Warm Pacific Decadal Oscillation Research Articles

Modulation of Pacific decadal oscillation on the relationship between El Niño–Southern Oscillation and rainy season onset over the Indo‐China Peninsula

AbstractMonsoon precipitation variability over the Indo‐China Peninsula (ICP) has become more complicated affected by global warming. In this study, the modulation of Pacific decadal oscillation (PDO) on the relationship between El Niño–Southern Oscillation (ENSO) and the rainy season onset over the ICP were investigated. The results showed that the ICP rainy season onset were predominantly correlated with winter sea surface temperature anomalies (SSTAs) in the East Pacific Ocean, with late and early onsets following El Niño and La Niña events, respectively. During the warm and cold PDO phase, the correlations tended to be substantially strengthened and weakened, respectively. Further analysis indicates that PDO significantly influenced the effects of ENSO on the ICP rainy season onset by modulating SSTAs and low‐level wind fields. During the El Niño events, abnormal easterlies over the Bay of Bengal (BoB) and southern ICP suppressed water vapour transporting to the ICP, which may be related to the zonal SST anomaly gradient between the Indian Ocean and the Northwest Pacific Ocean. When the El Niño occurred during the warm PDO phase, the rainy season onsets were later. The anomalous easterlies became stronger corresponds to the increasing zonal sea surface temperature anomaly (SSTA) gradient between the Indian Ocean and the Northwest Pacific Ocean. There was no significant anomaly on the rainy season onset during the cold PDO phase. During the La Niña events, the abnormal westerlies in BOB accelerated water vapour transport, and the rainy season onset were earlier during the warm and cold PDO phase. The modulating effects of PDO on La Niña were less than those on El Niño. These results suggest that the predictability of rainy season onset over the ICP can be improved through PDO and thus help agricultural planning and water resources management.

On the association of Pacific Decadal Oscillation with the interdecadal variability in Asian-Pacific Oscillation

The Asian-Pacific Oscillation (APO), featuring a seesaw pattern in the upper-tropospheric temperatures between Asia and the North Pacific, plays profound roles in the Northern Hemispheric climate anomalies. So, its variability and associated physical mechanisms are of great interest. Although progress has been achieved for the APO variability at the interannual time scale, the understanding of its interdecadal variability remains relatively poor. Based on the twentieth-century reanalysis and the simulations of the preindustrial control, Pacific pacemaker, and large ensemble experiments, this study reports a salient contribution of the Pacific Decadal Oscillation (PDO) to the interdecadal variability of the APO during summer, featured as a warm (cold) PDO phase accompanying a negative (positive) APO polarity. During the warm PDO phase, the sea surface temperature (SST) warming over the eastern Pacific is conducive to local ascending anomalies, which teleconnect with descending anomalies over the Tibetan Plateau through zonal vertical circulations. The anomalous ascent (descent) over the eastern Pacific (Tibetan Plateau) tends to strengthen (weaken) the atmospheric heating, beneficial for a warming (cooling) of the troposphere in situ. In addition, the PDO-related meridional SST gradient anomalies favor a southward shift of the subtropical jet stream, weakening the South Asian high and the North Pacific trough in the upper troposphere, which corresponds to the atmospheric situation of a negative APO phase. Quantitative analysis from the large ensemble simulations indicates that the PDO may contribute to approximately 48% of recent APO interdecadal variation from the negative phase to the positive phase in the late 1990s.

Characteristics of Marine Heatwaves in the Indonesian Waters during the PDO, ENSO, and IOD Phases and Their Relationships to Net Surface Heat Flux

