1,721,225 research outputs found
Extreme value metastatistical analysis of remotely sensed rainfall in ungauged areas: Spatial downscaling and error modelling
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Estimation of Daily Rainfall Extremes Through the Metastatistical Extreme Value Distribution: Uncertainty Minimization and Implications for Trend Detection
Full text linkThe accurate estimation of hydrologic extremes is central to planning and engineering mitigation and adaptation measures. The traditional extreme value theory is based on often overlooked assumptions that preclude the use of all available observations and negatively affect estimation uncertainty. The Metastatistical Extreme Value Distribution (MEVD) was introduced to make full use of available data and was shown to significantly improve estimation uncertainty for large extremes. However, no systematic understanding existed as to how to optimally apply the MEVD depending on the statistical properties of the observed variables. With reference to daily rainfall, we identify here the local climatic factors that define the optimal MEVD formulation. We analyze a large set of long daily rainfall records, as well as synthetic time series with prescribed statistical characteristics, and find that (1) in most climates the MEVD should be based on yearly estimates of the ordinary rainfall distributions, and only in climates with less than (Formula presented.) 20–25 year the estimation of distributional/year the estimation of distributional parameters requires samples longer than 1 year; (2) the interannual variability in the distributions of rainfall should be explicitly resolved when (Formula presented.) 20–25 rainy days/year. Finally, we use the optimized MEVD to study the variability of daily rainfall extremes over 294 years in Padova (Italy) and compare it to traditional extreme value estimates. We find that, through its improved accuracy for short observations, MEVD better resolves high-quantile fluctuations and allows the emergence of long-term trends over estimation noise
Thermal constriction and slab tearing at the origin of a super-inflated spreading ridge: the Marsili volcano (Tyrrhenian Sea)
No full textThermal constriction and slab tearing at the origin of a superinflated spreading ridge: Marsili volcano (Tyrrhenian Sea)
No full textRecently acquired swath bathymetry of the Marsili basin has offered an unprecedented opportunity to study the processes of back arc ocean basin development in the Tyrrhenian Sea. In particular, the detailed morphology of Marsili seamount, a large, strongly elongated volcano located in an axial position within the <2 Ma ocean crust floored Marsili basin, is a key to understanding the mechanisms governing lithosphere formation in this young basin. The basin is near circular in shape with diameter on the order of 120 km and is positioned in the southern Tyrrhenian Sea, above the steeply dipping Ionian oceanic slab of Mesozoic age. It is bounded southward by the Aeolian volcanic arc and the Calabrian accretionary wedge, surface evidence of the northwesterly directed subduction. The most outstanding feature of the basin is the elongated, 3000-m- high Marsili volcano which reveals distinctive morphology strikingly akin to the high-order segmentation and volcanic landforms described in mid-ocean slow spreading ridges. On the basis of its distinctive morphology and incremental growth relationship we propose that Marsili volcano represents a superinflated spreading ridge resulting from a distinct thermal pulse of increased melt production occuring within the young and immature Marsili basin. Surrounding cooler continental lithosphere thermally constricts ridge propagation and crust production in Marsili basin to the finite scale of Marsili volcano. Increased melt production to feed the superinflated Marsili ridge is generated by deep, lateral asthenospheric mantle flow produced at the edges of tears that bound the subducting ocean crust of the Ionian plate. Slow spreading plate separation, outpaced by the increase in magma generation, results in vertical accretion to produce the superinflated ridge. The existence of dip-directed tears delimiting the narrow Ionian slab is supported by the geological evolution of the surrounding foreland and Apennine/Maghrebid mountain belt during early/middle Pleistocene, i.e., the time of formation of the Marsili volcano. Present-day structure and volcanism furnish direct and indirect surface evidence of the presence and location of the slab tears
Subsurface flow and vegetation patterns in tidal environments
No full textTidal environments are characterized by a complex interplay of hydrological, geomorphic, and biological processes, and their understanding and modeling thus require the explicit description of both their biotic and abiotic components. In particular, the presence and spatial distribution of salt marsh vegetation (a key factor in the stabilization of the surface soil) have been suggested to be related to topographic factors and to soil moisture patterns, but a general, process-based comprehension of this relationship has not yet been achieved. The present paper describes a finite element model of saturated-unsaturated subsurface flow in a schematic salt marsh, driven by tidal fluctuations and evapotranspiration. The conditions leading to the establishment of preferentially aerated subsurface zones are studied, and inferences regarding the development and spatial distribution of salt marsh vegetation are drawn, with important implications for the overall ecogeomorphological dynamics of tidal environments. Our results show that subsurface water flow in the marsh induces complex water table dynamics, even when the tidal forcing has a simple sinusoidal form. The definition of a space-dependent aeration time is then proposed to characterize root aeration. The model shows that salt marsh subsurface flow depends on the distance from the nearest creek or channel and that the subsurface water movement near tidal creeks is both vertical and horizontal, while farther from creeks, it is primarily vertical. Moreover, the study shows that if the soil saturated conductivity is relatively low (10-6 m s-1, values quite common in salt marsh areas), a persistently unsaturated zone is present below the soil surface even after the tide has flooded the marsh; this provides evidence of the presence of an aerated layer allowing a prolonged presence of oxygen for aerobic root respiration. The results further show that plant transpiration increases the extent and persistence of the aerated layer, thereby introducing a strong positive feedback: Pioneer plants on marsh edges have the effect of increasing soil oxygen availability, thus creating the conditions for the further development of other plant communities
Lateral flow of African mantle below the nearby Tyrrhenian plate: geochemical and isotopic evidence
No full textReply to comment by Alicia M. Wilson and Leonard Robert Gardner on “Subsurface flow and vegetation patterns in tidal environments” by Marco Marani, Sonia Silvestri and Nadia Ursino.
No full textWe wish to clarify that the boundary condition on the lower boundary of the domain was assumed to be a constant pressure head, as described in paragraph 11. The term ‘‘impermeable layer’’ in paragraph 10 is thus improper and was mistakenly left from a previous version of the manuscript. We apologize for this inconsistenc
Codes and Bandwidth of Optical Fibre Communication Systems
No full textThe three-level Franaszek code is modified to a two-level code to be employed in optical communication systems. Its fundamental parameters are compared with those other codes, showing its advantages. To determine the transmission rate, the dispersion, i. e. the bandwidth, of some graded index fibers is calculated by the WKB method
Storia e colori in un frammento di Paesaggio, in 34° EDIZIONE DI ORTOGIARDINO- Fiera di Pordenone.
No full textIl giardino tematico "Storia e colori in un frammento di Paesaggio" rappresenta nel piccolo, il racconto della storia del giardino, rappresentato come "prodotto di stratificazioni successive di storia umana e di eventi naturali". I colori naturali estratti dalle piante tintorie sono visti come risorsa rinnovabile e non inquinante. Il progetto vuole lanciare un "messaggio ecologico" per sottolineare l'importanza della tutela del paesaggio e dell'ambiente, quale presupposto fondamentale per il "benessere dell'uomo"
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