Negative Southern Oscillation Index Research Articles

Quantifying the distribution of swordfish (Xiphias gladius) density in the Hawaii-based longline fishery

The Hawaii-based longline fishery targeting bigeye tuna and swordfish is the most economically important fishery in Hawaii. An improved understanding of the distribution of swordfish within this fishery and how it changes in response to environmental conditions is critical for predicting potential climate change impacts to the fishery. The multi-species Vector-Autoregressive Spatio-Temporal (VAST) model was used to estimate abundance and density of swordfish within the Hawaii-based longline fishing grounds. Swordfish and bigeye tuna catch per unit effort were used in a spatial dynamics factor analysis to help estimate swordfish density in time periods when the swordfish fishery was closed. Although the model was unable to account fully for the significant changes in fishery regulations in 2000, it provided quantified estimates of swordfish density and distribution and information on how those distributions may change in response to environmental variables. Swordfish density center of gravity was found to correlate with the Southern Oscillation Index (SOI) averaged during the swordfish spawning season (April – July), with densities centered further north and east during positive SOI (cooler sea temperatures) and further south and west during negative SOI (warmer sea temperatures).

Investigating relationship between drought severity in Botswana and ENSO

Influences of El Nino southern oscillation (ENSO) on weather systems have increased the frequency and amplitude of extreme events over the last century. This even continues to exacerbate the already warming earth, with 2014–2016 which coincided with the strongest El Nino years observed as the warmest period in recent past. This study presents an approach of characterizing droughts at various timescales and establishes teleconnections between ENSO and drought severity in Botswana. The study uses Standardized Precipitation Evaporation Index (SPEI) at timescales of 1, 3, 6, 12 and 24 month to characterize droughts and Pearson’s correlations to study the teleconnections between SPEIs and ENSO. Results from the study reveal that extreme droughts are a rare occurrence in Botswana though it is more prone to moderate droughts at 12 month SPEI with a probability of 19% in the north. The highest severe drought probability was 7% recorded in the east. Linear trends indicate increasing dryness of around 0.8% per decade. These results have demonstrated that warm sea surface temperatures combined with negative Southern Oscillation Index correspond to persistent negative SPEI values and thus are likely to result in dry conditions. Significant correlations were observed in the mid austral summer in December and January. Due to this relationship, the drought early warning systems could use ENSO as one of the instruments for predicting drought over the study area and hence in its management.

Bimodal climate control of shoreline change influenced by Interdecadal Pacific Oscillation variability along the Cooloola Sand Mass, Queensland, Australia

Wave climate in southeast Queensland, Australia has been correlated to changes in the Southern Oscillation Index (SOI), but observations of shoreline change associated with the variable wave climate have been limited due to a paucity of aerial photography, LiDAR, and other beach profiling datasets in this region. A multi-decadal, sub-annual temporal resolution shoreline dataset spanning 1996 to 2017 was produced using satellite imagery collected by Landsat 5, 7, and 8. A total of 147 shoreline positions were delineated using the Modified Normalized Difference Water Index on cloud-free imagery and corrected for horizontal offsets forced by variable tide stages at the satellite flyover time. The relative influence of SOI, the Southern Annular Mode (SAM), Pacific Decadal Oscillation (PDO), and Subtropical Ridge Latitude (STR-L) and Pressure (STR-P) on shoreline dynamics along the Cooloola Sand Mass in Queensland are assessed by performing cross correlations between their respective index values and shoreline change distances calculated by the Digital Shoreline Analysis System. A bimodal climate control of shoreline change is observed dependent upon the phase of the Interdecadal Pacific Oscillation (IPO). IPO modulates the impacts of ENSO on eastern Australia through its control over the position of the South Pacific Convergence Zone and elevating/lowering of tropical Pacific sea surface temperatures. During negative IPO, SOI is negatively correlated to the Cooloola Sand Mass shoreline indicating that the shoreline retreats during negative SOI phases. During positive IPO, the impacts of SOI are weakened and the STR becomes the primary driver of shoreline change with shoreline response being contingent upon its orientation. The SW-NE aligned Noosa North shoreline erodes in response to poleward movement of the STR, likely due to the enhanced cross-shore wave attack as a result of anti-clockwise wave rotation. The opposite response is shown at the SE-NW aligned Rainbow Beach shoreline, which is oriented almost parallel to the incident wave direction and is sheltered by the Double Island Point headland. These results suggest that climate control on shoreline change at Cooloola Sand Mass, and likely other sand islands in the region, is two-tiered, whereby interdecadal variability of the IPO governs the relative influence of SOI and STR under the different IPO phases. The linked climate and shoreline variability correlation shown in this study provides significant insight into how the Cooloola Sand Mass shoreline will respond to future climate changes under a global warming scenario.

