Interdecadal Climate Variability Research Articles

Decadal/interdecadal variations of the ocean temperature and its impacts on climate

Decadal/interdecadal climate variability is an important research focus of the CLIVAR Program and has been paid more attention. Over recent years, a lot of studies in relation to interdecadal climate variations have been also completed by Chinese scientists. This paper presents an overview of some advances in the study of decadal/interdecadal variations of the ocean temperature and its climate impacts, which includes interdecadal climate variability in China, the interdecadal modes of sea surface temperature (SST) anomalies in the North Pacific, and in particular, the impacts of interdecadal SST variations on the Asian monsoon rainfall. As summarized in this paper, some results have been achieved by using climate diagnostic studies of historical climatic datasets. Two fundamental interdecadal SST variability modes (7–10-years mode and 25–35-years mode) have been identified over the North Pacific associated with different anomalous patterns of atmospheric circulation. The southern Indian Ocean dipole (SIOD) shows a major feature of interdecadal variation, with a positive (negative) phase favoring a weakened (enhanced) Asian summer monsoon in the following summer. It is also found that the China monsoon rainfall exhibits interdecadal variations with more wet (dry) monsoon years in the Yangtze River (South China and North China) before 1976, but vice versa after 1976. The weakened relationship between the Indian summer rainfall and ENSO is a feature of interdecadal variations, suggesting an important role of the interdecadal variation of the SIOD in the climate over the south Asia and southeast Asia. In addition, evidence indicates that the climate shift in the 1960s may be related to the anomalies of the North Atlantic Oscillation (NAO) and North Pacific Oscillation (NPO). Overall, the present research has improved our understanding of the decadal/interdecadal variations of SST and their impacts on the Asian monsoon rainfall. However, the research also highlights a number of problems for future research, in particular the mechanisms responsible for the monsoon long-term predictability, which is a great challenge in climate research.

Interdecadal variation of the lower trophic ecosystem in the northern Pacific between 1948 and 2002, in a 3-D implementation of the NEMURO model

Regime shifts, consisting of decadal-scale oscillations in atmosphere–ocean systems, have recently been the focus of many marine ecosystem studies. These ‘regime shifts’ effect the sea surface temperature and mixed layer depth (MLD), changing the environment for marine ecosystems. We simulated changes in the marine ecosystem caused by interdecadal climate variability, using data from 1948 to 2002 to drive an ecosystem model, NEMURO, embedded in a global three-dimensional physical–biological coupled model, ‘3D-NEMURO’. The results were consistent with observations. Comparing before and after the late 1970s regime shift, primary production and biomass of phytoplankton increased in the north central Pacific but decreased in the sub-tropical northwestern and eastern Pacific. This corresponds to the Pacific decadal oscillation (PDO) index that indicates interdecadal climate variability in the sub-tropical and tropical Pacific. In the north central Pacific, biomass correlated positively with PDO while that in the north eastern and western Pacific correlated negatively with PDO.

Trends in Snowfall versus Rainfall in the Western United States

Abstract The water resources of the western United States depend heavily on snowpack to store part of the wintertime precipitation into the drier summer months. A well-documented shift toward earlier runoff in recent decades has been attributed to 1) more precipitation falling as rain instead of snow and 2) earlier snowmelt. The present study addresses the former, documenting a regional trend toward smaller ratios of winter-total snowfall water equivalent (SFE) to winter-total precipitation (P) during the period 1949–2004. The trends toward reduced SFE are a response to warming across the region, with the most significant reductions occurring where winter wet-day minimum temperatures, averaged over the study period, were warmer than −5°C. Most SFE reductions were associated with winter wet-day temperature increases between 0° and +3°C over the study period. Warmings larger than this occurred mainly at sites where the mean temperatures were cool enough that the precipitation form was less susceptible to warming trends. The trends toward reduced SFE/P ratios were most pronounced in March regionwide and in January near the West Coast, corresponding to widespread warming in these months. While mean temperatures in March were sufficiently high to allow the warming trend to produce SFE/P declines across the study region, mean January temperatures were cooler, with the result that January SFE/P impacts were restricted to the lower elevations near the West Coast. Extending the analysis back to 1920 shows that although the trends presented here may be partially attributable to interdecadal climate variability associated with the Pacific decadal oscillation, they also appear to result from still longer-term climate shifts.

