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111.
Projected changes in drought occurrence under future global warming from multi-model,multi-scenario,IPCC AR4 simulations 总被引:19,自引:3,他引:16
Recent and potential future increases in global temperatures are likely to be associated with impacts on the hydrologic cycle,
including changes to precipitation and increases in extreme events such as droughts. We analyze changes in drought occurrence
using soil moisture data for the SRES B1, A1B and A2 future climate scenarios relative to the PICNTRL pre-industrial control
and 20C3M twentieth century simulations from eight AOGCMs that participated in the IPCC AR4. Comparison with observation forced
land surface model estimates indicates that the models do reasonably well at replicating our best estimates of twentieth century,
large scale drought occurrence, although the frequency of long-term (more than 12-month duration) droughts are over-estimated.
Under the future projections, the models show decreases in soil moisture globally for all scenarios with a corresponding doubling
of the spatial extent of severe soil moisture deficits and frequency of short-term (4–6-month duration) droughts from the
mid-twentieth century to the end of the twenty-first. Long-term droughts become three times more common. Regionally, the Mediterranean,
west African, central Asian and central American regions show large increases most notably for long-term frequencies as do
mid-latitude North American regions but with larger variation between scenarios. In general, changes under the higher emission
scenarios, A1B and A2 are the greatest, and despite following a reduced emissions pathway relative to the present day, the
B1 scenario shows smaller but still substantial increases in drought, globally and for most regions. Increases in drought
are driven primarily by reductions in precipitation with increased evaporation from higher temperatures modulating the changes.
In some regions, increases in precipitation are offset by increased evaporation. Although the predicted future changes in
drought occurrence are essentially monotonic increasing globally and in many regions, they are generally not statistically
different from contemporary climate (as estimated from the 1961–1990 period of the 20C3M simulations) or natural variability
(as estimated from the PICNTRL simulations) for multiple decades, in contrast to primary climate variables, such as global
mean surface air temperature and precipitation. On the other hand, changes in annual and seasonal means of terrestrial hydrologic
variables, such as evaporation and soil moisture, are essentially undetectable within the twenty-first century. Changes in
the extremes of climate and their hydrological impacts may therefore be more detectable than changes in their means. 相似文献
112.
Most habitat complexity–species diversity relationships are specific to the habitat type, taxonomic group and spatial scale investigated. There is a need for a biologically relevant metric of habitat complexity that is transferable across systems and scales. Here, we introduce a novel metric of landscape microhabitat complexity that may overcome such constraints. It is scaled to the size of individual organisms and it numerically captures structural elements of the habitat that are biologically relevant to individuals. Our model ecosystem to develop this metric was a rocky shore in Eastern Australia. Here species richness of invertebrates was linked to habitat complexity quantified by the new metric. Importantly, measurements made at the scale of the organism predicted species richness at the landscape scale. Testing the generality of this approach across different systems may prove useful in a broader conservation biology context. 相似文献
113.
Salvatore Giammanco Barbara Justin Natalija Speh Marta Veder 《Environmental Geology》2009,57(1):75-89
The complex geochemical interactions in the groundwater of the industrial area of Šalek Valley (Slovenia) between natural
and anthropogenic fluids were studied by means of major (Ca, Mg, Na, K, HCO3
−, Cl− and SO4
2−) and trace elements’ (As , Cd, Cu, Pb, Zn, Hg, Se and V) abundances, geochemical classification and statistical analysis
of data. Cation abundances indicate mixing between a dolomitic end-member and an evaporitic or geothermal end-member. Anion
abundances indicate mixing between bicarbonate waters and either sulphate-enriched waters (suggesting hydrothermalism) or
chlorine-rich waters. Principal component analysis (PCA) allowed the extraction of seven factors, which describe, respectively:
water–rock interaction mainly on dolomitic rocks; redox conditions of water; Cd–Zn enrichment in chlorine-rich waters (probably
from industrial wastes); hydrothermal conditions in waters close to major faults; Pb and Cu pollution; V and K enrichments,
indicating their common organic source; the role of partial pressure of CO2 dissolved in water, which is highest in three wells with bubbling gases. Average underground discharge rates of solutes from
the Valley range between 0.09 t/a (V) and 1.8 × 104 t/a (HCO3
−) and indicate how natural fluids can significantly contribute to the levels of elements in the environment, in addition to
the amount of elements released by human activities. 相似文献
114.
115.