Geothermal, Oceanic, Wildfire, Meteorological and Anthropogenic Impacts on PM<sub>2.5</sub> Concentrations in the Fairbanks Metropolitan Area

The impacts of low and high-frequency variability from teleconnections between large scale atmospheric processes and local weather as well as emissions changes on concentrations of particulate matter of 2.5 μm or less in diameter ([PM2.5]) were examined for the Fairbanks Metropolitan Area (FMA). October to March and May to August mean [PM2.5] were 1.8 and 3.1 μg·m-3 higher for positive than negative annual mean Pacific Decadal Oscillation. Annual mean [PM2.5] were 3.8 μg·m-3 lower for positive than negative Southern Oscillation Index. On 1999-2018 average, [PM2.5] decreased 2.9 μg·m-3·decade-1. On average over October to March, decadal and inter-annual variability caused higher or similar differences in mean observed [PM2.5] and its species than emission-control measures. The 2006 implementation of Tier 2 for new vehicles decreased observed sulfate concentrations the strongest (~4.95 μg·m-3·decade-1) of all occurred emissions changes. On average, observed [PM2.5] showed elevated values at all sites when wind blew from directions of hot springs. The same was found for the sulfate, ammonium and non-metal components of PM2.5. Observations showed that these geothermal waters contain sulfate, ammonia, boric acid and non-metals. Hot springs of such composition are known to emit hydrogen sulfide and ammonia that can serve as precursors for ammonium and sulfate aerosols.

Local weather and regional climate influence breeding dynamics of Mountain Bluebirds (Sialia currucoides) and Tree Swallows (Tachycineta bicolor): a 35-year study

Many songbirds are under increasing pressure owing to habitat loss, land-use changes, and rapidly changing climatic conditions. Using citizen science data collected from 1980 to 2014, we asked how local weather and regional climate influenced the breeding dynamics of Mountain Bluebirds (Sialia currucoides (Bechstein, 1798)) and Tree Swallows (Tachycineta bicolor (Vieillot, 1808)). Mountain Bluebird reproduction was strongly associated with local weather: number of nestlings and fledglings both decreased in years of high rainfall. Clutch size and number of fledglings also declined over the study period. Abundance of Mountain Bluebirds was higher in years of lower early-season snowfall and warmer local temperatures, as well as more negative Southern Oscillation Index (SOI) values, indicating a positive influence of El Niño conditions. Tree Swallow reproduction (clutch size, number of nestlings, and number of fledglings) was negatively associated with SOI values, and the number of Tree Swallow nestlings decreased in years of higher rainfall and warmer temperatures. Tree Swallows also showed a marked decline in abundance over the period of the study, consistent with recent range-wide declines. Together, our results demonstrate that local weather and regional climate differentially affect the reproductive dynamics of Mountain Bluebirds and Tree Swallows and highlight the importance of long-term citizen science data sets.

