Validation of a full hydrodynamic model for large‐scale hydrologic modelling in the Amazon

A key aspect of large river basins partially neglected in large‐scale hydrological models is river hydrodynamics. Large‐scale hydrologic models normally simulate river hydrodynamics using simplified models that do not represent aspects such as backwater effects and flood inundation, key factors for some of the largest rivers of the world, such as the Amazon. In a previous paper, we have described a large‐scale hydrodynamic approach resultant from an improvement of the MGB‐IPH hydrological model. It uses full Saint Venant equations, a simple storage model for flood inundation and GIS‐based algorithms to extract model parameters from digital elevation models. In the present paper, we evaluate this model in the Solimões River basin. Discharge results were validated using 18 stream gauges showing that the model is accurate. It represents the large delay and attenuation of flood waves in the Solimões basin, while simplified models, represented here by Muskingum Cunge, provide hydrographs are wrongly noisy and in advance. Validation against 35 stream gauges shows that the model is able to simulate observed water levels with accuracy, representing their amplitude of variation and timing. The model performs better in large rivers, and errors concentrate in small rivers possibly due to uncertainty in river geometry. The validation of flood extent results using remote sensing estimates also shows that the model accuracy is comparable to other flood inundation modelling studies. Results show that (i) river‐floodplain water exchange and storage, and (ii) backwater effects play an important role for the Amazon River basin hydrodynamics. Copyright © 2011 John Wiley & Sons, Ltd.     

Community structure and dynamics in climate networks

We consider climate networks constructed from observed and model simulated fields of three climate variables and investigate their community structure. We find that for all fields the number of effective communities is rather small (four to five). We are able to trace the origin of these communities to certain dynamical properties of climate. Our results suggest that the complete complexity of the climate system condenses beyond the ??weather?? time scales into a small number of low-dimensional interacting components and provide clues as to the nature of the climate subsystems underlying these components.     

Clustering and forecasting of dissolved oxygen concentration on a river basin

The aim of this contribution is to combine statistical methodologies to geographically classify homogeneous groups of water quality monitoring sites based on similarities in the temporal dynamics of the dissolved oxygen (DO) concentration, in order to obtain accurate forecasts of this quality variable. Our methodology intends to classify the water quality monitoring sites into spatial homogeneous groups, based on the DO concentration, which has been selected and considered relevant to characterize the water quality. We apply clustering techniques based on Kullback Information, measures that are obtained in the state space modelling process. For each homogeneous group of water quality monitoring sites we model the DO concentration using linear and state space models, which incorporate tendency and seasonality components in different ways. Both approaches are compared by the mean squared error (MSE) of forecasts.     

Boulder deposition during major tsunami events

A remarkable accumulation of marine boulders located above the present spring tide level has occurred in two coastal lowlands of the Algarve (Portugal). The size‐interval of the particles studied here is seldom reported in the literature in association with extreme events of coastal inundation, thus making this study of relevance to many other coasts worldwide. The spreads of boulders extend several hundred meters inland and well beyond the present landward limit of storm activity. The marine origin of the boulders is demonstrated by well‐developed macro‐bioerosion sculpturing and in situ skeletal remains of endolithic shallow marine bivalves. The good state preservation of the fossils within the boulders indicates that abrasion during transport and redeposition was not significant. We envisage boulder deposition as having taken place during the Lisbon tsunami of ad 1755 through the simultaneous landward entrainment of coarse particles from nearshore followed by rapid shoreward suspended‐dominated transport and non‐graded redeposition that excluded significant sorting by weight or boulder dimensions. We use numerical hydrodynamic modeling of tsunami (and storm) waves to test the observational data on boulder dimensions (density, size, distribution) on the most likely processes of sediment deposition. This work demonstrates the effectiveness of the study of boulder deposits in tsunami reconstruction. Copyright © 2011 John Wiley & Sons, Ltd.     

Climate change in the Paraná state,Brazil: responses to increasing atmospheric CO 2 in reference evapotranspiration

The hydrological variable evapotranspiration (ET) is challenging to estimate because it cannot be measured directly in natural environments (except in small plots). The uncertainties associated with the models used for its prediction have increased under climate change conditions. We studied the influence of stomatal resistance on ET estimates using the Penman-Monteith method as projected by three general circulation models in two emission scenarios (RCP4.5 and RCP8.5) for future climates throughout the twenty-first century (2010–2039, 2040–2069, and 2070–2099). We also investigated the probable ET rate changes in relation to the current (30 years average, 1980–2009) climate conditions for the Paraná state in the southern region of Brazil. The results were regionalized to help policymakers assess climate change impacts and design adaptation measures. ET increases of up to 15% were found in future climate conditions, which may lead to a significant increase in the water demand for agricultural crops. However, we believe that plant morphophysiological changes may occur under atmospheric CO2 enrichment conditions and that a possible reduction in stomatal conductance will result in lower ET increases than those obtained with the traditional Penman-Monteith method. When considering future climate scenarios, we propose the equation be adjusted to consider stomatal resistance as a function of CO2 concentrations.     

