Mid-term Scale Research Articles

Combining a data-driven approach with seasonal forecasts data to predict reservoir water volume in the Mediterranean area

Prolonged droughts and water scarcity have become more frequent in recent years, exacerbating the problem of the artificial reservoirs management in the Mediterranean area. This study proposes a methodology which combines a Nonlinear AutoRegressive network with eXogenous input (NARX) data-driven model with Seasonal Forecasts (SFs) data, with the aim to predict the water volume stored in reservoirs at a mid-term scale, as requested by the local authority. The methodology is applied to four Sicilian reservoirs that experienced water scarcity in the recent past. SFs produced at the European Centre for Medium-Range Weather Forecasting are used to force the NARX models. Also, the reservoirs are in a typical data-scarce environment, where very scarce or no measures at all are available. The results show that the NARXs have the capability to reproduce the volumes stored in the considered reservoirs for the investigated period up to four months in advance. The performance of the modeling system strictly depends on: (i) the goodness of climate forecasts and (ii) the strength of the autocorrelation for the water volumes.

Bitcoin and S&P500: Co-movements of high-order moments in the time-frequency domain.

Interactions between stock and cryptocurrency markets have experienced shifts and changes in their dynamics. In this paper, we study the connection between S&P500 and Bitcoin in higher-order moments, specifically up to the fourth conditional moment, utilizing the time-scale perspective of the wavelet coherence analysis. Using data from 19 August 2011 to 14 January 2022, the results show that the co-movement between Bitcoin and S&P500 is moment-dependent and varies across time and frequency. There is very weak or even non-existent connection between the two markets before 2018. Starting 2018, but mostly 2019 onwards, the interconnections emerge. The co-movements between the volatility of Bitcoin and S&P500 intensified around the COVID-19 outbreak, especially at mid-term scales. For skewness and kurtosis, the co-movement is stronger and more significant at mid- and long-term scales. A partial-wavelet coherence analysis underlines the intermediating role of economic policy uncertainty (EPU) in provoking the Bitcoin-S&P500 nexus. These results reflect the co-movement between US stock and Bitcoin markets beyond the second moment of return distribution and across time scales, suggesting the relevance and importance of considering fat tails and return asymmetry when jointly considering US equity-Bitcoin trading or investments and the policy formulation for the sake of US market stability.

Multiscale and partial correlation networks analysis of risk connectedness in global equity markets

This paper investigates the multiscale properties and the evolution patterns of risk connectedness in global equity markets using the sample from January 03, 2000 to December 24, 2018. GARCH–EVT–VaR model is used to measure systemic risk of global equity markets. We deal with the application of Univariate Generalized Autoregressive Conditional Heteroskedasticity (GARCH) model and Extreme Value Theory (EVT) to measure the Value at Risk (VaR) of global equity markets. We then introduce the maximal overlap discrete wavelet transform (MODWT) method and partial correlation coefficients into the complex network theory to construct multiscale and partial correlation networks in global equity markets. We find the evidence of the strong risk connectedness among global equity markets in both the overall and multiscale networks, and their topological properties vary across time–frequency horizons. The US and Eurozone equity markets play a predominant role in the process of risk transmission. Most developing markets seem to remain inactive in the multiscale networks of risk connectedness. The rolling-window analysis based on time–frequency domain demonstrates that risk networks tend to be more concentrated not only at the mid-term scales but also during the financial crisis. Empirical results reveal multiscale risk connectedness characteristics, providing useful information for regulators to formulate macro prudential supervision policy and investors to update the portfolio strategies and risk prevention measures.

Evaluation of two satellite-based products against ground-based observation for drought analysis in the southern part of Iran

Water stress or more specifically drought assessment plays a key role in water management, especially in extreme climate conditions. Basically, globally gridded satellite-based precipitation products are potential sources of data as alternatives for ground-based measurements. However, for a reliable application, they should be evaluated in different regions. In this paper, two satellite-based rainfall products, namely Modern-Era Retrospective Analysis for Research and Applications (MERRA)-Land and Global Land Data Assimilation System-2 (GLDAS-2), have been evaluated against ground-based observations in terms of precipitation and their application for drought analysis. At first, the coarse-resolution MERRA-Land is downscaled to the finer resolution of interest for better comparison. After comparison of these datasets against ground-based observations in terms of precipitation, it is concluded that MERRA-Land can better estimate precipitation. Then, the nonparametric SPIs at various timescales are derived to analyze how well MERRA-Land performs in drought monitoring. Different categorical and statistical error indices are used to assess the efficiency of MERRA-Land in capturing drought events. The results revealed that the downscaled MERRA-Land data can properly detect short-term and mid-term drought events known as agricultural and meteorological droughts throughout the study area, respectively. In addition, drought maps show that the majority of lands experience mid-term scale drought which are in agreement with ground-based observations. The methodology adopted in this study can be applied in areas lacking in rain-gauge stations which significantly extend current capabilities for drought monitoring and early warning systems.