Linked trends in the South Pacific sea ice edge and Southern Oscillation Index

AbstractPrevious work have shown that sea ice variability in the South Pacific is associated with extratropical atmospheric anomalies linked to the Southern Oscillation (SO). Over a 32 year period (1982–2013), our study shows that the trend in Southern Oscillation Index (SOI) is also able to quantitatively explain the trends in sea ice edge, drift, and surface winds in this region. On average two thirds of the winter ice edge trend in this sector, linked to ice drift and surface winds, could be explained by the positive SOI trend, thus subjecting the ice edge to strong decadal SO variability. If this relationship holds, the negative SOI trend prior to the recent satellite era suggests that ice edge trends opposite to that of the recent record over a similar time scale. Significant low‐frequency ice edge trends, linked to the natural variability of SO, are superimposed upon any trends expected of anthropogenic forcing.

El Niño–Southern Oscillation influence on tropospheric mercury concentrations

AbstractThe El Niño–Southern Oscillation (ENSO) affects the tropospheric concentrations of many trace gases. Here we investigate the ENSO influence on mercury concentrations measured in the upper troposphere during Civil Aircraft for the Regular Investigation of the atmosphere Based on an Instrumented Container flights and at ground at Cape Point, South Africa, and Mace Head, Ireland. Mercury concentrations cross‐correlate with Southern Oscillation Index (SOI) with a lag of 8 ± 2 months. Highest mercury concentrations are always found at the most negative SOI values, i.e., 8 months after El Niño, and the amplitude of the interannual variations fluctuates between ~5 and 18%. The time lag is similar to that of CO whose interannual variations are driven largely by emissions from biomass burning (BB). The amplitude of the interannual variability of tropospheric mercury concentrations is consistent with the estimated variations in mercury emissions from BB. We thus conclude that BB is a major factor driving the interannual variation of tropospheric mercury concentrations.

The effects of habitat, climate, and Barred Owls on long-term demography of Northern Spotted Owls

ABSTRACT Estimates of species' vital rates and an understanding of the factors affecting those parameters over time and space can provide crucial information for management and conservation. We used mark–recapture, reproductive output, and territory occupancy data collected during 1985–2013 to evaluate population processes of Northern Spotted Owls (Strix occidentalis caurina) in 11 study areas in Washington, Oregon, and northern California, USA. We estimated apparent survival, fecundity, recruitment, rate of population change, and local extinction and colonization rates, and investigated relationships between these parameters and the amount of suitable habitat, local and regional variation in meteorological conditions, and competition with Barred Owls (Strix varia). Data were analyzed for each area separately and in a meta-analysis of all areas combined, following a strict protocol for data collection, preparation, and analysis. We used mixed effects linear models for analyses of fecundity, Cormack-Jolly-...

Longshore wind, waves and currents: climate and climate projections at Ninety Mile Beach, southeastern Australia

ABSTRACTIt is shown that Lakes Entrance, a township located at the northern end of Ninety Mile Beach in southeastern Australia, is situated in a region that may experience noticeable changes in longshore wind, wave and ocean currents compared to present day climate variability as a consequence of the southward shifting subtropical ridge (STR) predicted in global climate change models. These changes could modify sediment transport in the littoral zone and impact the coastline position. Thirty‐year hindcasts of winds, coastal currents and waves are shown to agree well with available observations and provide a long‐term dataset of the climate variability. Hindcasts of coastal ocean currents and waves indicate that while the annual net mean wave and current transport are in opposing directions, their seasonal adjusted monthly anomalies are positively correlated. Furthermore they are also correlated with the position of the STR location index. On seasonal to annual time scales a weak connection between the transport variables and Southern Oscillation Index (SOI) is found. It appears that during multiple years of positive (negative) SOI conditions the STR is located north (south) of its mean monthly position, resulting in anomalous eastward (westward) transport. The four climate models used in this study indicate a southward shift in the STR for most months under a high emission future. In summer months the shift in the STR results in both increased summer westward wind‐driven currents and westward wave forcing. Changes in winter months are less related to the STR location and it is discussed that the contraction and increased intensity of the westerly storm belt linked to Southern Annular Mode could possibly influence the transport. The analysis is presented at the coastal scale to provide insights into how these changes may affect net transport across the littoral zone in more detailed numerical nearshore sediment transport modelling.

