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Year-to-year Variability (year-to-year + variability)
Selected AbstractsTemperature-dependent stock-recruitment model for walleye pollock (Theragra chalcogramma) around northern JapanFISHERIES OCEANOGRAPHY, Issue 6 2007TETSUICHIRO FUNAMOTO Abstract Changes in fish year-class strength have been attributed to year-to-year variability in environmental conditions and spawning stock biomass (SSB). In particular, sea temperature has been shown to be linked to fish recruitment. In the present study, I examined the relationship between sea surface temperature (SST), SSB and recruitment for two stocks of walleye pollock (Theragra chalcogramma) around northern Japan [Japanese Pacific stock (JPS) and northern Japan Sea stock (JSS)] using a temperature-dependent stock-recruitment model (TDSRM). The recruitment fluctuation of JPS was successfully reproduced by the TDSRM with February and April SSTs, and February SST was a better environmental predictor than April SST. In addition, the JPS recruitment was positively related to February SST and negatively to April SST. The JSS recruitment modeled by the TDSRM incorporating February SST was also consistent with the observation, whereas the relationship between recruitment and February SST was negative, that is the opposite trend to JPS. These findings suggest that SST in February is important as a predictor of recruitment for both stocks, and that higher and lower SSTs in February act favorably on the recruitment of JPS and JSS respectively. Furthermore, Ricker-type TDSRM was not selected for either of the stocks, suggesting that the strong density-dependent effect as in the Ricker model does not exist for JPS and JSS. I formulate hypotheses to explain the links between SST and recruitment, and note that these relationships should be considered in any future attempts to understand the recruitment dynamics of JPS and JSS. [source] Evaluation of six process-based forest growth models using eddy-covariance measurements of CO2 and H2O fluxes at six forest sites in EuropeGLOBAL CHANGE BIOLOGY, Issue 3 2002K. Kramer Abstract Reliable models are required to assess the impacts of climate change on forest ecosystems. Precise and independent data are essential to assess this accuracy. The flux measurements collected by the EUROFLUX project over a wide range of forest types and climatic regions in Europe allow a critical testing of the process-based models which were developed in the LTEEF project. The ECOCRAFT project complements this with a wealth of independent plant physiological measurements. Thus, it was aimed in this study to test six process-based forest growth models against the flux measurements of six European forest types, taking advantage of a large database with plant physiological parameters. The reliability of both the flux data and parameter values itself was not under discussion in this study. The data provided by the researchers of the EUROFLUX sites, possibly with local corrections, were used with a minor gap-filling procedure to avoid the loss of many days with observations. The model performance is discussed based on their accuracy, generality and realism. Accuracy was evaluated based on the goodness-of-fit with observed values of daily net ecosystem exchange, gross primary production and ecosystem respiration (gC m,2 d,1), and transpiration (kg H2O m,2 d,1). Moreover, accuracy was also evaluated based on systematic and unsystematic errors. Generality was characterized by the applicability of the models to different European forest ecosystems. Reality was evaluated by comparing the modelled and observed responses of gross primary production, ecosystem respiration to radiation and temperature. The results indicated that: Accuracy. All models showed similar high correlation with the measured carbon flux data, and also low systematic and unsystematic prediction errors at one or more sites of flux measurements. The results were similar in the case of several models when the water fluxes were considered. Most models fulfilled the criteria of sufficient accuracy for the ability to predict the carbon and water exchange between forests and the atmosphere. Generality. Three models of six could be applied for both deciduous and coniferous forests. Furthermore, four models were applied both for boreal and temperate conditions. However, no severe water-limited conditions were encountered, and no year-to-year variability could be tested. Realism. Most models fulfil the criterion of realism that the relationships between the modelled phenomena (carbon and water exchange) and environment are described causally. Again several of the models were able to reproduce the responses of measurable variables such as gross primary production (GPP), ecosystem respiration and transpiration to environmental driving factors such as radiation and temperature. Stomatal conductance appears to be the most critical process causing differences in predicted fluxes of carbon and water between those models that accurately describe the annual totals of GPP, ecosystem respiration and transpiration. As a conclusion, several process-based models are available that produce accurate estimates of carbon and water fluxes at several forest sites of Europe. This considerable accuracy fulfils one requirement of models