Assessing regression‐based statistical approaches for downscaling precipitation over North America          下载免费PDF全文

Jie Chen  François P. Brissette  Robert Leconte 《水文研究》2014,28(9):3482-3504

This paper assesses linear regression‐based methods in downscaling daily precipitation from the general circulation model (GCM) scale to a regional climate model (RCM) scale (45‐ and 15‐km grids) and down to a station scale across North America. Traditional downscaling experiments (linking reanalysis/dynamical model predictors to station precipitation) as well as nontraditional experiments such as predicting dynamic model precipitation from larger‐scale dynamic model predictors or downscaling dynamic model precipitation from predictors at the same scale are conducted. The latter experiments were performed to address predictability limit and scale issues. The results showed that the downscaling of daily precipitation occurrence was rarely successful at all scales, although results did constantly improve with the increased resolution of climate models. The explained variances for downscaled precipitation amounts at the station scales were low, and they became progressively better when using predictors from a higher‐resolution climate model, thus showing a clear advantage in using predictors from RCMs driven by reanalysis at its boundaries, instead of directly using reanalysis data. The low percentage of explained variances resulted in considerable underestimation of daily precipitation mean and standard deviation. Although downscaling GCM precipitation from GCM predictors (or RCM precipitation from RCM predictors) cannot really be considered downscaling, as there is no change in scale, the exercise yields interesting information as to the limit in predictive ability at the station scale. This was especially clear at the GCM scale, where the inability of downscaling GCM precipitation from GCM predictors demonstrates that GCM precipitation‐generating processes are largely at the subgrid scale (especially so for convective events), thus indicating that downscaling precipitation at the station scale from GCM scale is unlikely to be successful. Although results became better at the RCM scale, the results indicate that, overall, regression‐based approaches did not perform well in downscaling precipitation over North America. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Preservation of Re‐Os isotope signatures in pyrite throughout low‐T,high‐P eclogite facies metamorphism     

David van Acken  Wen Su  Jun Gao  Robert A. Creaser 《地学学报》2014,26(5):402-407

Pyrite in LT–HP eclogites from the western Tianshan orogenic belt yields a Re‐Os age of 378.1 ± 8.9 Ma, which is 30–70 Ma older than ages previously obtained for the same rocks using the Rb–Sr, Sm–Nd, Ar–Ar, U–Pb, and Lu–Hf isotope systems. The Tianshan LT–HP eclogite experienced temperatures of up to ~570 °C combined with pressures of up to 2.1 GPa during metamorphism. These conditions are below the transition of pyrite to pyrrhotite, which defines both pyrite stability and possibly its closure temperature for Re‐Os. Pyrite can preserve Re‐Os signatures through eclogite facies peak metamorphic conditions, and thus allow determination of the formation age of pyrite in the protolith.  相似文献   

Trends and multi‐annual variability of water temperatures in the river Danube,Serbia          下载免费PDF全文

Biljana Basarin  Tin Lukić  Dragoslav Pavić  Robert L. Wilby 《水文研究》2016,30(18):3315-3329

The relationship between air (Ta) and water temperature (Tw) is very important because it shows how the temperature of a water body might respond to future changes in surface Ta. Mean monthly Tw records of three gauging stations (Bezdan, Bogojevo i Veliko Gradi?te) were analysed alongside mean monthly discharge (Q) for the same stations. Additionally, Ta series from two meteorological stations (Sombor and Veliko Gradi?te) were correlated with Tw variations over the period 1950–2012. Locally weighted scatter point smoothing (LOWESS) was used to investigate long‐term trends in the raw data, alongside the Mann–Kendall (MK) trend test. Trend significance was established using Yue–Pilon's pre‐whitening approaches to determine trends in climate data. Also, the rescaled adjusted partial sums (RAPS) method was used to detect dates of possible changes in the time series. Statistically significant warming trends were observed for annual and seasonal minimum and maximum Tw at all investigated sites. The strongest warming was observed at Bogojevo gauging station for seasonal maximum Tw, with +0.05 °C per year on average. RAPS established that the trend began in the 1980s. This behaviour is linked to climate patterns in the North and East Atlantic which determine the amount of heat advected onto mainland Europe. Statistically significant correlations were found for all Tw on an annual basis. Overall, the strongest correlations (p < 0.01) between Tw residuals and the North Atlantic Oscillation (NAO) were recorded for the winter period. These findings suggest possible predictability of Tw over seasonal time‐scales. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

