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21.
Sophie Dabo-Niang Leila Hamdad Camille Ternynck Anne-Françoise Yao 《Stochastic Environmental Research and Risk Assessment (SERRA)》2014,28(8):2075-2099
A nonparametric density estimate that incorporates spatial dependency has not been studied in the literature. In this article, we propose a new spatial density estimator that depends on two kernels: one controls the distance between observations while the other controls the spatial dependence structure. The uniform almost sure convergence of the density estimate is established with the rate of convergence. The consistency of the mode of this kernel density is also studied. Then a spatial hierarchical unsupervised clustering algorithm based on the mode estimate is presented. Some simulations as well as an application to the Monsoon Asia Drought Atlas data illustrate the efficiency of our algorithm, and a comparison of the spatial structures of these data detected by the density estimate and clustering algorithm are done. 相似文献
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Biomorphodynamics of alternate bars in a channelized,regulated river: An integrated historical and modelling analysis 
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下载免费PDF全文 Alyssa J. Serlet Angela M. Gurnell Guido Zolezzi Geraldene Wharton Philippe Belleudy Camille Jourdain 《地球表面变化过程与地形》2018,43(9):1739-1756
The development of alternate bars in channelized rivers can be explained theoretically as an instability of the riverbed when the active channel width to depth ratio exceeds a threshold. However, the development of a vegetation cover on the alternate bars of some channelized rivers and its interactions with bar morphology have not been investigated in detail. Our study focused on the co‐evolution of alternate bars and vegetation along a 33 km reach of the Isère River, France. We analysed historical information to investigate the development of alternate bars and their colonization by vegetation within a straightened, embanked river subject to flow regulation, sediment mining, and vegetation management. Over an 80 year period, bar density decreased, bar length increased, and bar mobility slowed. Vegetation encroachment across bar surfaces accompanied these temporal changes and, once established, vegetation cover persisted, shifting the overall system from an unvegetated to a vegetated dynamic equilibrium state. The unvegetated morphodynamics of the impressively regular sequence of alternate bars that developed in the Isère following channelization is consistent with previous theoretical morphodynamic work. However, the apparent triggering dynamics of vegetation colonization needs to be investigated, based on complex biophysical instability processes. If instability related to vegetation colonization is confirmed, further work needs to focus on the relevance of initial conditions for this instability, and on related feedback effects such as how the morphodynamics of bare‐sediment alternate bars may have affected vegetation development and, in turn, how vegetation has created a new dynamic equilibrium state. Copyright © 2018 John Wiley & Sons, Ltd. 相似文献
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Anna Lintern Shuci Liu Camille Minaudo Rémi Dupas Danlu Guo Kefeng Zhang Ulrike Bende-Michl Clément Duvert 《水文研究》2021,35(12):e14423
For effective water quality management and policy development, spatial variability in the mean concentrations and dynamics of riverine water quality needs to be understood. Using water chemistry (calcium, electrical conductivity, nitrate-nitrite, soluble reactive phosphorus, total nitrogen, total phosphorus and total suspended solids) data for up to 578 locations across the Australian continent, we assessed the impact of climate zones (arid, Mediterranean, temperate, subtropical, tropical) on (i) inter-annual mean concentration and (ii) water chemistry dynamics as represented by constituent export regimes (ratio of the coefficients of variation of concentration and discharge) and export patterns (slope of the concentration-discharge relationship). We found that inter-annual mean concentrations vary significantly by climate zones and that spatial variability in water chemistry generally exceeds temporal variability. However, export regimes and patterns are generally consistent across climate zones. This suggests that intrinsic properties of individual constituents rather than catchment properties determine export regimes and patterns. The spatially consistent water chemistry dynamics highlights the potential to predict riverine water quality across the Australian continent, which can support national riverine water quality management and policy development. 相似文献
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Impact of snow variability on the Swiss winter tourism sector: implications in an era of climate change 总被引：1，自引：0，他引：1
Camille Gonseth 《Climatic change》2013,118(2):307-320
