Decadal-scale Variability Research Articles

Increasing storm tides in New York Harbor, 1844-2013

Three of the nine highest recorded water levels in the New York Harbor region have occurred since 2010 (March 2010, August 2011, and October 2012), and eight of the largest twenty have occurred since 1990. To investigate whether this cluster of high waters is a random occurrence or indicative of intensified storm tides, we recover archival tide gauge data back to 1844 and evaluate the trajectory of the annual maximum storm tide. Approximately half of long-term variance is anticorrelated with decadal-scale variations in the North Atlantic Oscillation, while long-term trends explain the remainder. The 10 year storm tide has increased by 0.28 m. Combined with a 0.44 m increase in local sea level since 1856, the 10 year flood level has increased by approximately 0.72 ± 0.25 m, and magnified the annual probability of overtopping the typical Manhattan seawall from less than 1% to about 20–25%.

Phytoplankton primary production in the world's estuarine-coastal ecosystems

Abstract. Estuaries are biogeochemical hot spots because they receive large inputs of nutrients and organic carbon from land and oceans to support high rates of metabolism and primary production. We synthesize published rates of annual phytoplankton primary production (APPP) in marine ecosystems influenced by connectivity to land – estuaries, bays, lagoons, fjords and inland seas. Review of the scientific literature produced a compilation of 1148 values of APPP derived from monthly incubation assays to measure carbon assimilation or oxygen production. The median value of median APPP measurements in 131 ecosystems is 185 and the mean is 252 g C m−2 yr−1, but the range is large: from −105 (net pelagic production in the Scheldt Estuary) to 1890 g C m−2 yr−1 (net phytoplankton production in Tamagawa Estuary). APPP varies up to 10-fold within ecosystems and 5-fold from year to year (but we only found eight APPP series longer than a decade so our knowledge of decadal-scale variability is limited). We use studies of individual places to build a conceptual model that integrates the mechanisms generating this large variability: nutrient supply, light limitation by turbidity, grazing by consumers, and physical processes (river inflow, ocean exchange, and inputs of heat, light and wind energy). We consider method as another source of variability because the compilation includes values derived from widely differing protocols. A simulation model shows that different methods reported in the literature can yield up to 3-fold variability depending on incubation protocols and methods for integrating measured rates over time and depth. Although attempts have been made to upscale measures of estuarine-coastal APPP, the empirical record is inadequate for yielding reliable global estimates. The record is deficient in three ways. First, it is highly biased by the large number of measurements made in northern Europe (particularly the Baltic region) and North America. Of the 1148 reported values of APPP, 958 come from sites between 30 and 60° N; we found only 36 for sites south of 20° N. Second, of the 131 ecosystems where APPP has been reported, 37% are based on measurements at only one location during 1 year. The accuracy of these values is unknown but probably low, given the large interannual and spatial variability within ecosystems. Finally, global assessments are confounded by measurements that are not intercomparable because they were made with different methods. Phytoplankton primary production along the continental margins is tightly linked to variability of water quality, biogeochemical processes including ocean–atmosphere CO2 exchange, and production at higher trophic levels including species we harvest as food. The empirical record has deficiencies that preclude reliable global assessment of this key Earth system process. We face two grand challenges to resolve these deficiencies: (1) organize and fund an international effort to use a common method and measure APPP regularly across a network of coastal sites that are globally representative and sustained over time, and (2) integrate data into a unifying model to explain the wide range of variability across ecosystems and to project responses of APPP to regional manifestations of global change as it continues to unfold.

The bi-decadal rainfall cycle, Southern Annular Mode and tropical cyclones over the Limpopo River Basin, southern Africa

The association between bi-decadal rainfall variability over southern Africa and the rainfall contributed by tropical cyclonic systems from the Southwest Indian Ocean (SWIO) provides a potential means towards understanding decadal-scale variability over parts of the region. A multi-decadal period is considered, focusing on the anomalous tropospheric patterns that induced a particularly wet 8-year long sub-period over the Limpopo River Basin. The wet sub-period was also characterized by a larger contribution to rainfall by tropical cyclones and depressions. The findings suggest that a broadening of the Hadley circulation underpinned by an anomalous anticyclonic pattern to the east of southern Africa altered tropospheric steering flow, relative vorticity and moisture contents spatially during the sub-period of 8 years. These circulation modulations induced enhanced potential for tropical systems from the SWIO to cause precipitation over the Limpopo River Basin. The same patterns are also conducive to increasing rainfall over the larger subcontinent, therefore explaining the positive association in the bi-decadal rainfall cycle and rainfall contributed by tropical cyclonic systems from the SWIO. An overview of regional circulation anomlies during alternating near-decadal wet and dry epochs is given. The regional circulation anomalies are also explained in hemispheric context, specifically in relation to the Southern Annular Mode, towards understanding variation over other parts of the Southern Hemisphere at this time scale.