Quantification of river water infiltration in shallow aquifers using acesulfame and anthropogenic gadolinium          下载免费PDF全文

Andrea Bichler  Christian Muellegger  Robert Brünjes  Thilo Hofmann 《水文研究》2016,30(11):1742-1756

This study has investigated the use of the artificial sweetener acesulfame and the magnetic resonance imaging contrast agent gadolinium as quantitative tracers for river water infiltration into shallow groundwater. The influence of a river on alluvial groundwater in a subalpine catchment in western Europe has been assessed using the ‘classical’ hydrochemical tracer chloride and the trace contaminants acesulfame and anthropogenic gadolinium. Mixing ratios for riverine bank filtrate with ambient groundwater and the uncertainties associated with the temporal and spatial tracer variability were calculated using acesulfame and gadolinium and compared with those obtained using chloride. The temporal variability of tracer concentrations in river water of gadolinium (standard deviation SD: 63%) and acesulfame (SD: 71%) both exceeded that of chloride (SD: 27%), and this was identified as the main source of uncertainty in the mixing analysis. Similar spatial distributions were detected in the groundwater for chloride and gadolinium, but not for acesulfame. Mixing analyses using acesulfame resulted in calculated mixing ratios that differed from those obtained using gadolinium and chloride by up to 83% and 92%, respectively. At the investigated site, which had oxic conditions and moderate temperatures, acesulfame was found to be a less reliable tracer than either gadolinium or chloride, probably because of natural attenuation and input from other sources. There was no statistically significant difference between the mixing ratios obtained using chloride or gadolinium, the mixing ratios obtained using gadolinium were 40–50% lower than those obtained using chloride. This is mainly due to a bias of the mean gadolinium concentration in river water towards higher values. In view of the uncertainties of the two tracers, neither could be preferred over the other for the quantification of bank filtrate in groundwater. At this specific site gadolinium was able to reliably identify river water infiltration and was a more precise tracer than chloride at low mixing ratios (<20%), because of the exclusive occurrence of gadolinium in river water and its high dynamic range. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

Mapping climate change-caused health risk for integrated city resilience modeling     

Amin M. Owrangi  Robert Lannigan  Slobodan P. Simonovic 《Natural Hazards》2015,77(1):67-88

  相似文献   

Conductive cooling of spherical bodies with emphasis on the Earth          下载免费PDF全文

Robert E. Criss  Anne M. Hofmeister 《地学学报》2016,28(2):101-109

To explore planetary evolution, we provide conductive cooling profiles that account for planet size, phonon diffusivity and various internal heating scenarios. Our new analytical solution for simple cooling of spheres reveals that heat is removed from only Earth's outermost ~1000 km over geological time. Numerical models with decaying heat production show that any upward concentration of radionuclides causes high temperatures at shallow depths, forcing interior temperatures to increase with time while producing a thermal gradient that forbids lower mantle convection. Hence, differentiation drives upper mantle magmatism and tectonics, leaving a quiescent but hot deep interior, while slowly melting the core.  相似文献   

Soil paludification and Sphagnum bog initiation: the influence of indurated podzolic soil and fire     

Alice Schaffhauser  Serge Payette  Michelle Garneau  Élisabeth C. Robert 《Boreas: An International Journal of Quaternary Research》2017,46(3):428-441

