Showing papers in "Climate Research in 2012"

RegCM4 : model description and preliminary tests over multiple CORDEX domains

Abstract: A new version of the RegCM regional climate modeling system, RegCM4, has been recently developed and made available for public use. Compared to previous versions, RegCM4 includes new land surface, planetary boundary layer, and air–sea flux schemes, a mixed convection and tropical band configuration, modifications to the pre-existing radiative transfer and boundary layer schemes, and a full upgrade of the model code towards improved flexibility, portability, and user friendliness. The model can be interactively coupled to a 1D lake model, a simplified aerosol scheme (including organic carbon, black carbon, SO4, dust, and sea spray), and a gas phase chemistry module (CBM-Z). After a general description of the model, a series of test experiments are presented over 4 domains prescribed under the CORDEX framework (Africa, South America, East Asia, and Europe) to provide illustrative examples of the model behavior and sensitivities under different climatic regimes. These experiments indicate that, overall, RegCM4 shows an improved performance in several respects compared to previous versions, although further testing by the user community is needed to fully explore its sensitivities and range of applications.

Uncertainties in monsoon precipitation projections over China: results from two high-resolution RCM simulations

Abstract: A high-resolution climate change simulation at a grid spacing of 25 km was conducted over East Asia with the Abdus Salam International Centre for Theoretical Physics’ (ICTP) regional climate model RegCM3, for the period 1951−2100. The model is driven at the lateral boundaries by the global model CCSR/NIES/FRCGC MIROC3.2_hires. Two time slices, 1961− 1990 for present-day and 2071−2100 for future climate conditions were analyzed and compared with a previous high-resolution simulation of RegCM3 driven by the NASA/NCAR global model FvGCM. The focus of the present paper is on mean temperature and precipitation and their changes during the monsoon season (May−September). Overall, for present-day conditions, the regional model improves the simulation of both temperature and precipitation patterns compared to the driving global climate models, with greater agreement between the RegCM3 simulations than with the corresponding driving models. When driven by the 2 global models, RegCM3 simulates a consistent precipitation change pattern over western China, characterized by an increase over the northwest and a decrease over the Tibetan Plateau and Southwest China. These latter precipitation decreases have opposite signs compared those from the driving global models, and the causes of these differences (mostly associated with the different topographic representations) are discussed in the paper. This implies that over these regions the internal model physics and processes can be dominant factors. On the other hand, warming patterns are essentially driven by the large-scale boundary forcing. Our results show that precipitation change projections by current global models need to be considered cautiously and that the use of nested regional models adds an element of uncertainty which needs to be properly characterized.

Response of crop yields to climate trends since 1980 in China

Abstract: We used improved datasets on both climate and crop production to investigate climate trends during the crop growing period and their impacts on yields of major crops (rice, wheat, maize and soybean) in China by county, during 1980-2008. We found clear regional climate trends during this period, particularly for temperature. Such trends have had measurable impacts on crop yields, with a distinct spatial pattern. For the entire country, the planting area-weighted average showed that climate trends from 1980-2008 reduced wheat, maize and soybean yields by 1.27, 1.73 and 0.41%, respectively, while increasing rice yields by 0.56%. As a result, climate trends as a whole reduced wheat and maize production by 3.60 x 10(5) t and 1.53 x 10(6) t, respectively, and increased rice and soybean production by 7.44 x 10(4) t and 4.16 x 10(3) t, respectively. Estimates of climate impacts are smaller than previous estimates that used different scales, datasets and methods. The particular crops and regions that have been most affected and should be priorities for adaptation are maize and wheat in arid and semi-arid areas of northern and northeast China, where droughts induced by increases in temperature and solar radiation could limit the benefits of improved thermal conditions. Climate warming decreases crop yields by accelerating crop development rate, and thus reducing crop growth duration and yield accumulation, and by increasing temperature extremes and heat stress.

Macroclimate and viticultural zoning in Europe: observed trends and atmospheric forcing

Abstract: Temperature and precipitation are major forcing factors influencing grapevine phenology and yield, as well as wine quality. Bioclimatic indices describing the suitability of a particular region for wine production are a commonly used tool for viticultural zoning. For this research these indices were computed for Europe by using the E-OBS gridded daily temperature and precipitation data set for the period from 1950 to 2009. Results showed strong regional contrasts based on the different index patterns and reproduced the wide diversity of local conditions that largely explain the quality and diversity of grapevines being grown across Europe. Owing to the strong inter-annual variability in the indices, a trend analysis and a principal component analysis were applied together with an assessment of their mean patterns. Significant trends were identified in the Winkler and Huglin indices, particularly for southwestern Europe. Four statistically significant orthogonal modes of variability were isolated for the Huglin index (HI), jointly representing 82% of the total variance in Europe. The leading mode was largely dominant (48% of variance) and mainly reflected the observed historical long-term changes. The other 3 modes corresponded to regional dipoles within Europe. Despite the relevance of local and regional climatic characteristics to grapevines, it was demonstrated via canonical correlation analysis that the observed inter-annual variability of the HI was strongly controlled by the large-scale atmospheric circulation during the growing season (April to September).