Small influence of solar variability on climate over the past millennium

Climate variations over the past 1,000 years correspond to solar fluctuations, but the magnitude of the solar variability is unclear. An analysis of numerical simulations and climate reconstructions suggests that the amplitude of solar forcing was small over this interval, with the main climate forcing derived from volcanic eruptions and greenhouse gas concentrations. The climate of the past millennium was marked by substantial decadal and centennial scale variability in the Northern Hemisphere1. Low solar activity has been linked to cooling during the Little Ice Age (AD 1450–1850; ref. 1) and there may have been solar forcing of regional warmth during the Medieval Climate Anomaly2,3,4,5 (AD 950–1250; ref. 1). The amplitude of the associated changes is, however, poorly constrained5,6, with estimates of solar forcing spanning almost an order of magnitude7,8,9. Numerical simulations tentatively indicate that a small amplitude best agrees with available temperature reconstructions10,11,12,13. Here we compare the climatic fingerprints of high and low solar forcing derived from model simulations with an ensemble of surface air temperature reconstructions14 for the past millennium. Our methodology15 also accounts for internal climate variability and other external drivers such as volcanic eruptions, as well as uncertainties in the proxy reconstructions and model output. We find that neither a high magnitude of solar forcing nor a strong climate effect of that forcing agree with the temperature reconstructions. We instead conclude that solar forcing probably had a minor effect on Northern Hemisphere climate over the past 1,000 years, while, volcanic eruptions and changes in greenhouse gas concentrations seem to be the most important influence over this period.

Summer rainfall variability in European Mediterranean mountains from the sixteenth to the twentieth century reconstructed from tree rings

Since the end of the last glacial period, European Mediterranean mountains have provided shelter for numerous species of Eurosiberian and Boreal origin. Many of these species, surviving at the southern limit of their range in Europe and surrounded by Mediterranean ones, are relatively intolerant to summer drought and are in grave danger of loss, as a result of increasingly long and frequent droughts in this region. This is the case of the Scots pine (Pinus sylvestris) and the Austrian pine (Pinus nigra ssp. salzmannii) which are found on Central Iberian Peninsula at the edge of their natural range. We used a tree ring network of these two species to reconstruct past variations in summer rainfall. The reconstruction, based upon a tree ring composite chronology of the species, dates back to 1570 (adjusted R(2) = 0.49, P < 0.000001) and captures interannual to decadal scale variability in summer precipitation. We studied the spatial representativeness of the rainfall patterns and described the occurrence rate of extremes of this precipitation. To identify associations between macroclimatic factors and tree radial growth, we employed a principal component analysis to calculate the resultant of the relationship between the growth data of both species, using this resultant as a dependent variable of a multiple regression whose independent variables are monthly mean temperature and precipitation from the average records. Spatial correlation patterns between instrumental precipitation datasets for southern Europe and reconstructed values for the 1950-1992 period indicate that the reconstruction captures the regional signal of drought variability in the study region (the origin of this precipitation is convective: thermal low pressure zones induced in the inland northeastern areas of the Iberian Peninsula). There is a clear increase in the recurrence of extreme dry events as from the beginning of twentieth century and an abrupt change to drier conditions. There appears to be a tendency toward recurrent exceptionally dry summers, which could involve a significant change for the Eurosiberian refugee species.

Global sea level trend during 1993–2012

Projection of future sea level change relies on the understanding of present sea-level trend and how it has varied in the past. Here we investigate the global-mean sea level (GMSL) change during 1993–2012 using Empirical Mode Decomposition, in an attempt to distinguish the trend over this period from the interannual variability. It is found that the GMSL rises with the rate of 3.2±0.4mm/yr during 1993–2003 and started decelerating since 2004 to a rate of 1.8±0.9mm/yr in 2012. This deceleration is mainly due to the slowdown of ocean thermal expansion in the Pacific during the last decade, as a part of the Pacific decadal-scale variability, while the land-ice melting is accelerating the rise of the global ocean mass-equivalent sea level. Recent rapid recovery of the rising GMSL from its dramatic drop during the 2011 La Niña introduced a large uncertainty in the estimation of the sea level trend, but the decelerated rise of the GMSL appears to be intact.