Climate Change and Floodplain Management in the United States

Federal agencies use flood frequency estimates to delineate flood risk, manage the National Flood Insurance Program, and ensure that Federal programs are economically efficient. The assumption behind traditional flood risk analysis is that climate is stationary, but anthropogenic climate change and better knowledge of interdecadal climate variability challenge the validity of the assumption. This paper reviews several alternative statistical models for flood risk estimation that do not assume climate stationarity. Some models require subjective judgement or presuppose an understanding of the causes of the underlying non-stationarity, which is problematic given our current knowledge of the interaction of climate and floods. Although currently out of favor, hydrometeorological models have been used for engineering design as alternatives to statistical models and could be adapted to different climate conditions. Floodplain managers should recognize the potentially greater uncertainty in flood risk estimation due to climate change and variability and try to incorporate the uncertainties into floodplain management decision-making and regulation.

Mid-Wisconsin sediment record from Baldwin Lake reveals hemispheric climate dynamics (Southern CA, USA)

Recently acquired cores from Baldwin Lake, Southern California, document the first regional, terrestrial-based evidence for glacial period millennial-to-orbital scale climate variability. Eight AMS 14C dates on a 14-m core from the lake's present day depocenter provide initial age control over the interval from 20,000 to 48,000 years before present (BP). A linear age model extends the record to a minimum age of 65,000 years BP. A combination of lithologic description and one cm contiguous sedimentological analyses indicates significant changes in the dominant type of depositional environment over the length of the record at millennial-to-orbital time scales. As a first-order interpretation, the dominant sedimentary environments alternate between permanent and ephemeral lake systems. Orbital-scale forcing includes long-term winter-summer insolation variability and its modulation of winter storm tracks and the North American monsoon, respectively. Millennial-scale variability is attributed to extra-tropical, ocean–atmosphere dynamics akin to historical interdecadal Pacific climate variability. In addition, there is notable correspondence to the independently dated Greenland Ice Core record (GISP 2) at millennial-to-orbital time scales suggesting that Baldwin Lake contains, in addition to its local/regional record, a hemispheric record of climate change — similar to Owens, Pyramid, and Summer Lake of central and northwestern North America. An initial comparison to GISP2 δ 18O (ice) indicates that North Atlantic interstadials correlate to permanent lake environments in coastal southwestern North America. These results present a notable conflict with the proposed “super-ENSO” phenomenon in the western tropical Pacific. These results also highlight the necessity for acquiring additional high-resolution glacial period records for resolving questions of spatial–temporal phasing of late-Quaternary climates.

Interdecadal variability and climate change in the eastern tropical Pacific: A review

In this paper, we review interdecadal climatic variability in the eastern tropical Pacific Ocean. This variability dominates the climatic fluctuations in the North Pacific on scales between ENSO and the centennial trend and is commonly referred to as the Pacific Decadal Oscillation or PDO. We include a historical overview and a summary of observational work that describes the surface, tropospheric and subsurface signatures of this variability. Descriptions of interdecadal variability are incomplete at best, mostly due to limitations in the observational record. We emphasize that the well-known “ENSO-like” sea surface temperature (SST) pattern describing the PDO may not be an accurate representation. In the eastern tropical Pacific, the SST maxima are displaced north and south of the equator with larger amplitudes in the northern branch near the coast of North America, which has significant implications for the troposphere-driven circulations. Several mechanisms have been proposed to explain the PDO. We review these mechanisms and models, which capture our present level of understanding of the problem. We conclude by reporting there is little evidence of both multidecadal variability and the centennial trend in the eastern tropical Pacific. This paper is part of a comprehensive review of the oceanography of the eastern tropical Pacific.

