As temperature extremes have a deep impact on environment, hydrology, agriculture, society and economy, the analysis of the mechanisms underlying their occurrence, including their relationships with the large-scale atmospheric circulation, is particularly pertinent and is discussed here for Europe and in the period 1961–2010 (50 yr). For this aim, a canonical correlation analysis, coupled with a principal component analysis (BPCCA), is applied between the monthly mean sea level pressure fields, defined within a large Euro-Atlantic sector, and the monthly occurrences of two temperature extreme indices (TN10p – cold nights and TX90p – warm days) in Europe. Each co-variability mode represents a large-scale forcing on the occurrence of temperature extremes. North Atlantic Oscillation-like patterns and strong anomalies in the atmospheric flow westwards of the British Isles are leading couplings between large-scale atmospheric circulation and winter, spring and autumn occurrences of both cold nights and warm days in Europe. Although summer couplings depict lower coherence between warm and cold events, important atmospheric anomalies are key driving mechanisms. For a better characterization of the extremes, the main features of the statistical distributions of the absolute minima (TNN) and maxima (TXX) are also examined for each season. Furthermore, statistically significant downward (upward) trends are detected in the cold night (warm day) occurrences over the period 1961–2010 throughout Europe, particularly in summer, which is in clear agreement with the overall warming

Climate change projections for spatial-temporal distributions of temperatures in Portugal are analysed using a 13-member ensemble of regional climate model simulations (A1B scenario for 2041-2070). Bias corrections are carried out using an observational gridded dataset (E-OBS) and equally-weighted ensemble statistics are discussed. Clear shifts toward higher future seasonal mean temperatures, in central tendency and also in both tails of the distributions, are found (2-4 • C), particularly for summer and autumn maximum temperatures. Furthermore, frequencies of occurrence of daily extremes are projected to increase, particularly in summer maximum temperatures over inland Portugal. Wintertime changes are weaker than in other seasons.

The anomalously wet winter of 2010 had a very important impact on the Portuguese hydrological system. Owing to the detrimental effects of reduced precipitation in Portugal on the environmental and socio-economic systems, the 2010 winter was predominantly beneficial by reversing the accumulated precipitation deficits during the previous hydrological years. The recorded anomalously high precipitation amounts have contributed to an overall increase in river runoffs and dam recharges in the 4 major river basins. In synoptic terms, the winter 2010 was characterised by an anomalously strong westerly flow component over the North Atlantic that triggered high precipitation amounts. A dynamically coherent enhancement in the frequencies of mid-latitude cyclones close to Portugal, also accompanied by significant increases in the occurrence of cyclonic, south and southwesterly circulation weather types, are noteworthy. Furthermore, the prevalence of the strong negative phase of the North Atlantic Oscillation (NAO) also emphasises the main dynamical features of the 2010 winter. A comparison of the hydrological and atmospheric conditions between the 2010 winter and the previous 2 anomalously wet winters (1996 and 2001) was also carried out to isolate not only their similarities, but also their contrasting conditions, highlighting the limitations of estimating winter precipitation amounts in Portugal using solely the NAO phase as a predictor.

ABSTRACT:The severest winter precipitation deficits in Portugal result from an enhancement in the stationary wave pattern of the atmospheric large-scale circulation over the Northern Hemisphere, which implies a strengthening of the axially asymmetric eddies, mainly over the North Atlantic and adjacent continental areas. This enhancement leads to a strong warm-core ridge westward of Iberia, with a nearly equivalent barotropic structure, and a clear separation between the subtropical and polar-front jet. These atmospheric conditions are clearly unfavourable to the establishment of rain-generating mechanisms over Portugal, leading to a lack of precipitation and to extremely dry conditions with a high potential to trigger drought episodes. Conversely, the atmospheric flow during extremely wet winters contrasts highly with the above-described conditions by presenting a significantly weakened North Atlantic ridge and a relatively unclear separation between the two westerly jets. A diagnosis of the main forcing dynamical mechanisms that generate and maintain the anomalous flow is carried out in two ways: by analyzing the Eliassen-Palm fluxes, zonally averaged over a North Atlantic window, and by calculating the third and sixth components of the empirical forcing functions. The former approach enables a quantification of the contributions made by the transient and stationary-eddy transports of enthalpy and momentum to the establishment of the contrasting dynamical structures. The latter approach explores the role of local transient transports of enthalpy and angular momentum in forcing large-scale asymmetries.

