainfall variations was experienced by cluster 5, Gondang and Jatiblimbing. Trend in rainfall only experienced by cluster 2 (Sumberejo and Mekuris) for December – January but another clusters didn’t experience such significant rainfall pattern change. October and November have been the most influenced month caused by ENSO; and positive ENSO anomaly caused prolonged dry season up to November. October and November’s rainfall can be predicted using SSTA Nino 3.4 index 3 months before.

Seismic-Perturbed Obliquity Change as a Discrete Trigger Mechanism of El Niño and La Niña Episodes

The global climate disruptor El Niño Southern Oscillation (ENSO) is difficult to forecast some years in advance due to lack of understanding of its root cause. An alternative physical mechanism is hereby proposed to describe the nature and sustaining force, and predict the occurrence of El Niño and La Niña phenomena. This is based on the earthquake-perturbed obliquity change model previously proposed as a major mechanism of the global climate change problem. Massive quakes can impart a very strong oceanic force that can move the moon which in turn pulls the earth’s axis and change the planetary obliquity. Analysis of the annual geomagnetic north-pole shift and global seismic data revealed this previously undiscovered force. Using a higher obliquity and constant greenhouse gas forcing in the global climate model EdGCM showed that the seismic-induced polar motion and associated enhanced obliquity could be the major mechanism governing the mysterious climate anomalies attributed to El Nino and La Nina cycles. The apparent eastward migration of high SST in the Pacific and the warming of the Indian and Atlantic Oceans south of the equator during ENSO years were correctly simulated by the model. The annual time series of global surface temperatures computed by EdGCM was compared with the observed global temperature and the results showed relatively good agreement. In addition, the heat wave that occurred in Europe during the summer of 2003 and the Russian heat wave of 2010 that killed over 55,000 people appeared to have been correctly simulated with higher obliquity. This study can help affected countries in water shortage contingency planning, disaster mitigation and may help prevent adverse economic and commercial impacts due to ENSO.

On the Southern Hemisphere Stratospheric Response to ENSO and Its Impacts on Tropospheric Circulation

Abstract As the leading mode of Pacific variability, El Niño–Southern Oscillation (ENSO) causes vast and widespread climatic impacts, including in the stratosphere. Following discovery of a stratospheric pathway of ENSO to the Northern Hemisphere surface, here we aim to investigate if there is a substantial Southern Hemisphere (SH) stratospheric pathway in relation to austral winter ENSO events. Large stratospheric anomalies connected to ENSO occur on average at high SH latitudes as early as August, peaking at around 10 hPa. An overall colder austral spring Antarctic stratosphere is generally associated with the warm phase of the ENSO cycle, and vice versa. This behavior is robust among reanalysis and six separate model ensembles encompassing two different model frameworks. A stratospheric pathway is identified by separating ENSO events that exhibit a stratospheric anomaly from those that do not and comparing to stratospheric extremes that occur during neutral ENSO years. The tropospheric eddy-driven jet response to the stratospheric ENSO pathway is the most robust in the spring following a La Niña, but extends into summer, and is more zonally symmetric compared to the tropospheric ENSO teleconnection. The magnitude of the stratospheric pathway is weaker compared to the tropospheric pathway and therefore, when it is present, has a secondary role. For context, the magnitude is approximately half that of the eddy-driven jet modulation due to austral spring ozone depletion in the model simulations. This work establishes that the stratospheric circulation acts as an intermediary in coupling ENSO variability to variations in the austral spring and summer tropospheric circulation.

Large-Scale Environments of Successive Atmospheric River Events Leading to Compound Precipitation Extremes in California

Abstract Successive atmospheric river (AR) events—known as AR families—can result in prolonged and elevated hydrological impacts relative to single ARs due to the lack of recovery time between periods of precipitation. Despite the outsized societal impacts that often stem from AR families, the large-scale environments and mechanisms associated with these compound events remain poorly understood. In this work, a new reanalysis-based 39-yr catalog of 248 AR family events affecting California between 1981 and 2019 is introduced. Nearly all (94%) of the interannual variability in AR frequency is driven by AR family versus single events. Using k-means clustering on the 500-hPa geopotential height field, six distinct clusters of large-scale patterns associated with AR families are identified. Two clusters are of particular interest due to their strong relationship with phases of El Niño–Southern Oscillation (ENSO). One of these clusters is characterized by a strong ridge in the Bering Sea and Rossby wave propagation, most frequently occurs during La Niña and neutral ENSO years, and is associated with the highest cluster-average precipitation across California. The other cluster, characterized by a zonal elongation of lower geopotential heights across the Pacific basin and an extended North Pacific jet, most frequently occurs during El Niño years and is associated with lower cluster-average precipitation across California but with a longer duration. In contrast, single AR events do not show obvious clustering of spatial patterns. This difference suggests that the potential predictability of AR families may be enhanced relative to single AR events, especially on subseasonal to seasonal time scales.