Premonsoon precipitation variability in Kumaon Himalaya, India over a perspective of ∼300 years

Variability in premonsoon precipitation, which has direct impact on rabi crop productivity in the Himalayan region, is not well understood in a long-term perspective, largely due to the paucity of weather data. We developed an annually resolved February–May (FM) precipitation record extending back to AD 1730 using tree-ring width data of Himalayan cedar for the first time from the Kumaon region, eastern sector of the western Himalaya, India. The FM precipitation reconstruction, capturing 58% of the variance in instrumental data over the calibration period (1901–1968), is the strongest so far from the Indian region. The reconstruction revealed inter-annual to decadal-scale variations in precipitation anomalies. Twentieth-century decadal-scale droughts occurred in the 1920s, and 1960s to early 1970s, and pluvials in the 1910s and 1980s. However, the droughts in 1920–1924 were the most severe of any other comparable period in last three centuries. Pre-instrumental droughts of the 1740s, 1780s, and 1840s were widespread in a large part of the western Himalaya. The drying tendency noted in the last two decades, which is widespread in the western Himalaya and western Nepal, in view of increased hydrological demand is alarming, and could cause severe water stress in the region unless adaptive measures are taken.

Importance of decadal scale variability in shoreline response: examples from soft rock cliffs, East Anglian coast, UK

Rapidly eroding soft rock cliffs typically retreat at rates in excess of several metres per year, thus allowing the resolution of linkages between cliff dynamics and a range of climatic and marine forcing factors. New evidence from UK coastline of East Anglian coastline, southern North Sea shows that unprotected soft rock cliffs at three widely-spaced locations all show similar variability in retreat behaviour on decadal timescales, which we attribute to changing patterns of storminess in these decades. The 1990s were characterized by frequent months in which the North Atlantic Oscillation (NAO; a well-established measure of inter-annual climatic variability in North-West Europe) was extremely positive (more positive than +3) or extremely negative (more negative than −3), while the 2000s showed few occurrences of such extreme values. Depression tracks in positive NAO phases make the East Anglian coast prone to storm surges in which raised water levels result from deeply developed low pressure systems, generally associated with westerly air streams. In negative NAO phases the region is prone to easterly airflow which results in periods of strong onshore wind. Both phases are associated with high energetics in the forcing factors. Decadal-scale variability in cliffline retreat rates has implications for the practice of coastal management and policy making and suggests that cliff system responses to global environmental change are not simply driven by secular sea level rise.

Variation in feeding ecology within the fish community in the north Yellow Sea

Our objective was to evaluate ecosystem status before and after fishery enhancement.We analyzed the feeding habits,food consumption,and trophic level of the species constituting 90% of total biomass in bottom trawl surveys conducted in May and August of 2010.We compared the traits of the five dominant species(by total biomass) with those collected in 1985 and 2000.In addition,we evaluated decadal-scale variation in the mean TL of the fish community in the north Yellow Sea. The fish community in the north Yellow Sea was dominated by nine species,though these differed between May and August.The most dominant species in May included small yellow croaker Pseudosciaena polyactis,elongate eelpout Enchelyopus elongates,half-fin anchovy Setipinna taty,angler Lophius litulon,pointhead plaice Cleisthenes herzensteini,Pacific cod Gadus macrocephalus,and sea perch Lateolabrax japonicus.Conversely,in August the fishery was dominated by anchovy Engraulis japonicus,sea snail Liparis tanakae,small yellow croaker,elongate eelpout,and Pacific cod.Thus,the assemblage in May was characterized by a lack of nektivores,a decrease in the proportion of generalist predators,and an increase in the proportion of zooplanktivores relative to August.The mean trophic level of the fish community was 3.75 in May and 3.57 in August. The primary prey groups included euphausiids,copepods,hyperiid amphipods,crustacea larva,shrimps,ophiuroidea,bivalvia,polychaeta,and other fish species.We estimated the fish community consumed 0.5 million tons and 19.6 million tons of these prey items in May and August,respectively.Fish and shrimp were the dominant prey groups in May,accounting for 46.9% and 39.2% of the total food consumption,respectively.Similarly,fish,shrimp,and zooplankton were the dominant prey groups in August,accounting for 33.9%,31.4%,and 30.8% of the total food consumed,respectively.The primary prey species were Crangon affinis,Eualus sinensis,Euphausia pacifica,small yellow croaker,Johnius belengerii,and Ophiura sarsii in May.Consumption of these species equaled 0.3 million tons,accounting for 65% of the total food consumption.The primary prey species in August were C.affinis,E.sinensis,Themisto gracilipes,Calanus sinicus,and anchovy.Consumption of these species equaled 12.4 million tons,accounting for 62.9% of the total food consumption.Thus,as in the central and southern Yellow Sea,T.gracilipes,C.sinicus,C.affinis,E.sinensis,small yellow croaker,and anchovy were the most im-portant prey species in the north Yellow Sea. The mean trophic level of fish community declined from 4.26 in 1985 to 3.66 in 2010 in the north Yellow Sea,or 0.24 decade?1.This decrease was more rapid than in the Bohai Sea and central and southern Yellow Sea and was caused by a shift in the dominant species in the fish community.The percentage of nektivores decreased concomi-tantly with an increase in generalist predators between 1985 to 2010.The rate of change in trophic level has de-creased from 0.28 decade?1 between 1985 and 2000 to 0.18 decade-1 between 2000 and 2010,but has remained higher than the global rate.Given this,we recommend continuing efforts to enhance the fishery.