We conducted an investigation into the characteristics of marine heatwaves (MHWs) in Indonesian waters, aiming to understand the underlying mechanisms responsible for their formation, particularly the ones generated by net surface heat flux. To accomplish this, we utilized remote sensing data from the National Oceanic and Atmospheric Administration and the European Centre for Medium-Range Weather Forecasts. The dataset covered a 40-year period (1982–2021) encompassing both warm (1982–2007) and cold (2008–2021) phases of the Pacific Decadal Oscillation (PDO). Statistical analysis methods were employed to process the data. Our study reveals significant findings regarding MHWs in Indonesian waters. We observed the highest average frequency and maximum intensity of MHWs, occurring approximately 2–3 times a year and exceeding 1.5 °C, respectively, during the warm phase of PDO (with El Niño events occurring more frequently than La Niña). Conversely, the longest durations of MHWs in Indonesian waters were recorded during the cold phase of PDO (with La Niña events occurring more frequently than El Niño), spanning approximately 7–15 days. We identified local forcing in the form of net surface heat flux as the primary driver of MHW frequency and maximum intensity. During the warm phase of PDO, the net surface heat flux was notably higher, primarily due to increased shortwave radiation (heat gain) and reduced latent heat flux (heat loss) through the evaporation process. These factors collectively contributed to maintaining warmer ocean temperatures. Moreover, our study provides valuable insights into the interannual variability of MHWs through the application of composite calculations. We discovered a strong correlation between the occurrence of El Niño and positive Indian Ocean Dipole (IOD) events during the warm PDO phase and the highest frequency and maximum intensity of MHWs, with approximately 2.52 events and 1.54 °C, respectively. In contrast, we found that MHWs with the longest durations were closely linked to La Niña and negative IOD events during the cold PDO phase, lasting approximately 10.90 days. These findings highlight the complex interplay between climate phenomena and MHW characteristics, further deepening our understanding of their dynamics.

Contribution of PDO to Decadal Variations of Glaze Dipole Pattern in China

Abstract Based on the in situ observations, reanalysis, and model simulation, the variations in glaze dipole pattern in China and its underlying physical mechanism have been explored. The glaze dipole pattern features an out-of-phase relationship between winter glaze in the south of the Yangtze River valley (YRV) and northern China, accompanied by pronounced interdecadal variation around the late 1970s. The results from synoptic analyses suggest that cold air brought by the northerly winds and warm moist air by the southwesterly winds, as well as the occurrence of inversion layer are vital to the glaze weather in the south of YRV. Further analyses indicate that the interdecadal shift of the Pacific decadal oscillation (PDO) contributes largely to variations in glaze dipole pattern. Specifically, the warm PDO provides a beneficial environment for the occurrence of glaze dipole pattern by stimulating the tropical–extratropical circulation configuration with the deepened East Asian trough, strengthened East Asian westerly jet, anomalous anticyclone over the tropical western Pacific Ocean, and cyclone over the southern Tibetan Plateau at the decadal time scale. Consequently, the enhanced moisture transport brought by southwesterly and cold air intrusion induced by the deepened East Asian trough benefit the glaze weather in the south of YRV, while the decreased precipitation and a much lower temperature in northern China depress the generation of glaze. Moreover, the results from the CAM4 model simulation indicate the atmospheric circulation anomalies forced by PDO-like SST can roughly reproduce the extratropical configuration related to the glaze, but it has difficulties in capturing the tropical circulation anomalies. Significance Statement The purpose of this study is to better understand how the glaze dipole pattern in China responds to climate anomalies, which focuses on the spatial–temporal evolution of glaze days and its underlying physical mechanism. This study highlights the important role of Pacific Ocean sea surface temperature anomalies in the interdecadal variations in glaze dipole pattern, and it gives a clear clarification to demonstrate the impacts of Pacific decadal oscillation on the climatological background for the occurrence of glaze. Our results provide a guide on what drives the interdecadal variation in the glaze dipole pattern and help to understand the climate dynamic mechanism of variations in freezing events in China.

Role of solar activity and Pacific decadal oscillation in the hydroclimatic patterns of eastern China over the past millennium

