Mediterranean climate extremes in synoptic downscaling assessments

The behaviour of precipitation and maximum temperature extremes in the Mediterranean area under climate change conditions is analysed in the present study. In this context, the ability of synoptic downscaling techniques in combination with extreme value statistics for dealing with extremes is investigated. Analyses are based upon a set of long-term station time series in the whole Mediterranean area. At first, a station-specific ensemble approach for model validation was developed which includes (1) the downscaling of daily precipitation and maximum temperature values from the large-scale atmospheric circulation via analogue method and (2) the fitting of extremes by generalized Pareto distribution (GPD). Model uncertainties are quantified as confidence intervals derived from the ensemble distributions of GPD-related return values and described by a new metric called “ratio of overlapping”. Model performance for extreme precipitation is highest in winter, whereas the best models for maximum temperature extremes are set up in autumn. Valid models are applied to a 30-year period at the end of the twenty-first century (2070–2099) by means of ECHAM5/MPI-OM general circulation model data for IPCC SRES B1 scenario. The most distinctive future changes are observed in autumn in terms of a strong reduction of precipitation extremes in Northwest Iberia and the Northern Central Mediterranean area as well as a simultaneous distinct increase of maximum temperature extremes in Southwestern Iberia and the Central and Southeastern Mediterranean regions. These signals are checked for changes in the underlying dynamical processes using extreme-related circulation classifications. The most important finding connected to future changes of precipitation extremes in the Northwestern Mediterranean area is a reduction of southerly displaced deep North Atlantic cyclones in 2070–2099 as associated with a strengthened North Atlantic Oscillation. Thus, the here estimated future changes of extreme precipitation are in line with the discourse about the influence of North Atlantic circulation variability on the changing climate in Europe.     

Measuring the impact of pollution on property prices in Madrid: objective versus subjective pollution indicators in spatial models

Much work has been done in the context of the hedonic price theory to estimate the impact of air quality on housing prices. Research has employed objective measures of air quality, but only slightly confirms the hedonic theory in the best of cases: the implicit price function relating housing prices to air pollution will, ceteris paribus, be negatively sloped. This paper compares the performance of a spatial Durbin model when using both objective and subjective measures of pollution. On the one hand, we design an Air Pollution Indicator based on measured pollution as the objective measure of pollution. On the other hand, the subjective measure of pollution employed to characterize neighborhoods is the percentage of residents who declare that the neighborhood has serious pollution problems, the percentage being referred to as residents’ perception of pollution. For comparison purposes, the empirical part of this research focuses on Madrid (Spain). The study employs a proprietary database containing information about the price and 27 characteristics of 11,796 owner-occupied single family homes. As far as the authors are aware, it is the largest database ever used to analyze the Madrid housing market. The results of the study clearly favor the use of subjective air quality measures.     

Fighting for a future: an actor-oriented planning approach to landscape preservation in Galicia

Modification and channelization of streams and rivers have been conducted extensively throughout the world during the past century. Subsequently, much effort has been directed at re-creating the lost habitats and thereby improving living conditions for aquatic organisms. However, as restoration methods are plentiful, it is difficult to determine which one to use to get the anticipated result. The aim of this study was to compare two commonly used methods in small Danish streams to improve the physical condition: re-meandering and passive restoration through cease of maintenance. Our investigation included measurement of the physical conditions in 29 stream reaches covering four different groups: (1) re-meandered streams, (2) LDC streams (the least disturbed streams available), (3) passively restored streams (>10?years stop of maintenance) and (4) channelized and non-restored streams. The in-stream habitats were compared through analysis of the measured physical parameters and by applying a habitat model. We found that re-meandering is a more effective way of re-creating near-natural physical conditions in small streams compared to passive restoration. This is probably due to the limited energy in small streams which restricts re-shaping of the stream channel. However, based on habitat suitability modelling, the change to the physical condition did not translate into improved habitat suitability for young of the year brown trout highlighting the value of using several methods when evaluating restoration success.     

Groundwater evolution and mean water age inferred from hydrochemical and isotopic tracers in a tropical confined aquifer

The coastal confined aquifer in the Gulf of Urabá (Colombia) is an important water source for the banana agro‐industry as well as for urban and rural communities. However, the main processes controlling recharge and mixing in the aquifer are still poorly understood. Hydrochemical analyses and stable isotope monitoring were conducted to (a) determine groundwater recharge origin, mean groundwater age, and the main processes governing groundwater chemistry and the potential mixing of marine water and the influence of diffusive processes from the two surrounding aquitard layers. Hydrochemical data indicate that the main processes affecting the dissolved chemical composition include cation exchange, dissolution of carbonated and CO₂, and silicate weathering. δ¹⁸O and δ²H compositions combined with ¹⁴C data highlight the differences in climatic conditions between the recharge zone and the confined section of the aquifer, which is close to the Atlantic Ocean. Groundwater samples with ¹⁴C ages from recent to 28,300 years BP show a depleted isotopic trend ranging from ?6.43‰ to ?9.14‰ in δ¹⁸O and from ?43.2‰ to ?65.7‰ in δ²H. The most depleted δ¹⁸O and δ²H compositions suggest a cooler recharge climate than the current conditions (corresponding to the last glacial period of the late Pleistocene). Depleted δ¹³C values in the total dissolved inorganic carbon indicate the existence of organic material oxidation processes within the geologic formation. These results can be used or transferred to enhance groundwater modelling efforts in other confined coastal aquifers of South America where scarcity of long‐term monitoring data limits water resources planification under a changing climate.     