to be able to predict the impacts of climate change on the carbon balance of European forests. However, the generality of the models should be further evaluated by expanding the range of testing over both time and space. In addition, differences in behaviour between models at the process level indicate requirement of further model testing, with special emphasis on modelling stomatal conductance realistically. [source] Application of the distributed hydrology soil vegetation model to Redfish Creek, British Columbia: model evaluation using internal catchment dataHYDROLOGICAL PROCESSES, Issue 2 2003Andrew Whitaker Abstract The Distributed Hydrology Soil Vegetation Model is applied to the Redfish Creek catchment to investigate the suitability of this model for simulation of forested mountainous watersheds in interior British Columbia and other high-latitude and high-altitude areas. On-site meteorological data and GIS information on terrain parameters, forest cover, and soil cover are used to specify model input. A stepwise approach is taken in calibrating the model, in which snow accumulation and melt parameters for clear-cut and forested areas were optimized independent of runoff production parameters. The calibrated model performs well in reproducing year-to-year variability in the outflow hydrograph, including peak flows. In the subsequent model performance evaluation for simulation of catchment processes, emphasis is put on elevation and temporal differences in snow accumulation and melt, spatial patterns of snowline retreat, water table depth, and internal runoff generation, using internal catchment data as much as possible. Although the overall model performance based on these criteria is found to be good, some issues regarding the simulation of internal catchment processes remain. These issues are related to the distribution of meteorological variables over the catchment and a lack of information on spatial variability in soil properties and soil saturation patterns. Present data limitations for testing internal model accuracy serve to guide future data collection at Redfish Creek. This study also illustrates the challenges that need to be overcome before distributed physically based hydrologic models can be used for simulating catchments with fewer data resources. Copyright © 2003 John Wiley & Sons, Ltd. [source] On the interannual wintertime rainfall variability in the Southern AndesINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 5 2010M. H. González Abstract The paper concentrates on the analysis of the interannual variability of wintertime rainfall in the Southern Andes. Besides the socio-economic relevance of the region, mainly associated with hydroelectric energy production, the study of the climate variability in that area has not received as much attention as others along the Andes. The results show that winter rainfall explains the largest percentage of regional total annuals. A principal component analysis (PCA) of the winter rainfall anomalies showed that the regional year-to-year variability is mostly explained by three leading patterns. While one of them is significantly associated with both the El Niño Southern Oscillation (ENSO), and the Southern Annular Mode (SAM), the other two patterns are significantly related to interannual changes of the sea surface temperature (SST) anomalies in the tropical Indian Ocean. Specifically, changes in the ocean surface conditions at both tropical basins induce in the atmospheric circulation the generation of Rossby wave trains that extend along the South Pacific towards South America, and alter the circulation at the region under study. The relationship between variability in the Indian Ocean and the Andes climate variability has not been previously addressed. Therefore, this result makes a significant contribution to the identification of the sources of predictability in South America with relevant consequences for future applications in seasonal predictions. Copyright © 2009 Royal Meteorological Society [source] Australian drought: the interference of multi-spectral global standing modes and travelling wavesINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 6 2003Warren B. White Abstract Extreme drought has devastated the flora, fauna, and regional economy in rangeland grazing districts over Australia for 3,5 years duration every 20 to 30 years throughout the 20th century. We investigate the source of drought occurring in five example grazing districts in eastern and central Australia. We find year-to-year variability in grazing district rainfall (GDR) during the summer rainy season (November to March) composed of quasi-biennial, interannual, quasi-decadal, and interdecadal signals from 1900 to 1999. However, the longer period signals dominate, accounting for the interdecadal quasi-periodicity of the drought/flood cycle. We find these GDR signals associated with corresponding global standing modes and travelling waves in covarying sea-surface temperature (SST) and sea-level pressure (SLP) anomalies. These global SST/SLP modes/waves influence the GDR signals by altering the troposphere moisture flux converging onto the grazing districts from regional tropical and extra-tropical oceanic source regions. We construct statistical models to determine whether the evolution of these global SST/SLP modes/waves