Evidence of increasing drought severity caused by temperature rise in southern Europe

We use high quality climate data from ground meteorological stations in the Iberian Peninsula (IP) and robust drought indices to confirm that drought severity has increased in the past five decades, as a consequence of greater atmospheric evaporative demand resulting from temperature rise. Increased drought severity is independent of the model used to quantify the reference evapotranspiration. We have also focused on drought impacts to droughtsensitive systems, such as river discharge, by analyzing streamflow data for 287 rivers in the IP, and found that hydrological drought frequency and severity have also increased in the past five decades in natural, regulated and highly regulated basins. Recent positive trend in the atmospheric water demand has had a direct influence on the temporal evolution of streamflows, clearly identified during the warm season, in which higher evapotranspiration rates are recorded. This pattern of increase in evaporative demand and greater drought severity is probably applicable to other semiarid regions of the world, including other Mediterranean areas, the Sahel, southern Australia and South Africa, and can be expected to increasingly compromise water supplies and cause political, social and economic tensions among regions in the near future.This work has been supported by research projects CGL201127574CO202, CGL201127536 and CGL2011–24185 financed by the Spanish Commission of Science and Technology and FEDER, ‘Demonstration and validation of innovative methodology for regional climate change adaptation in the Mediterranean area (LIFE MEDACC)’ financed by the LIFE programme of the European Commission, CTTP1/12, financed by the Comunidad de Trabajo de los Pirineos, and QSECA (PTDC/AAGGLO/ 4155/2012) funded by the Portuguese Foundation for Science and Technology (FCT). ASL was supported by a postdoctoral fellowship from the Catalan Government (2011 BPB 00078) and CAM was supported by a Juan de la Cierva fellowship by the Spanish Government

Control of style-of-faulting on spatial pattern of earthquake-triggered landslides

Predictive mapping of susceptibility to earthquake-triggered landslides (ETLs) commonly uses distance to fault as spatial predictor, regardless of style-of-faulting. Here, we examined the hypothesis that the spatial pattern of ETLs is influenced by style-of-faulting based on distance distribution analysis and Fry analysis. The Yingxiu–Beichuan fault (YBF) in China and a huge number of landslides that ruptured and occurred, respectively, during the 2008 Wenchuan earthquake permitted this study because the style-of-faulting along the YBF varied from its southern to northern parts (i.e. mainly thrust-slip in the southern part, oblique-slip in the central part and mainly strike-slip in the northern part). On the YBF hanging-wall, ETLs at 4.4–4.7 and 10.3–11.5 km from the YBF are likely associated with strike- and thrust-slips, respectively. On the southern and central parts of the hanging-wall, ETLs at 7.5–8 km from the YBF are likely associated with oblique-slips. These findings indicate that the spatial pattern of ETLs is influenced by style-of-faulting. Based on knowledge about the style-of-faulting and by using evidential belief functions to create a predictor map based on proximity to faults, we obtained higher landslide prediction accuracy than by using unclassified faults. When distance from unclassified parts of the YBF is used as predictor, the prediction accuracy is 80%; when distance from parts of the YBF, classified according to style-of-faulting, is used as predictor, the prediction accuracy is 93%. Therefore, mapping and classification of faults and proper spatial representation of fault control on occurrence of ETLs are important in predictive mapping of susceptibility to ETLs

Modelling the initiation and runout of rainfall induced debris flows in the Cardoso basin (Apuan Alps, Italy)

