Analysis of the precipitation and cloudiness associated with COLs occurrence in the Iberian Peninsula

Summary The Iberian Peninsula is one of the regions in the world with higher occurrence of cut-off low systems (COL). The aim of this paper is to analyse the weather events (rainfall and cloudiness layer) associated to COLs in the Iberian Peninsula with tools not previously used: (a) the use of the new multidecadal COLs database developed by Nieto et al (2005) that permit us to study a 41 years period (1958–1998), (b) the checking of the expected weather events (rainfall and cloudiness layer) associated with COLs in a conceptual model (Winkler et al, 2005) and (c) the extensive use of radiosoundings to analyse convective instability in areas inside and close to the COL. Two points of view are used to make the analysis: (1) a source oriented method, when a particular COL is followed and its associated precipitation and cloudiness is analysed over four quadrants in which Iberia was divided and (2) a receptor oriented method, when the precipitation associated to COLs is analysed in given areas, defined by patterns of precipitation. Results reveal that the precipitation and cloudiness patterns associated to COLs in the conceptual model reproduce quite well the main characteristics found over the Iberian Peninsula. The generalized idea that most of the COLs produce intense convective rainfall is show to be misleading. Convective phenomena are important usually when the centre of the COL is located on the Mediterranean region. Most of the rainfall associated with COLs comes from the baroclinic shield; specially in cases located over the west half of the Iberian Peninsula. It is shown that nearly 30% of COLs do not induce any rainfall; most of them located in the southern half of the Peninsula, and mainly during autumn. Only 30% of COLs produce generalized rainfall over the whole analysed territory, being most of them (about 90%) located over the western half of the Iberian Peninsula.     

Changes in Fire and Climate in the Eastern Iberian Peninsula (Mediterranean Basin)

Fire is a dominant ecological factor in Mediterranean ecosystems, and changes in the fire regime can have important consequences for the stability of our landscapes. In this framework I asked firstly, what is the trend in fire number and area burned in the eastern Iberian Peninsula, and then, to what extent is the inter-annual variability of fires determined by climatic factors. To answer these questions I analysed the meteorological data (temperature and precipitation) from 350 stations covering the eastern Iberian Peninsula (1950–2000), and the fire records for the same area (historical data, 1874–1968, and data from recent decades, 1968–2000). The results suggested a slight tendency towards decreasing summer rainfall and a clear pattern of increasing annual and summer temperatures (on average, annual temperatures increased 0.35 °C per decade from 1950 to 2000). The analysis of fire records suggested a clear increase in the annual number of fires and area burned during the last century; however, in the last three decades the number of fires also increased but the area burned did not show a clear trend. For this period the inter-annual variability in area burned was significantly related to the summer rainfall, that is, in wet summers the area burned was lower that in dry summers. Furthermore, summer rainfall was significantly cross-correlated with summer area burned for a time-lag of 2 years, suggesting that high rainfall may increase fuel loads that burn 2 years later.     

Nocturnal offshore precipitation near the Mediterranean coast of the Iberian Peninsula

While nocturnal offshore precipitation, which produces rain cells and bands, has been studied in tropical areas, few studies have analyzed the occurrence of this phenomenon at higher latitudes. Using radar reflectivity, nocturnal rainfall in the western Mediterranean area has been detected near the coast of the Iberian Peninsula and North Africa. More than 50 events have been recorded since 2009. MM5 mesoscale simulations of some of the recorded events allow us to establish that the most likely causes for these precipitation events are: (1) the interaction between cold air masses conducted by drainage and katabatic winds, and (2) a wetter and warmer synoptic wind. Two different episodes are presented: one in the northeastern Iberian Peninsula, caused by stratiform clouds, which occurred at the mouths of three rivers; the other case, produced by convective clouds, occurred at the southern Iberian Peninsula and was caused by the drainage winds flowing down from some mountain ranges located close to the coast.     

