Hydrological responses to rainfall events including the extratropical cyclone Gloria in two contrasting Mediterranean headwaters in Spain; the perennial font del Regàs and the intermittent Fuirosos

Catchment hydrological responses to precipitation inputs, particularly during exceptionally large storms, are complex and variable, and our understanding of the associated runoff generation processes during those events is limited. Hydrological monitoring of climatically and hydrologically distinct catchments can help to improve this understanding by shedding light on the interplay between antecedent soil moisture conditions, hydrological connectivity, and rainfall event characteristics. This knowledge is urgently needed considering that both the frequency and magnitude of extreme precipitation events are increasing worldwide as a consequence of climate change. In autumn 2018, we installed water level sensors to monitor stream water and near-stream groundwater levels at two Mediterranean forest headwater catchments with contrasting hydrological regimes: Font del Regàs (sub-humid climate, perennial flow regime) and Fuirosos (semi-arid climate, intermittent flow regime). Both catchments are located in northeastern Spain, where the extratropical cyclone Gloria hit in January 2020 and left in ca. 65 h outstanding accumulated rainfalls of 424 mm in Font del Regàs and 230 mm in Fuirosos. During rainfall events of low mean intensity, hydrological responses to precipitation inputs at the semi-arid Fuirosos were more delayed and more variable than at the sub-humid Font del Regàs. We explain these divergences by differences in antecedent soil moisture conditions and associated differences in catchment hydrological connectivity between the two catchments, which in this case are likely driven by differences in local climate rather than by differences in local topography. In contrast, during events of moderate and high mean rainfall intensities, including the storm Gloria, precipitation inputs and hydrological responses correlated similarly in the two catchments. We explain this convergence by rapid development of hydrological connectivity independently of antecedent soil moisture conditions. The data set presented here is unique and contributes to our mechanistic understanding on how streams respond to rainfall events and exceptionally large storms in catchments with contrasting flow regimes.     

The Tous dam disaster of 1982 and the origins of integrated flood risk management in Spain

The failure of the Tous dam in 1982 caused one of the most important socio-natural disasters in Spain during the twentieth century. That event triggered a paradigm change in the way disaster risks were perceived and managed, not only locally, but also at multiple levels of governance. Fifteen interviews with relevant stakeholders, content analysis of scientific literature, and review of historical and media accounts indicate that the collapse of the Tous dam had the two major effects. First, it prompted a process of institutional development, which led to the growth, and increase in complexity of the organizations involved both in vertical and horizontal communication of disaster risk reduction. Second, actions taken and experiences gained in dealing with disaster risk reduction in the Tous area were used as a benchmark to develop new strategies, as well as new mechanisms for communication and planning in other territories and other risk domains in Spain. This paper also identified the three main stages in the evolution of disaster risk reduction planning in the area: (1) After the collapse of the Tous dam, disaster risk reduction strategies in Spain focused on improving preparedness in order to reduce short-term risks. (2) Disaster management in the 1990s was strongly influenced by international initiatives, which emphasized the contextualization of risk and the importance in long-term disaster risk reduction measures such as land-use planning. (3) The European Water Framework Directive (2000) and, more recently, the Floods Directive (2007) are exerting a strong influence on the development of a new Spanish flood policy that focuses on preventive measures. However, this process is far from complete and many issues still remain unresolved: dealing with different domains of risk action, integrating concepts of ecological resilience and climate change, and promoting public awareness and effective participation.     

Climate change transformation: A definition and typology to guide decision making in urban environments

Climate change presents a threat to the sustainability of cities and their societies, and must be adequately addressed. Urban environments (cities) are responsible for the creation of a significant amount of greenhouse gas emissions which are the source of climate change. Cities have been increasingly the focus of action to address climate change, yet emissions are not significantly reducing. Additionally, there a lack of integration between adaptation and mitigation. This prevents responses adequate to limit global warming to 1.5^OC, and to be well adapted to anticipated changes. This paper critically analyses existing definitions and typologies of climate change actions. A definition of ‘climate change transformation’ is proposed which includes the integration of adaptation and mitigation goals to enable a new regime in which global warming is limited to 1.5^OC. A new three-part typology: ‘coping, malaction and transformation,’ is presented for categorising climate change actions by the extent to which they integrate adaptation and mitigation, and define a new regime. The typology is accompanied by illustrations to demonstrate the relationship between adaptation and mitigation. The definition, typology and illustration serve to guide effective climate change decision making, and provides principles to guide application in urban environments.     

Aquifer heat storage: sulphate reduction with acetate at increased temperatures

Aquifer thermal energy storage in urban and industrial areas can lead to an increase in subsurface temperature to 70 °C and more. Besides its impacts on mineral and sorption equilibria and chemical reaction kinetics in an aquifer, temperature sensitively influences microbial activity and thus redox processes, such as sulphate reduction. Microorganism species can only operate within limited temperature ranges and their adaptability to temperature is a crucial point for the assessment of the environmental consequences of subsurface heat storage. Column experiments with aquifer sediment and tap water at 10, 25, 40, and 70 °C showed that under the constant addition of acetate sulphate reduction could be initiated after 26–63 pore volumes exchanged at all temperatures. Fastest initiation of sulphate reduction with the highest reduction rates was found at 40 °C. Maximum rate constants during experimental run-time were 0.56 h^?1 at 40 °C and 0.33, 0.36, and 0.25 h^?1 at 10 and, 25, and 70 °C, respectively. Hence, microbial activity was enhanced by a temperature increase to 40 °C but was significantly lowered at 70 °C. At 25 °C methane was found in solution, indicating the presence of fermenting organisms; at 10, 40, and 70 °C no methane production was observed. It could be shown that redox processes in an aquifer generally can adapt to temperatures significantly higher than in situ temperature and that the efficiency of the reduction process can be enhanced by temperature increase to a certain limit. Enhancement of sulphate reduction in an aquifer due to temperature increase could also allow enhanced degradation of organic ground water contaminants such as BTEX, where sulphate is an important electron acceptor.     

