V. Homar

The paradoxical increase of Mediterranean extreme daily rainfall in spite of decrease in total values

] Earlier reports indicated some specific isolated regionsexhibiting a paradoxical increase of extreme rainfall in spite ofdecrease in the totals. Here, we conduct a coherent study of thefull-scale of daily rainfall categories over a relatively largesubtropical region- the Mediterranean- in order to assess whetherthis paradoxical behavior is real and its extent. We show that thetorrential rainfall in Italy exceeding 128 mm/d has increasedpercentage-wise by a factor of 4 during 1951–1995 with strongpeaks in El-Nino years. In Spain, extreme categories at both tails ofthe distribution (light: 0-4 mm/d and heavy/torrential: 64 mm/d andup) increased significantly. No significant trends were found inIsrael and Cyprus. The consequent redistribution of the dailyrainfall categories -torrential/heavy against the moderate/lightintensities - is of utmost interest particularly in the semi-aridsub-tropical regions for purposes of water management, soilerosion and flash floods impacts. I

HYMEX , a 10-year Multidisciplinary Program on the mediterranean water cycle.

The Mediterranean countries are experiencing important challenges related to the water cycle, including water shortages and floods, extreme winds, and ice/snow storms, that impact critically the socioeconomic vitality in the area (causing damage to property, threatening lives, affecting the energy and transportation sectors, etc.). There are gaps in our understanding of the Mediterranean water cycle and its dynamics that include the variability of the Mediterranean Sea water budget and its feedback on the variability of the continental precipitation through air–sea interactions, the impact of precipitation variability on aquifer recharge, river discharge, and soil water content and vegetation characteristics specific to the Mediterranean basin and the mechanisms that control the location and intensity of heavy precipitating systems that often produce floods. The Hydrological Cycle in Mediterranean Experiment (HyMeX) program is a 10-yr concerted experimental effort at the international level that aims to advance the scientific knowledge of the water cycle variability in all compartments (land, sea, and atmosphere) and at various time and spatial scales. It also aims to improve the processes-based models needed for forecasting hydrometeorological extremes and the models of the regional climate system for predicting regional climate variability and evolution. Finally, it aims to assess the social and economic vulnerability to hydrometeorological natural hazards in the Mediterranean and the adaptation capacity of the territories and populations therein to provide support to policy makers to cope with water-related problems under the influence of climate change, by linking scientific outcomes with related policy requirements.

Diagnosis and numerical simulation of a torrential precipitation event in Catalonia (Spain)

SummaryA torrential precipitation event occurred in Catalonia (northeastern part of Spain) during 9 and 10 October 1994. More than 400mm were registered in the south of Catalonia. A diagnostic study shows that most of the ingredients to produce heavy rain (large scale upward vertical motion, instability, high moisture content in all the troposphere) were present over the Spanish coast and western Mediterranean. Mesoscale triggering mechanisms have been associated with the orographic forcing, not only through physical lifting of moist air by the coastal mountains, but also by the redistribution of the surface pressure field induced by the Atlas and Pyrenees ranges. A numerical simulation of the event using a meso-β model has been performed. The model forecasts qualitatively well the rainfall distribution but underestimates the maximum rainfalls. The effects of the orography and the evaporation from the sea have been also studied. The simulations have shown that the action of the orography is decisive for the rainfall, pressure and wind distrbutions over the Spanish coast and the western Mediterranean. The isolated action of the evaporation turns to be much less important. However the combined effect of orography and evaporation is the most important factor in the areas where the greatest amount of rainfall occurred.

Tornadoes and waterspouts in the Balearic Islands: phenomena and environment characterization

Abstract In the Balearic Islands, located in the Western Mediterranean, 27 tornadoes and 54 waterspouts have been recorded during the period 1989–1999. A climatology focusing, which focuses on path length, F-scale velocity, season and time of occurrence, is presented. September and October appear to be the months with the highest frequency of appearance. The environment in which thunderstorm producing tornadoes and waterspouts developed has been analysed. Main thermodynamic stability indices reveal that no specific conditions are required for the tornado and waterspout genesis. It is also found that these events form in air masses colder than that indicated by the climatology of the region. Analyses of helicity and CAPE demonstrate that, in most of the cases, the environments were not favourable for mesocyclone formation and supercell development.

