Contrasting regional discharge evolutions in the Amazon basin (1974–2004)

Former hydrological studies in the Amazon Basin generally describe annual discharge variability on the main stem. However, the downstream Amazon River only represents the mean state of the Amazonian hydrological system. This study therefore uses a new data set including daily discharge in 18 sub-basins to analyze the variability of regional extremes in the Amazon basin, after recalling the diversity of the hydrological annual cycles within the Amazon basin. Several statistical tests are applied in order to detect trends and breaks in the time series. We show that during the 1974–2004 period, the stability of the mean discharge on the main stem in Óbidos is explained by opposite regional features that principally involve Andean rivers: a decrease in the low stage runoff, particularly important in the southern regions, and an increase in the high stage runoff in the northwestern region. Both features are observed from the beginning of the nineties. These features are also observed in smaller meridian sub-basins in Peru and Bolivia. Moreover we show that the changes in discharge extremes are related to the regional pluriannual rainfall variability and the associated atmospheric circulation as well as to tropical large-scale climatic indicators.     

Contribution of Sponge Spicules to the Composition of Biogenic Silica in the Ligurian Sea

Abstract. The importance of sponge spicules in the turnover of biogenic silica (BSi) in the detritic bottoms of the Eastern Ligurian Riviera was evaluated by studying sediment cores and the detrital matter collected by a trap over a one year period.
This study made evident that: i) Sponge spicules represent the main component of the BSi both in the sediments and in the trapped matter; ii) A correlation exists between the sponge biomass present on the overhanging cliff and the amount of sponge spicules found in the sediment below; iii) Inside the sediments, a superficial layer (10 cm deep) characterized by intensive silica dissolution processes can be observed; and iv) The amount of spicules collected using the trap is not constant throughout the year, but shows a characteristic trend with low values in spring and summer and high values in autumn and winter.     

基于分布式大流域径流模型的中国西北黑河流域水文模拟

水资源短缺是中国西北干旱地区长期的问题,区域人口增加、城市化扩张,加之气候变化的影响进一步加剧了西北地区水资源短缺,也使生活用水、灌溉用水、工业用水和维持生态系统稳定的用水危险加剧.采用分布式大流域径流模型(DLBRM)模拟黑河流域水文(中国第二大内陆河,流域面积128 000 km2)来理解区域的冰川和积雪融化水、地下水、地表水、蒸散发等方面的分布,评估气候变化对水文的影响和冰川退缩对中游和下游来水量的影响.模拟结果表明,黑河流域的大部分产流那源于黑河上游地区的祁连山.模拟1990-2000年黑河河流日流量变化结果认为,黑河中游正义峡给下游的供水为10×108m3,其中地表径流占51%,层间流占49%.中游地区沙土具有较高的蒸腾发能力,近一半的地表水被蒸发掉.模拟实践证明,分布式大流域径流模型可以结合气候变化、水资源管理方面的成果,改进流域水文模拟的精度.     

Azimut di una geodetica ellissoidica passante per due punti molto lontani fra loro

Riassunto L'Autore presenta un procedimento per la ricerca dell'azimut di una geodetica ellissoidica passante per due punti molto lontani fra loro. Istituisce dapprima una corrispondenza fra la geodetica ed un arco di cerchio massimo, corrispondenza definita con l'imporre uguali coordinate agli estremi dei due archi e la latitudine sferica normale uguale a quella ellissoidica. Sviluppa poi la longitudine ellissoidicaw in funzione di quella sferical, e poichè l fra gli estremi dell'arco di cerchio deve essere uguale a w, ne deduce una equazione per ricavare l'azimut.

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Summary The Author outlines a procedure to research the azimuth of an ellipsoidal geodesic, which passes through two points far distant from another. A corrispondence is first instituted between the geodesic and a bow of maximum circle; this correspondence may be defined by imposing the same coordinates to the extreme parts of the two bows and the spherical normal latitude equal to the ellipsoidal one. The ellipsoidal longitudew is next developed as a function of the spherical onel and, as l between the extreme parts of the circle bow must equal w, an equation is hereby deduced to find out the azimuth.