Effects of interdecadal climate variability on marine trophic interactions: rhinoceros auklets and their fish prey

This paper presents time-series information on the diet composition and breeding performance of rhinoceros auklet Cerorhinca monocerata at Triangle Island, British Columbia, Canada, during 15 breeding seasons between 1976 and 2001. Three shifts in ocean climate occurred within British Columbia during this period (1976–77, 1989–90, 1998–99), allowing us to evaluate associations between marine environmental conditions and the reproduction of this piscivorous seabird. Lipid-rich Pacific sand lance Ammodytes hexapterus was the single most important prey delivered to chicks across years (15 yr avg. 38%; annual range 4 to 86%). Interannual variability was high, but in general breeding performance was strongest when 0+ sand lance predominated chick diets. Other annually important prey taxa included Pacific saury Cololabis saira, juvenile rockfishes Sebastes spp., Pacific herring Clupea pallasi and juvenile salmonid Oncorhynchus spp. The dietary importance of these prey also varied seasonally. Marine environmental conditions (evaluated using sea surface temperatures, SSTs) were clearly associated with reproduction of rhinoceros auklet, as both occurrence of sand lance in the diet and the growth rates of chicks diminished as spring SSTs increased (r = –0.680, p < 0.01, and r = –0.697, p < 0.01, respectively). We hypothesized that recruitment to local sand lance populations was temperature dependent. The strong negative relationship between dietary occurrence of 0+ sand lance and spring SST (r = –0.560, p < 0.05), coupled with the lack of a similar relationship for 1+ sand lance (p > 0.20), was consistent with the temperature-dependent recruitment hypothesis. Our data suggest that SSTs could interact with population age structure to affect the recruitment dynamics of Pacific sand lance. We estimated the annual dietary importance of 0+ sand lance to rhinoceros auklets using spring SST and the importance of 0+ sand lance in the diet the previous year.

ENSO and interdecadal climate variability over the last century documented by geochemical records of two coral cores from the South West Pacific

Abstract. The south west Pacific is affected by climatic phenomena such as ENSO (El Niño Southern Oscillation) or the PDO (Pacific Decadal Oscillation). Near-monthly resolution calibrations of Sr/Ca, U/Ca and δ18Oc were made on corals taken from New Caledonia and Wallis Island. These geochemical variations could be linked to SST (sea surface temperature) and SSS (sea surface salinity) variations over the last two decades, itselves dependent on ENSO occurrences. On the other hand, near-half-yearly resolution over the last century smoothes seasonal and interannual climate signals, but emphasizes low frequency climate variability.

Simulating multi-decadal variability of Caspian Sea level changes using regional climate model outputs

The Caspian Sea is the largest enclosed body of water on earth, covering approximately 4×105 km2 and sharing its coast with five countries (Iran, Azerbaijan, Kazakhstan, Russia and Turkmenistan). Because it has no outlet to the ocean the Caspian Sea level (CSL) has undergone rapid shifts in response to climatic forcings, and these have been devastating for the surrounding countries. In this paper we present the initial results of a modeling effort aimed at building a regional climate model for the Caspian Sea basin suitable to study the response of the CSL to interdecadal climate variability and anthropogenic climate change. Simulations are performed using the International Centre for Theoretical Physics (ICTP) regional climate model RegCM at a 50 km grid spacing for the period 1948–1990. During this period an abrupt shift occurred in the sea level after 1977, when the CSL rose about two meters until the early 1990s. Using a simple equation of hydrologic balance for the Caspian Sea basin to predict the CSL, we show that the model is able to reproduce the observed CSL changes at interannual to multidecadal scales. The correlation coefficient between the simulated and observed annual CSL changes is 0.91 and the model is able to reproduce the abrupt shift in CSL which occurred after 1977. Analysis of the climatologies before and after 1977 indicate that the CSL rise was mostly due to an increase in precipitation over the northern basin and a decrease in evaporation over the sea, primarily during the warm season. We plan to apply our model to the investigation of the response of the CSL to anthropogenic climate forcings.