over the oceanic source regions can hindcast corresponding GDR signals from one year to the next. When these models allow for modulation of the modes/waves, they hindcast ,1/3 of the variance in the GDR indices at 1 year lead, including the drought episodes. We find drought resulting from the constructive interference of the dry phases of the quasi-decadal and interdecadal global SST/SLP modes/waves, accompanied by a weakening of year-to-year variability associated with either weak quasi-biennial and interannual modes/waves or their destructive interference. Copyright © 2003 Royal Meteorological Society [source] Freezing height distribution in the tropicsINTERNATIONAL JOURNAL OF SATELLITE COMMUNICATIONS AND NETWORKING, Issue 6 2003Merhala Thurai Abstract The calculation of fade margins required to meet the user-specified availability criteria needs to take into consideration a number of meteorological factors specific to the earth-station location. One such factor is the annual average of the freezing level height. Information on this height is available in ITU-R Recommendation P. 839-3, which provides contours that are generated on a 1.5° by 1.5° latitude by longitude resolution grid. This paper compares these heights with the bright-band heights (BBH) obtained from the precipitation radar on-board the TRMM (Tropical Rainfall Measuring Mission) satellite. Four years of TRMM radar data have been analysed, and their averages are compared within the latitude range covered by the satellite orbit (35°N to 35°S). Comparisons show that the radar bright-band heights typically occur 300 m below the 0°C isotherm heights. However, results also indicate that this difference may be latitude dependent. Also examined are the year-to-year variability and the seasonal variation. In the former case, only 1998 showed BBH values which are somewhat higher in tropical regions, this year having had one of the strongest El Niño events recorded. In the latter case, results show significant seasonal variation, becoming more pronounced at higher latitudes. Copyright © 2003 John Wiley & Sons, Ltd. [source] Earlywood vessel size of oak as a potential proxy for spring precipitation in mesic sitesJOURNAL OF BIOGEOGRAPHY, Issue 12 2008Patrick Fonti Abstract Aim, In this study, we evaluate the importance of the mean earlywood vessel size of oaks as a potential proxy for climate in mesic areas. Location, The study was conducted in Switzerland at three forest sites dominated by oak (Quercus petraea and Q. pubescens). The three sites were in different climatic zones, varying mainly in terms of precipitation regime. Methods, Three 50-year-long site chronologies of mean earlywood vessel size and tree-ring widths were obtained at each site and related to monthly meteorological records in order to identify the main variables controlling growth. The responses of mean vessel size to climate were compared with those of the width variables to evaluate the potential climatic information recorded by the earlywood vessels. Results, The results show that the mean vessel size has a different and stronger response to climate than ring-width variables, although its common signal and year-to-year variability are lower. This response is better in particular at mesic sites, where it is linked to precipitation during spring, i.e. at the time of vessel formation, and is probably related to the occurrence of only a few processes controlling vessel growth, whereas radial increment is controlled by multiple and varying factors. Main conclusions, The mean earlywood vessel size of oak appears to be a promising proxy for future climate reconstructions of mesic sites, where radial growth is not controlled by a single limiting factor. [source] Intra- and Interannual Vegetation Change: Implications for Long-Term ResearchRESTORATION ECOLOGY, Issue 1 2008Julie E. Korb Abstract To draw reliable conclusions from forest restoration experiments, it is important that long-term measurements be repeatable or year-to-year variability may interfere with the correct interpretation of treatment effects. We used permanent plots in a long-term restoration study in southwestern Colorado to measure herbaceous and shrub vegetation at three dates within a single year (June, July, and August), and between years (2003 and 2005), on untreated control plots in a warm, dry mixed conifer forest. Growing season precipitation patterns were similar between 2003 and 2005, so differences in vegetation should be related primarily to differences in the sampling month. Significant indicator species for each sampling month were present within a single year (2005), primarily reflecting early-season annuals. We found no significant differences for total species abundance (2005). Species richness, abundance, and indicator species were significantly different between years for different sampling months indicating that sampling should be conducted within a similar time frame to avoid detecting differences that are not due to treatment effects or variations in year-to-year climate. These findings have implications for long-term research studies where the objectives are to detect changes over time in response to treatments, climate variation, and natural processes. Long-term sampling should occur within a similar phenological time frame each year over a short amount