Climatic fluctuations in southern Italy since the 17th century: reconstruction with precipitation records at Benevento

This work analyses the climatic information of 607 weather anomalies belonging to a large documentary sources heritage of the continental southern Italy during the period 1675–1868. The collected information, mainly originating in Samnium River Region (SRR), were codified to obtain quantitative indices representative of a preliminary reconstruction of the precipitation anomalies. Historical written records of weather conditions that affect agriculture and living conditions have been taken as a proxy for instrumental observations of the relative wetness and dryness. As a consequence a numerical index was established to characterize the rainfall regime and its evolution. So, for the first time a series of the precipitation anomalies in SRR–continental southern Italy during the second half of the Little Ice Age was generated, and subsequently jointed to the instrumental series (1869–2002). Afterwards, in order to identify possible climatic change situations from 1675 today Normalized Cumulative Anomalies (NCA)–serie's and Climograms were produced. This historical period offered a sufficient range of natural variability in climate and circulation together with their relationships. Wettest period were detected in the 19th century, while that driest in the 18th century. However, the Mediterranean climate appearing from our study is far more complex than can be captured by a simple classification. In this way, the final picture is one switching between significantly different climate modes becoming apparent on several space-time-scales during the Late Little Ice Age.     

Trends in Precipitation Concentration and Extremes in the Mediterranean Penedès-Anoia Region, Ne Spain

The high variability of the Mediterranean climate from year to year and within each year makes it difficult to assess changes that could be associated with a climate change. In this paper some indices, such as changes in the precipitation concentration during the year, maximum 1-day and 5-day precipitation, number of wet days (total and those with precipitation higher than the 75th and 95th percentile), magnitude and frequency of extreme events (considered as the rainfall higher than that corresponding to the 99th percentile), fraction of annual total precipitation due to events exceeding the 95th and 99th percentile, strength of the events, and length and frequency of dry period (days between consecutive rains) are evaluated for the Penedès-Anoia region (NE Spain). A 80-year daily dataset (1923–2002) and two 40-year series were used to assess possible trends. The indices indicate an increase in precipitation in winter and summer and a positive trend of concentration in autumn, with a higher number of extreme events separated by longer dry periods. The total number of wet days per year increased, although it was irregularly distributed over the year, with an increase in the extremes and in the fraction of total rainfall that these events represent in autumn and winter, and with an increase of the strength of the events in autumn. These changes in rainfall distribution have negative effects on water availability for crops and contribute to accelerate erosion processes in the area.     

Climate change and impacts in the Eastern Mediterranean and the Middle East

The Eastern Mediterranean and the Middle East (EMME) are likely to be greatly affected by climate change, associated with increases in the frequency and intensity of droughts and hot weather conditions. Since the region is diverse and extreme climate conditions already common, the impacts will be disproportional. We have analyzed long-term meteorological datasets along with regional climate model projections for the 21st century, based on the intermediate IPCC SRES scenario A1B. This suggests a continual, gradual and relatively strong warming of about 3.5–7°C between the 1961–1990 reference period and the period 2070–2099. Daytime maximum temperatures appear to increase most rapidly in the northern part of the region, i.e. the Balkan Peninsula and Turkey. Hot summer conditions that rarely occurred in the reference period may become the norm by the middle and the end of the 21st century. Projected precipitation changes are quite variable. Annual precipitation is expected to decrease in the southern Europe – Turkey region and the Levant, whereas in the Arabian Gulf area it may increase. In the former region rainfall is actually expected to increase in winter, while decreasing in spring and summer, with a substantial increase of the number of days without rainfall. Anticipated regional impacts of climate change include heat stress, associated with poor air quality in the urban environment, and increasing scarcity of fresh water in the Levant.     

Sensitivity of the Iberian Peninsula climate to a land degradation

Two six-year simulations, a land degradation scenario and a control, were performed by applying a regional climate model nested in ECMWF analyzed data to the Iberian Peninsula. The simulated time period (1993-98) includes extremely anomalous dry and rainy years. The land degradation scenario assumed a decrease in vegetation cover and an alteration of the soil properties resulting from future increases of greenhouse gases and human activity. Simulation results show that the impact of land degradation on the climate of the Iberian Peninsula depends on local factors (the intensity of degradation and geographical location) but some noticeable non-local effects are also present. Local factors result in an increase of the surface temperature which is almost linearly related to the degradation intensity. A stronger decrease in precipitation is observed in the less degraded regions, indicating that non-local effects are more relevant to changes in precipitation. The highest sensitivity to land degradation is observed in the summer season, consisting of an increase in 2 m temperature and a reduction in precipitation. In winter, the rainiest season on the Iberian Peninsula, the impact of land degradation on precipitation is almost negligible.     