Comparing Cyclone Life Cycle Characteristics and Their Interannual Variability in Different Reanalyses

Abstract Characteristics of Northern Hemisphere extratropical cyclone activity were compared for five concurrent reanalyses: the NCEP–U.S. Department of Energy (DOE) reanalysis (herein NCEP–DOE), the Japanese 25-year Reanalysis Project (JRA-25), the ECMWF Interim Re-Analysis (ERA-Interim), the National Aeronautics and Space Administration's Modern-Era Retrospective Analysis for Research and Applications (NASA-MERRA), and the NCEP Climate Forecast System Reanalysis (NCEP-CFSR), for the period 1979–2010 using a single cyclone tracking algorithm. The total number of cyclones, ranging from 1400 to more than 1800 yr−1, was found to depend strongly on the spatial resolution of the respective reanalysis. The largest cyclone population was identified using NASA-MERRA data, which also showed the highest occurrence of very deep cyclones. Of the reanalyses, two (NCEP–DOE and ERA-Interim) are associated with statistically significant positive trends in the total number of cyclones from 1% to 2% decade−1. These trends result from moderate and shallow cyclones contributing to approximately 90% of the total cyclone count on average. The number of very deep cyclones (&amp;lt;960 hPa) in the North Atlantic increased in most reanalyses until 1990 and then declined during the last decade. In the North Pacific, the number of these events reached a peak in 2000 and then decreased during the last decade. The winter pattern is characterized by robust trends in cyclone numbers, with an enhancement of the North Atlantic storm track and a weakening of the North Pacific subtropical storm track. In the summer, there is a robust intensification of the Mediterranean storm track and a decrease in counts over the North Atlantic. Interannual variability and decadal-scale variations of the cyclone counts are highly correlated among the reanalyses, with the greatest agreement in moderate and deep cyclones.

The influence of decadal-scale variability on trends in long European streamflow records

Abstract. This study seeks to provide a long-term context for the growing number of trend analyses which have been applied to river flows in Europe. Most studies apply trend tests to fixed periods, in relatively short (generally 1960s–present) records. This study adopts an alternative "multi-temporal" approach, whereby trends are fitted to every possible combination of start and end years in a record. The method is applied to 132 catchments with long (1932–2004) hydrometric records from northern and central Europe, which were chosen as they are minimally anthropogenically influenced and have good quality data. The catchments are first clustered into five regions, which are broadly homogenous in terms of interdecadal variability of annual mean flow. The multi-temporal trend approach was then applied to regional time series of different hydrological indicators (annual, monthly and high and low flows). The results reveal that the magnitude and even direction of short-term trends are heavily influenced by interdecadal variability. Some short-term trends revealed in previous studies are shown to be unrepresentative of long-term change. For example, previous studies have identified post-1960 river flow decreases in southern and eastern Europe: in parts of eastern Europe, these trends are resilient to study period, extending back to the 1930s; in southern France, longer records show evidence of positive trends which reverse from the 1960s. Recent (post-1960) positive trends in northern Europe are also not present in longer records, due to decadal variations influenced by the North Atlantic Oscillation. The results provide a long-term reference for comparison with published and future studies. The multi-temporal approach advocated here is recommended for use in future trend assessments, to help contextualise short-term trends. Future work should also attempt to explain the decadal-scale variations that drive short-term trends, and thus develop more sophisticated methods for trend detection that take account of interdecadal variability and its drivers.