Adaptive neighborhoods: The interrelation of urban form, social capital, and responses to coastal hazards in Jakarta

This paper analyzes the relationship between the urban form of neighborhoods and collective bottom-up adaptation processes. The adaptive capacity of urban populations in marginal settlements of the Global South is critically related to social capital, as manifested through social networks, self-organization, and collective action. We analyze these responses and hypothesize that they are significantly shaped by the specific spatial forms of neighborhoods, particularly in the presence and form of places to meet. Drawing on mix-method research, we investigate socio-spatial practices and collective responses to hazards in coastal neighborhoods of Jakarta, including a standardized household survey (n = 300) and cultural mapping. Our findings demonstrate that social capital is key to community-based hazard responses. Importantly, the presence of different types of public meeting places enhances different forms of social networks due to highly diversified locations and user groups. We found that North Jakarta's urban form facilitates bonding social capital, which enables the formation of 'responsive neighborhoods' capable of responding on mid-term scales. Meeting places in neighborhood centers foster bonding ties, which, together with attachment to place and social belonging, appear to be key local assets for dealing with natural hazards e.g. by creating informal 'insurance systems'. However, there is insufficient evidence to suggest that the current urban form of North Jakarta supports the formation of 'adaptive neighborhoods' in the long- term, which would require bridging and linking ties to the outside world. Our findings suggest that a spatial perspective on collective hazard response action is important for urban planning strategies to empower local communities.

Bedset characterization within a wave-dominated shallow-marine succession: An evolutionary model related to sediment imbalances

A high-resolution analysis of small-scale sequence stratigraphic units is presented here in order to bring new information that may help to understand the dynamic evolution of shallow-marine systems in the order of thousands to hundreds of thousands of years. Through an exhaustive architectural analysis, several bedsets were identified and described within outcrops of a parasequence in the Lower Cretaceous Pilmatué Member of the Agrio Formation in central Neuquén Basin. The bedsets were mapped with 20 sections in a 12 to 5 km long transect. Successive bedsets were built by wave-dominated shoreface-offshore deposits, most of them accumulated in a regressive context, which were disrupted by minor transgressive episodes that developed the bedset bounding surfaces. These bounding surfaces were generated by wave-ravinement processes that resulted in thin transgressive lag deposits; bedsets thus show a T-R sequence architecture. Bedset sequence architecture also shows sedimentary and architectural differences, such as facies distribution, thickness and orientation that is attributed to a complex sequence-stratigraphic evolution. Waves and currents dynamics conditioned the system morphology, and hence controlled the preserved record within different bedsets.The transgressive-regressive architecture of the Pilmatué bedsets, as well as the nature of the bounding surfaces indicate that their evolution could not be attributed to already reported controls, such as changes in storminess or high-frequency relative sea-level cycles. These attributes fit better with the concept of climatic variations impacting in the nature of accretion versus retrogradation. In that sense, resulting interpretations suggest that changes in the wave climate were the main controlling process on its evolution. In consideration of that, a feasible model related to along strike sediment supply imbalances and shoreline rotation phenomena, is proposed as the developer of intra-parasequence units at a mid-term scale (1 to 100 k.y.). The interpretations made, suggest that mid-term evolution of shallow-marine systems can be strongly controlled by changes in its transport own dynamics and the necessity of the system to heal sediment supply imbalances, which result in a complex sequence-stratigraphic architecture.