Indices for extreme events in projections of anthropogenic climate change

Indices for temperature and precipitation extremes are calculated on the basis of the global climate model ECHAM5/MPI-OM simulations of the twentieth century and SRES A1B and B1 emission scenarios for the twenty-first century. For model evaluation, the simulated indices representing the present climate were compared with indices based on observational data. This comparison shows that the model is able to realistically capture the observed climatological large-scale patterns of temperature and precipitation indices, although the quality of the simulations depends on the index and region under consideration. In the climate projections for the twenty-first century, all considered temperature-based indices, minimum Tmin, maximum Tmax, and the frequency of tropical nights, show a significant increase worldwide. Similarly, extreme precipitation, as represented by the maximum 5-day precipitation and the 95th percentile of precipitation, is projected to increase significantly in most regions of the world, especially in those that are relatively wet already under present climate conditions. Analogously, dry spells increase particularly in those regions that are characterized by dry conditions in present-day climate. Future changes in the indices exhibit distinct regional and seasonal patterns as identified exemplarily in three European regions.     

Potential future changes in the characteristics of daily precipitation in Europe simulated by the HIRHAM regional climate model

In this study the potential future changes in various aspects of daily precipitation events over Europe as a consequence of the anticipated future increase in the atmospheric greenhouse gas concentrations are investigated. This is done by comparing two 3-member ensembles of simulations with the HIRHAM regional climate model for the period 1961–1990 and 2071–2100, respectively. Daily precipitation events are characterized by their frequency and intensity, and heavy precipitation events are described via 30-year return levels of daily precipitation. Further, extended periods with and without rainfall (wet and dry spells) are studied, considering their frequency and length as well as the average and extreme amounts of precipitation accumulated during wet spells, the latter again described via 30-year return levels. The simulations show marked changes in the characteristics of daily precipitation in Europe due to the anticipated greenhouse warming. In winter, for instance, the frequency of wet days is enhanced over most of the European continent except for the region on the Norwegian west coast and the Mediterranean region. The changes in the intensity and the 30-year return level of daily precipitation are characterized by a similar pattern except for central Europe with a tendency of decreased 30-year return levels and increased precipitation intensity. In summer, on the other hand, the frequency of wet days is decreased over most of Europe except for northern Scandinavia and the Baltic Sea region. In contrast, the precipitation intensity and the 30-year return level of daily precipitation are increased over entire Scandinavia, central and eastern Europe. The changes in the 30-year return level of daily precipitation are generally stronger than the corresponding changes in the precipitation intensity but can have opposite signs in some regions. Also the distribution of wet days is changed in the future. During summer, for instance, both the frequency and the length of dry spells are substantially increased over most of the European continent except for the Iberian Peninsula. The frequency and the length of wet spells, on the other hand, are generally reduced during summer and increased during winter, again, with the exception of the Iberian Peninsula. The future changes in the frequency of wet days in winter are related to a change in the large-scale flow over the North Atlantic and a corresponding shift of the North Atlantic storm track. The reduction in the frequency of wet days in summer is related to a northward extension of the dry subtropical region in the future, with a reduction of the convective activity because of the large-scale sinking motion in the downward branch of the Hadley cell. Because the atmosphere contains more moisture in the warmer future climate, the amount of precipitation associated with individual low-pressure systems or with individual convective events is increased, leading to a general increase in the intensity of individual precipitation events. Only in regions, where all the moisture evaporates from the ground already in spring, the intensity of precipitation events is reduced in summer.     