A GIS based mass flow model was used to simulate debris flow triggering and evolution: a saturated/unsaturated soil water model was used to simulate the distribution of soil water and the generation of excess pore pressure leading to slope instability during a rainfall event. The model is able to detect potential instability due both to the development of a perched watertable at the colluvium/bedrock interface, and to the development of a saturated top layer because of the direct infiltration of rainfall during an intense event. Stability conditions are evaluated at the bottom of the saturated zones, i.e. at the wetting front and at the soil-rock contact. The safety factor, ratio of stabilizing forces or shear strength to destabilizing forces or shear stress, is calculated assuming the infinite slope model. The geotechnical parameters c' and phi can be introduced with uncertainty (mean value and variance); confidence intervals are calculated using a first order second moment (FOSM) method. This also allows to the estimate the failure probabilities. A flow routing model is then used to simulate the spreading and deposition of the mud/debris mixture on the hillslopes: once a landslide has been predicted, the location and released volume are used as inputs to a second model to simulate the spreading of the debris on the hillslope. The dynamic model has been built with PCRaster Software, based on the Bingham rheological expression. This model is applied to simulate the debris flow triggering and evolution in the Cardoso Torrent basin (Upper Versilia, NW Tuscany - Italy), where an extremely heavy rainstorm (about 500 mm within 12 hours) hit some restricted areas on June 19th, 1996, involving a few basins of the Versilia and Garfagnana areas and inducing various effects on the slopes (soil slips and debris flows). A large number of data is available thanks to detailed surveys, which provided the characterization of the main factors (pluviometric, hydrogeological, geological, geomorphological and geotechnical) contributing to the landslide triggering. In particular, some factors were recurrent in the landslide sites: bedrock features (impermeable bedrock, discontinuity dipping downslope), slope morphology (hollow shape), geotechnical characteristics (fine, scarcely permeable cover material)

Comparison of uncertainty sources for climate change impacts: flood frequency in England

This paper investigates the uncertainty in the impact of climate change on flood frequency in England, through the use of continuous simulation of river flows. Six different sources of uncertainty are discussed: future greenhouse gas emissions; Global Climate Model (GCM) structure; downscaling from GCMs (including Regional Climate Model structure); hydrological model structure; hydrological model parameters and the internal variability of the climate system (sampled by applying different GCM initial conditions). These sources of uncertainty are demonstrated (separately) for two example catchments in England, by propagation through to flood frequency impact. The results suggest that uncertainty from GCM structure is by far the largest source of uncertainty. However, this is due to the extremely large increases in winter rainfall predicted by one of the five GCMs used. Other sources of uncertainty become more significant if the results from this GCM are omitted, although uncertainty from sources relating to modelling of the future climate is generally still larger than that relating to emissions or hydrological modelling. It is also shown that understanding current and future natural variability is critical in assessing the importance of climate change impacts on hydrology

Spatio‐temporal variability of daily precipitation concentration in Spain based on a high‐resolution gridded data set

An analysis of the spatial and temporal variability of daily precipitation concentration (CI) in Spain was made based on a high‐resolution (5 × 5 km) daily gridded precipitation data set for the 1950–2012 period. For each grid point in the Iberian Peninsula (IP) and Balearic and Canary Islands, the average annual CI was computed, as well as its coefficient of variation and the 5th and 95th percentiles. Annual values were also computed, and the time series of the index were used to assess temporal trends over the whole period. The spatial distribution of the CI showed a strong relationship with the orographic barriers near the coastlines. The Canary Islands showed the highest values of CI, along with the eastern Mediterranean facade of the IP. The highest inter‐annual variations of the CI occurred in the southern IP and in the southern Canary Islands. The trends of CI were, overall, positive and significant, which indicates an increase of daily precipitation concentration over the study period and an increasing environmental risks scenario where erosivity, torrentiality, and floods may become more frequent.This study was supported by research projects CGL2015-69985-R and CGL2014-52135 C3-1-R, and financed by the Spanish Ministerio de Economía y Competitividad (MINECO) and EU FEDER-ERDF funds. RSN, MDL, MAS, and LAL were supported by the Government of Aragón through the ‘Programme of research groups’ (group H38, ‘Clima, Agua, Cambio Global y Sistemas Naturales’), as well as SB (group ‘E68, Geomorfología y Cambio Global’). The authors would also like to thank the Climatology Group (2014SGR300, Catalan Government), the Convenio de Desempeño UTA-MINEDUC, and the FONDECYT Project 11160059 of the Chilean Government.Peer Reviewe