Contrasting effect of Saharan dust and UVR on autotrophic picoplankton in nearshore versus offshore waters of Mediterranean Sea

AbstractAutotrophic picoplankton (APP) is responsible for the vast majority of primary production in oligotrophic marine areas, such as the Alboran Sea. The increase in atmospheric dust deposition (e.g., from Sahara Desert) associated with global warming, together with the high UV radiation (UVR) on these ecosystems, may generate effects on APP hitherto unknown. We performed an observational study across the Alboran Sea to establish which factors control the abundance and distribution of APP, and we made a microcosm experiment in two distinct areas, nearshore and offshore, to predict the joint UVR × dust impact on APP at midterm scales. Our observational study showed that temperature (T) was the main factor explaining the APP distribution whereas total dissolved nitrogen positively correlated with APP abundance. Our experimental study revealed that Saharan dust inputs reduced or inverted the UVR damage on the photosynthetic quantum yield (ΦPSII) and picoplanktonic primary production (PPP) in the nearshore area but accentuated it in the offshore. This contrasting effect is partially explained by the nonphotochemical quenching, acting as a photorepair mechanism. Picoeukaryotes reflected the observed effects on the physiological and metabolic variables, and Synechococcus was the only picoprokaryotic group that showed a positive response under UVR × dust conditions. Our study highlights a dual sensitivity of nearshore versus offshore picoplankton to dust inputs and UVR fluxes, just at the time in which these two global‐change factors show their highest intensities and may recreate a potential future response of the microbial food web under global‐change conditions.

Saharan dust inputs and high UVR levels jointly alter the metabolic balance of marine oligotrophic ecosystems.

The metabolic balance of the most extensive bioma on the Earth is a controversial topic of the global-change research. High ultraviolet radiation (UVR) levels by the shoaling of upper mixed layers and increasing atmospheric dust deposition from arid regions may unpredictably alter the metabolic state of marine oligotrophic ecosystems. We performed an observational study across the south-western (SW) Mediterranean Sea to assess the planktonic metabolic balance and a microcosm experiment in two contrasting areas, heterotrophic nearshore and autotrophic open sea, to test whether a combined UVR × dust impact could alter their metabolic balance at mid-term scales. We show that the metabolic state of oligotrophic areas geographically varies and that the joint impact of UVR and dust inputs prompted a strong change towards autotrophic metabolism. We propose that this metabolic response could be accentuated with the global change as remote-sensing evidence shows increasing intensities, frequencies and number of dust events together with variations in the surface UVR fluxes on SW Mediterranean Sea. Overall, these findings suggest that the enhancement of the net carbon budget under a combined UVR and dust inputs impact could contribute to boost the biological pump, reinforcing the role of the oligotrophic marine ecosystems as CO2 sinks.

Investigating Chaos and Nonlinear Forecasting in Short Term and Mid-term River Discharge

In the present study, an attempt is made to investigate and identify chaos using various techniques as well as river flow forecasting in short-term (daily) and mid-term (monthly) scales using nonlinear local approximation method (NLA) and ARIMA method. Daily and monthly flow data of Daintree River in Australia from 1969 to 2011 are used. In this respect, seven nonlinear dynamic methods including (1) average mutual information function; (2) phase space reconstruction; (3) false nearest neighbour algorithm; (4) method of surrogate data; (5) correlation dimension method; (6) Lyapunov exponent method; and (7) nonlinear local approximation are employed. The Takens’ theorem, mutual information and false nearest neighbour are used to determine the delay time and embedding dimension for the phase space reconstruction. The correlation dimensions obtained for the short term and mid-term river flow are 6.7 and 3.3, respectively. The finite dimensions obtained for the short term and mid-term river flow time series indicate the possible existence of chaos. The comparative analyses show that the NLA method is superior to ARIMA in mid-term scale while both models are acceptable for short term scale forecasting.

Arsenic and lead mobility: From tailing materials to the aqueous compartment

This study concerns the mineralogy of the tailings of a former Ag–Pb mine (Auzelles district, France) and the contribution of the waste materials to the heavy metal dissemination in the environment. Accumulation of metals in fish flesh was reported and this pollution is attributed to past mining activities. Tailings were studied to establish the major transfer schemes of As and Pb in order to understand their mobility that leads to contamination of a whole ecosystem. Mineralogical investigation, solubility and compliance tests were performed to assess the stability of the metal-bearing phases. Among the various metallic elements measured, As and Pb show the highest bulk concentrations (up to 0.7% and 6.3% respectively) especially for samples presenting near neutral pH values. According to X-ray diffraction (XRD), Scanning Electron Microscopy (SEM-EDX), Electron Probe Micro-Analysis (EPMA) and micro-Raman spectrometry (μRS), tailings mineralogy still contain primary minerals such as sulfides (e.g., galena, pyrite), phosphates (monazite, apatite) and/or carbonates (e.g., (hydro-)cerussite, dolomite, siderite). Sulfates (e.g., anglesite, lanarkite, plumbojarosite and beudantite) are the main secondary metal-bearing phases with other interesting phases accounting for metals mobility such as Fe and/or Pb and/or Mn oxides (e.g., lepidocrocite, goethite -up to 15 wt% of Pb was measured-, plumboferrite-type phase, mimetite). The lowest Pb solubilities were obtained at pH 8–9 and at a larger range than for As for which the lowest solubilities are reached around pH 6–7. At this minimum solubility pH value, Pb concentrations released still over exceed the National Environmental Quality Standards (NEQS), whatever the samples. The highest solubility is reached at pH 2 for both elements whatever the considered sample. This represents up to 51% of total Pb and up to 46% of total As remobilized and concentrations exceeding the NEQS. As and Pb released mainly depends on the Fe/Mn oxides (e.g., goethite, lepidocrocite) and carbonates (cerussite) which are the less stable phases. Compliance tests also show that Pb concentrations released are higher than the upper limit for hazardous waste landfills. Determination of the mineralogy allows understanding both the solubility and leaching test experiments results, as well as to forecast the impact of the residues on the water quality at a mid-term scale.