The hydroclimatic patterns in eastern China (EC) over the past millennium, both influenced by solar activity and Pacific decadal oscillation (PDO), are presented based on the climatic reconstructions and simulations. For strong solar activity, a consistent pattern exists where drought appears in the majority of EC initialized from the cold PDO phase, which is related to less moisture caused by the negative East Asia/Pacific-like (EAP-like) pattern and the enhanced western Pacific subtropical high (WPSH). When the initial condition with a neutral or warm PDO phase is set up, there is a tripole-like pattern from north to south, i.e., drought–flood–drought for the neutral PDO phase and flood–drought–flood for the warm PDO phase, which is related to the positive EAP-like pattern with various moisture transportation paths. For weak solar activity, there are dipole-like patterns where drought occurs in the northern part of the Yangtze River and flood appears in the southern part initialized from the cold or warm PDO phase, which is possibly related to the influence of the weakened WPSH. When the initial condition is the neutral PDO phase, there is a tripole-like pattern from north to south (flood–drought–flood) in EC affected by the weakened WPSH and the intensive India–Burma trough. Notably, the vertical velocity anomalies of airflow, representing the vertical moisture transportations, correspond well with the hydroclimatic patterns in EC whenever the various initialization strategies of PDO phases are employed. • Hydroclimatic patterns in eastern China (EC) are related to solar activity and PDO. • A consistent pattern in EC for strong solar period (SS) and cold PDO initial phase. • The tripole-like patterns for SS and the neutral or warm PDO initial phase. • A tripole-like pattern for weak solar period (WS) and neutral PDO initial phase. • The dipole-like patterns for WS and the cold or warm PDO initial phase.

Synchronous spatio-temporal changes in potential habitats of Trachurus murphyi and Dosidicus gigas off Chile in relation to regime shift of Pacific decadal oscillation

Understanding concurrent responses of habitat pattern of pelagic fish species to climate variability is favorable for sustainable exploitation and fisheries management. In this study, the key environmental factors affecting Dosidicus gigas (sea surface salinity (SSS), sea surface height anomaly (SSHA) and water temperature at 400 m (Temp_400m), and Trachurus murphyi (sea surface temperature (SST), mixed layer depth (MLD) and Temp_400m), were used in combination with the Pacific Decadal Oscillation (PDO) index to examine synchronous habitat variations off Chile based on habitat suitability index model (HSI). All environmental factors were significantly related to the PDO. A significantly negative relationship was found between the HSI of D.gigas and the PDO index, while a significantly positive correlation was observed in the HSI of T.murphyi. In the warm PDO regime, MLD was shallower, SST increased, and SSHA decreased from the northeast to the southwest off Chile. SSS and Temp_400m in northern waters off Chile were higher than those in southern waters. The suitable habitats of D.gigas contracted and shifted southwestward. While the area and distribution of T.murphyi changed little, but its habitat quality enhanced. In the cold PDO regime, SST and SSHA decreased, and MLD deepened. Variations in SSS and Temp_400m were consistent with those in the warm PDO regime. The suitable habitats of D.gigas enlarged and moved northeastward. Whereas the suitable habitats of T.murphyi slightly reduced with small change occurred with its spatial location. Our findings suggested that the PDO played important roles in the long-term concurrent habitat variations of Chilean T.murphyi and D.gigas.

Pacific Decadal Oscillation modulates the Arctic sea-ice loss influence on the midlatitude atmospheric circulation in winter

Abstract. The modulation of the winter impacts of Arctic sea-ice loss by the Pacific Decadal Oscillation (PDO) is investigated in the IPSL-CM6A-LR ocean–atmosphere general circulation model. Ensembles of simulations are performed with constrained sea-ice concentration following the Polar Amplification Model Intercomparison Project (PAMIP) and initial conditions sampling warm and cold phases of the PDO. Using a general linear model, we estimate the simulated winter impact of sea-ice loss, PDO and their combined effects. On the one hand, a negative North Atlantic Oscillation (NAO)-like pattern appears in response to sea-ice loss together with a modest deepening of the Aleutian Low. On the other hand, a warm PDO phase induces a large positive Pacific–North America pattern, as well as a small negative Arctic Oscillation pattern. Both sea-ice loss and warm PDO responses are associated with a weakening of the poleward flank of the eddy-driven jet, an intensification of the subtropical jet and a weakening of the stratospheric polar vortex. These effects are partly additive; the warm PDO phase therefore enhances the response to sea-ice loss, while the cold PDO phase reduces it. However, the effects of PDO and sea-ice loss are also partly non-additive, with the interaction between both signals being slightly destructive. This results in small damping of the PDO teleconnections under sea-ice loss conditions, especially in the stratosphere. The sea-ice loss responses are compared to those obtained with the same model in atmosphere-only simulations, where sea-ice loss does not significantly alter the stratospheric polar vortex.