Assessment of climate extremes in the Eastern Mediterranean

Summary Several seasonal and annual climate extreme indices have been calculated and their trends (over 1958 to 2000) analysed to identify possible changes in temperature- and precipitation-related climate extremes over the eastern Mediterranean region. The most significant temperature trends were revealed for summer, where both minimum and maximum temperature extremes show statistically significant warming trends. Increasing trends were also identified for an index of heatwave duration. Negative trends were found for the frequency of cold nights in winter and especially in summer. Precipitation indices highlighted more regional contrasts. The western part of the study region, which comprises the central Mediterranean and is represented by Italian stations, shows significant positive trends towards intense rainfall events and greater amounts of precipitation. In contrast, the eastern half showed negative trends in all precipitation indices indicating drier conditions in recent times. Significant positive trends were revealed for the index of maximum number of consecutive dry days, especially for stations in southern regions, particularly on the islands.Current affiliation: National Observatory of Athens, Athens, Greece.     

Future evolution of extreme precipitation in the Mediterranean

Mediterranean basins can be impacted by severe floods caused by extreme rainfall, and there is a growing awareness about the possible increase in these heavy rainfall events due to climate change. In this study, the climate change impacts on extreme daily precipitation in 102 catchments covering the whole Mediterranean basin are investigated using nonstationary extreme value model applied to annual maximum precipitation in an ensemble of high-resolution regional climate model (RCM) simulations from the Euro-CORDEX experiment. Results indicate contrasted trends, with significant increasing trends in Northern catchments and conversely decreasing trends in Southern catchments. For most cases, the time of signal emergence for these trends is before the year 2000. The same spatial pattern is obtained under the two climate scenarios considered (RCP4.5 and RCP8.5) and in most RCM simulations, suggesting a robust climate change signal. The strongest multi-model agreement concerns the positive trends, which can exceed +?20% by the end of the twenty-first century in some simulations, impacting South France, North Italy, and the Balkans. For these areas, society-relevant strong impacts of such Mediterranean extreme precipitation changes could be expected in particular concerning flood-related damages.     

Circulation indices over the Mediterranean and Europe and their relationship with rainfall conditions across the Mediterranean

Summary Circulation types were identified by means of zonal and meridional indices calculated separately over ten different regions of 20° × 20° over the Mediterranean and Europe. Seasonal and annual rainfall totals in four stations Lisbon, Luqa (Malta), Athens and Jerusalem, were compared with circulation types for the period 1873–1991. Correlation coefficients of circulation indices with precipitation, for each station in each season were calculated and mapped.An oscillation in the meridional index during the winter and the spring, between the western and eastern Mediterranean, was detected.Time series analysis of the circulation indices demonstrates a significant reduction in zonality and an increase in meridionality mainly in spring and in summer, over most of the study area.With 9 Figures     

Teleconnection–extreme precipitation relationships over the Mediterranean region

The relationship between five teleconnection patterns (North Atlantic Oscillation (NAO), Arctic Oscillation (AO), East Atlantic/Western Russian (EAWR) pattern, Scandinavian (SCAND) pattern, and El Niño Southern Oscillation (ENSO)) and the frequency of occurrence of days (per month) with extreme precipitation in the Euro-Mediterranean region is investigated with National Centers for Environmental Prediction–National Center for Atmospheric Research reanalysis data. To quantify the teleconnection–precipitation relationships over the Euro-Mediterranean region, linear correlations are calculated between the monthly teleconnection indices for the five patterns and time series at each grid point of the monthly frequency of days with extreme precipitation, focusing on daily precipitation amounts that exceed a particular threshold value (a 90 % threshold is used). To evaluate dynamical processes, the teleconnection indices are also correlated with the frequencies of days with extreme values of dynamic tropopause pressure and precipitable water. The former quantity is used as a proxy for potential vorticity intrusions and the latter to identify regions of enhanced moisture. The results of this analysis indicates positive, statistically significant correlations between the NAO, AO, and SCAND indices and the frequency of extreme precipitation in the western Mediterranean; positive (negative) correlations between the EAWR index and the extreme precipitation frequency in the eastern (western) Mediterranean; and a positive correlation between the Niño3.4 index and the extreme precipitation frequency over the Iberian Peninsula and the Middle East. For all of the teleconnection patterns other than ENSO, the dynamic tropopause pressure correlation patterns resemble those for the precipitation. In contrast, similar precipitation and precipitable water correlation patterns are observed only for ENSO. These findings suggest that the teleconnections affect the interannual variation of the frequency of days with extreme precipitation over a large part of the Euro-Mediterranean region through their impact on the spatial distribution of regions with enhanced potential vorticity and air moisture.     