No abstract

Projections of Köppen-Geiger climate classifications under future climate change for the Iberian Peninsula are investigated using a 7-ensemble mean of regional climate models obtained from EURO-CORDEX. Maps with predicted future scenarios for temperature, precipitation and Köppen-Geiger classification are analyzed for RCP4.5 and RCP8.5 in Iberia. Widespread statistically significant shifts in temperature, precipitation and climate regimes are projected in the 2041-2070 period, with greater shifts occurring under RCP8.5. An overall increase in temperature and a decrease in precipitation in the south-southeast is predicted. Of the two climate types, dry (B) and temperate (C), the dominant one was C in 86% of Iberia for 1961-1990, predicted to decrease by 8.0% by 2041-2070 under RCP4.5 (9.5% under RCP8.5). The hot-summer Mediterranean climate (CSa) will progressively replace CSb (warm-summer climate) in the northwestern half of Iberia until 2070. This shift, depicted by the SSIM index, is particularly noticeable in Portugal, with the projected establishment of the CSa climate by 2041-2070. The predicted retreat of humid subtropical (Cfa) and temperate oceanic (Cfb) areas in the northeast towards the Pyrenees region is noteworthy, as is the increase of desert (BW) and semi-desert (BS) climates (7.8 and 9%) in the southeast (between Granada and Valencia). Climate types BSh and BWh (hot semi-desert and hot desert, respectively), non-existent in the 1961-1990 period, are projected to represent 2.8% of the territory in 2041-2070 under RCP4.5 (5% under RCP8.5). The statistically significant projected changes hint at the disappearance of some vegetation species in certain regions of Iberia, with an expected increase in steppe, bush, grassland and wasteland vegetation cover, typical of dry climates in the southeast.

Climate change projections for the four major divisions of the Worldwide Bioclimatic Classification System in the Iberian Peninsula (IP) are analysed using a six‐member ensemble (EURO‐CORDEX) for 1961–1990, 1981–2010, 2011–2040, and 2041–2070 periods for RCP4.5 and RCP8.5. The direct forcing method was used to correct the bias of the simulated data using an observational gridded dataset (E‐OBS). Results show a decrease of the temperate areas in the north‐western region of the IP, with higher expression in RCP8.5 for 2041–2070. Major changes in bioclimates, ombrotypes, and thermotypes are projected to occur in northernmost regions, as well as, central and south‐eastern areas of Iberia. The projected decrease of Mediterranean pluviseasonal areas hint at a decrease of several evergreen or deciduous forest types. Conversely, due to the projected increase of Mediterranean xeric and desertic areas, it can be expected an increase of microforests or dense shrubby lands, as well as the appearance of half deserts or low‐density scrublands. Finally, the continentality index patterns revealed a strengthening of the coastal‐inner climate contrasts in the future, mainly for RCP8.5.

Reservoirs are fundamental for water and energy supply but vulnerable to impacts including climate change. This paper outlines the steps in the development of a model to predict how climate, land use and hydrological change could affect the physiochemical and ecological quality of reservoirs in Portugal's Douro region. Climatic data will be downscaled for subsequent finer spatial scale models to develop scenarios and outputs. Field observations and satellite imagery analysis will create dynamic maps providing data on change in land use and vegetation cover, while Artificial Neural Networks will determine how climate, land use and vegetation cover change may influence catchment hydrology. Data from field surveys of biological indicators, greenhouse gas emissions plus additional research will be applied in the Stochastic Dynamic Methodology, a sequential modelling process based on statistical parameter estimation, developed to predict and model physiochemical and ecological changes in reservoirs. This interdisciplinary approach will provide vital modelling tools for end users essential for water resource management in Portugal and to comply with the EU Water Framework Directive. ReferencesAllan J D, Erickson D L and Fay J 1997 The influence of catchment land use on stream integrity across multiple spatial scales Freshwater Biology 37 149-61 Andrade C, Santos J A, Pinto J G and Corte-Real J 2011 The wet 2010 winter in Portugal: hydrological impacts and large-scale atmospheric dynamics Climate Research 46 29-41 A 2012 Testing a novel spatially-explicit dynamic modelling approach in the Figure 5 A flow diagram of the separate modules that will contribute to the development of the predictive model 440 Hughes et al.