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1.
Few long-term studies have explored how intensively managed short rotation forest plantations interact with climate variability. We examine how prolonged severe drought and forest operations affect runoff in 11 experimental catchments on private corporate forest land near Nacimiento in south central Chile over the period 2008–2019. The catchments (7.7–414 ha) contain forest plantations of exotic fast-growing species (Pinus radiata, Eucalyptus spp.) at various stages of growth in a Mediterranean climate (mean long-term annual rainfall = 1381 mm). Since 2010, a drought, unprecedented in recent history, has reduced rainfall at Nacimiento by 20%, relative to the long-term mean. Pre-drought runoff ratios were <0.2 under 8-year-old Eucalyptus; >0.4 under 21-year-old Radiata pine and >0.8 where herbicide treatments had controlled vegetation for 2 years in 38% of the catchment area. Early in the study period, clearcutting of Radiata pine (85%–95% of catchment area) increased streamflow by 150 mm as compared with the year before harvest, while clearcutting and partial cuts of Eucalyptus did not increase streamflow. During 2008–2019, the combination of emerging drought and forestry treatments (replanting with Eucalyptus after clearcutting of Radiata pine and Eucalyptus) reduced streamflow by 400–500 mm, and regeneration of previously herbicide-treated vegetation combined with growth of Eucalyptus plantations reduced streamflow by 1125 mm (87% of mean annual precipitation 2010–2019). These results from one of the most comprehensive forest catchment studies in the world on private industrial forest land indicate that multiple decades of forest management have reduced deep soil moisture reservoirs. This effect has been exacerbated by drought and conversion from Radiata pine to Eucalyptus, apparently largely eliminating subsurface supply to streamflow. The findings reveal tradeoffs between wood production and water supply, provide lessons for adapting forest management to the projected future drier climate in Chile, and underscore the need for continued experimental work in managed forest plantations. 相似文献
2.
Effects of the geometry of two‐dimensional fractures on their hydraulic aperture and on the validity of the local cubic law 下载免费PDF全文
Flow through rough fractures is investigated numerically in order to assess the validity of the local cubic law for different fracture geometries. Two‐dimensional channels with sinusoidal walls having different geometrical properties defined by the aperture, the amplitude, and the wavelength of the walls' corrugations, the corrugations asymmetry, and the phase shift between the two walls are considered to represent different fracture geometries. First, it is analytically shown that the hydraulic aperture clearly deviates from the mean aperture when the walls' roughness, the phase shift, and/or the asymmetry between the fracture walls are relatively high. The continuity and the Navier–Stokes equations are then solved by means of the finite element method and the numerical solutions compared to the theoretical predictions of the local cubic law. Reynolds numbers ranging from 0.066 to 66.66 are investigated so as to focus more particularly on the effect of flow inertial effects on the validity of the local cubic law. For low Reynolds number, typically less than 15, the local cubic law properly describes the fracture flow, especially when the fracture walls have small corrugation amplitudes. For Reynolds numbers higher than 15, the local cubic law is valid under the conditions that the fracture presents a low aspect ratio, small corrugation amplitudes, and a moderate phase lag between its walls. 相似文献
3.
V. Delouille J. De Patoul J. F. Hochedez L. Jacques J. P. Antoine 《Solar physics》2005,228(1-2):301-321
The extreme ultraviolet imaging telescope (EIT) of SOHO offers a unique record of the solar atmosphere for its sampling in
temperature, field of view, resolution, duration, and cadence. To investigate globally and locally its topology and evolution
during the solar cycle, we consider a multi-scale approach, and more precisely we use the wavelet spectrum.
We present three results among the applications of such a procedure. First, we estimate the typical dimension of the supergranules
as seen in the 30.4 nm passband, and we show that the evolution of the characteristic network scale is almost in phase with
the solar cycle. Second, we build pertinent time series that give the evolution of the signal energy present in the corona
at different scales. We propose a method that detects eruptions and post-flaring activity in EUV image sequences. Third, we
introduce a new way to extract active regions in EIT images, with perspectives in, e.g., long-term irradiance analysis. 相似文献
4.
The conodont colour alteration index (CAI) is potentially valuable in thermal history investigations, but there are problems in its use. An approach is proposed herein to overcome the problem of establishing reliable geothermal palaeogradients in areas with burial metamorphism, based on knowledge of the stratigraphic succession thickness, the boundaries of chronostratigraphic units, and the age and duration of deformation episodes. Although also problematical that a correlation between CAI and Kübler index (KI) values does not exist, there are areas where CAI and KI values are notably consistent for the anchizone boundaries; however, anomalous correlations between CAI and KI values have also been found in some areas. A CAI anchizone (or ancaizone) is defined in order to enable CAI values to be used independently to establish a metamorphic zonation. 相似文献
5.