Mechanism of Interdecadal Thermohaline Circulation Variability in a Coupled Ocean–Atmosphere GCM

Abstract Interdecadal variability of the Atlantic thermohaline circulation (THC) is studied in the third version of the Hadley Centre global coupled atmosphere–ocean sea-ice general circulation model (HadCM3). A diagnostic approach is used to elucidate the mechanism that governs the variability and its impacts on climate. An irregular and heavily damped THC oscillation with a period around 25 yr is identified. The oscillation appears to be forced by the atmosphere but the ocean is responsible for setting the time scale. Following a minimum in the THC, the mechanism for phase reversal involves the accumulation of cold water in the subpolar gyre, leading to an acceleration of the gyre circulation and the North Atlantic Current. This acceleration increases the transport of saline waters into the regions of active deep convection, raising the upper-ocean density and leading, after adjustment, to acceleration of the THC. The atmosphere stimulates this THC variability in two ways: 1) by forcing the subpolar gyre through (North Atlantic Oscillation) NAO-related wind stress curl and heat flux anomalies; and 2) by direct forcing of the region of active deep convection, also through wind stress curl and heat flux anomalies. The latter is not closely related to the NAO. The mechanism for phase reversal has many similarities to that found in a previous study with a much lower resolution coupled model, suggesting that this mechanism may be quite robust. However the time scale, and details of the atmospheric forcing, differ. The THC variability in HadCM3 has significant impacts on the atmosphere not just in the Atlantic region but also more widely, throughout the global Tropics. The mechanism involves modulation by the THC of the cross-equator SST gradient in the tropical Atlantic. The SST anomalies induce a displacement of the ITCZ in the Atlantic basin with knock-on effects over the other ocean basins. These findings highlight the potential importance of the Atlantic THC as a cause of interdecadal climate variability on a global scale.

Interdecadal Variability in a Hybrid Coupled Ocean–Atmosphere–Sea Ice Model

Interdecadal climate variability in an idealized coupled ocean-atmosphere-sea-ice model is studied. The ocean component is a fully three-dimensional primitive equation model and the atmospheric component is a two-dimensional (2D) energy balance model of Budyko-Sellers-North type, while sea ice is represented by a 2D thermodynamic model. In a wide range of parameters the model climatology resembles certain aspects of observed climate. Two types of interdecadal variability are found. The first one is characterized by northward-propagating upper-ocean temperature anomalies in the northwestern part of the ocean basin and a westward-propagating, wavelike temperature pattern at depth. The other type has larger-scale temperature anomalies that propagate westward in both the upper and deep ocean, along the sea ice edge. Both types of oscillations have been found previously in similar models that do not include sea ice. Therefore, the oscillation mechanism does not depend on sea-ice feedbacks nor is it modified very much by the inclusion of sea ice. For some parameter values, the interdecadal oscillations are self-sustained, while for others they are damped. Stochastic-forcing experiments show that, in the latter case, significant interdecadal signals can still be identified in the time series of oceanic heat transport. The periods of these signals, however, do not closely match those identified in a stability analysis of the deterministic model when linearized about its steady state. The authors show that linearization around the actual climatology of the stochastically forced integrations provides a better match for some of the modes that were poorly explained when linearizing about the deterministic model's steady state. The main difference between the two basic states is in the distribution of climatological convective depth, which is affected strongly by intermittent atmospheric forcing.

A review of decadal/interdecadal climate variation studies in China

Decadal/interdecadal climate variability is an important element in the CLIVAR (Climate Variability and Predictability) and has received much attention in the world. Many studies in relation to interdecadal variation have also been completed by Chinese scientists in recent years. In this paper, an introduction in outline for interdecadal climate variation research in China is presented. The content includes the features of interdecadal climate variability in China, global warming and interdecadal temperature variability, the NAO (the North Atlantic Oscillation)/NPO (the North Pacific Oscillation) and interdecadal climate variation in China, the interdecadal variation of the East Asian monsoon, the interdecadal mode of SSTA (Sea Surface Temperature Anomaly) in the North Pacific and its climate impact, and abrupt change feature of the climate.