Interdecadal Modulation of ENSO‐Related Anomalous Equatorial Intermediate Currents in the Western Pacific by the PDO

AbstractAs the most prominent decadal variability in the Pacific Ocean, the Pacific Decadal Oscillation (PDO) can influence the El Niño‐Southern Oscillation‐related atmospheric and upper oceanic motions. Based on results from ocean reanalysis products and linear continuously stratified model experiments, we reveal that the PDO can further extend its interdecadal modulation effect to the equatorial intermediate currents below the thermocline. For the maximum El Niño‐related intermediate eastward transport anomaly in the western Pacific, its magnitude during the warm PDO is nearly twice as large as that during the cold PDO, and its occurrence time in the warm PDO leads that in the cold PDO by about 2 months. Such modulation is achieved through westward and downward propagation of the reflected Kelvin‐to‐Rossby waves, triggered by enhanced and eastward‐displaced anomalous westerly wind. The decisive wind forcing region for the modulation is located over the equatorial central Pacific of 5°S–5°N and 180°–140°W.

Variability of PDO identified by a last 300-year stalagmite δ18O record in Southwest China

Stalagmite oxygen isotope (δ18O) record has been widely used in characterizing Asian Monsoon variations. In southwest (SW) China, although the stalagmite δ18O was usually suggested as a precipitation proxy, it remains a subject of debate. Here we present two replicated, high-precise-dated stalagmite δ18O records for the interval 1710–2003 AD from Yunnan province, SW China. The stalagmite δ18O shows no correlation with the local monsoon precipitation, but a significantly positive correlation with the Pacific Decadal Oscillation (PDO) index. It demonstrates that the stalagmite δ18O in SW China is most likely influenced by the atmospheric circulation associated with the PDO through the upstream depletion mechanism. During the warm (cold) PDO period, the deficit rainfall over India would make the δ18O of water vapor transporting to SW China less (more) negative due to the weaker Rayleigh distillation process, which would lead to the less (more) negative stalagmite δ18O. Consequently, the stalagmite δ18O in SW China is suitable to reconstruct the PDO variations. It is important to note that the other factors, such as El Niño–Southern Oscillation (ENSO) or sea surface temperature (SST) also possibly affect the stalagmite δ18O in SW China, and the relationship between them requires further studies.

Climatic Variation of Maximum Intensification Rate for Major Tropical Cyclones over the Western North Pacific

To analyze the dependence of intensification rates of tropical cyclones (TCs) on the variation of environmental conditions, an index is proposed here to measure the lifetime maximum intensification rates (LMIRs) for the Saffir–Simpson scale category 4–5 TCs over the western North Pacific. To quantitatively describe the intensification rate of major TCs, the LMIR is defined as the maximum acceleration in the sustained-wind-speed over a 24-h period of an overwater TC. This new index, LMIR, is generally independent of the indices for RI frequency. The results show that the Pacific Decadal Oscillation (PDO) modulates the inter-annual relationship between the LMIR and El Niño/Southern Oscillation (ENSO). The PDO’s modulation on the ENSO’s effect on the LMIR is explored here by considering the relationship between the LMIR and the environmental conditions in different PDO phases. While the ENSO’s effect on the LMIR for the warm PDO phase is generally by affecting the variations of upper ocean heat content, ENSO mainly influences the variations of zonal wind and vertical wind shear for the cold PDO phase. Our results suggest that fast translating TCs tend to attain strong intensification during the warm PDO phase, while a warm subsurface condition may permit slow-translating TCs also to become strongly intensified during the cooling PDO phase. These findings have an important implication for both prediction of RI and the long-term projection of TC activities in the western North Pacific.

