Temporary Migration and the Labour Market in Australia     

Graeme Hugo 《The Australian geographer》2006,37(2):211-231

Australia's labour market is most influenced by international migration among OECD nations, but Australian research on this issue focuses almost exclusively on permanent settlement migration. The present paper, however, demonstrates that non-permanent migration has an important impact on the Australian labour market, although such migrants are not included in standard data collections and research on migrants and the labour market. A number of data sources are utilised to estimate the labour-market impact of Working Holiday Makers, Temporary Business Entrants, Overseas Students, and New Zealand temporary migrants. It is shown that their impact is equivalent to more than 400?000 full-time jobs. However, the effect is magnified because it is concentrated in particular sectors of the economy and in particular communities within Australia. A number of issues relating to temporary migration are discussed, including the nature of its relationship with permanent migration, the effects on job training, and the implications for regional development.  相似文献   

Phreatic Surface in Island Aquifers with Regular Geometry and Time-Independent Recharge and Pumping     

Hugo A. Loáiciga 《Mathematical Geosciences》2008,40(2):199-211

The equation of groundwater flow in marine island aquifers in which there is time-independent, spatially-variable recharge and pumping is solved in closed form for rectangular, circular, and elliptical island geometries. The solution of the groundwater flow equation is expressed in terms of the elevation of the phreatic surface within the flow domain. The depth of the seawater-freshwater interface below mean sea level follows from the Dupuit–Ghyben–Herzberg relation. The method of solution presented in this work relies on expanding the hydraulic head and forcing function (recharge and groundwater extraction) as Fourier series that transforms the two-dimensional Poisson-type flow equations into second-order ordinary differential equations solvable using classical theory. The important case of constant recharge (without groundwater extraction) leads to solutions in which the hydraulic head is expressible as the product of a flow factor equal to the squared root of the ratio of recharge over hydraulic conductivity times a geometric factor involving island shape parameters and flow boundary conditions. Estimability conditions for the hydraulic conductivity are derived for the cases of constant recharge and spatially variable recharge with pumping.  相似文献   

Origins of differences in climate sensitivity, forcing and feedback in climate models     

Mark J. Webb  F. Hugo Lambert  Jonathan M. Gregory 《Climate Dynamics》2013,40(3-4):677-707

We diagnose climate feedback parameters and CO₂ forcing including rapid adjustment in twelve atmosphere/mixed-layer-ocean (“slab”) climate models from the CMIP3/CFMIP-1 project (the AR4 ensemble) and fifteen parameter-perturbed versions of the HadSM3 slab model (the PPE). In both ensembles, differences in climate feedbacks can account for approximately twice as much of the range in climate sensitivity as differences in CO₂ forcing. In the AR4 ensemble, cloud effects can explain the full range of climate sensitivities, and cloud feedback components contribute four times as much as cloud components of CO₂ forcing to the range. Non-cloud feedbacks are required to fully account for the high sensitivities of some models however. The largest contribution to the high sensitivity of HadGEM1 is from a high latitude clear-sky shortwave feedback, and clear-sky longwave feedbacks contribute substantially to the highest sensitivity members of the PPE. Differences in low latitude ocean regions (30°N/S) contribute more to the range than those in mid-latitude oceans (30–55°N/S), low/mid latitude land (55°N/S) or high latitude ocean/land (55–90°N/S), but contributions from these other regions are required to account fully for the higher model sensitivities, for example from land areas in IPSL CM4. Net cloud feedback components over the low latitude oceans sorted into percentile ranges of lower tropospheric stability (LTS) show largest differences among models in stable regions, mainly due to their shortwave components, most of which are positive in spite of increasing LTS. Differences in the mid-stability range are smaller, but cover a larger area, contributing a comparable amount to the range in climate sensitivity. These are strongly anti-correlated with changes in subsidence. Cloud components of CO₂ forcing also show the largest differences in stable regions, and are strongly anticorrelated with changes in estimated inversion strength (EIS). This is qualitatively consistent with what would be expected from observed relationships between EIS and low-level cloud fraction. We identify a number of cases where individual models show unusually strong forcings and feedbacks compared to other members of the ensemble. We encourage modelling groups to investigate unusual model behaviours further with sensitivity experiments. Most of the models fail to correctly reproduce the observed relationships between stability and cloud radiative effect in the subtropics, indicating that there remains considerable room for model improvements in the future.  相似文献   