The Regional Ocean Modeling System (ROMS) 4-dimensional variational data assimilation systems: Part III - Observation impact and observation sensitivity in the California Current System

The critical role played by observations during ocean data assimilation was explored when the Regional Ocean Modeling System (ROMS) 4-dimensional variational (4D-Var) data assimilation system was applied sequentially to the California Current circulation. The adjoint of the 4D-Var gain matrix was used to quantify the impact of individual observations and observation platforms on different aspects of the 4D-Var circulation estimates during both analysis and subsequent forecast cycles. In this study we focus on the alongshore and cross-shore transport of the California Current System associated with wind-induced coastal upwelling along the central California coast. The majority of the observations available during any given analysis cycle are from satellite platforms in the form of SST and SSH, and on average these data exert the largest controlling influence on the analysis increments and forecast skill of coastal transport. However, subsurface in situ observations from Argo floats, CTDs, XBTs and tagged marine mammals often have a considerable impact on analyses and forecasts of coastal transport, even though these observations represent a relatively small fraction of the available data at any particular time.During 4D-Var the observations are used to correct for uncertainties in the model control variables, namely the initial conditions, surface forcing, and open boundary conditions. It is found that correcting for uncertainties in both the initial conditions and surface forcing has the largest impact on the analysis increments in alongshore transport, while the cross-shore transport is controlled mainly by the surface forcing. The memory of the circulation associated with the control variable increments was also explored in relation to 7 day forecasts of the coastal circulation. Despite the importance of correcting for surface forcing uncertainties during analysis cycles, the coastal transport during forecast cycles initialized from the analyses has less memory of the surface forcing corrections, and is controlled primarily by the analysis initial conditions.Using the adjoint of the entire 4D-Var system we have also explored the sensitivity of the coastal transport to changes in the observations and the observation array. A single integration of the adjoint of 4D-Var can be used to predict the change that occurs when observations from different platforms are omitted from the 4D-Var analysis. Thus observing system experiments can be performed for each data assimilation cycle at a fraction of the computational cost that would be required to repeat the 4D-Var analyses when observations are withheld. This is the third part of a three part series describing the ROMS 4D-Var systems.     

Nekton migration and feeding location in a coastal area – A stable isotope approach

Stable isotope analysis was used to investigate nekton movements and feeding location in a coastal area adjacent to a major European river, the Tagus, Portugal. Particulate organic matter isotopic signatures presented a gradient from the river towards the sea. Phytoplankton, zooplankton, polychaetes and the crab, Polybius henslowii, provided evidence of the incorporation of terrestrial organic matter into the lower levels of the food web, reflecting local isotopic signatures. Two fish species reflected the coastal isotopic gradient in δ¹³C, Diplodus vulgaris and Arnoglossus imperialis and the latter also presented isotopic differerences among the sites for δ¹⁵N. Alloteuthis subulata, Trisopterus luscus and Callionymus lyra were isotopicaly distinct among sites for δ¹⁵N. An increase of δ¹⁵N with length was detected for T. luscus and C. lyra, possibly showing ontogenic trophic level changes. Since A. subulata did not present differences in length and still showed isotopic distinction for δ¹⁵N, among areas, it was concluded that local biogeochemical factors may also have an influence. Diplodus bellottii and Dicologlossa cuneata did not reflect any isotopic signature reflecting their wide migration and feeding across the coastal area. Central isotopic ranges, defined as the site mean values for δ¹³C and δ¹⁵N ± 1‰ were determined for each species and site and those deviating from these were considered transient individuals. Central isotopic ranges accounted for 87% of A. imperialis, 80% of A. subulata, 77% of T. luscus, 67% of C. lyra and 50% of D. vulgaris. The number of individuals within each central isotopic range was surprisingly high for an open coastal area and comparable to those of more structured environments.     

MPA as management tools for small-scale fisheries: The case study of Arrábida Marine Protected Area (Portugal)

Marine protected areas (MPA) have been widely suggested as a tool for both fisheries management and conservation goals. These multiple objectives are hard to achieve simultaneously as sustainable development implies the balance between the specific interests of conservation and economical activities. MPA success, namely for fisheries management, entails the implementation of restrictive measures that in a short-time frame may have negative effects on local fishermen communities. It is extremely important to evaluate their performance and effectiveness aiming at a quasi-optimal management, minimizing potential impacts on the social domain. In this study, a methodology for assessing the effectiveness of MPA as a small-scale fisheries management tool was developed, based on a set of indicators grouped in four dimensions (ecological, economic, social and management and governance). The indicators were scored individually according to an original score scale of five values and a median score was calculated for every dimension. Finally, the median overall score was calculated including the scores of the four dimensions. The scores were attributed for two distinct periods: before and after MPA implementation, in order to evaluate the performance of MPA. This methodology can be applied even with few scientific data available and taking into account experts and stakeholders’ judgements. The Arrábida MPA (Portugal) was used as a case study and it was found that with the implementation of the MPA social and economical aspects were impaired (median scores decreased near one value for the period after MPA implementation), while the other two dimensions showed an improvement trend. Thus, the overall score was the same before and after MPA implementation, an intermediate scale score. Results from the application of this method can give important indications about the state of an MPA and evaluate if the initial goals are being achieved through the implemented measures. The method is of easy communication and can be a useful tool for decision making and fisheries management processes.