Influence of Pacific Decadal Oscillation on global precipitation extremes

While the influence of the Pacific Decadal Oscillation (PDO) on precipitation has been extensively studied, its influence on precipitation extremes remains not well-known. Based on a series of generalized extreme value modeling experiments, this paper demonstrates some distinct regional patterns of the PDO’s influence on precipitation extremes worldwide. In eastern China, the well-known ‘southern flood (drought) and northern drought (flood)’ pattern in summer corresponds well to the positive (negative) phase of the PDO. In Australia, there tends to be a tripole pattern, with positive correlation between precipitation extremes and the PDO in the central region, and negative correlation in both eastern and western Australia. The precipitation extremes in northwestern Europe and western Russia roughly hold positive correlation with the PDO. These regional patterns of the PDO’s influences are explained via comparative analyses of the atmospheric circulation conditions between cold and warm PDO phases. Certain precipitation extremes tend to be missed or happen more than once during different phases of the PDO at more than 2/3 of stations in a typical region. The cold phase tends to exert more consistent influences than the warm phase in these typical regions. These findings not only indicate different risks of extreme precipitation for the typical regions during different phases of the PDO, but also have important implications for the near-term projection of variable regional climate extremes under global warming.

Impact of Pacific Decadal Oscillation in relation to QBO on Indian summer monsoon rainfall

The relationship between Indian Summer Monsoon (ISM) rainfall (June to September) and Pacific Decadal Oscillation (PDO) Index for the concurrent and succeeding seasons over all India and its three specific regions, i.e., northeast, northwest, and peninsular region has been examined from the years 1953 to 2016. The information is shared for the full series as well as by grouping the seasonal rainfall of India and PDO data according to the different phases (westerly/easterly) of quasi-biennial oscillation (QBO) at the 50 hPa level. The results suggest that for full series, the concurrent season July–August–September (JAS) shows higher degree of association as compared with June–July–August (JJA). When the seasonal rainfall and the PDO index data are stratified according to the phase of QBO, correlation coefficient (CC) values are showing a strong inverse association during the easterly phase of QBO over all India and the northwest region of India while the CC value is reduced during the westerly phase. For the northeast Indian region, concurrent CC values are showing high (low) during the westerly (easterly) phase of QBO. In addition, the warm PDO events are persistent during the summer monsoon period in association of easterly (westerly) phase of QBO causes drought (flood) events over India. However, the cold phase of PDO follows the easterly and westerly phase of QBO where the indication of drought and flood events is not persistent.

CP El Niño and PDO Variability Affect Summer Precipitation over East China

The summer precipitation produced by the East Asian summer monsoon (EASM) is significantly affecting agriculture and socioeconomics. Based on the Precipitation Reconstruction dataset in East China from 1950 to 2017, we investigate the spatiotemporal variations of summer precipitation, influencing environmental factors and their relation with the EASM and the Pacific Decadal Oscillation (PDO) in both central Pacific (CP) El Niño developing and decaying years. Results indicate the following: (1) The evolutions of CP El Niño events modulate the summer precipitation anomalies in East China. In the cool PDO phase, CP El Niño causes enhanced precipitation anomalies in the decaying years but less precipitation anomalies in the developing years, and vice versa for the warm PDO phase. (2) Atmospheric circulation anomalies drive the moisture transportation and combine the motion of western Pacific subtropical high resulting in the variation of precipitation patterns. Anomalous cyclone over the western North Pacific and the sustained Western Pacific Subtropical High (WPSH) are favorable for the increment of summer precipitation. (3) The different CP El Niño-EASM relationship is caused by the influences of PDO on the evolution of CP El Niño. CP El Niño develops slowly (decays rapidly) and is associated with rapidly developing (slowly decaying) anomalous warming in the north Indian Ocean during the developing (decaying) years.

Combined impacts of the El Niño‐Southern Oscillation and Pacific Decadal Oscillation on global droughts assessed using the standardized precipitation evapotranspiration index

AbstractUsing the standardized precipitation evapotranspiration index, this study examines the combined effects of El Niño‐Southern Oscillation (ENSO) and Pacific Decadal Oscillation (PDO) on global droughts in terms of magnitude, timing, and duration. The ENSO‐affected drought hotspots are identified based on drought magnitude and probability of occurrence: five hotspots for El Niño (Amazon, India, central China, Indonesia, and eastern Australia) and four hotspots for La Niña (southeastern United States, southern South America, East Africa, and Southwest Asia). When ENSO and PDO are in phase, most of the hotspots exhibit an intensification and expansion of drought, more clearly at longer time scales (6–12 months), supporting previous studies. Interestingly, the in‐phase PDO advances El Niño‐induced drought onset by early summer of the previous year, whereas it delays the withdrawal of La Niña‐induced drought until the end of the event year. This asymmetric response is found to be in part associated with the earlier start and later end of El Niño itself during warm PDO, which does not hold for the La Niña/cold PDO composites. Further analyses of the responses of precipitation (P) and potential evapotranspiration (PET) to different ENSO‐PDO combinations suggest the important role of P reduction in determining drought magnitude and timing over most of the hotspots, with some contribution of enhanced PET to drier conditions over a few La Niña hotspots. It is also found that the PDO modulation of El Niño‐induced drought occurs primarily through the eastern Pacific El Niño with a limited influence on the central Pacific El Niño.