1200 years of decadal-scale variability of Mediterranean vegetation and climate at Pantelleria Island, Italy

A new sedimentary sequence from Lago di Venere on Pantelleria Island, located in the Strait of Sicily between Tunisia and Sicily was recovered. The lake is located in the coastal infra-Mediterranean vegetation belt at 2 m a.s.l. Pollen, charcoal and sedimentological analyses are used to explore linkages among vegetation, fire and climate at a decadal scale over the past 1200 years. A dry period from ad 800 to 1000 that corresponds to the ‘Medieval Warm Period’ (WMP) is inferred from sedimentological analysis. The high content of carbonate recorded in this period suggests a dry phase, when the ratio of evaporation/precipitation was high. During this period the island was dominated by thermophilous and drought-tolerant taxa, such as Quercus ilex, Olea, Pistacia and Juniperus. A marked shift in the sediment properties is recorded at ad 1000, when carbonate content became very low suggesting wetter conditions until ad 1850–1900. Broadly, this period coincides with the ‘Little Ice Age’ (LIA), which was characterized by wetter and colder conditions in Europe. During this time rather mesic conifers (i.e. Pinus pinaster), shrubs and herbs (e.g. Erica arborea and Selaginella denticulata) expanded, whereas more drought-adapted species (e.g. Q. ilex) declined. Charcoal data suggest enhanced fire activity during the LIA probably as a consequence of anthropogenic burning and/or more flammable fuel (e.g. resinous Pinus biomass). The last century was characterized by a shift to high carbonate content, indicating a change towards drier conditions, and re-expansion of Q. ilex and Olea. The post-LIA warming is in agreement with historical documents and meteorological time series. Vegetation dynamics were co-determined by agricultural activities on the island. Anthropogenic indicators (e.g. Cerealia-type, Sporormiella) reveal the importance of crops and grazing on the island. Our pollen data suggest that extensive logging caused the local extinction of deciduous Quercus pubescens around ad1750.

The ability of the adjoint technique to recover decadal variability of the North Atlantic circulation

Different oceanic data assimilation products show rather different decadal-scale variability, in particular for the Atlantic meridional overturning circulation (MOC). In order to understand these differences we evaluate the ability of the adjoint technique to reproduce MOC variability using surface heat flux forcing as the control parameter. We find that in a perfect model framework and for a reasonable weighting the adjoint method is, in principle, successful at reproducing decadal-scale MOC variability if adequate synthetic observations and a priori information of the control parameter are given. Temperature of the upper 1000m and sea surface height and a priori information about surface heat fluxes contain the most useful information. Using only salinity or only synthetic hydrography below 1000m, the method fails to converge and to reconstruct MOC variability, given surface heat flux as the only control parameter.In order to provide error bounds for current assimilation products, prescribed artificial errors for a priori control parameter, synthetic observations and initial conditions are introduced systematically to our setup. We find that errors with reasonable magnitude in synthetic observations as well as a priori information of the surface heat fluxes lead to a reconstructed decadal-scale MOC variability with tolerable errors of less than a few percent. Errors in initial conditions lead to a “cold start” problem and can degrade the quality of the MOC reconstruction, but can be damped by sufficient a priori information about the surface forcing in the subsequent integration, even without including the initial conditions as a control parameter. The impact of a model error is analyzed by assimilating synthetic observations from different model configurations, which resembles most likely an underestimation of the “real” model error. Even with this optimistic estimate, the reconstruction is very sensitive to the model error and leads to a large error in the reconstructed MOC variability. Taking all possible errors together, the error of decadal MOC reconstruction in current data assimilation products appears to be larger than 60% (about 1Sv) with a correlation with the “real” MOC variability by less than 0.5.