Response of Subalpine Conifers in the Sierra Nevada, California, U.S.A., to 20th-Century Warming and Decadal Climate Variability

Four independent studies of conifer growth between 1880 and 2002 in upper elevation forests of the central Sierra Nevada, California, U.S.A., showed correlated multidecadal and century-long responses associated with climate. Using tree-ring and ecological plot analysis, we studied annual branch growth of krummholz Pinus albicaulis; invasion by P. albicaulis and Pinus monticola into formerly persistent snowfields; dates of vertical branch emergence in krummholz P. albicaulis; and invasion by Pinus contorta into subalpine meadows. Mean annual branch growth at six treeline sites increased significantly over the 20th century (range 130–400%), with significant accelerations in rate from 1920 to 1945 and after 1980. Growth stabilized from 1945 to 1980. Similarly, invasion of six snowfield slopes began in the early 1900s and continued into snowfield centers throughout the 20th century, with significantly accelerated mean invasion from 1925 to 1940 and after 1980. Rate of snowfield invasion decreased between 1950 and 1975. Meadow invasion and vertical leader emergence showed synchronous, episodic responses. Pinus contorta invaded each of ten subalpine meadows in a distinct multidecadal pulse between 1945 and 1976 (87% of all trees) and vertical release in five krummholz P. albicaulis sites also occurred in one pulse between 1945 and 1976 (86% of all branches). These synchronies and lack of effect of local environments implicate regional climate control. Composite weather records indicated significant century-long increases in minimum monthly temperature and multidecadal variability in minimum temperature and precipitation. All ecological responses were significantly correlated with minimum temperature. Significant interactions among temperature, precipitation, Pacific Decadal Oscillation (PDO) indices, and multiyear variability in moisture availability further explained episodic ecological responses. Four multidecadal periods of the 20th century that are defined by ecological response (<1925; 1925–1944; 1945–1976; >1976) correlate with positive and negative PDO phases, as well as with steps in the rate of temperature increase. These diverse factors in spatially distributed upper-montane and treeline ecosystems respond directionally to century-long climate trends, and also exhibit abrupt and reversible effects as a consequence of interdecadal climate variability and complex interactions of temperature and moisture.

Pacific Interdecadal Climate Variability: Linkages between the Tropics and the North Pacific during Boreal Winter since 1900

This study examines the tropical linkages to interdecadal climate fluctuations over the North Pacific during boreal winter through a comprehensive and physically based analysis of a wide variety of observational datasets spanning the twentieth century. Simple difference maps between epochs of high sea level pressure over the North Pacific (1900‐24 and 1947‐76) and epochs of low pressure (1925‐46 and 1977‐97) are presented for numerous climate variables throughout the tropical Indo-Pacific region, including rainfall, cloudiness, sea surface temperature (SST), and sea level pressure. The results support the notion that the Tropics play a key role in North Pacific interdecadal climate variability. In particular, SST anomalies in the tropical Indian Ocean and southeast Pacific Ocean, rainfall and cloudiness anomalies in the vicinity of the South Pacific convergence zone, stratus clouds in the eastern tropical Pacific, and sea level pressure differences between the tropical southeast Pacific and Indian Oceans all exhibit prominent interdecadal fluctuations that are coherent with those in sea level pressure over the North Pacific. The spatial patterns of the interdecadal tropical climate anomalies are compared with those associated with ENSO, a predominantly interannual phenomenon; in general, the two are similar with some differences in relative spatial emphasis. Finally, a published 194-yr coral record in the western tropical Indian Ocean is shown to compare favorably with the twentieth-century instrumental records, indicating the potential for extending knowledge of tropical interdecadal climate variability to earlier time periods.