Five centuries of reconstructed streamflow in Athabasca River Basin, Canada: Non-stationarity and teleconnection to climate patterns

Given the challenge to estimate representative long-term natural variability of streamflow from limited observed data, a hierarchical, multilevel Bayesian regression (HBR) was developed to reconstruct the 1489–2006 annual streamflow data at six Athabasca River Basin (ARB) gauging stations based on 14 tree ring chronologies. Seven nested models were developed to maximize the applications of available tree ring predictors. Based on results of goodness-of-fit tests, the HBR developed was skillful and reliable in reconstructing the streamflow of ARB. From five centuries of reconstructed streamflow for ARB, five or six abrupt change points are detected. The streamflow time series obtained from a backward moving, 46-year window for six gauging sites in ARB vary significantly over five centuries (1489–2006) and at times could exceed the 90% and/or 95% confidence intervals, denoting significant non-stationarities. Apparently changes in the mean state and the lag-1 autocorrelation of reconstructed streamflow across the gauging sites can be similar or radically different from each other. These nonstationary features imply that the default stationary assumption is not applicable in ARB. Further, the reconstructed streamflow shows statistically significant oscillations at interannual, interdecadal and multidecadal time scales and are teleconnected to climate patterns such as El Niño Southern Oscillation (ENSO), Pacific Decadal Oscillation (PDO) and Atlantic Multi-decadal Oscillation (AMO). A composite analysis shows that La Niña (El Niño), cold (warm) PDO, and cold (warm) AMO events are typically associated with increased (decreased) streamflow anomalies of ARB. The reconstructed streamflow data provides us the full range of streamflow variability and recurrence characteristics of extremes spanned over five centuries from which it is useful for us to evaluate and manage the current water systems of ARB more effectively and a better risk analysis of future droughts of ARB.

Warming Trends in the Central Equatorial Indian Ocean and the Associated Coupled Feedback Processes

Mohapatra, S. and Gnanaseelan, C., 2020. Warming trends in the central equatorial Indian Ocean and the associated coupled feedback processes. In: Sheela Nair, L.; Prakash, T.N.; Padmalal, D., and Kumar Seelam, J. (eds.), Oceanic and Coastal Processes of the Indian Seas. Journal of Coastal Research, Special Issue No. 89, pp. 39-45. Coconut Creek (Florida), ISSN 0749-0208.The recent increasing trends in the tropical Indian Ocean (TIO) temperature have strong impact on the regional as well as global climate variability. In this work we studied the changes in the boreal summer monsoon winds and the associated monsoon currents on modulating the surface and subsurface temperature of the equatorial Indian Ocean. The reduction in the meridional sea surface temperature (SST) gradient and strengthening of zonal SST gradient over the Indian Ocean reduced the northward propagation of south-westerly wind, thereby enhancing the surface westerlies over the equator. The strengthened surface westerlies increased the equatorial downwelling Kelvin waves and deepened the thermocline. The present study unravels the causes for the observed confinement of strong SST trend over the central equatorial Indian Ocean (CEIO) even though surface westerlies and the associated downwelling extend upto the eastern equatorial Indian Ocean (EEIO). In contrast to the CEIO surface warming, EEIO experienced strong subsurface warming at thermocline. Our analysis suggests that the upper ocean stratification plays an important role in the observed warming trend of both CEIO surface and EEIO subsurface. The eastward equatorial currents bring warm salty water from Arabian Sea and WEIO towards east and warms CEIO, however the high saline surface water is found to sink in the EEIO, thereby warming the subsurface instead of surface. The composite of temperature anomaly for the period 1978-2002, the period of warm Pacific Decadal Oscillation, shows patterns similar to temperature trends, which clearly suggests the dominance of decadal variability on the TIO temperature trends.

