On the stability of the moments of the maximum entropy wind wave spectrum

The stability of some current wind wave parameters as a function of high-frequency cut-off and degrees of freedom of the spectrum has been numerically investigated when computed in terms of the moments of the wave energy spectrum.From the Pierson-Moskovitz wave spectrum type, a sea surface profile is simulated and its wave energy spectrum is estimated by the Maximum Entropy Method (MEM). As the degrees of freedom of the MEM spectral estimation are varied, the results show a much better stability of the wave parameters as compared to the classical periodogram and correlogram spectral approaches. The stability of wave parameters as a function of high-frequency cut-off result the same as obtained by the classical techniques.     

The Gulf of California: Review of ecosystem status and sustainability challenges

The Gulf of California is unique because of its geographical location and conformation. It hosts diverse ecosystems and important fisheries that support industry and provide livelihood to coastal settlements. It is also the site of interests and problems, and an intense interaction among managers, producers, and conservationists. In this report, we scrutinize the abiotic (hydrography, climate, ocean circulation, and chemistry) and biotic (phyto- and zooplankton, fish, invertebrates, marine mammals, birds, and turtles) components of the marine ecosystem, and some particular aspects of climate variability, endemisms, harmful algal blooms, oxygen minimum layer, and pollution. We also review the current conditions and conflicts around the main fisheries (shrimp, small and large pelagic fishes, squid, artisanal and sportfishing), the most important human activity in the Gulf of California. We cover some aspects of management and conservation of fisheries, especially the claimed overexploitation of fish resources and the ecosystems, and review proposals for creating networks of marine protected areas. We conclude by identifying main needs for information and research, particularly the integration of data bases, the implementation of models and paleoreconstructions, establishment of monitoring programs, and the evaluation of fishing impacts and management actions.     

Sedimentological analysis of the tephra from the 12–15 August 1991 eruption of Hudson volcano

The tephra fallout from the 12–15 August 1991 explosive eruption of Hudson volcano (Cordillera de los Andes, 45°54 S-72°58 W; Chile) was dispersed on a narrow, elongated ESE sector of Patagonia, covering an area (on land) of more than 100 000 km². The elongated shape of the deposit, together with the relatively coarse mean and median values of the particles at a considerable distance from the vent, were the result of strong winds blowing to the southeast during the eruption. The thickness of the fall deposit decreases up to 250 km ESE from Hudson volcano, where it begins to thicken again. Secondary maxima are well developed at approximately 500 km from the vent. Secondary maxima, together with grainsize bimodality in individual layers and in the bulk deposit suggest that particle aggregation played an important role in tephra sedimentation. The fallout deposit is well stratified, with alternating fine-grained and coarsegrained layers, which is probably a result of strong eruptive pulses followed by relatively calm periods and/or changes in the eruptive style from plinian to phreatoplinian. The tephra is mostly composed of juvenile material: the coarse mode (mostly pumice) shifts to finer sizes with distance from the volcano; the fine mode (mostly glass shards) is always about 5/6 phi. Glass shards and pumice are mostly light gray to colorless. However, considerable amounts of dark, poorly vesiculated, blocky shards, suggest a hydromagmatic component in the eruption. A land-based tephra volume of 4.35 km³ was estimated, and a total volume of 7.6 km³ arose from an extrapolation, which took into account the probable volume sedimented in the sea. Bulk density ranges from 0.9 to 1.10 gr/cm³ (beyond 110 km from the vent). Rather uniform density values measured in crushed samples (2.45–2.50 gr/cm³ at all distances from the vent) reveal a relatively homogeneous composition. Mean and median sizes decrease rapidly up to 270 km from the vent; beyond that point they are more or less constant, whereas the maximum size (1 phi) shows a steady decrease up to 550 km. A concomitant improvement in sorting is observed. This is attributed to sorting due to wind transport combined with particle aggregation at different times and distances from the vent. The Hudson tephra fallout shares some strikingly similar features with the Mount St. Helens (18 May 1980) and Quizapu (1932) eruptions.     