Some Statistical Characteristics of Monthly and Annual Pluviometric Irregularity for the Spanish Mediterranean Coast

Summary  Seven series of monthly pluviometric amounts, sometimes exceeding recording periods of 100 years and compiled by the Instituto Nacional de Meteorología (Spain), are used to study the irregularity of the pluviometric regime along the Spanish Mediterranean coast and nearby Atlantic coast. First of all, three statistical functions (gamma, log-normal and a combination of Poisson and gamma distributions) and moment-ratio diagrams are used to model the monthly and annual empirical distributions of precipitation amounts, each distribution being tested by means of the Kolmogorov-Smirnov test. It is noteworthy that, whereas most of the monthly cases require the gamma distribution, the pluviometric behaviour of the summer months is well described by the Poisson-gamma distribution. Moreover, both the log-normal and the gamma distributions satisfactorily model empirical annual amounts. Consequently, rainfall amounts are not identically distributed along a year for each gauge tested. Second, temporal trends deduced for annual and seasonal amounts are computed and their statistical significance evaluated. The most notable fact is that, although some linear trends are close to 1 mm/year, their significance levels exceed the assumed threshold value and, excepting the winter season for Barcelona, they are considered non-significant from a statistical point of view. Finally, by again using monthly and annual amounts, three temporal irregularity indexes are computed for each pluviometric series, the temporal disparity of the rainfall patterns of the Mediterranean region being enhanced as a result. It addition to the temporal irregularity, a change with latitude is observed both in the parameters of the statistical distributions and the temporal irregularity indexes for the rain gauges analysed. The two most southerly rain gauges constitute a special case in comparison with the remaining stations, because they also receive the Atlantic influences due to their proximity to this ocean. Received February 25, 1999/Revised August 2, 1999     

FGOALS-g2模式模拟和预估的全球季风区极端降水及其变化

利用LASG/IAP（中国科学院大气物理研究所大气科学和地球流体力学数值模拟国家重点实验室）全球耦合模式FGOALS-g2,评估了其对全球季风区极端气候指标的模拟能力,并讨论了RCP8.5排放情景下21世纪季风区极端气候指标的变化特征。总体而言,模式对季风区总降水和极端气候指标1997～2014年气候态和年际变率的空间分布均具有一定的模拟能力。偏差主要表现在模式低估了亚洲季风强降水中心,低估了中雨（10～20 mm d-1）和大雨（20～50 mm d-1）的频率而高估了暴雨（>50 mm d-1）频率。在RCP8.5排放情景下,由于可降水量的增加,模式预估的全球季风区极端降水、降水总量和降水强度将持续增加。到2076～2095年,极端降水和降水强度在北美季风区增加最显著（约22%和17%）,降水总量在澳大利亚增加最显著（约37%）。然而,FGOALS-g2对全球季风区平均的日降水量低于1 mm的连续最大天数（CDD）的预估变化不显著,这是由于预估的CDD在陆地季风区将增加,而在海洋季风区将减少。对各子季风区的分析显示,CDD在南美季风区变长最显著,达到30%,在澳洲季风区变短最显著,达到40%,这与两季风区日降水量低于1 mm的降水事件发生频率变化不同有关。     

Variations in cereal crop phenology in Spain over the last twenty-six years (1986–2012)

Over recent years, the Iberian Peninsula has witnessed an increase both in temperature and in rainfall intensity, especially in the Mediterranean climate area. Plant phenology is modulated by climate, and closely governed by water availability and air temperature. Over the period 1986–2012, the effects of climate change on phenology were analyzed in five crops at 26 sites growing in Spain (southern Europe): oats, wheat, rye, barley and maize. The phenophases studied were: sowing date, emergence, flag leaf sheath swollen, flowering, seed ripening and harvest. Trends in phenological response over time were detected using linear regression. Trends in air temperature and rainfall over the period prior to each phenophase were also charted. Correlations between phenological features, biogeographical area and weather trends were examined using a Generalized Lineal Mixed Model approach. A generalized advance in most winter-cereal phenophases was observed, mainly during the spring. Trend patterns differed between species and phenophases. The most noticeable advance in spring phenology was recorded for wheat and oats, the “Flag leaf sheath swollen” and “Flowering date” phenophases being brought forward by around 3 days/year and 1 day/year, respectively. Temperature changes during the period prior to phenophase onset were identified as the cause of these phenological trends. Climate changes are clearly prompting variations in cereal crop phenology; their consequences could be even more marked if climate change persists into the next century. Changes in phenology could in turn impact crop yield; fortunately, human intervention in crop systems is likely to minimize the negative impact.     