The initiation and growth of boreal peatlands developed on well‐drained, sandy landforms are closely associated with podzolic soil paludification processes. The origin of Sphagnum bogs extending on large deltaic plains was examined to test the hypothesis of the dual impact of indurated (ortstein) podzols and fire on forest soil paludification and concurrent peatland initiation and expansion. Mineral soil, basal organic matter and peat monoliths were sampled for soil and macrofossil analyses along an 800‐m toposequence starting from a mixed‐wood boreal forest to a Sphagnum bog (Lebel bog, eastern Quebec, Canada), and ending at a peat dome in the thickest section of the peatland. Mineral soils along the toposequence are ortstein humo‐ferric podzols distributed in the forest environment and beneath Sphagnum peat in the bog, except at the peat dome. Initial peatland growth occurred c. 6000 cal. a BP. Soil paludification coincided with the cessation of fire occurrence as recorded in the organic and mineral layers preceding Sphagnum expansion. Unlike most temperate and boreal raised bogs, the Sphagnum bog developed directly from a forest environment without passing through a transitional fen stage. Conifer forests regenerated successively after several fires between 4200 and 1600 cal. a BP before bog expansion. Pre‐bog forests were composed of fire‐prone black spruce (Picea mariana) and jack pine (Pinus banksiana) trees, and ericaceous species. Given the distribution and thickness of ortstein horizons progressively decreasing and disappearing towards the peatland dome, growth and expansion of the Sphagnum bog was not caused by soil induration processes, which could have potentially impeded vertical and horizontal drainage. The development of indurated podzols outside and several hundred metres inside the peatland preceded the initiation and expansion of the Sphagnum bog. Cessation of fire activity appears to be a key factor facilitating the lateral expansion of the Sphagnum bog under wet soil conditions.  相似文献   

Holocene survival of the wild horse in Europe: a matter of open landscape?     

Robert S. Sommer  Norbert Benecke  Lembi Lõugas  Oliver Nelle  Ulrich Schmölcke 《第四纪科学杂志》2011,26(8):805-812

The wild horse Equus ferus was one of the most frequent species of the Late Pleistocene large ungulate fauna in Eurasia and played an important role in the subsistence of human groups, especially at the end the Late Glacial. It is frequently assumed that E. ferus became extinct in Europe at the beginning of the Holocene because of the development of woodlands and loss of open habitats. Because of its preference for open habitats and in spite of its adaptability, the appearance or disappearance of the wild horse could therefore be a suitable palaeoecological indicator for the opening of the Holocene primeval woodlands. We revised the dating and reliability of the subfossil record and dated several bones by atomic mass spectrometry ¹⁴C dating. From the beginning of the Holocene (9600 cal a BC) to the end of the Atlantic Period (3750 cal a BC) there are 207 archaeological sites with wild horse records available in Europe. E. ferus survived the Pleistocene Holocene transition in Europe, but the spatiotemporal dynamics of populations fluctuated remarkably in the early and middle Holocene. Small and sparse populations increasingly became extinct during the early Holocene, until between 7100 and 5500 cal a BC the wild horse was almost absent in central parts of the European Lowlands. Particular conditions in natural open patches in the canopy forests, chalklands and floodplains may have maintained the local survival of the horse in some regions of the Lowlands, however. In the Late Atlantic, between 5500 and 3750 cal a BC the range of the wild horse was again extended. It re‐immigrated into central and western Europe, probably as a consequence of increasing landscape opening by Neolithic peoples. The data presented here may be a valuable part of the debate on the degree of openness of the early and middle Holocene landscape. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

The British Devonian Crinoidea: Part 1, Introduction and Camerata by Stephen K. Donovan and Fiona E. Fearnhead. Monograph of the Palaeontographical Society,London, 168 (no. 643), 2014. No. of pages: 55+viii. Price: UK£135‐00. ISSN 0269‐3445 (paperback).     

Jeffrey Robert Thompson 《Geological Journal》2015,50(4):550-551

  相似文献   

Modelling the influences of climate change-associated sea-level rise and socioeconomic development on future storm surge mortality     

Simon J. Lloyd  R. Sari Kovats  Zaid Chalabi  Sally Brown  Robert J. Nicholls 《Climatic change》2016,134(3):441-455

  相似文献