A Probit Regression model approach for Predicting Drought Probabilities in Zimbabwe using the Southern Oscillation Index

This paper focuses on the methodology of determining probabilities of meteorological droughts in Zimbabwe. The Probit regression method is used. Mean annual rainfall for the years 1974 to 2009 is used in this study. The results show that a very low value of the Southern Oscillation Index (SOI) for September precedes the occurrence of a meteorological drought in Zimbabwe by at least a year. Mean annual rainfall drought threshold value of 570 mm is used to categorize drought years from 1974 to 2009. Results show that a negative Southern Oscillation Index value for September predicts at least 67% chance of drought in the coming year. DOI: 10.5901/mjss.2014.v5n20p656

Evaluating the distribution of water resources in western Canada using synoptic climatology and selected teleconnections. Part 2: summer season

AbstractMinor changes to seasonal air temperature and precipitation can have a substantial impact on the availability of water resources within large watersheds. Two such watersheds, the north‐flowing Mackenzie and east‐flowing Saskatchewan Basins, have been identified as highly vulnerable to such changes and, therefore, selected for study as part of the Climatic Redistribution of western Canadian Water Resources project. This project aims to evaluate spatial and temporal changes to water resource distribution through the analysis of a suite of hydroclimatic and streamflow variables. As part of this analysis, dominant summer (May–October) circulation patterns at 500 hPa for 1950–2011 are identified using the method of self‐organizing maps. Surface climate variables associated with these patterns are then identified, including both daily air temperature and precipitation and seasonal Standardized Precipitation Evapotranspiration Index values. Statistical methods are applied to assess the relationships between dominant circulation patterns and the Southern Oscillation Index (SOI) and Pacific Decadal Oscillation (PDO). Results indicate that mid‐summer (July–August) is dominated by a split‐flow blocking pattern, resulting in cool (warm), wet (dry) conditions in the southern (northern) portion of the study area. By contrast, the shoulder season (May and October) is dominated by a trough of low pressure over the North Pacific Ocean. The frequency of weak split‐flow blocking is higher during positive SOI and negative PDO, whereas ridging over the western continent is more frequent during negative SOI and positive PDO. Results from this analysis increase our knowledge of processes, controlling the distribution of summer water resources in western Canada. Copyright © 2014 John Wiley & Sons, Ltd.

The climatological relationship between tropical cyclones in the southwest Pacific and the southern annular mode

ABSTRACTIn this study, we focus on possible climatological relationships between southwest Pacific tropical cyclone (TC) activity and the Southern Annular Mode (SAM) and ENSO, at both interannual and synoptic time‐scales. The investigation focuses on TC seasonal characteristics (e.g. cyclogenesis, track characteristics, extratropical transition, and intensity) as modulated according to the polarity of the SAM and ENSO. At synoptic time‐scales, we also look at possible triggers of TC cyclogenesis in the SAM signal up to 20 days in advance. The physical basis for this relationship is assessed using a number of different gridded data fields. During seasons characterized by positive phases of SAM and both positive and negative Southern Oscillation Index (SOI) values, there is an increased frequency of TCs undergoing extratropical transition near New Zealand. At synoptic time‐scales, we found an interesting yet inconclusive relationship between the SAM and tropical cyclogenesis during SOI positive seasons. While statistically significant, there is no clear physical mechanism linking the mid‐latitude SAM phenomenon to the genesis of TCs. In summary, the results show a clear interannual climatological relationship between an increased frequency of TCs undergoing extratropical transition near New Zealand and the positive phase of SAM.