Microstructure of Lightweight and Decorative Renders with Modified Composition

Within the research presented in this article the attention was paid to the study of microstructure of lightweight and decorative renders. The composition of these renders was modified using alternative raw materials in amount of 5 % substituting the finest aggregate fractions. For evaluation of microstructure and its changes the combination of three methods SEM, XRD and DTA was used. Samples for the analysis were prepared from 90-day old specimens. The reason was the evaluation of material structural changes within the mid-term scale because considering the character and amount of used raw materials including the results of physical-mechanical tests no more significant changes were assumed in a short-term period. The performed analyses showed only inessential changes in microstructure of modified materials in comparison with the results of physical-mechanical tests.

Interactive effects of phosphorus loads and ambient ultraviolet radiation on the algal community in a high-mountain lake

Interactions among multiple stressors generated by global change exert cumulative effects on ecosys- tems. In order to identify the long-term interactive effects of ultraviolet radiation (UVR) and increasing atmospheric nutrient inputs (P-inputs) on aggregate (growth rate, chlorophyll a and abundance) and emergent (evenness and diaersity) algal community variables, a 2 x 5 factorial experiment [two levels of light quality (+ UVR, ― UVR) and five levels of nutrient enrichment] was conducted using in situ mesocosms in a high-mountain lake in the Sierra Nevada (Spain) over a 70-day period. Addition of P suppressed and inverted the stimulatory UVR effect on the non-flagellate growth rate (mid-term scale). This interactive effect was propagated as increased harmful UVR effect on chlorophyll a and abundance across the P-gradient. Interestingly, P-pulse reversed the positive effect of UVR on phytoplankton evenness and diversity on the long-term scale. These findings support our hypothesis that the UVR x P interactive effect would favor a few UVR-tolerant rapid-growing species. We show that the algal community is acclimated to UVR-flux but not to high P-pulse. The loss of diversity and disappearance of mixotrophic flagellates may have important implications for the functioning of clear-water ecosystems.

Ten-year optical monitoring of PKS 0735+178: historical comparison, multiband behavior, and variability timescales

New data and results on the optical behaviour of the blazar PKS 0735+178 are presented. In addition the whole historical light curve, and a new photometric calibration of comparison stars are reported. Optical spectral indexes are calculated and studied on years scales, while several methods for time-series analysis are applied to the whole historical series and to each observing season of our data set. This allowed to search and identify optical variability modes, characteristic timescales and the signal power spectrum over 3 decades in time. In the last 10 years the optical flux of PKS 0735+178 exhibited a rather achromatic long-term behaviour and a variability mode resembling the shot-noise. The brightness level was in an intermediate/low state with a mild flaring activity and a superimposition/succession of rapid and slower flares, with no extraordinary/isolated outbursts but, at any rate, characterized by 1 major active phase in 2001. Several mid-term scales (days, weeks) were found, the more common falling into values of about 27-28 days, 50-56 days and 76-79 days. The rapid variability in the historical curve appear to be modulated by a general, slower and rather oscillating trend, where typical timescales of about 4.5, 8.5 and 11-13 years can be identified. This spectral and temporal analysis, accompanying our data publication, suggests the occurrence of distinctive variability signatures at days/weeks scales, that can likely be of transitory nature. On the other hand the possible pseudo-cyclical or multi-component modulations at long times could be more stable, recurrent and correlated to the bimodal radio flux behaviour and the twisted radio structure observed by many years in this blazar.