Diurnal, seasonal, and altitudinal trends in microclimate across a tropical montane cloud forest

Abstract: Altitudinal gradients are often used as natural laboratories to study ecosystem dynamics, biodiversity, and species’ distribution response to climate gradients. However, the underlying climate gradients are rarely described in detail, especially in the tropics. In this study, we describe the diurnal and seasonal patterns in microclimate across a 3900 m altitudinal gradient in and adjacent to the Kosñipata Valley in Manu National Park, Peru, on the eastern slope of the tropical Andes. We focus on the understudied altitudinal range between 1500 and 3500 m using micrometeorological data associated with a permanent tree plot network designed to study cloud forest biodiversity and ecosystem dynamics. Data from this plot network were supplemented with data in the public domain across a 20 000 km2 area with time series at individual sites lasting from 2 to 17 yr. Observed diurnal and seasonal trends in microclimate variables were explained by diurnal and seasonal variation in solar radiation and atmospheric moisture flux. Altitudinal trends in microclimate varied seasonally, with solar radiation, vapor pressure deficit, and temperature reaching their annual maximum earlier at higher altitudes, likely because of seasonally shifting cloud dynamics. Cloud dynamics were important in determining diurnal, seasonal, and altitudinal trends in several microclimate variables, suggesting that changes to cloud frequency and altitudinal occurrence associated with global climate change could have important impacts on cloud forest ecosystem dynamics, in addition to those of rising temperatures.

Radiative and climatic effects of dust over West Africa, as simulated by a regional climate model

Abstract: We used the Regional Circulation Model (RegCM) to investigate the direct effect of dust aerosol on climate over West Africa, with a specific focus on the Sahel region. First, we characterized the mechanisms linking dust radiative forcing and convective activity over Sahel and the net impact of dust on precipitation: The mean effect of dust over 11 summer seasons is to reduce precipitation over most of the Sahel region as a result of strong surface cooling and elevated diabatic warming inhibiting convection. However, on the very northern Sahel and in the vicinity of dust sources, a relative increase of precipitation is obtained as a result of enhanced diabatic warming in the lower atmosphere associated with high dust concentrations at low altitude. In the second part of the paper, we investigated the robustness of this signal with regards to different modeling conditions that are thought to be sensitive, namely the extension of the domain, the effect of dust on sea surface temperature, the land surface scheme, the convective scheme and the dust single scattering albedo. The simulated dust induced precipitation anomaly over West Africa is consistent and robust in these tests, but significant variations over the northern Sahel region are nevertheless pointed out. Among different factors, single scattering and surface albedo, as well as the nature of the convective scheme, have the greatest influence on the simulated response of West African climate to dust forcing

Loss potentials associated with European windstorms under future climate conditions

Abstract: Possible changes in the frequency and intensity of windstorms under future climate conditions during the 21st century are investigated based on an ECHAM5 GCM multi-scenario en- semble. The intensity of a storm is quantified by the associated estimated loss derived with using an empirical model. The geographical focus is 'Core Europe', which comprises countries of Western Europe. Possible changes of losses are analysed by comparing ECHAM5 GCM data for recent (20C, 1960 to 2000) and future climate conditions (B1, A1B, A2; 2060 to 2100), each with 3 ensemble members. Changes are quantified using both rank statistics and return periods (RP) esti- mated by fitting an extreme value distribution using the peak over threshold method to potential storm losses. The estimated losses for ECHAM5 20C and reanalysis events show similar statistical features in terms of return periods. Under future climate conditions, all climate scenarios show an increase in both frequency and magnitude of potential losses caused by windstorms for Core Eu- rope. Future losses that are double the highest ECHAM5 20C loss are identified for some countries. While positive changes of ranking are significant for many countries and multiple scenarios, signif- icantly shorter RPs are mostly found under the A2 scenario for return levels correspondent to 20 yr losses or less. The emergence time of the statistically significant changes in loss varies from 2027 to 2100. These results imply an increased risk of occurrence of windstorm-associated losses, which can be largely attributed to changes in the meteorological severity of the events. Additionally, fac- tors such as changes in the cyclone paths and in the location of the wind signatures relative to highly populated areas are also important to explain the changes in estimated losses.

Sensitivity of seasonal climate and diurnal precipitation over Central America to land and sea surface schemes in RegCM4

Abstract: Multi-annual simulations over the Central America CORDEX domain are conducted with the latest version of regional climate model RegCM4 driven by ERA-Interim reanalysis fields. The RegCM4 system can reproduce both the annual cycle and the spatial patterns of mean summer precipitation over Central America and Mexico. Regional circulation features are also reproduced, although the intensity of the Caribbean Low-Level Jet is underestimated and it is located too far south. Over most land areas, RegCM4 surface air temperatures are lower than observations by 1 to 3°C, which however may also be related to biases in the reanalysis forcing data. The model can realistically simulate the amplitude of the convective diurnal cycle in areas where the convective triggering is dominated by non-local gravity wave effects. However, the simulation of the phase of the diurnal cycle of convection is less satisfactory, with the peak precipitation occurring earlier than observed, a common fault in atmospheric models. Sensitivity experiments are carried out to investigate the model sensitivity to land surface and a prognostic diurnal sea surface temperature scheme. Use of the Community Land Model (CLM) instead of the Bio sphere-Atmosphere Transfer Scheme (BATS) results in a warmer and drier land surface and a better simulation of the seasonal average spatial pattern of precipitation. However, with BATS, RegCM4 has a more realistic simulation of the mid-summer drought over the region. The impact of the prognostic sea surface temperature (SST) scheme is generally small. In general, neither of these surface physics upgrades results in a clearly superior model performance.