Generalized migration in frequency-wavenumber domain (MGF-K) in anisotropic media

In this paper, the background of MGF-K migration in dual domain (wavenumber-frequency K-F and space-time) in anisotropic media is presented. Algorithms for poststack (zero-offset) and prestack migration are based on downward extrapolation of acoustic wavefield by shift-phase with correction filter for lateral variability of medium’s parameters. In anisotropic media, the vertical wavenumber was determined from full elastic wavefield equations for two dimensional (2D) tilted transverse isotropy (TTI) model. The method was tested on a synthetic wavefield for TTI anticlinal model (zero-offset section) and on strongly inhomogeneous vertical transverse isotropy (VTI) Marmousi model. In both cases, the proper imaging of assumed media was obtained.     

SEDIMENT SOURCES OF NEBKHAS IN THE SAHEL ZONE OF BURKINA FASO

Owing to the decline in rainfall and intensified land use in the Sahel during the past 25 years, wind erosion is causing increasing problems in this region. The aim of the present paper is to identify possible sources for the material found in nebkhas in northern Burkina Faso. Nebkhas are plant-obstacle dunes that frequently occur in semi-arid areas. Grain-size distributions of nebkha sediments and five other subenvironments were analyzed using univariate and multivariate methods. Quartz-grain surface textures were studied by Scanning Electron Microscopy (SEM).

The SEM and grain-size analyses together indicate that the nebkhas have experienced considerable recent aeolian abrasion and sorting as compared with the five other sub-environments. It was concluded that the material in the nebkhas investigated is local in origin and that it mainly has been eroded by wind from adjacent disturbed soils or deflated from loose material made available for wind erosion by sheet-wash processes. This means that wind erosion is an important process in the removal of topsoil in this Sahelian environment and that measures to reduce wind erosion should be taken to protect sensitive soils. [Key words: Nebkhas, wind erosion, Sahel, Burkina Faso.]     

2012 Urban Geography Plenary Lecture Topological City

The purpose of this paper is to explore the idea of the topological city, both by sharing some observations about the use of topology in critical human geography today and also by demonstrating how different modes of topological analyses of the city may work. This paper suggests that while topology is not new to the social sciences in general or geography in particular, an uptick in interest in topology in the past decade is likely due to its role in the work of Deleuze and Agamben. Topology, I suggest, can help geographers think in creative ways about spatial ontology, thereby offering some insights into the relationship between the subject and the city. I build this argument by discussing the topological workings of three cinematic cities: The Adjustment Bureau (2011), Midnight in Paris (2011), and Inception (2010). [Key words: topology, film, Lacan, subject, spatial theory.]     

Spectro-Polarimetric Observations and Non-Lte Modeling of Ellerman Bombs

Ellerman bombs are bright emission features observed in the wings of Hα, usually in the vicinity of magnetic concentrations. Here we show that they can also be detected in the Ca II infrared triplet lines, which are easier to interpret and therefore allow for more detailed diagnostics. We present full Stokes observations of the 849.8 and 854.2 nm lines acquired with the new spectro-polarimeter SPINOR. The data show no significant linear polarization at the level of 3 × 10⁻⁴. The circular polarization profiles exhibit measureable signals with a very intricate pattern of peaks. A non-LTE analysis of the spectral profiles emerging from these features reveals the presence of strong downflows (∼10 {km s⁻¹}) in a hot layer between the upper photosphere and the lower chromosphere. Visiting Astronomers, National Solar Observatory, operated by the Association of Universities for Research in Astronomy, Inc. (AURA), under cooperative agreement with the National Science Foundation. The National Center for Atmospheric Research (NCAR) is sponsored by the National Science Foundation, USA.     

Fluid inclusion evidence for deep burial of the Tertiary accretionary wedge of the Carpathians

Hydrothermal quartz from mineralized joints of the Carpathian accretionary wedge contains immiscible aqueous, oil‐condensate, methane and carbon dioxide‐rich fluid inclusions. Distribution patterns of the inclusion trapping PT parameters point to a crack‐seal mechanism during upward and lateral migration of hot methane‐rich fluids from overpressured sediments at the base of the accretionary wedge. A simple equation is proposed to calculate depths from densities and trapping pressures of the buoyant inclusion fluids. In the Carpathian accretionary wedge, the paleofluid pressures of 52–306 MPa correspond to a 5‐ to 11‐km‐thick overburden. Prior to exhumation, thickness of the wedge must have attained 10–25 km, of which only c. 50% was preserved until recently. Anomalously high methane densities (up to 0.43 g cm^?3) recorded in the lowermost nappe sheets are provisionally interpreted as a result of supralithostatic overpressure due to thermal cracking of oil and kerogen to methane and pyrobitumen at temperatures above 200 °C.