Large‐Scale and Local Climatic Controls on Large Herbivore Productivity: Implications for Adaptive Rangeland Management

Rangeland ecosystems worldwide are characterized by a high degree of uncertainty in precipitation, both within and across years. Such uncertainty creates challenges for livestock managers seeking to match herbivore numbers with forage availability to prevent vegetation degradation and optimize livestock production. Here, we assess variation in annual large herbivore production (LHP, kg/ha) across multiple herbivore densities over a 78-yr period (1940-2018) in a semiarid rangeland ecosystem (shortgrass steppe of eastern Colorado, USA) that has experienced several phase changes in global-level sea surface temperature (SST) anomalies, as measured by the Pacific Decadal Oscillation (PDO) and the El Nino-Southern Oscillation (ENSO). We examined the influence of prevailing PDO phase, magnitude of late winter (February-April) ENSO, prior growing-season precipitation (prior April to prior September) and precipitation during the six months (prior October to current April) preceding the growing season on LHP. All of these are known prior to the start of the growing season in the shortgrass steppe and could potentially be used by livestock managers to adjust herbivore densities. Annual LHP was greater during warm PDO irrespective of herbivore density, while variance in LHP increased by 69% (moderate density) and 91% (high density) under cold-phase compared to warm-phase PDO. No differences in LHP attributed to PDO phase were observed with low herbivore density. ENSO effects on LHP, specifically La Nina, were more pronounced during cold-phase PDO years. High herbivore density increased LHP at a greater rate than at moderate and low densities with increasing fall and winter precipitation. Differential gain, a weighted measure of LHP under higher relative to lower herbivore densities, was sensitive to prevailing PDO phase, ENSO magnitude, and precipitation amounts from the prior growing season and current fall-winter season. Temporal hierarchical approaches using PDO, ENSO, and local-scale precipitation can enhance decision-making for flexible herbivore densities. Herbivore densities could be increased above recommended levels with lowered risk of negative returns for managers during warm-phase PDO to result in greater LHP and less variability. Conversely, during cold-phase PDO, managers should be cognizant of the additional influences of ENSO and prior fall-winter precipitation, which can help predict when to reduce herbivore densities and minimize risk of forage shortages.

The Pacific decadal oscillation modulates the relation of ENSO with the rainfall variability in coast of Ecuador

AbstractWorldwide and likewise in Ecuador, the 1982–1983 and 1997–1998 El Niño Southern Oscillation (ENSO) events had devastating effects in the economic and human dimension. Thus, scientists and decision markers look for a deeper knowledge about ENSO and its phases El Niño (EN)/La Niña (LN). Recent research highlights the changing nature of ENSO under opposite conditions of the Pacific Decadal Oscillation (PDO), making the assessment of the ENSO–PDO relation in Ecuador urgent. This study explores the time‐frequency characteristics of rainfall in the coast of Ecuador from January to April (PC‐JA) and evaluates the influence of PDO in the relation of ENSO with PC‐JA. For this, wavelet analysis was used to asses this nonstationary problem, Five long‐term (1964–2014) ground stations were used. The main results indicate that during the warm PDO period 1980–2000, the high wavelet coherence (ca. 0.9) implies a strong coupling between ENSO and PC‐JA. For cold PDO periods, prior to 1980 and after 2005, such coupling weakens with coherence about 0.5. This might indicate that PDO influence the relation between ENSO and rainfall in the coast of Ecuador. This coupling, during warm PDO, enhances high rainfall when in phase with EN, and drought conditions in LN events. The weak coupling of ENSO‐PC‐JA during cold PDO produces high rainfall amounts in Niño Neutral conditions and droughts during Neutral and LN. To account for ENSO flavours variability, the wavelet coherence between PC‐JA and the two ENSO uncorrelated indices E and C from Takahashi et al. was studied. Interestingly, we show that PDO warm phase influences the relation of Eastern Pacific related E index with PC‐JA from 2 to 8 years periods, and that the orthogonal Central Pacific related C index is not affected. These results raise questions about the validity of ENSO indices for contrasting PDO phases.