A Statistical Adjustment of Regional Climate Model Outputs to Local Scales: Application to Platja de Palma, Spain

AbstractProjections of climate change effects for the System of Platja de Palma (SPdP) are derived using a novel statistical technique. Socioeconomic activities developed in this settlement are very closely linked to its climate. Any planning for socioeconomic opportunities in the mid- and long term must take into account the possible effects of climate change. To this aim, daily observed series of minimum and maximum temperatures, precipitation, relative humidity, cloud cover, and wind speed have been analyzed. For the climate projections, daily data generated by an ensemble of regional climate models (RCMs) have been used. To properly use RCM data at local scale, a quantile–quantile adjustment has been applied to the simulated regional projections. The method is based on detecting changes in the cumulative distribution functions between the recent past and successive time slices of the simulated climate and applying these, after calibration, to the recent past (observed) series. Results show an overall ...

Tornadoes over complex terrain: an analysis of the 28th August 1999 tornadic event in eastern Spain

Abstract On 28 August 1999, a tornadic storm developed during the afternoon over the Gudar range, near the border between Teruel and Castellon provinces ( Sistema Iberico , eastern Spain). The area has a characteristic complex terrain with peaks up to 2000 m. At least one tornado developed, which attained F3 intensity, producing severe damage in the forest that covers the mountains. The region is well known as a summer convective storm nest and, not surprisingly, a range in the Sistema Iberico is called Sierra del Rayo (lightning range). The meteorological situation on 28 August 1999 shows the presence of a thermal low over the Iberian peninsula, producing warm and moist air advection towards inland Castellon at low levels. Meanwhile, a cold trough crossed the Iberian Peninsula from west to east at upper levels. Deep convection is identified on the Meteosat images during the afternoon, when the upper level trough reached the area where warm and humid Mediterranean air was concentrated. The radar images reveal signals indicating the supercellular character of the tornado-producing storm. Weak echo region, frontal and rear inflow notches are identified on the low-level CAPPIs images. In order to study the roles of the orography and the solar radiation on the ingredients associated with the tornadic storm development, numerical simulations of the event were performed, using the non-hydrostatic MM5 model. Very fine grid resolution, up to 2 km in the horizontal, allows us to determine the role of the complex terrain in favoring environmental conditions associated with the onset of severe convection. In fact, interaction of certain low-level flows with particular topographic features with scales of about 20 to 50 km is found to generate intense small-scale circulations over the storm nesting region. A more detailed analysis of the orographic effect shows that fine scale terrain features (2–5 km) are responsible for the intensification of the convective storms, whereas modification of the low-level flow by the large-scale features (20–50 km) is able to trigger the convective systems. The effect of the solar-induced surface heating is also analyzed and it turns to be crucial not only by intensifying the Iberian thermal low and the easterly warm and moist air advection towards the area but also by promoting mountain breezes.

A synoptic and mesoscale diagnosis of a tornado outbreak in the Balearic Islands

A tornadic event occurred over the Balearic Islands (Western Mediterranean) during the evening of 11 September 1996 and the following night. A total of six tornadoes were observed, affecting populated areas, with an economical damage of more than 6 million Euro. The meteorological situation in which severe weather developed was characterised at low levels by a low covering all the Western Mediterranean with well-marked warm advection towards the Balearic Islands. At mid and upper levels, a low was located to the southwest of the Iberian peninsula, producing southwesterly winds over the region. Satellite imagery shows that the first tornado, observed over the Ibiza Island, was produced by a mature thunderstorm, which presented a well-defined V-shape on the IR images. Tornadoes occurring in Majorca and Minorca islands were produced by convective systems, which were in their initial development state. Most of these tornadogenetic convective systems developed over a low-level convergence line formed as a consequence of the existence of a low moving northeastwards along the south of the Balearics and a very small and deep cyclone formed offshore in front of the Valencia coast. Positive interaction between the low-level convergence line and an upper-level jet streak for producing the lift of low-level parcels has also been identified.