Geochemical evidence from corals for changes in the amplitude and spatial pattern of South Pacific interdecadal climate variability over the last 300 years

In the Pacific Ocean, the coherent pattern of interdecadal variations in sea surface temperature (SST) over the last ∼100 years has been termed the Interdecadal Pacific Oscillation (IPO). To examine past variations in the IPO we have generated time series of Sr/Ca and oxygen isotopes (δ18O) from South Pacific Porites coral colonies growing at Rarotonga (1997 to 1726) and Fiji (1997 to 1780). At both sites skeletal Sr/Ca is highly correlated with instrumental SST at least back to ∼1970 and δ18O appears to reflect both SST and South Pacific Convergence Zone (SPCZ) effects on seawater δ18O. Comparison of our results to a New Caledonia coral δ18O record and to indices of interdecadal Pacific climate variability demonstrates that these South Pacific corals have accurately recorded twentieth century variations in the IPO and SPCZ. The coral records also indicate that higher amplitude and more spatially coherent IPO-related variability existed from 1880 to 1950 with notably poor between-site correlations in the mid-1800s. These observations suggest that the spatial IPO pattern in South Pacific SST was significantly more complex and/or poorly defined in the mid-1800s compared to that observed in the twentieth century. Comparison with North Pacific IPO indices also indicates that the degree of cross-hemispheric symmetry of interdecadal oceanographic variability has changed over time with a lower correlation between the North and South Pacific in the mid-1800s. This evidence suggests that the spatial pattern of the IPO at least in the South Pacific has varied over the last 300 years, with a major reorganization occurring after ∼1880 A.D.

Potential Feedbacks Between Pacific Ocean Ecosystems and Interdecadal Climate Variations

Scripps Institution of Oceanography, University of California, San Diego, Lajolla, CaliforniaNOAA/Climate Diagnostics Center, Boulder, ColoradoMeteorological Service of Canada, University of Victoria, Victoria, British Columbia, CanadaUniversity of Maine, Orono, MaineOak Ridge National Laboratory, Oak Ridge, TennesseeGriffith University, Nathan, AustraliaUniversity of Hawaii at Manoa, Honolulu, HawaiiDalhousie University, Halifax, Nova Scotia, CanadaUniversity of Wisconsin—Madison, Madison, WisconsinUniversity of Maryland, College Park, College Park, MarylandAdvanced Earth Science and Technology Organization, Tokyo, JapanUniversity of California, Santa Barbara, Santa Barbara, CaliforniaFisheries and Oceans Canada, Nanaimo, British Columbia, CanadaInstitut für Meereskunde, Kiel, GermanyCORRESPONDING AUTHOR: Dr. Arthur J. Miller, Climate Research Division, Scripps Institution of Oceanography, University of California, San Diego, La Jolla, CA 92093-0224, E-mail: ajmiller@ucsd.edu

Interdecadal Variation of the Transition Zone Chlorophyll Front : A Physical-Biological Model Simulation between 1960 and 1990

The interdecadal climate variability affects marine ecosystems in both the subtropical and subarctic gyres, consequently the position of the Transition Zone Chlorophyll Front (TZCF). A three-dimensional physical-biological model has been used to study interdecadal variation of the TZCF using a retrospective analysis of a 30-year (1960–1990) model simulation. The physical-biological model is forced with the monthly mean heat flux and surface wind stress from the COADS. The modeled winter mixed layer depth (MLD) shows the largest increase between 30°N and 40°N in the central North Pacific, with a value of 40–60% higher during 1979–90 relative to 1964–75 values. The winter Ekman pumping velocity difference between 1979–90 and 1964–75 shows the largest increase located between 30°N and 45°N in the central and eastern North Pacific. The modeled winter surface nitrate difference between 1979–90 and 1964–75 shows increase in the latitudinal band between 30°N and 45°N from the west to the east (135°E–135°W), the modeled nitrate concentration is about 10 to 50% higher during the period of 1979–90 relative to 1964–75 values depending upon locations. The increase in the winter surface nitrate concentration during 1979-90 is caused by a combination of the winter MLD increase and the winter Ekman pumping enhancement. The modeled nitrate concentration increase after 1976–77 enhances primary productivity in the central North Pacific. Enhanced primary productivity after the 1976–77 climatic shift contributes higher phytoplankton biomass and therefore elevates chlorophyll level in the central North Pacific. Increase in the modeled chlorophyll expand the chlorophyll transitional zone and push the TZCF equatorward.