Recent multiyear trends in the Baltic Sea level

Sea level rise is one of the most direct consequences of climate change. It has been documented that sea level rise is globally subject to considerable spatial heterogeneity. There is an increased awareness of the need to create regional data records and projections of sea level trends, because specific regional processes can cause regional trends to diverge significantly from global averages. In this paper available multimission satellite altimetry data were used to estimate the multiyear trend in the Baltic Sea level. The estimated trend is about 0.33cmyr−1, similar to the globally averaged sea level trend, but significantly larger than the regional trends estimated in the North Sea and North Atlantic. The decadal scale variability in the sea level trend in the Baltic Sea does not indicate a significant acceleration of the trend in recent years. Our analysis confirms that the interannual variability of sea level in the Baltic in winter is significantly correlated with the North Atlantic Oscillation index.

Hydrological processes behind annual and decadal-scale variations in the water quality of runoff in Finnish catchments with acid sulfate soils

Summary In this study we assess long- and short term temporal variations in the impact of acid sulfate (a.s.) soils on river water quality. We demonstrate how such variations depend on changes in hydrological conditions driven by land use, meteorological variations and potential changes in climate with important implications on mitigation strategies, water ecology and utilization of water resources. Quality of river water discharging into the Larsmo-Oja Lake in Midwestern Finland was studied by using long term water data collected during 1963–2009. Acid sulfate soils are extremely acidic soils (pH

Replicated stalagmite-inferred centennial-to decadal-scale monsoon precipitation variability in southwest China since the mid Holocene

A lack of agreement between stalagmite records of the centennial- to decadal-scale Asian summer monsoon (ASM) variability since the mid Holocene limited our understanding of forcings and the possible impacts on culture evolution. Here we present replicated high-resolution stalagmite δ18O profiles from Dark Cave in Guizhou province, southwest China, established with 512 oxygen isotope data and 28 230Th ages, providing a continuous history of the ASM precipitation from 6100 to 300 years before present (yr BP, before ad 1950). Consistency of stalagmite δ18O-inferred long-term decreasing ASM trends since the mid Holocene between caves at this site and others in the Indian and East Asian monsoon realms on orbital timescales supports the effect of primary orbital solar forcings on monsoonal precipitation. The Dark Cave records display significant centennial- to decadal-scale variations, more evident than previous stalagmite records. Spectral analysis of the Dark Cave δ18O time series yields periodicities of 731–723, 281, 91–83, 67, and 55–54 yr, implying ASM intensity for the last 6 kyr could be associated with solar activity and variability of El Niño-Southern Oscillation.

A Millennial Proxy Record of ENSO and Eastern Australian Rainfall from the Law Dome Ice Core, East Antarctica

Abstract ENSO causes climate extremes across and beyond the Pacific basin; however, evidence of ENSO at high southern latitudes is generally restricted to the South Pacific and West Antarctica. Here, the authors report a statistically significant link between ENSO and sea salt deposition during summer from the Law Dome (LD) ice core in East Antarctica. ENSO-related atmospheric anomalies from the central-western equatorial Pacific (CWEP) propagate to the South Pacific and the circumpolar high latitudes. These anomalies modulate high-latitude zonal winds, with El Niño (La Niña) conditions causing reduced (enhanced) zonal wind speeds and subsequent reduced (enhanced) summer sea salt deposition at LD. Over the last 1010 yr, the LD summer sea salt (LDSSS) record has exhibited two below-average (El Niño–like) epochs, 1000–1260 ad and 1920–2009 ad, and a longer above-average (La Niña–like) epoch from 1260 to 1860 ad. Spectral analysis shows the below-average epochs are associated with enhanced ENSO-like variability around 2–5 yr, while the above-average epoch is associated more with variability around 6–7 yr. The LDSSS record is also significantly correlated with annual rainfall in eastern mainland Australia. While the correlation displays decadal-scale variability similar to changes in the interdecadal Pacific oscillation (IPO), the LDSSS record suggests rainfall in the modern instrumental era (1910–2009 ad) is below the long-term average. In addition, recent rainfall declines in some regions of eastern and southeastern Australia appear to be mirrored by a downward trend in the LDSSS record, suggesting current rainfall regimes are unusual though not unknown over the last millennium.