Episodic outbreaks of small mammals influence predator community dynamics in an east African savanna ecosystem

Little is known about the dynamics of small mammals in tropical savanna: a critical gap in our understanding of Africa's best known ecosystems. Historical evidence suggested small mammals peak in abundance (outbreak) in Serengeti National Park (SNP), as in agricultural systems. We asked 1) what are bottom–up drivers of small mammals and 2) do predators have top–down effects? We documented dynamics of small mammals, birds of prey, and mammalian carnivores in SNP and agricultural areas. We used climatic fluctuations and differences between unmodified and agricultural systems as perturbations to examine trophic processes, key to understanding responses to climate change and increasing human pressures. Data were derived from intermittent measures of abundance collected 1968–1999, combined with systematic sampling 2000–2010 to construct a 42‐year time series. Data on abundance of black‐shouldered kites (1968–2010), eight other species of rodent‐eating birds (1997–2010), and 10 carnivore species (1993–2010) were also collated. Outbreaks occurred every 3–5 years in SNP, with low or zero abundance between peaks. There was a positive relationship between rainfall in the wet season and 1) small mammal abundance and 2) the probability of an outbreak, both of which increased with negative Southern Oscillation Index values. Rodent‐eating birds and carnivores peaked 6–12 months after small mammals. In agricultural areas, abundance remained higher than in natural habitats. Abundances of birds of prey and mammalian carnivores were extremely low in these areas and not related to small mammal abundance. Small mammals are an important food resource for higher trophic levels in the Serengeti ecosystem. Changes in climate and land use may alter their future dynamics, with cascading consequences for higher trophic levels, including threatened carnivores. Although outbreaks cause substantial damage to crops in agricultural areas, small mammals also play a vital role in maintaining some of the diversity and complexity found in African savanna ecosystems.

Influence of climate on Pelorus Sound mussel aquaculture yields: predictive models and underlying mechanisms

Multiple regression models were used to predict aquaculture production in Pelorus Sound, a 50 km long estuary supporting 68% of New Zealand's greenshell mussel Perna canali - culus aquaculture industry (worth NZ$ 204 million per annum). Mussel meat yield was modelled using both biological predictors, including seston (indexed by particulate nitrogen, PN), phyto- plankton and nutrients collected over 9 yr (July 1997 to November 2005) by the mussel industry, and physical, climatic predictors, including Southern Oscillation Index (SOI), along-shelf winds, sea surface temperature (SST) and Pelorus River flow, held in New Zealand national databases. Yield was best predicted using biological predictors collected locally at the farms inside the sound, but it was also predictable using only physical predictors collected distant from the farming region. Seston (mussel food) was also predictable using the physical predictors. Optimal predictor sets for yield and seston differed between summer and winter half-years. In summer, deep water (which enters the sound through the estuarine circulation) at the sound entrance was nitrate (NO3 � )-rich during upwelling conditions (negative SOI, NNW wind stress and cool SST). The increased NO3 � levels, in turn, triggered increased PN within the sound. In the winter half-year, PN was unrelated to upwelling and NO3 � effects at the entrance and was instead related to river flow. Remotely-sensed SST data showed that in summer, upwelling affected the entrance waters of the sound under negative SOI and upwelling-favourable wind stress, patterns which dissipated in winter. Overall, these results show that time series of physical drivers can be useful for explain- ing production variation of farmed bivalves and indicate the prospects for using data routinely col- lected in national databases for predicting mussel yield.

Sub-daily rainfall events in an arid environment with marked climate variability: Variation among wet and dry years at Fowlers Gap, New South Wales, Australia

The nature of rainfall events is explored through six years of below average rainfall, associated with negative Southern Oscillation Index (SOI), and three years of above average rainfall, associated with positive SOI (and strong La Niña conditions), at arid Fowlers Gap, Australia. There is a greater probability of rainfall in wet years, but the events themselves also change significantly. Rainfall depth per event was 116% larger on average in wet years than dry, and average event rainfall rate was 85% higher. However, these results are influenced by a small number of very large events in the wet years, and events of <2 mm occur at about the same rate in dry and wet years. Rainfall event profiles in dry years showed more Huff first quartile events likely to promote partitioning of rain into infiltration. In contrast, larger events in wet years showed a preponderance of Huff third quartile profiles likely to be associated with greater partitioning of rainfall into overland flow. This co-variation in rainfall event profile with annual rainfall, not previously described, is reasoned to increase the amplitude of ecological impacts of the SOI-related rainfall variability at this site.