The Recent Droughts of 2019/20 in Southern Africa and Its Teleconnection with ENSO Events

This study is motivated to highlight the variability of recent drought hotspots in the region of southern Africa in terms of the seasonal and annual rainfall regimes and their possible spatial linkage with the 1950-2020 seasonal El Niño/Southern Oscillation (ENSO). Some evidence is found on possible links between the occurrence of drought hotspots in the region in terms of seasonal and mean annual runoff and warm ENSO events. This was revealed by the existence of a strong and nearly-strong positive linear correlation between Seasonal and annual rainfall depths and the warm seasonal ENSO indices explained by the southern oscillation index represented by the sea level pressure (SLP) anomalies data obtained from the National Oceanographic and Aeronautics Administration (NOAA). Considering the entire southern African region, 41% of the surface areas exhibit moderate (r > 0.25) and strong (r > 0.5) correlation coefficients in terms of the December to February quarter rainfall and ENSO indices. Above 50% confidence interval in the correlation between seasonal rainfall and ENSO during DJF quarters is found in 74% of the surface area of the region of southern Africa. The high confidence interval of the positive correlation coefficients is an indication that substantial variance of precipitation during ENSO years is accounted for by the warm ENSO events. The areas with pronounced lower rainfalls and droughts associated with ENSO activity in the region include larger and some pockets of various countries in southern Africa, including but not limited to Angola, Botswana, Lesotho, Namibia, Zambia, Zimbabwe, South Africa and Mozambique. The recent drought events of 2019/2020, and previously in 2015/16 in this region with wider regional impacts can be explained by the ENSO phenomena.

Changes of Extreme Precipitation and Possible Influence of ENSO Events in a Humid Basin in China

In this study, 11 extreme precipitation indices were selected to examine the spatiotemporal variation of extreme precipitation in the Poyang Lake Basin during 1960–2017. The responses of extreme precipitation indices to El Nino/Southern Oscillation (ENSO) events of different Pacific Ocean areas were further investigated. The results show that the temperature in the Poyang Lake Basin has increased significantly since the 1990s, and the inter-decadal precipitation fluctuated. Most extreme precipitation indices showed an increasing trend with abrupt changes occurring around 1991. Spatially, most of the extreme precipitation indices decreased from northeast to southwest. The increasing trend of most indices in the center and south of the basin was relatively prominent. The linear correlations between the extreme precipitation indices and Nino 1 + 2 were the most significant. On the timescale of 2–6 years, a common oscillation period between the extreme precipitation of the basin and the four ENSO indices can be observed. After 2010, the positive correlation between the precipitation of the Poyang Lake Basin and the SST (sea surface temperature) anomalies in the equatorial Pacific increased significantly. Additionally, annual total wet–day precipitation in most areas of the Poyang Lake Basin increased with varying degrees in warm ENSO years. The results of this study will improve the understanding of the complex background and driving mechanism of flood disasters in the Poyang Lake Basin.

Comparative assessment of evapotranspiration in Bhima sub-basin using spatial analysis for normal and ENSO years

Evapotranspiration (ET) estimation is important for hydrological modelling and water management for irrigation. The present study estimates the reference evapotranspiration using FAO Penman-Monteith (FAO P-M) method and SWAT hydrological model, and its spatial variation during ENSO events during 1996 to 2013. The spatial variation of crop coefficient and actual evapotranspiration (ETa) is also analyzed. The results from these methods are compared for various El Niño-Southern Oscillation (ENSO) events and normal years. MODIS NDVI data was used to generate crop coefficients which were further used for generation of ETa.The results show that the ET0 estimated using FAO P-M is less during the pre-monsoon period than ET0 estimated using SWAT model. ET0values from FAO P-M show decreasing trends while those by SWAT show increasing trends. Also, ET0 shows higher values during post monsoon period of El Niño years as compared to La Niña and normal years.