An analysis procedure is developed to explore the robustness and overall productivity of reservoir management under plausible assumptions about climate fluctuation and change. Results are presented based on a stylized version of a multi-use reservoir management model adapted from Angat Dam, Philippines. Analysis focuses on October-March, during which climatological inflow declines as the dry season arrives, and reservoir management becomes critical and challenging. Inflow is assumed to be impacted by climate fluctuations representing interannual variation (white noise), decadal to multidecadal variability (MDV, here represented by a stochastic autoregressive process) and global change (GC), here represented by a systematic linear trend in seasonal inflow total over the simulation period of 2008–2047. Stochastic (Monte Carlo) simulations are undertaken to explore reservoir performance. In this way, reservoir reliability and risk of extreme persistent water deficit are assessed in the presence of different combinations and magnitudes of GC and MDV. The effectiveness of dynamic management is then explored as a possible climate change adaptation practice, focusing on reservoir performance in the presence of a 20 % downward inflow trend. In these dynamic management experiments, the October-March water allocation each year is adjusted based on seasonal forecasts and updated climate normals. The results illustrate how, in the near-term, MDV can be as significant as GC in impact for this kind of climate-related problem. The results also illustrate how dynamic management can mitigate the impacts. Overall, this type of analysis can deliver guidance on the expected benefits and risks of different management strategies and climate scenarios. 相似文献
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Late Quaternary histories of two North American desert biomes—C4 grasslands and C3 shrublands—are poorly known despite their sensitivity and potential value in reconstructing summer rains and winter temperatures. Plant macrofossil assemblages from packrat midden series in the northern Chihuahuan Desert show that C4 grasses and annuals typical of desert grassland persisted near their present northern limits throughout the last glacial–interglacial cycle. By contrast, key C3 desert shrubs appeared somewhat abruptly after 5000 cal. yr BP. Bioclimatic envelopes for select C4 and C3 species are mapped to interpret the glacial–interglacial persistence of desert grassland and the mid‐to‐late Holocene expansion of desert shrublands. The envelopes suggest relatively warm Pleistocene temperatures with moist summers allowed for persistence of C4 grasses, whereas winters were probably too cold (or too wet) for C3 desert shrubs. Contrary to climate model results, core processes associated with the North American Monsoon and moisture transport to the northern Chihuahuan Desert remained intact throughout the last glacial–interglacial cycle. Mid‐latitude effects, however, truncated midsummer (July–August) moisture transport north of 35° N. The sudden expansion of desert shrublands after 5000 cal. yr BP may be a threshold response to warmer winters associated with increasing boreal winter insolation, and enhanced El Niño–Southern Oscillation variability. Published in 2006 by John Wiley & Sons, Ltd. 相似文献
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Alan L. Mayo Stephen T. Nelson John H. McBride Camille Durrant Mease David G. Tingey Dan Aubrey 《Natural Hazards》2013,69(1):545-571
At the Midway, Utah, USA fish hatchery, a groundwater development program was conducted to help transition the facility from surface to groundwater in response to contamination by whirling disease, which is caused by a trout parasite. The unconfined aquifer system that provided the hatchery water became infected through the recharge of infected irrigation water obtained from the Provo River. Whirling disease was first discovered in Utah in 1991 at a private fish farm. Infected fish from the farm quickly infected many of Utah’s waterways and infected the hatchery in 2000. Because the parasite completes its life cycle in multiple organisms and can survive for decades in a variety of harsh environments, a comprehensive study of the hydrostratigraphy and hydrodynamics at the hatchery was critical in order to understand the hazard and avoid further contamination. Drilling revealed the presence of a shallow unconfined (surface to 10 m) and two deeper confined aquifer systems (~20–35 m and >40 m bgs). Confinement is related to tufa layers, detected both by drilling and reflection seismology. The tufa layers are associated with past discharge of the thermal system. Vertical leakage is apparent from upward hydraulic head gradients and incrementally increasing unconfined aquifer discharge into downstream on-site drainage canals. High-resolution seismic profiles reveal small-offset faults that provide pathways for upward flow. Analysis of water quality data demonstrates an inverted geochemical gradient in that apparent 14C ages, solute concentrations, and temperatures decrease with depth. The origin of the inverted geochemical gradient is related to mixing of upwelling thermal, high-TDS waters with cold, low-TDS systems several kilometers up-gradient from the hatchery. Thermal upwelling appears to be fault controlled. Up-gradient of the hatchery, near-surface groundwater mixes with a larger proportion of thermal groundwater than does deeper groundwater. As these mixed systems flow toward the hatchery, a major locus of groundwater discharge, they are segregated into confined and unconfined compartments. Our study requires integration of hydrological, geochemical, and geophysical strategies in order to understand a complex natural hazard and thus may serve as a model for other similarly complex hydrological environments. 相似文献