     

La risoluzione dell'equazione di Laplace nel campo esterno a uno sferoide

Riassunto L'Autore dimostra che, nel sistema di coordinate polari , , , si possono determinare un numeros di funzioni della sola variabile :Q ₁,Q ₃, ....Q _2s–1 tali che la sommatoria delleQ _2i–1/^2i–1 rappresenti il potenzialeV di un geoide di rotazione. La condizione di armonicità determina ciascunaQ (che si riduce a un polinomio nelle potenze di sen ) a meno di una costante arbitraria; si dispone pertanto dis costanti che servono per soddisfare la natura dellaV sulla superficie del geoide. Come esempio l'Autore ha determinato la gravità sul geoide sferico, confermando i risultati delSomigliana, e su uno sferoide generico dove ha ritrovato la relazione diClairaut.

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Summary The Author proofs that, in the system of polar coordinates , , , it is possible to determine a numbers of functions only of the variable :Q ₁,Q ₃ ....Q _2s–1 in such a way as to make the summatory of theQ _2i–1/^2i–1 represent the potential function of a rotational geoid. The condition of harmonicity determines, saving an arbitrary constant, each of theQ which is reduced to a polynom developed by the sin powers; therefore one disposes of a number of constants to make use for satisfing theV on the geoid. To illustrate his theory the Author determines the gravity on the spherical geoid, thus confirmingSomigliana's formulas and on a spheroidal on which he pointed outClairaut's relations.

     

Effects of Amazon basin deforestation on regional atmospheric circulation and water vapor transport towards tropical South America

The water cycle over the Amazon basin is a regulatory mechanism for regional and global climate. The atmospheric moisture evaporated from this basin represents an important source of humidity for itself and for other remote regions. The deforestation rates that this basin has experienced in the past decades have implications for regional atmospheric circulation and water vapor transport. In this study, we analyzed the changes in atmospheric moisture transport towards tropical South America during the period 1961–2010, according to two deforestation scenarios of the Amazon defined by Alves et al. (Theor Appl Climatol 100(3-4):337–350, 2017). These scenarios consider deforested areas of approximately 28% and 38% of the Amazon basin, respectively. The Dynamic Recycling Model is used to track the transport of water vapor from different sources in tropical South America and the surrounding oceans. Our results indicate that under deforestation scenarios in the Amazon basin, continental sources reduce their contributions to northern South America at an annual scale by an average of between 40 and 43% with respect to the baseline state. Our analyses suggest that these changes may be related to alterations in the regional Hadley and Walker cells. Amazon deforestation also induces a strengthening of the cross-equatorial flow that transports atmospheric moisture from the Tropical North Atlantic and the Caribbean Sea to tropical South America during the austral summer. A weakening of the cross-equatorial flow is observed during the boreal summer, reducing moisture transport from the Amazon to latitudes further north. These changes alter the patterns of precipitable water contributions to tropical South America from both continental and oceanic sources. Finally, we observed that deforestation over the Amazon basin increases the frequency of occurrence of longer dry seasons in the central-southern Amazon (by between 29 and 57%), depending on the deforestation scenario considered, as previous studies suggest.     

Late Holocene glacial and periglacial evolution in the upper Orco Valley, northwestern Italian Alps

The sediments present in some areas of the Orco Valley provide indications on climatic variations that occurred during the last 6000 years on the southern slopes of the Alps. In particular, distribution and ages of peat layers help define periods and extent of glacial fluctuation in the last 2200 years. Sampling of soils involved in periglacial processes provided a basis for development of a chronological framework of late Holocene environmental change. The data indicate a trend toward cooler climate in the second half of the Holocene. A strong relationship exists between phases of River Po flooding and expansion/retreat phases of the Swiss glaciers: major glacial advances were coeval with periods of intense flooding of the River Po, whereas the phases of glacial retreat coincided with periods of little flooding of the Po. Only in three cases do relationships between glacier activity and floods show weak correlations; two of the cases relate to the warmest periods in approximately the last 2200 years, while the third is the present period. Paleoclimatic evidence from the study region indicates the relatively warm Roman Period between about 2200 and 1900 cal yr BP appears to better represent modern conditions than does the Medieval Warm Period.     