The effects of large-scale afforestation and climate change on water allocation in the Macquarie River catchment, NSW, Australia

Widespread afforestation has been proposed as one means of addressing the increasing dryland and stream salinity problem in Australia. However, modelling results presented here suggest that large-scale tree planting will substantially reduce river flows and impose costs on downstream water users if planted in areas of high runoff yield. Streamflow reductions in the Macquarie River, NSW, Australia are estimated for a number of tree planting scenarios and global warming forecasts. The modelling framework includes the Sacramento rainfall-runoff model and IQQM, a streamflow routing tool, as well as various global climate model outputs from which daily rainfall and potential evaporation data files have been generated in OzClim, a climate scenario generator. For a 10% increase in tree cover in the headwaters of the Macquarie, we estimate a 17% reduction in inflows to Burrendong Dam. The drying trend for a mid-range scenario of regional rainfall and potential evaporation caused by a global warming of 0·5°C may cause an additional 5% reduction in 2030. These flow reductions will decrease the frequency of bird-breeding events in Macquarie Marshes (a RAMSAR protected wetland) and reduce the security of supply to irrigation areas downstream. Inter-decadal climate variability is predicted to have a very significant influence on catchment hydrologic behaviour. A further 20% reduction in flows from the long-term historical mean is possible, should we move into an extended period of below average rainfall years, such as occurred in eastern Australia between 1890 and 1948. Because current consumptive water use is largely adapted to the wetter conditions of post 1949, a return to prolonged dry periods would cause significant environmental stress given the agricultural and domestic water developments that have been instituted.

The effects of large-scale afforestation and climate change on water allocation in the Macquarie River catchment, NSW, Australia

Widespread afforestation has been proposed as one means of addressing the increasing dryland and stream salinity problem in Australia. However, modelling results presented here suggest that large-scale tree planting will substantially reduce river flows and impose costs on downstream water users if planted in areas of high runoff yield. Streamflow reductions in the Macquarie River, NSW, Australia are estimated for a number of tree planting scenarios and global warming forecasts. The modelling framework includes the Sacramento rainfall-runoff model and IQQM, a streamflow routing tool, as well as various global climate model outputs from which daily rainfall and potential evaporation data files have been generated in OzClim, a climate scenario generator. For a 10% increase in tree cover in the headwaters of the Macquarie, we estimate a 17% reduction in inflows to Burrendong Dam. The drying trend for a mid-range scenario of regional rainfall and potential evaporation caused by a global warming of 0·5°C may cause an additional 5% reduction in 2030. These flow reductions will decrease the frequency of bird-breeding events in Macquarie Marshes (a RAMSAR protected wetland) and reduce the security of supply to irrigation areas downstream. Inter-decadal climate variability is predicted to have a very significant influence on catchment hydrologic behaviour. A further 20% reduction in flows from the long-term historical mean is possible, should we move into an extended period of below average rainfall years, such as occurred in eastern Australia between 1890 and 1948. Because current consumptive water use is largely adapted to the wetter conditions of post 1949, a return to prolonged dry periods would cause significant environmental stress given the agricultural and domestic water developments that have been instituted.

カムチャツカ半島の近年の氷河質量収支変動と気候変動復元

More than 400 glaciers exist in the mountains of Kamchatka Peninsula and they constitute the southern boundary of present-day glacierization along the eastern coast of the Eurasian continent. The mass balances of the glaciers are characterized by decadal and interdecadal oscillations, and they are closely related to those observed in the glaciers of Pacific North America. A negative relation was also found for the net accumulation timeseries reconstructed by ice cores from Ushkovsky Volcano, Kamchatka, and Mt. Logan, Canada, for the last 170 years. Because the oscillations of the net accumulation rate and the average annual δ 18O reconstructed from Ushkovsky-ice-core seem to be closely correlated with the so-called Pacific Decadal Oscillation (PDO) Index, it was suggested that the mass balances of the glaciers at both sides of the North Pacific had been affected not only by global warming trends but also by the interdecadal climate variability that had dominantly been occurring over the North Pacific.