The ENSO signature and other hydrological characteristics in Patos and adjacent coastal lagoons, south-eastern Brazil

With a surface area of over 10,000 km2, Patos Lagoon is Brazil's largest (choked) coastal lagoon. Directly or indirectly, Patos is associated with two other coastal lagoons, Mirim and Mangueira. Patos Lagoon reaches maximum water level height during the austral winter, in coherence with the rainy season. The longest (1961–2011) available rainfall (recorded at nearby Porto Alegre, Southern Brazil) and river discharge time series (1940–2011, in the tributary Jacuí River, at Rio Pardo) shows an overall increasing trend through the application of Mann–Kendall analysis. If, however, the series are split in two segments, negative trends become evident for the 1990–2011 period; in both cases earlier data showed a positive trend until ∼1989. Coherent with water inflow, the lagoon's water height level shows a seasonal Kendall's τ coefficient that is consistently negative for the month of April (statistically significant p). Rainfall over Patos' drainage basin is actively teleconnected with ENSO occurrences in the equatorial Pacific. This can be verified in Porto Alegre's rainfall as well as in the Jacuí River discharge time series and in the lagoon's water level variability; a distinctly negative Southern Oscillation Index (SOI) usually results in excess precipitation, high riverine discharge and, accordingly, above normal lagoon water level. The use of a method for harmonic analysis (Continuous Wavelet Transform or CWT) allows detecting decadal and inter-annual periodicities in the rainfall and discharge frequencies and in the lagoon's water level time series. Also, a change in the frequency pattern appears to have occurred in the late 1990s (i.e., simultaneous with the 1997 ENSO event?) and suggests that it may be connected with the trend change which resulted in the current negative slope observed in deseasonalized hydrological data and a fainter ENSO signal for the region.

Evidence for centennial scale sea level variability during the Medieval Climate Optimum (Crusader Period) in Israel, eastern Mediterranean

The current study provides evidence supporting a sea-level drop of up to about 50±20cm at the eastern coasts of the Mediterranean basin during the period AD 900–1300. The estimate is based on a variety of archaeological remains, mostly from the Crusader period, compared with other archaeological and biological proxies of sea level from the periods before and after.The Crusader low levels overlap the period known as the ‘Medieval Warm Period’ (MWP) or the ‘Medieval Climate Anomaly’ (MCA). On the basis of published data it appears that a positive North Atlantic Oscillation (NAO) phase coincided with a negative Southern Oscillation Index (SOI), the former affecting the temperature and freshwater flux in the Mediterranean Sea and most of its rivers, and the latter affecting the Nile outflow. Changes of 0.125psu in salinity and 0.4°C are estimated as upper limits for the change, and these are expected to cause a sea-level drop consistent in magnitude with the observed values. These provide the upper limit for a regional climate-forcing attribution of the observed sea level low. The possibility of crustal uplifts contributing to the observed changes is also discussed.

Non-stationary influence of El Niño-Southern Oscillation and winter temperature on oak latewood growth in NW Iberian Peninsula

The properties of El Niño-Southern Oscillation (ENSO), such as period, amplitude, and teleconnection strength to extratropical regions, have changed since the mid-1970s. ENSO affects the regional climatic regime in SW Europe, thus tree performance in the Iberian Peninsula could be affected by recent ENSO dynamics. We established four Quercus robur chronologies of earlywood and latewood widths in the NW Iberian Peninsula. The relationship between tree growth and the Southern Oscillation Index (SOI), the atmospheric expression of ENSO, showed that only latewood growth was correlated negatively with the SOI of the previous summer-autumn-winter. This relationship was non-stationary, with significant correlations only during the period 1952-1980; and also non-linear, with enhanced latewood growth only in La Niña years, i.e. years with a negative SOI index for the previous autumn. Non-linear relationship between latewood and SOI indicates an asymmetric influence of ENSO on tree performance, biassed towards negative SOI phases. During La Niña years, climate in the study area was warmer and wetter than during positive years, but only for 1952-1980. Winter temperatures became the most limiting factor for latewood growth since 1980, when mean regional temperatures increased by 1°C in comparison to previous periods. As a result, higher winter respiration rates, and the extension of the growing season, would probably cause an additional consumption of stored carbohydrates. The influence of ENSO and winter temperatures proved to be of great importance for tree growth, even at lower altitudes and under mild Atlantic climate in the NW Iberian Peninsula.