Synthetic SH seismograms in a laterally varying medium by the discrete wavenumber method 总被引:1,自引:0,他引:1
Summary. We present a new method to calculate the SH wavefield produced by a seismic source in a half-space with an irregular buried interface. The diffracting interface is represented by a distribution of body forces. The Green's functions needed to solve the boundary conditions are evaluated using the discrete wavenumber method. Our approach relies on the introduction of a periodicity in the source-medium configuration and on the discretization of the interface at regular spacing. The technique developed is applicable to boundaries of arbitrary shapes and is valid at all frequencies. Some examples of calculation in simple configurations are presented showing the capabilities of the method. 相似文献
6.
Z. Balog † A. J. Delgado ‡ A. Moitinho G. Frész † G. Kaszás † J. Vinkó E. J. Alfaro 《Monthly notices of the Royal Astronomical Society》2001,323(4):872-886
CCD photometry in Johnson UBV and Strömgren uvby systems and medium-resolution spectroscopy of the galactic open cluster NGC 7128 are presented. Spectral types of the brightest 12 stars in the cluster field were determined based on equivalent widths of the H α and the He i 6678-Å line. The spectroscopic observations also revealed two obvious and one probable Be-type stars showing H α emission. The analysis of the photometric diagrams gave a colour excess of E ( B − V )=1.03±0.06 mag, a distance modulus DM =13.0±0.2 mag and an age above 10 Myr. Time-resolved photometric observations obtained on one night resulted in the detection of short time-scale light variations of seven new and three already known variable stars in the cluster field. 相似文献
7.
Published in Astrofizika, Vol. 38, No. 4, pp. 677–680, October–December, 1995. 相似文献
8.
ABSTRACT Lead isotope variability of magmatic arc rocks and associated mineralization of the Central Andes is usually considered to be the result of mixing between a homogeneous mantle and heterogeneous continental crust. About 230 new lead isotope data on the Northern and Central Andes allow us to compare for the first time lead isotope systematics of the Late Cretaceous – Tertiary arc magmatism and associated mineralization along the Andean chain between 8°N and 40°S. Lead isotope compositions indicate mixing between mantle and upper crustal rocks along the whole Andean chain. Additionally, we have found that mantle end-members of the Late Cretaceous – Tertiary magmatism are heterogeneous and systematically shifted towards less radiogenic 206 Pb/204 Pb compositions from north to south along the Andes. This heterogeneity most likely results from mixing between a low radiogenic mantle, possibly carrying a DMM or EM I component, and a more radiogenic mantle, possibly carrying an HIMU component. Thus, our results imply that lead isotope variability of Andean magmas at the continental scale is caused not only by crustal but also by mantle heterogeneity. 相似文献
9.
Pierre Antoine 《地学学报》1994,6(5):453-464
Recent research on the Somme Valley terrace deposits, that began in 1987, has resulted in an integrated sequence of geological and geomorphological evidence for this area that is of particular significance for prehistoric investigations. This has been achieved using previous evidence and new results from archaeological and geological excavations. These include longitudinal profiles, cartography and detailed synthesis of sections of alluvial deposits, stratigraphy of river deposits and overlying loess sequences. The work, based on a study of the geometry of the terrace system, has resulted in the identification of ninestepped alluvial formations that occur along 70 km of the valley. Detailed study permits the integration of the various alluvial sequences. This suggests that each alluvial sequence results from sedimentation through a single glacial-interglacial climatic cycle. This hypothesis is confirmed by investigation of soil and loess sequences of the deposits overlying the fluvial sediments. The synthesis presented provides a basis for understanding the deposition of the terrace system and an initial chronostratigraphic interpretation for the deposits. 相似文献
10.
刘少明 《大地测量与地球动力学》2004,24(4):13-19
对1999年8月11日日全食阴影扫过欧洲期间,设在Annelles,Uccle,Walferdange和Bondy弹簧和超导重力仪的记录进行了分析.为了确定月亮对太阳万有引力可能的遮挡效应的极限,对超导和弹簧重力仪记录进行了比较.同时也对LCR和阿斯卡尼亚重力仪观测结果进行了讨论.结论是如果日食重力吸引效应存在,它应在超导重力仪±1 nm/s2(0.1×10-8ms-2)的观测精度范围之内.研究发现在以上情形下,弹簧和超导重力仪都在它们的精度范围内工作,并且日食引起的异常环境干扰可能使重力信号有重大的改变. 相似文献