Present and future climate resources for various types of tourism in the Bay of Palma, Spain

The Bay of Palma, in Mallorca, is a leading region for beach holidays in Europe. It is based on a mass tourism model strongly modulated by seasonality and with high environmental costs. Main tourism stakeholders are currently implementing complementary activities to mitigate seasonality, regardless of climate change. But climate is—and will remain—a key resource or even a limitation for many types of tourism. Assessing the present conditions and exploring the future evolution of climate potential for these activities have become a priority in this area. To this end, the climate index for tourism (CIT)—originally designed to rate the climate resource of beach tourism—is adapted to specifically appraise cycling, cultural tourism, football, golf, motor boating, sailing and hiking. Climate resources are derived by using observed and projected daily meteorological data. Projections have been obtained from a suite of Regional Climate Models run under the A1B emissions scenario. To properly derive CITs at such local scale, we apply a statistical adjustment. Present climate potentials ratify the appropriateness of the Bay of Palma for satisfactorily practicing all the examined activities. However, optimal conditions are projected to degrade during the peak visitation period while improving in spring and autumn. That is, climate change could further exacerbate the present imbalance between the seasonal distributions of ideal climate potentials and high attendance levels. With this information at hand, policy makers and regional tourism stakeholders can respond more effectively to the great challenge of local adaptation to climate change.

A Comparison of Ensemble Strategies for Flash Flood Forecasting: The 12 October 2007 Case Study in Valencia, Spain

AbstractOn 12 October 2007, several flash floods affected the Valencia region, eastern Spain, with devastating impacts in terms of human, social, and economic losses. An enhanced modeling and forecasting of these extremes, which can provide a tangible basis for flood early warning procedures and mitigation measures over the Mediterranean, is one of the fundamental motivations of the international Hydrological Cycle in the Mediterranean Experiment (HyMeX) program. The predictability bounds set by multiple sources of hydrological and meteorological uncertainty require their explicit representation in hydrometeorological forecasting systems. By including local convective precipitation systems, short-range ensemble prediction systems (SREPSs) provide a state-of-the-art framework to generate quantitative discharge forecasts and to cope with different sources of external-scale (i.e., external to the hydrological system) uncertainties. The performance of three distinct hydrological ensemble prediction systems (H...

PREGRIDBAL 1.0: towards a high-resolution rainfall atlas for the Balearic Islands (1950–2009)

This work presents a catalog of daily precipitation fields in the Balearic Islands created with data from AEMET (State Meteorological Agency) assistant observations, including records from 1912. The original digital daily data file has been interpolated onto a regular 100 m-resolution grid (namely PREGRIDBAL), defined with the aim of becoming a valid standard for future methodological improvements and catalog upgrades. Daily precipitation amounts on each grid point are calculated using an analysis method based on ordinary kriging, using the daily anomaly with respect to the annual mean for all available observations each day. Due to quality concerns, the time span for products derived from the catalog is limited to the 1950–2009 period, when the number of operating stations reached 200. Therefore, from the time series of daily maps, monthly-, annual-, quinquennial-, and decadal-accumulations are produced. Similarly, the catalog allowed for quantification of climate trends in rainfall amounts in the Balearic Islands, with the significant advantage of minimizing the biases originated from heterogeneities in the spatial distribution of stations across the archipelago. Results show a general decrease in precipitation during the 1950–2009 period. From 1950 to 1979, the average annual precipitation across the islands was 624.3 mm, while from 1980 to 2009 it diminished to 555.36 mm. Changes in precipitation patterns, which vary among the different areas, are also detected. The most significant reductions are found in the northern half of the archipelago and especially in Mallorca, where the Tramuntana mountain range stands out. All seasonal trends show a decrease, with values ranging between 1 and 3 mm decade 1, with the exception of autumn, which reaches a positive trend up to 7 mm decade 1. October shows the most dramatic decrease ( 10.34 mm decade 1) and, conversely, September and November show an increase in precipitation (3.28 and 1.82 mm decade 1, respectively) with a statistical significance above 85 % across almost the entire archipelago, and even exceeding 95 % in Eivissa and Formentera.