of time and should be based on the following criteria: (1) the sampling period is congruent with research objectives such as detecting rare species or peak understory abundance and (2) the sampling period is feasible in regard to personnel and financial constraints. [source] Ensemble simulations of the cold European winter of 2005-2006THE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 636 2008A. A. Scaife Abstract There is only limited understanding of the processes driving year-to-year variability in European winter climate and the skill of seasonal forecasts for Europe in winter is generally low. The winter of 2005-2006 is a useful case-study because it was the coldest winter in large parts of western Europe for over a decade, and the coldest in central England since 1995-1996. Here, we present results of experiments with a range of general circulation models to investigate the importance of both the Atlantic Ocean and stratospheric circulation in producing the unusually cold winter of 2005-2006. We use models with different combinations of horizontal and stratospheric vertical resolution, allowing the sensitivity of the response to model formulation to be tested. The response to Atlantic sea-surface temperature (SST) anomalies is improved in a more recent model with higher horizontal resolution. The results show that both Atlantic SSTs and the January 2006 sudden stratospheric warming are likely to have contributed to the cold 2005-2006 European winter. © Crown Copyright 2008. Reproduced with the permission of HMSO. Published by John Wiley & Sons Ltd. [source] A new fast stratospheric ozone chemistry scheme in an intermediate general-circulation model.THE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 610 2005I: Description, evaluation Abstract Simulation of future climate-composition changes requires simulations of coupled dynamical-radiative-chemical models of many decades in length. Yet, to assure the generality of the simulation's results against uncertainties in emissions, unforced year-to-year variability and dependence on initial conditions, it is necessary to repeat them a significant number of times. The computational cost of such an exercise is still too large when using complex three-dimensional coupled models. We introduce in this paper a computationally efficient chemical scheme, the FAst STratospheric Ozone Chemistry (FASTOC) scheme, which has advantages over many existing fast methods, as it does not rely on relaxation to assumed conditions, does not rely on tuning parameters, and does not rely on linearization approximations. The scheme is nevertheless three orders of magnitude faster than a stiff kinetic equations solver. Part I of the paper gives a detailed description of the FASTOC model and some performance evaluations when incorporated in a general-circulation model (GCM). In Part II, the FASTOC model, coupled to a GCM, is specifically applied to study the impact of climate,chemistry interactions on stratospheric ozone in the middle of the twenty-first century. Copyright © 2005 Royal Meteorological Society [source] Geospatial identification of optimal straw-to-energy conversion sites in the Pacific Northwest,BIOFUELS, BIOPRODUCTS AND BIOREFINING, Issue 4 2010George W. Mueller-Warrant Abstract Previous attempts to develop straw-based bioenergy systems have stumbled at costs of transporting this low-density resource to large-scale, centralized facilities. Success in developing small-scale, distributed technologies (e.g. syngas or pyrolysis bio-oil) that reduce these costs will depend on closely matching system requirements to spatial distribution of available straw. We analyzed straw distribution in the Pacific Northwest to identify optimal sites for facilities ranging from a pilot plant currently under development to larger ones of previous studies. Sites for plants with capacities of 1, 10, or 100 million kg straw y -1 were identified using a ,lowest-hanging-fruit' iterative siting process in which the location of maximum density of straw over an appropriately sized neighborhood was identified, distance from that point necessary to include desired quantity of straw measured, straw assigned to that plant removed from the raster, and the process repeated until all available straw had been assigned. Compared to K-means, our new method sited the first 44% of plants at superior locations in terms of local straw density (i.e. lower transportation costs) and the next 39% at equivalent locations. K-means produced better locations for the final 17% of plants along with superior average results. For the smallest facilities at locations defined by 3-year average available straw density, 1.2 km buffers were adequate to provide straw for the first 10% of plants, with twice that distance sufficient for the first 70%. For the largest plants, 12 km buffers satisfied the first 10% of plants, with 24 km buffers satisfying the first 60%. Buffer distances exceeded 68 km for the final 20% of the largest plants. Siting patterns for the smallest plants were more evenly distributed than larger ones, suggesting that farm-scale technology may be more politically appealing. Smaller plants, however, suffered from higher year-to-year variability in straw supply within pre-defined distances. Published in 2010 by John Wiley & Sons, Ltd. [source] | ||||||||||||||||