A new objective procedure for classifying New Zealand synoptic weather types during 1958–2008

AbstractA set of 12 daily weather types has been obtained for the New Zealand region from the 51‐year NCAR/NCEP dataset by using a two‐stage classification procedure (rotated T‐mode principal component analysis followed by convergent K‐means clustering). Analysis of this classification confirms previous studies and provides further insight into the variation features of the regional synoptic weather on the seasonal, interannual and longer‐time scales.There are seasonal variations in both intensity and frequency of synoptic weather types. For example, southern highs are more frequent in summer and autumn, while troughs and lows occur more often in winter and secondarily spring. The high and low centres of weather types tend to be more intense in winter than summer.The frequency and lifetime of synoptic weather types fluctuate on the interannual and decadal scales; there exist significant correlations between frequencies of individual weather types and Southern Oscillation Index (SOI). In all seasons, the frequencies of weather types can change with phases of SOI. The most significant changes in weather type frequencies during the negative SOI phase occur in spring, and characterized by more frequent occurrence of weather types which provide prevailing southwesterly to westerly winds and reduced prominence of anticyclonic situations. The most significant changes in type frequencies during the positive SOI phase occur in summer, with more frequent anticyclonic types but less frequent cyclonic types. The frequency change in winter seems different from other seasons, although consistent with previous studies. In addition, the probability of extremely frequent occurrence or lack of occurrence of certain weather types during a month also varies significantly with SOI phases and with seasons, indicating that the chance for extreme weather conditions to occur is conditional on SOI.The results can be useful for climate forecasts, studies of climate extremes, air pollution, climatic impacts on human health and other environmental problems. Copyright © 2010 Royal Meteorological Society

Non‐stationarity in rainfall and temperature in the Murray Darling Basin

AbstractTwo analyses, one based on multiple regression and the other using the Holt–Winters algorithm, for investigating non‐stationarity in environmental time series are presented. They are applied to monthly rainfall and average maximum temperature time series of lengths between 38 and 108 years, from six stations in the Murray Darling Basin and four cities in eastern Australia. The first analysis focuses on the residuals after fitting regression models which allow for seasonal variation, the Pacific Decadal Oscillation (PDO) and the Southern Oscillation Index (SOI). The models provided evidence that rainfall is reduced during periods of negative SOI, and that the interaction between PDO and SOI pronounces this effect during periods of negative PDO. Following this, there was no evidence of any trend in either the PDO or SOI time series. The residuals from this regression were analysed with a cumulative sum (CUSUM) technique, and the statistical significance was assessed using a Monte Carlo method. The residuals were also analysed for volatility, autocorrelation, long‐range dependence and spatial correlation. For all ten rainfall and temperature time series, CUSUM plots of the residuals provided evidence of non‐stationarity for both temperature and rainfall, after removing seasonal effects and the effects of PDO and SOI. Rainfall was generally lower in the first half of the twentieth century and higher during the second half. However, it decreased again over the last 10 years. This pattern was highlighted with 5‐year moving average plots. The residuals for temperature showed a complementary pattern with increases in temperature corresponding to decreased rainfall. The second analysis decomposed the rainfall and temperature time series into random variation about an underlying level, trend and additive seasonal effects and changes in the level; trend and seasonal effects were tracked using a Holt–Winters algorithm. The results of this analysis were qualitatively similar to those of the regression analysis. Copyright © 2010 John Wiley &amp; Sons, Ltd.