A Case of Convection Development over the Western Mediterranean Sea: A Study through Numerical Simulations

Summary  A convective case producing heavy precipitation in the western Mediterranean region, characterized by pronounced upper level forcing and main rainfall over the sea, is studied. On the day of the event (September 28^th, 1994), more than 140 mm of precipitation were recorded in coastal lands of eastern Spain, and 180 mm were estimated over the sea with radar data. Synoptically, the case appears to combine warm and moist easterly advection at low levels, typically observed in torrential rainfall events of the region, with a less common strong upper level dynamical forcing. A set of mesoscale numerical simulations using the Hirlam model is performed to investigate the mechanisms responsible for the convection development, and to assess the influence of the orography on the rainfall field. Model output diagnosis indicates that in addition to the lower level forcing, a two-jets interaction is decisive for the triggering and driving of the convection during the event. Moreover, a non-topographic simulation reveals a relatively weak influence of the orography on this event when compared with other similar heavy precipitation cases in eastern Spain. Previous studies have shown an orographic influence of more than 90% on the rainfall whereas in this case about 50% of the precipitation over the area is attributed to the orographic forcing. The study is extended with an analysis of the individual effects of the Atlas and Iberian Peninsula, by means of a factor separation technique. It is shown that the Atlas range induces a redistribution of the precipitation over the Mediterranean, whereas local enhancements can be attributed to the Iberian topography. Received March 2, 1999     

Fire regime changes in the Western Mediterranean Basin: from fuel-limited to drought-driven fire regime

Wildfires are an integral part of Mediterranean ecosystems; humans impact on landscapes imply changes in fuel amount and continuity, and thus in fire regime. We tested the hypothesis that fire regime changed in western Mediterranean Basin during the last century using time series techniques. We first compiled a 130-year fire history for the Valencia province (Spain, Eastern Iberian Peninsula, Western Mediterranean Basin) from contemporary statistics plus old forest administration dossiers and newspapers. We also compiled census on rural population and climatic data for the same period in order to evaluate the role of climate and human-driven fuel changes on the fire regime change. The result suggested that there was a major fire regime shift around the early 1970s in such a way that fires increased in annual frequency (doubled) and area burned (by about an order of magnitude). The main driver of this shift was the increase in fuel amount and continuity due to rural depopulation (vegetation and fuel build-up after farm abandonment) suggesting that fires were fuel-limited during the pre-1970s period. Climatic conditions were poorly related to pre-1970s fires and strongly related to post-1970s fires, suggesting that fire are currently less fuel limited and more drought-driven than before the 1970s. Thus, the fire regime shift implies also a shift in the main driver for fire activity, and this has consequences in the global change agenda.     

A spectral analysis of Iberian Peninsula monthly rainfall

Summary A spectral analysis of Iberian Peninsula monthly rainfall series was carried out. The data set consists of monthly precipitation records from 40 meteorological observatories over 74 years (1919–1992). The stations are representative of most of the Iberian Peninsula. The rainfall series were analyzed spatially by means of Principal Component Analysis (PCA) and temporally by means of the Multi-Taper Method (MTM) of spectral analysis of by Monte-Carlo Singular Spectrum Analysis (MCSSA). The PCA gave six dominant modes of variation which explain 75% of the variance with each component affecting a different region of the Peninsula. The spectral analysis showed 7 year oscillations for the dominant pattern and 2.7 and 16 years for the third pattern. The 7-year oscillation seems to be related to other climatic oscillations recorded in the northern hemisphere while the 2.7-year oscillation could be related to the ENSO phenomenon. Received July 18, 2000 Revised April 19, 2001