Topological redundancy and ‘small‐world’ patterns in a food web in a subtropical ecosystem of Brazil          下载免费PDF全文

Hugo Bornatowski  Rodrigo Barreto  Andrés F. Navia  Alberto Ferreira de Amorim 《Marine Ecology》2017,38(2)

According to graph theory, the frequency distribution of trophic interactions within a food web has deep structural implications, as it can highlight the presence of patterns associated with the web and indicate whether the properties of the web are independent of its size. A hypothesis is that ‘small‐world’ food webs are sensitive to the loss of species with the highest values. Therefore, the present work aimed to evaluate the degree to which a subtropical food web in Southern Brazil displays small‐world patterns and their resistance. As part of the assessment, we evaluated the topological redundancy values of species in the food web and then we simulated the exclusion of these species (such as sharks and sea birds), and also the exclusion of high centrality species (such as squids Loligo sp., portunid swimming crabs and the cutlassfish Trichiurus lepturus). The food web showed a ‘broad‐scale’ distribution of connections by node, and a small‐world pattern. As expected, a simplification of the network was observed after elimination of some species with high centrality. However, the food web was resistant to the loss of species with low topological redundancy, probably because these species occupy a high trophic level and do not participate in lots of routes within the food web. We highlight however, the importance of the application of multiple analyses to evaluate the importance of components in food webs, and fisheries management plans should consider both species of high centrality values and species with low topological redundancy.  相似文献   

Multicell Model for Ground Water Recharge Analysis: The Ibi River Basin, Japan     

Takeshi Sato  Junichi Kojima  Hugo A. Loaiciga 《Ground water》1999,37(1):58-69

  相似文献   

Can climate variability information constrain a hydrological model for an ungauged Costa Rican catchment?          下载免费PDF全文

Beatriz Quesada‐Montano  Ida K. Westerberg  Diana Fuentes‐Andino  Hugo G. Hidalgo  Sven Halldin 《水文研究》2018,32(6):830-846

Long‐term hydrological data are key to understanding catchment behaviour and for decision making within water management and planning. Given the lack of observed data in many regions worldwide, such as Central America, hydrological models are an alternative for reproducing historical streamflow series. Additional types of information—to locally observed discharge—can be used to constrain model parameter uncertainty for ungauged catchments. Given the strong influence that climatic large‐scale processes exert on streamflow variability in the Central American region, we explored the use of climate variability knowledge as process constraints to constrain the simulated discharge uncertainty for a Costa Rican catchment, assumed to be ungauged. To reduce model uncertainty, we first rejected parameter relationships that disagreed with our understanding of the system. Then, based on this reduced parameter space, we applied the climate‐based process constraints at long‐term, inter‐annual, and intra‐annual timescales. In the first step, we reduced the initial number of parameters by 52%, and then, we further reduced the number of parameters by 3% with the climate constraints. Finally, we compared the climate‐based constraints with a constraint based on global maps of low‐flow statistics. This latter constraint proved to be more restrictive than those based on climate variability (further reducing the number of parameters by 66% compared with 3%). Even so, the climate‐based constraints rejected inconsistent model simulations that were not rejected by the low‐flow statistics constraint. When taken all together, the constraints produced constrained simulation uncertainty bands, and the median simulated discharge followed the observed time series to a similar level as an optimized model. All the constraints were found useful in constraining model uncertainty for an—assumed to be—ungauged basin. This shows that our method is promising for modelling long‐term flow data for ungauged catchments on the Pacific side of Central America and that similar methods can be developed for ungauged basins in other regions where climate variability exerts a strong control on streamflow variability.  相似文献   

Semi-empirical prediction method for monthly precipitation prediction based on environmental factors and comparison with stochastic and machine learning models     