The 15 m.y. geomagnetic reversal periodicity: a quantitative test

We have analyzed the three most commonly used geomagnetic polarity time scales that cover the past 100 m.y.. In the three cases, different spectral analyses show a 13–16 m.y. periodicity in the rate of reversal occurrence. To test whether this periodicity is real or simply arises from a random generator we have compared these polarity time scales with a large number of synthetic sequences produced by a random process, characterized by a linear time variation of its mean activity. Geomagnetic and generated sequences were regularly sampled by using sliding windows, anf then the Fourier spectra of the obtained frequency signals were compared. This test shows that the detected periodicity is presumably not a simple statistical fluctuation of an aperiodic generator, and consequently that a long-term periodicity in the geodynamo must be seriously considered.     

The impact of dredge-fill on Posidonia oceanica seagrass meadows: regression and patterns of recovery

Posidonia oceanica meadows can be severely damaged by dredge-fill operations. We report on the construction of gas pipelines that occurred between 1981 and 1993 in SW Sicily, Italy. A large portion of the meadow was mechanically removed, and the excavated trench was filled with a mosaic of substrates, ranging from sand to consolidated rock debris. Meadow loss and recovery were quantified over 7 years after the end of operations. We recorded an overall loss of 81.20 ha of meadow. Substrate strongly affected recovery as the percent cover by P. oceanica consistently increased on calcareous rubble, reaching values of 44.37 ± 3.05% in shallow sites after 7 years, whereas no significant increase occurred on other substrates. As in the Mediterranean Sea exploitation of coastal areas continues to grow with consequent impacts on P. oceanica meadows, this case study illustrates how artificial rubble-like materials could be employed to support the restoration of damaged meadows.     

A land-use-based modelling chain to assess the impacts of Natural Water Retention Measures on Europe’s Green Infrastructure

This article details the process of integrating models to answer a specific policy-driven question: ‘What could be the impact of proposed Natural Water Retention Measures (NWRMs) on Europe’s Green Infrastructure (GI)?’ It describes the new Land Use Modelling Platform (LUMP), now enabling a high spatial scale (100-m) and large coverage (pan-European), whereby several sector-specific models contribute to assessing the impact of regional-level policy on a given spatial topic of concern. The configuration (land claims and land allocations modules) and calibration (accessibility and biophysical suitability) of the LUMP are explained. Four NWRM scenarios (riparian areas, afforestation, grassland and baseline scenario) are configured to run the simulations. For the reference: year 2006, the spatial representation of GI is based on land-use features of a refined version of the CORINE Land Cover (CLC), and resumed as connected components made of nodes and links.

Mathematical morphological image processing and network graph theory model, available from the free software package GUIDOS (the Joint Research Center of the European Commission), enabled the measurement of the GI connectivity and identified most critical links. Results show that the competition for land claimed by different economic sectors, combined with policy-driven rule-sets for the implementation of different NWRMs, yields very different results for the 2030 land-use projections, and subsequently for the morphology of GI. Three indicators associated with the morphology of GI are computed in order to assess the model outputs for 2030. The indicators are computed to answer the following questions: (1) How is the quantity of GI affected by each of the NWRM, and what proportion of that GI is most valuable? (2) What is the location of the most critical nodes and connectors of GI, and what land-use conversions occur under these? (3) Are the average components getting larger or smaller?

Whereas the grassland measure results in the largest net increase of GI, the afforestation measure results in the overall largest number of hectares of key nodes and links within the network. Land conversions occur under the critical GI nodes and links, with a large increase in agricultural areas, especially for the riparian measure under critical nodes and the grassland measure under critical links. Also predominant is the swapping of land from pasture to forest under critical links with the afforestation measure. The riparian measure most increases the average size of GI components, and all three measures contribute to bridging two large components which were divided in the 2006 land-use map, thus increasing the size of the largest component by more than 50%.