Deformation structures associated with the Tazo landslide (La Gomera, Canary Islands)

Deformation structures below the basal plane of gravitational slides can provide useful information about the state of stress undergone by rocks prior to the sliding process and about the triggering forces acting at each particular sliding event. In the present work we conducted a structural analysis of the rocks below the surface of the gravitational slide of Tazo (La Gomera, Canary Islands) and determined the epigenetic processes involved in the filling of the amphitheatre. We also inferred the possible triggering phenomena related to the Tazo landslide. The rocks located below the surface of the gravitational slide of Tazo -i.e., the basaltic lava flows, sills and dikes of the Lower Old Edifice and the submarine volcanic rocks, gabbros, pyroxenites and dikes of the Basal Complex of La Gomera- are strongly deformed close to this sliding surface. The lava flows and dikes of the Lower Old Edifice are folded, with fault breccias and gouges, and locally foliated, defining the sliding surface. The dikes of the Basal Complex are also folded, and the gabbros and pyroxenites are affected by a large number of small faults. In the Basal Complex, the sliding surface is defined by a foliated granular gouge. In the damage zone, the Basal Complex rocks show an incipient fracture cleavage. The sliding amphitheatre has been filled by the debris avalanche or cohesive debris flow generated within the slide, as well as by later debris flows, hyperconcentrated flows, sheet flows, and by interspersed lava flows from the Upper Old Edifice. We suggest here that the collapse of the north-western flank of the Lower Old Edifice at Tazo could in part have been triggered by continuous magma injection, associated with the emplacement of dikes in a rift zone with an ENE-WSW direction, enhanced by the mechanical weakness of the Basal Complex unit, which was affected by hydrothermal metamorphism under greenschist facies conditions and by the displacement along the Montaña de Alcalá and Guillama normal faults, which are deeply entrenched in the altered rocks of the Basal Complex.     

Modelling the effect of soil burn severity on soil erosion at hillslope scale in the first year following wildfire in NW Spain

Fire severity is recognized as a key factor in explaining post‐fire soil erosion. However, the relationship between soil burn severity and soil loss has not been fully established until now. Sediment availability may also affect the extent of post‐fire soil erosion. The objective of this study was to determine whether soil burn severity, estimated by an operational classification system based on visual indicators, can significantly explain soil loss in the first year after wildfire in shrubland and other areas affected by crown fires in northwest (NW) Spain. An additional aim was to establish indicators of sediment availability for use as explanatory variables for post‐fire soil loss. For these purposes, we measured hillslope‐scale sediment production rates and site characteristics during the first year after wildfire in 15 experimental sites using 65 plots. Sediment yields varied from 0.2 Mg ha^?1 to 50.1 Mg ha^?1 and soil burn severity ranged from low (1.8) to very high (4.5) in the study period. A model that included soil burn severity, annual precipitation and a land use factor (as a surrogate for sediment availability) as explanatory variables reasonably explained the erosion losses measured during the first year after fire. Model validation confirmed the usefulness of this empirical model. The proposed empirical model could be used by forest managers to help evaluate erosion risks and to plan post‐fire stabilization activities. Copyright © 2015 John Wiley & Sons, Ltd.     

An Elliptical Model for Deformation Due to Groundwater Fluctuations

Historically, surface subsidence as a result of subsurface groundwater fluctuations have produced important and, at times, catastrophic effects, whether natural or anthropogenic. Over the past 30?years, numerical and analytical techniques for the modeling of this surface deformation, based upon elastic and poroelastic theory, have been remarkably successful in predicting the magnitude of that deformation (Le Mouélic and Adragna in Geophys Res Lett 29:1853, 2002). In this work we have extended the formula for a circular-shaped aquifer (Geertsma in J Petroleum Tech 25:734–744, 1973) to a more realistic elliptical shape. We have improved the accuracy of the approximation by making use of the cross terms of the expansion for the elliptic coordinates in terms of the eccentricity, e, and the mean anomaly angle, M, widely used in astronomy. Results of a number of simulations, in terms of e and M developed from the transcendental Kepler equation, are encouraging, giving realistic values for the elliptical approximation of the vertical deformation due to groundwater change. Finally, we have applied the algorithm to modeling of groundwater in southern California.     

Using a Mesoscale Meteorological Model to Reduce the Effect of Tropospheric Water Vapour from DInSAR Data: A Case Study for the Island of Tenerife, Canary Islands

Measurements of ground displacement through classical Differential Interferometric SAR (DInSAR) and advanced DInSAR techniques have been carried out over the entire actively volcanic island of Tenerife, Canary Islands. However, a detailed analysis of the effect of tropospheric water vapour on DInSAR at Tenerife should be carried out to evaluate its influence, including correction models that might improve the accuracy of DInSAR derived deformation signals. Unlike water vapour correction models that are based on space platforms (e.g. MODIS and MERIS), we present an alternative approach that is based on precise water vapour estimations derived from mesoscale numerical meteorological models, in particular the Weather Research and Forecasting (WRF) model. The application of this approach to a set of DInSAR observations of the island of Tenerife shows encouraging results.