Huihui Zhang  Hugo A. Loáiciga  Fu Ren  Da Ha 《水文科学杂志》2020,65(11):1928-1942

ABSTRACT

Precipitation prediction is central in hydrology and water resources planning and management. This paper introduces a semi-empirical predictive model to predict monthly precipitation and compares its predictive skill with those of machine learning (ML) methods. The stochastic method presented herein estimates monthly precipitation with one-step-ahead prediction properties. The ML predictive skill of the algorithms is evaluated by predicting monthly precipitation relying on the statistical association between precipitation and environmental and topographic factors. The semi-empirical predictive model features non-negative matrix factorization (NMF) for investigating the influence of multiple predictor variables on precipitation. The semi-empirical predictive model’s parameters are optimized with the hybrid genetic algorithm (GA) and Levenberg-Marquardt algorithm (LM), or GALMA, yielding a validated model with high predictive skill. The methodologies are illustrated with data from Hubei Province, China, which comprise 27 meteorological station datasets from 1988–2017. The empirical results provide valuable insights for developing semi-empirical rainfall prediction models.  相似文献   

Transportation mode-based segmentation and classification of movement trajectories     

Filip Biljecki  Hugo Ledoux  Peter van Oosterom 《International journal of geographical information science》2013,27(2):385-407

The knowledge of the transportation mode used by humans (e.g. bicycle, on foot, car and train) is critical for travel behaviour research, transport planning and traffic management. Nowadays, new technologies such as the Global Positioning System have replaced traditional survey methods (paper diaries, telephone) because they are more accurate and problems such as under reporting are avoided. However, although the movement data collected (timestamped positions in digital form) have generally high accuracy, they do not contain the transportation mode. We present in this article a new method for segmenting movement data into single-mode segments and for classifying them according to the transportation mode used. Our fully automatic method differs from previous attempts for five reasons: (1) it relies on fuzzy concepts found in expert systems, that is membership functions and certainty factors; (2) it uses OpenStreetMap data to help the segmentation and classification process; (3) we can distinguish between 10 transportation modes (including between tram, bus and car) and propose a hierarchy; (4) it handles data with signal shortages and noise, and other real-life situations; (5) in our implementation, there is a separation between the reasoning and the knowledge, so that users can easily modify the parameters used and add new transportation modes. We have implemented the method and tested it with a 17-million point data set collected in the Netherlands and elsewhere in Europe. The accuracy of the classification with the developed prototype, determined with the comparison of the classified results with the reference data derived from manual classification, is 91.6%.  相似文献   

Trace-element heterogeneity in rutile linked to dislocation structures: Implications for Zr-in-rutile geothermometry     

Rick Verberne  Hugo W. van Schrojenstein Lantman  Steven M. Reddy  Matteo Alvaro  David Wallis  Denis Fougerouse  Antonio Langone  David W. Saxey  William D. A. Rickard 《Journal of Metamorphic Geology》2023,41(1):3-24

The trace-element composition of rutile is commonly used to constrain P–T–t conditions for a wide range of metamorphic systems. However, recent studies have demonstrated the redistribution of trace elements in rutile via high-diffusivity pathways and dislocation-impurity associations related to the formation and evolution of microstructures. Here, we investigate trace-element migration in low-angle boundaries formed by dislocation creep in rutile within an omphacite vein of the Lago di Cignana unit (Western Alps, Italy). Zr-in-rutile thermometry and inclusions of quartz in rutile and of coesite in omphacite constrain the conditions of rutile deformation to around the prograde boundary from high pressure to ultra-high pressure (~2.7 GPa) at temperatures of 500–565°C. Crystal-plastic deformation of a large rutile grain results in low-angle boundaries that generate a total misorientation of ~25°. Dislocations constituting one of these low-angle boundaries are enriched in common and uncommon trace elements, including Fe and Ca, providing evidence for the diffusion and trapping of trace elements along the dislocation cores. The role of dislocation microstructures as fast-diffusion pathways must be evaluated when applying high-resolution analytical procedures as compositional disturbances might lead to erroneous interpretations for Ca and Fe. In contrast, our results indicate a trapping mechanism for Zr.  相似文献