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Pablo Ortega Didier Swingedouw Valérie Masson-Delmotte Camille Risi Bo Vinther Pascal Yiou Robert Vautard Kei Yoshimura 《Climate Dynamics》2014,43(9-10):2585-2605
Greenland ice cores offer seasonal to annual records of δ18O, a proxy for precipitation-weighted temperature, over the last few centuries to millennia. Here, we investigate the regional footprints of the North Atlantic weather regimes on Greenland isotope and climate variability, using a compilation of 22 different shallow ice-cores and the atmospheric pressure conditions from the twentieth century reanalysis (20CR). As a first step we have verified that the leading modes of winter and annual δ18O are well correlated with oceanic (Atlantic multidecadal oscillation) and atmospheric [North Atlantic oscillation (NAO)] indices respectively, and also marginally with external forcings, thus confirming earlier studies. The link between weather regimes and Greenland precipitation, precipitation-weighted temperature and δ18O is further explored by using an isotope simulation from the LMDZ-iso model, where the 3-dimensional wind fields are nudged to those of 20CR. In winter, the NAO+ and NAO? regimes in LMDZ-iso produce the largest isotopic changes over the entire Greenland region, with maximum anomalies in the South. Likewise, the Scandinavian blocking and the Atlantic ridge also show remarkable imprints on isotopic composition over the region. To assess the robustness and model dependency of our findings, a second isotope simulation from the isotopic model is also explored. The percentage of Greenland δ18O variance explained by the ensemble of weather regimes is increased by a factor near two in both LMDZ-iso and IsoGSM when compared to the contribution of the NAO index only. Similarly, weather regimes provide a net gain in the δ18O variance explained of similar magnitude for the whole set of ice core records. Greenland δ18O also appears to be locally affected by the low-frequency variations in the centres of action of the weather regimes, with clearer imprints in the LMDZ-iso simulation. This study opens the possibility for reconstructing past changes in the frequencies of occurrence of the weather regimes, which would rely on the sensitive regions identified here, and the use of additional proxies over the North Atlantic region. 相似文献
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Benjamin W. Abbott Kevin Bishop Jay P. Zarnetske David M. Hannah Rebecca J. Frei Camille Minaudo F.Stuart Chapin Stefan Krause Lafe Conner David Ellison Sarah E. Godsey Stephen Plont Jean Marais Tamara Kolbe Amanda Huebner Tyler Hampton Sen Gu Madeline Buhman Sayedeh Sara Sayedi Ovidiu Ursache Melissa Chapin Kathryn D. Henderson Gilles Pinay 《水文研究》2019,33(23):3046-3052
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Olivine dissolution in molten silicates: An experimental study with application to chondrule formation 下载免费PDF全文
下载免费PDF全文 Mg‐rich olivine is a ubiquitous phase in type I porphyritic chondrules in various classes of chondritic meteorites. The anhedral shape of olivine grains, their size distribution, as well as their poikilitic textures within low‐Ca pyroxene suggest that olivines suffer dissolution during chondrule formation. Owing to a set of high‐temperature experiments (1450–1540 °C) we determined the kinetics of resorption of forsterite in molten silicates, using for the first time X‐ray microtomography. Results indicate that forsterite dissolution in chondrule‐like melts is a very fast process with rates that range from ~5 μm min?1 to ~22 μm min?1. Forsterite dissolution strongly depends on the melt composition, with rates decreasing with increasing the magnesium and/or the silica content of the melt. An empirical model based on forsterite saturation and viscosity of the starting melt composition successfully reproduces the forsteritic olivine dissolution rates as a function of temperature and composition for both our experiments and those of the literature. Application of our results to chondrules could explain the textures of zoned type I chondrules during their formation by gas‐melt interaction. We show that the olivine/liquid ratio on one hand and the silica entrance from the gas phase (SiOg) into the chondrule melt on the other hand, have counteracting effects on the Mg‐rich olivine dissolution behavior. Silica entrance would favor dissolution by maintaining disequilibrium between olivine and melt. Hence, this would explain the preferential dissolution of olivine as well as the preferential abundances of pyroxene at the margins of chondrules. Incipient dissolution would also occur in the silica‐poorer melt of chondrule core but should be followed by crystallization of new olivine (overgrowth and/or newly grown crystals). While explaining textures and grain size distributions of olivines, as well as the centripetal distribution of low‐Ca pyroxene in porphyritic chondrules, this scenario could also be consistent with the diverse chemical, isotopic, and thermal conditions recorded by olivines in a given chondrule. 相似文献