Spatial Habitat Shifts of Oceanic Cephalopod (Ommastrephes bartramii) in Oscillating Climate

Short- and long-term climate oscillations impact seascapes, and hence, marine ecosystem structure and dynamics. Here, we explored the spatio-temporal patterns of potential squid habitat in the western and central North Pacific across inter-decadal climate transitions, coincident with periods of persistent warming and cooling. Potential habitat distributions of Ommastrephes bartramii were derived from the outputs of multi-ensemble species distribution models, developed using the most influential environmental factors to squid distribution and occurrence data. Our analyses captured the underlying temporal trends in potential squid habitat in response to environmental changes transpiring at each climatic transition, regulated by phase shifts in Pacific decadal oscillation (PDO) from 1999–2013. The spatial differences in environmental conditions were apparent across transitions and presumably modulate the local changes in suitable squid habitat over time. Specifically, during a cold to warm PDO shift, decreases in the summer potential habitat (mean rate ± standard deviation: −0.04 ± 0.02 habitat suitability index (HSI)/yr) were observed along the southern edge of the subarctic frontal zone (162°E–172°W). Coincidentally, this area also exhibits a warming trend (mean temporal trend: 0.06 ± 0.21 °C/yr), accompanied with the prevalence of cold-core mesoscale eddies, west of the dateline (mean temporal trend in sea surface height: −0.19 ± 1.05 cm/yr). These conditions potentially generate less favorable foraging habitat for squid. However, a warm-to-cold PDO transition underpins a northward shift of suitable habitat and an eastward shift of regions exhibiting the highest rate of potential squid habitat loss (170–160°W; mean temporal trend: −0.05 ± 0.03 HSI/yr). Nonetheless, the emergence of the areas with increasingly suitable habitat regardless of climate transitions suggests the ecological importance of these regions as potential squid habitat hotspots and climatic refugia.

Large-scale and local climatic controls on large herbivore productivity: implications for adaptive rangeland management.

Rangeland ecosystems worldwide are characterized by a high degree of uncertainty in precipitation, both within and across years. Such uncertainty creates challenges for livestock managers seeking to match herbivore numbers with forage availability to prevent vegetation degradation and optimize livestock production. Here, we assess variation in annual large herbivore production (LHP, kg/ha) across multiple herbivore densities over a 78-yr period (1940-2018) in a semiarid rangeland ecosystem (shortgrass steppe of eastern Colorado, USA) that has experienced several phase changes in global-level sea surface temperature (SST) anomalies, as measured by the Pacific Decadal Oscillation (PDO) and the El Niño-Southern Oscillation (ENSO). We examined the influence of prevailing PDO phase, magnitude of late winter (February-April) ENSO, prior growing-season precipitation (prior April to prior September) and precipitation during the six months (prior October to current April) preceding the growing season on LHP. All of these are known prior to the start of the growing season in the shortgrass steppe and could potentially be used by livestock managers to adjust herbivore densities. Annual LHP was greater during warm PDO irrespective of herbivore density, while variance in LHP increased by 69% (moderate density) and 91% (high density) under cold-phase compared to warm-phase PDO. No differences in LHP attributed to PDO phase were observed with low herbivore density. ENSO effects on LHP, specifically La Niña, were more pronounced during cold-phase PDO years. High herbivore density increased LHP at a greater rate than at moderate and low densities with increasing fall and winter precipitation. Differential gain, a weighted measure of LHP under higher relative to lower herbivore densities, was sensitive to prevailing PDO phase, ENSO magnitude, and precipitation amounts from the prior growing season and current fall-winter season. Temporal hierarchical approaches using PDO, ENSO, and local-scale precipitation can enhance decision-making for flexible herbivore densities. Herbivore densities could be increased above recommended levels with lowered risk of negative returns for managers during warm-phase PDO to result in greater LHP and less variability. Conversely, during cold-phase PDO, managers should be cognizant of the additional influences of ENSO and prior fall-winter precipitation, which can help predict when to reduce herbivore densities and minimize risk of forage shortages.