Predicting Rice Production in Central Thailand Using the WOFOST Model with ENSO Impact

The World Food Studies Simulation Model (WOFOST) model is a daily crop growth and yield forecast model with interactions with the environment, including soil, agricultural management, and especially climate conditions. An El Niño–Southern Oscillation (ENSO) phenomenon directly affected climate change and indirectly affected the rice yield in Thailand. This study aims to simulate rice production in central Thailand using the WOFOST model and to find the relationship between rice yield and ENSO. The meteorological data and information on rice yields of Suphan Buri 1 variety from 2011 to 2018 in central Thailand were used to study the rice yields. The study of rice yield found that the WOFOST model was able to simulate rice yield with a Root Mean Square Error (RMSE) value of 752 kg ha−1, with approximately 16% discrepancy. The WOFOST model was able to simulate the growth of Suphan Buri 1 rice, with an average discrepancy of 16.205%, and Suphan Buri province had the least discrepancy at 6.99%. Most rice yield simulations in the central region were overestimated (except Suphan Buri) because the model did not cover crop damage factors such as rice disease or insect damage. The WOFOST model had good relative accuracy and could respond to estimates of rice yields. When an El Niño phenomenon occurs at Niño 3.4, it results in lower-than-normal yields of Suphan Buri 1 rice in the next 8 months. On the other hand, when a La Niña phenomenon occurs at Niño 3.4, Suphan Buri 1 rice yields are higher than normal in the next 8 months. An analysis of the rice yield data confirms the significant impact of ENSO on rice yields in Thailand. This study shows that climate change leads to impacts on rice production, especially during ENSO years.

The influence of groundwater abstraction on interpreting climate controls and extreme recharge events from well hydrographs in semi-arid South Africa

There is a scarcity of long-term groundwater hydrographs from sub-Saharan Africa to investigate groundwater sustainability, processes and controls. This paper presents an analysis of 21 hydrographs from semi-arid South Africa. Hydrographs from 1980 to 2000 were converted to standardised groundwater level indices and rationalised into four types (C1–C4) using hierarchical cluster analysis. Mean hydrographs for each type were cross-correlated with standardised precipitation and streamflow indices. Relationships with the El Niño–Southern Oscillation (ENSO) were also investigated. The four hydrograph types show a transition of autocorrelation over increasing timescales and increasingly subdued responses to rainfall. Type C1 strongly relates to rainfall, responding in most years, whereas C4 notably responds to only a single extreme event in 2000 and has limited relationship with rainfall. Types C2, C3 and C4 have stronger statistical relationships with standardised streamflow than standardised rainfall. C3 and C4 changes are significantly (p < 0.05) correlated to the mean wet season ENSO anomaly, indicating a tendency for substantial or minimal recharge to occur during extreme negative and positive ENSO years, respectively. The range of different hydrograph types, sometimes within only a few kilometres of each other, appears to be a result of abstraction interference and cannot be confidently attributed to variations in climate or hydrogeological setting. It is possible that high groundwater abstraction near C3/C4 sites masks frequent small-scale recharge events observed at C1/C2 sites, resulting in extreme events associated with negative ENSO years being more visible in the time series.

Quantitative contribution of ENSO to precipitation-temperature dependence and associated compound dry and hot events

Compound dry and hot events (CDHEs) are closely related to negative precipitation-temperature (P-T) dependence that is commonly observed during warm seasons over global land areas. The P-T dependence can be induced by El Niño-Southern Oscillation (ENSO) or other non-ENSO factors (e.g., local coupled feedbacks). However, the disentanglement of impacts from ENSO on the P-T dependence and associated CDHEs is not clear. By comparing the impacts during ENSO years and neutral years, we quantify the contribution of ENSO to the P-T dependence and likelihood of CDHEs during warm seasons over global land areas. For the regions with significant impacts of ENSO on CDHEs (e.g., southern North America, northern South America, northern and southern Africa, southern and southeastern Asia, and Australia), the mean P-T dependence (measured by Kendall's rank correlation) enhances from −0.16 for neutral years to −0.24 for ENSO years. Accordingly, El Niño (La Niña) could induce an increase of around 60% (a decrease of around 35%) in the likelihood of CDHEs in these regions. Results from this study could be useful for understanding driving factors of CDHEs over global land areas.