Aquifer storage capacity and maximum annual yield from long-term aquifer fluxes

Long-term time series data of aquifer recharge, groundwater extraction, and discharge are used to estimate aquifer storage capacity and maximum annual yield. Aquifer storage capacity is defined as the maximum volume of water that can be stored in an aquifer. It is estimated using a transient water-balance approach. The maximum annual yield is defined as the maximum combined groundwater extraction plus discharge that can be sustained in an aquifer judged by the historical record of recharge. It is determined according to a graphical mass-curve method. These two quantities are useful in aquifer characterization and groundwater management, the apportionment of groundwater rights and aquifer storage and recovery operations being two frequent applications. Time series data from the Edwards Aquifer, Texas, USA, illustrate the application of the methods presented.

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Résumé Des données sur le long terme de la recharge d’aquifère, de l’exploitation de l’eau souterraine et de la vidange sont utilisées pour estimer la capacité d’emmagasinement de l’aquifère et la capacité annuelle maximum. La capacité d’emmagasinement de l’aquifère est définit comme le volume maximum de l’eau qui peut être emmagasinée dans le réservoir. Elle est estimée en utilisant une approche par bilan hydrologique en transitoire. La capacité annuelle maximum est définit comme la combinaison de l’extraction de l’eau souterraine et de la vidange, combinaison qui peut être jugée durable ou non au regard de l’examen des valeurs de recharge. Elle est déterminée au moyen d’une méthode de courbe des valeurs cumulées. Ces deux quantités sont très utiles pour caractériser les aquifères et pour gérer les eaux souterraines, l’imputation des droits aux eaux souterraines, et du fait que les opérations de recharge des aquifères et de récupération sont très fréquentes. Les données temporelles provenant de l’aquifère Edwards, Texas, USA, illustrent l’application de la méthode présentée.

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Resumen Para estimar la capacidad de almacenamiento de un acuífero y su rendimiento máximo anual, se han utilizado series temporales largas de datos de recarga al acuífero, de extracciones de agua subterránea y de descarga. La capacidad de almacenamiento de un acuífero se define como el volumen máximo de agua que puede ser almacenado en el mismo. Se estima utilizando una aproximación con un balance de agua en régimen transitorio. El rendimiento máximo anual se define como el máximo resultante de la combinación de la extracción de aguas subterráneas y la descarga que puede ser sostenido por un acuífero según los registros históricos de recarga y se define según un método gráfico masa-curva. Estos dos valores son útiles en la caracterización de los acuíferos y en la gestión de las aguas subterráneas, el reparto de los derechos sobre las aguas subterráneas y las operaciones de almacenaje y recuperación de los acuíferos, que son dos aplicaciones frecuentes. Las series de tiempo para el Acuífero Edwards, Texas, USA, ilustra la aplicación de los métodos presentados.

     

Effects of Explicit Urban-Canopy Representation on Local Circulations Above a Tropical Mega-City

The Advanced Regional Prediction System (ARPS) is coupled with the tropical town energy budget (tTEB) scheme to analyze the effects of the urban canopy circulation over the metropolitan area of São Paulo and its interactions with the sea breeze and mountain-valley circulation in the eastern state of São Paulo, Brazil. Two experiments are carried out for the typical sea-breeze event occurring on 22 August 2014 under weak synoptic forcing and clear-sky conditions: (a) a control run with the default semi-desert surface parametrization and; (b) a tTEB run for the urban canopy of São Paulo. A realistic land-use database over the south-eastern domain of Brazil is used in the downscaling simulation to a horizontal grid resolution of 3 km. Our results indicate that ARPS effectively simulates features of the nighttime and early morning land-breeze circulation, which is affected by the surrounding hills and the nocturnal heat island of São Paulo. By early afternoon, the south-eastern sea-breeze circulation moves inland perpendicular to the upslope of the Serra do Mar scarp, which generates a line of moisture convergence and updrafts further inland. Later, the convergence line reaches São Paulo and interacts with the circulation arising from the urban heat island (UHI), which increases the moisture convergence and strength of updrafts. The surface energy balance indicates that the UHI is caused by large sensible heat storage within the urban canopy during the day, which is later released in the afternoon and at night. The simulations are verified with available radiosonde and surface weather station data, land-surface-temperature estimates from the moderate resolution imaging spectroradiometer, as well as the National Center for Atmospheric Research reanalysis databases. The three-dimensional geometry of the urban canyons within the tTEB scheme consistently improves the thermodynamically-induced circulation over São Paulo.     