STAGES,CYCLICITY AND TRENDS OF AIR TEMPERATURE IN THE SUBTROPICAL ZONE OF SOUTH CHINA DURING 1901-2011

Understanding the regional air temperature changing process will significantly improve the knowledge of global temperature pattern and its future trend.In this paper,we analyzed the air temperature variations over the period of 1901—2011in the South China subtropical zone based on the instrumental data from eight weather stations,and reached the conclusions as follows.(1)The annual temperature had experienced an overall rising tendency at an average rate of 1.26 ℃/100aduring the period 1901—2011,which was equivalent to the global mean rate.(2)Due to the urban heat island effect,some stations in the study area showed significantly higher warming rates than the global value and the mean values within China,while other stations such as Hengchun,Penghu and Macau had little effect of urbanization and showed a warming rate of 0.97 ℃/100a.(3)Two significant warming periods,i.e.,the period from the mid-1910sto the mid-1950sand the period since the mid-1980s,were identified in the last 110years,suggesting multidecadal climatic variations.(4)Wavelet analysis further indicated that some interannual oscillations such as 3~6years ENSO cycles were superimposed on the decadal-scale variations.(5)Trend analysis suggests that the current warming period since 1998will continue until the mid-2020s,and the temperature in 2100will be(1.2±0.5)℃above the mean value of the period of 1961—1990.

HOW TO WEIGH COASTAL HAZARD AGAINST ECONOMIC CONSEQUENCE

It is well recognised that sea level change over the coming century will have an extraordinary economic impact on coastal communities. To overcome the uncertainty that still surrounds the mechanics of shoreline recession and stochastic forcing, landuse&#x0D; planning and management decisions will require a robust and quantitative risk-based approach. A new approach is presented, which has been evaluated using field measurements and assessed in economic terms. The paper discusses a framework for coastal risk analysis which combines four main components 1) the effects of non-stationary&#x0D; climate, including decade scale variability and anthropogenic change; 2) a full probabilistic assessment of incident wave and surge conditions; 3) determination of storm erosion extents; and 4) the economic impact of combined coastal erosion and&#x0D; recession. The framework is illustrated in Figure 1. The operation of this framework has been demonstrated, building upon previous work (Callaghan et al., 2008; Jongejan et al., 2011; Ranasinghe et al., 2011). The first three components relate to physical hazards. Using stochastic simulation, we quantify the 'likelihood' side of risk.&#x0D; That likelihood is typically represented by lines indicating a projected extreme landward shoreline condition and an associated quantitative probability. For the first time, the effects of non-stationary climate (e.g. sea level rise) have been included. This&#x0D; can be extended to include decadal scale climate variation effects such as beach rotation.&#x0D; The fourth component requires the determination of values associated with land threatened by coastal erosion during the time frame being considered. We assign a spatially varying value density relationship. The exceedance probability of erosion is&#x0D; combined with the value density to calculate the expected value of damage at a given point in time. In a non-stationary climate scenario, the exceedance probabilities change with time, and this is also considered. Given a known rate of return on investment, the differentials in the rates of return (between coastal and inland property&#x0D; investments) are subsequently used to determine the efficient position of the setback line. The results are presented within a GIS framework to effectively feed into the coastal land use planning process. We demonstrate the framework by applying it to&#x0D; using real data (both physical and economic) for our subject site, Narrabeen Beach in Sydney.

St Helena Bay (southern Benguela) then and now: muted climate signals, large human impact

The development of suitable reference states for ecosystem-based management requires documentation of changes in structure and functioning of marine ecosystems, including assessment of the relative importance of bottom-up and top-down processes as drivers of change. We used monitoring data available from St Helena Bay, the most productive bay and an important nursery area situated on the west coast of South Africa, during 1950–2010 to reveal changes in the abiotic and biotic components. St Helena Bay in the 1950s showed similarities to 2000–2010 in terms of wind patterns, hydrology and phytoplankton. Upwelling, oxygen and nutrient concentrations in subthermocline water displayed pronounced decadal-scale variability. Primary production in St Helena Bay is variable, but consistently higher than that on the adjacent Namaqua shelf. Zooplankton size composition and biomass in August have changed markedly since the 1950s. During 2001–2010, mesozooplankton biomass in autumn was considerably lower than in summer, probably due to predation by small pelagic fish. Pelagic fish catch patterns and distributions have altered dramatically. Conservation measures, implemented to reverse past negative human impact, have benefitted marine mammals, the abundance of which has increased in the area, but additional conservation measures are necessary to reverse the decline in African penguins Spheniscus demersus. St Helena Bay shows a muted response to long-term change in the southern Benguela, with marked decadal variability but no clear long-term trend in oceanography and biogeochemistry. Changes in ecosystem boundary conditions and fishing pressure cannot be ignored as important drivers of change in the southern Benguela since the 1950s.