Nancy B. Rybicki Dwilette G. McFarland Henry A. Ruhl Justin T. Reel John W. Barko 《Estuaries and Coasts》2001,24(3):407-424
The establishment of submersed aquatic vegetation (SAV) at unvegetated sites in the freshwater tidal Potomac River was limited primarily by factors other than propagule availability. For two years, traps were used to quantify the amount of plant material reaching three unvegetated sites over the growing season. The calculated flux values provided a gross estimate of the flux of propagules that could potentially survive if other site factors were suitable. The mean flux ofHydrilla verticillata and all other species (≥0.01 gdw m?2 d?1) appeared sufficient to favor the establishment of vegetation, particularly considering the high viability (70–100%) of whole plants and fragments under controlled conditions. However, median water clarity values (i.e., for light attenuation, Secchi depth, total suspended solids, and chlorophylla) were below SAV restoration goals at all unvegetated sites. Additionally, sediments from unvegetated sites showed a potential for nitrogen limitation of the growth ofH. verticillata. Our findings support the hypothesis that in the tidal Potomac River, water clarity and nutrient (especially nitrogen) levels in sediment are key to plant community establishment. 相似文献
116.
The Senafe area reveals a pile of stratoid volcanic rocks (“Senafe” ignimbrite), of considerable extent and thickness, which are the products of the first volcanic event which took place in this sector, close to the upper margin of the Afar escarpment.The Senafe ignimbrite is composed prevalently of trachyte with differing degrees of alkalinity: trachy-dacite of transitional series, and trachyte s.s. of mildly alkaline series. K/Ar radiometric measurements carried out on three samples give ages ranging between 21 and 23 Ma (Lower Miocene) and show that the Senafe ignimbrite with transitional character is an extension of the Serae rhyolite of the Central Eritrean Plateau, and may also be correlated with the Miocene Alaji rhyolite of the Central Ethiopian Plateau. In contrast, the more alkaline ignimbrite shows good correlations with the trachyte emitted by the Miocene Termaber alkaline central volcanoes of Ethiopia.It is noted that, in the course of the Miocene volcanism in Eritrea, the volumetric ratio between associated basalt and ignimbrite diminishes from west to east, i.e., approaching the Afar escarpment.The stratoid volcanic rocks are injected by thick trachytic and rhyolitic dykes. As radiometric measurements on them could not be performed, their age is unknown, but it is probably more recent than that of the injected ignimbrite, according to Merla and Minucci [Merla, G., Minucci, E., 1938. Missione geologica nel Tigrai. In: La serie dei terreni, vol. 1. Regia Accademia d’Italia, Centro Studi per l’Africa Orientale Italiana, Rome, Italy, pp. 1–362] for similar dykes and domes occurring in the Adwa-Axum area (Tigrai, Ethiopia), not far from Senafe.A section is devoted to the dyke feeders of the Eritrean and Adwa-Axum volcanism. 相似文献
117.
118.
Acta Geochimica - Manganese is ubiquitous in terrestrial environments and most studies have focused on dissolution of Mn oxides, but aluminosilicates also release Mn. Here, we evaluated oxic Mn... 相似文献
119.
Fulbert Mbowou Ngantche Igor Sébastien Owona Boris Chako Tchamabe Justin Lissom Bruno Lanson Emmanuel Ekodeck Georges 《中国地球化学学报》2020,39(6):830-861
Acta Geochimica - Pozzolans from the Tombel Plain, Bamileke Plateau, and Noun Plain, 3 monogenetic volcanic fields in the central part of the Cameroon Volcanic Line (the Tombel Plain, Bamileke... 相似文献
120.
Justin C. Stout Ian Rutherfurd James Grove J. Angus Webb Adrian Kitchingman Zeb Tonkin 《地球表面变化过程与地形》2017,42(4):647-656
Reporting uncertainty in environmental measurements and estimates is important for cross‐comparison and inter‐comparison of sites and other spatial units. One such measure is the load of large in‐stream wood in river systems. In this paper we propose the use of the Weibull distribution to describe the central tendency and variability of wood loads along a river reach. We illustrate the link between the average wood load and the central tendency or scale parameter of the Weibull distribution. The shape of the Weibull distribution is strongly related to the ability of rivers to transport and rearrange the wood in a reach. We use six Victorian rivers to test the fit of the Weibull distribution, showing that the Weibull is a useful and flexible distribution that provides common reporting metrics useful for future studies. Using common reporting metrics provides a stronger tool for comparisons of wood loads between rivers and with reaches. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献