The cost of achieving South Africa’s ‘fair share’ of global climate change mitigation

Global climate change mitigation action is hampered by systematic under-assessment of national ‘fair shares’, largely on the basis of perceived national interests. This paper aims to inform discussions centred on South Africa’s nationally determined contribution (NDC) by estimating (1) emissions reduction pathways for the country using the Climate Equity Reference Calculator (CERC) assuming a maximum 2°C aggregate warming target and (2) the likely economy-wide net mitigation costs or savings associated with reaching these pathways if known lower-cost mitigation measures, identified through the national mitigation potential analysis, are prioritised. The cumulative net savings associated with achieving the CERC ‘fair share’ emissions pathway, assuming the moderate use of low carbon power generation measures, would reach $5.3 billion by 2030. Net savings could be substantially greater reaching $46.8 billion by 2030 assuming power generation focuses on moving towards full decarbonisation. An unconditional commitment to the mitigation action implied by the ‘fair share’ emissions pathway therefore seems reasonable and prudent purely from the point of view of net country-wide savings. Only if power generation moves towards full decarbonisation would there be a reasonable chance of achieving the more ambitious CERC domestic emissions pathway. However, the significant additional cost associated with achieving the domestic emissions pathway should be conditional on international assistance.

Key policy insights

• South Africa can only achieve its ‘fair share’ of the global mitigation effort if greater use is made of renewable energy options, and can realise significant net savings if it does so.

• Further emissions reductions would incur costs and require significant upscaling of the share of renewable energy and full implementation of all non-power generation mitigation measures available.

• Committing to this further mitigation action contingent on international finance would both strengthen the nation’s position in climate negotiations and support the provision of finance for those vulnerable developing nations that bear little or no responsibility for climate change.

     

Surface water quality in a sulfide mineral‐rich arid zone in North‐Central Chile: Learning from a complex past,addressing an uncertain future

This study presents an analysis of up to 30 years of hydrological variables and selected water quality parameters (pH, SO₄, Fe, Cu, and As) in the upper area of the Elqui River basin in North‐Central Chile. A correlation analysis determined statistically significant positive relationship for SO₄‐Cu, Fe‐As, and Fe‐Cu. In terms of historical behaviour, no statistically significant trends were detected for precipitation or temperature. In contrast, for flow, there is an overall decreasing pattern for the entire area of study, although only in one case this trend was statistically significant. Along with the aforementioned analysis, a characterization of the flow‐water quality relationships is considered for the time period analyzed. Although erratic behaviours were confirmed, a negative (i.e., inverse) flow‐concentration relationship was identified for SO₄, a positive (i.e., direct) relationship for Fe, and undefined relationships for As and Cu were obtained. From these analyses and based on previous studies on projections regarding climate change for the Andean region, and in particular for the upper Elqui zone, an estimation of the possible effects of the change in water regimes on water quality in the area of study is developed. It is likely that a decrease in surface flow, as a consequence of climate change could translate into improvements in water quality in terms of Fe and eventually As and Cu, but into an impairment in the case of SO₄. In any case, this is a complex situation that demands special attention in the face of industrial activities that could be developed in tributaries like the Claro River, which currently play an important role in depurating or diluting contaminants in the waters of the Elqui River. Finally, it should be noted that this study addresses an issue that goes beyond the local interest and could be used as a reference to compare other transitional environments containing sulphide ores or areas of hydrothermal alterations, which are considered to be highly vulnerable to climate change and variability.