Simulation of temperature and precipitation climatology for the Central Asia CORDEX domain using RegCM 4.0

Abstract: The Coordinated Regional Climate Downscaling Experiment (CORDEX) is a framework designed to coordinate international efforts on regional climate simulations. CORDEX domains encompass the majority of land areas of the world. Region 8 of the CORDEX basically covers Central Asia, with the corners of the domain at 54.76° N, 11.05° E; 56.48° N, 139.13° E; 18.34° N, 42.41° E; and 19.39° N, 108.44° E and with a horizontal resolution of 50 km. In the present study, the results of an experiment with the ICTP regional climate RegCM 4.0 model that was run for seasonal mean air temperature and precipitation total series are presented. The experiment consists of one simulation from 1989 to 2010 using ERA-Interim reanalysis data as the boundary condition, another simulation for the period 1970−2000 using the global climate model ECHAM5 A1B scenario data for forcing, and finally a simulation for the period 2070−2100 using the ECHAM5 A1B scenario projection data for forcing. Between these 3 simulations we determined the temperature and precipitation climatology obtained from RegCM 4.0 downscaling for Region 8 of the CORDEX framework. In spite of the diverse topography of the region, the temperature and precipitation climatology obtained by RegCM 4.0 from hindcast data captures the general characteristics of the climate of Central Asia. In winter, the warm temperature bias of the forcing data is slightly decreased by regional downscaling. The influences of the Indian monsoon system are well represented, as this region covers a large area towards the southern boundary of Region 8, even though the focus of this work was to capture the general characteristics of the whole region.

Projecting climate change, drought conditions and crop productivity in Turkey

Abstract: This paper focuses on the evaluation of regional climate model simulation for Turkey for the 21st century. A regional climate model, ICTP-RegCM3, with 20 km horizontal resolution, is used to downscale the reference and future climate scenario (IPCC-A2) simulations. Characteristics of droughts as well as the crop growth and yields of first- and second-crop corn are then calculated and simulated based on the data produced. The model projects an increase in air temperature of 5 to 7°C during the summer season over the west and an increase of 3.5°C for the winter season for the eastern part of the country. Precipitation is predicted to be 40% less in the southwest, although it may increase by 25% in the eastern part of the Black Sea region and northeastern Turkey. Trends in drought intensity and crop growth are related to climate changes. The results suggest more frequent, intense and long-lasting droughts in the country particularly along the western and southern coasts under future climate conditions. A shift of climate classes towards drier conditions is also projected for the western, southern and central regions during the 21st century. Evaluating the role of the climate change trends in crop production reveals significant decreases in yield and shortened growth seasons for first- and second-crop corn, a likely result of high temperatures and water stresses. In addition to rising temperatures and declining precipitation, increasing frequency, severity and duration of drought events may significantly affect food production and socio-economic conditions in Turkey. Our results may help policy makers and relevant sectors to implement appropriate and timely measures to cope with climate-change-induced droughts and their effects in the future.

INTRODUCTION The road towards RegCM4 F. Giorgi1,*, R. O. Anyah2

Abstract: The RegCM model system was originally developed in the late 1980s, and it was the first limited area model applied to climate studies. Over the last 25 yr, the system has been im - proved through successive model versions (RegCM1 to RegCM4), incorporating increasingly comprehensive physics packages and interactively coupled components of the climate system (chemistry/aerosol, ocean, lake, biosphere). The present Climate Special includes studies using RegCM3 and the latest version RegCM4. The papers illustrate that RegCM is a flexible and ver- satile system which can be used for different regions of the World and for a wide range of applica- tions. Plans for the development of the next non-hydrostatic version RegCM5 are also described.

Change in climate and berry composition for grapevine varieties cultivated in the Loire Valley

Abstract: We analyzed the nature and trends of climate variables and bioclimatic indices for 6locations situated in the Loire Valley, northwest France, along with the berry composition of the 6main grapevine varieties cultivated there, from 1960 to 2010. Results show significant increases inmean temperature (by 1.3 to 1.8°C) over the growing season (April to September) throughout theLoire Valley, with maximum temperatures increasing more strongly than minimum temperatures.Temperature variables, such as spring and summer temperatures, the number of days with maxi-mum temperatures >30°C and bioclimatic indices increased significantly. The Huglin Index indi-cated that the 6 locations in the Loire Valley have shifted from a cool climate to a temperate cli-mate between 1960 and 2010, and increases in growing degree-days were highly correlated withearlier harvest dates. The berry composition of the 6 main white and red grapevine varietieschanged significantly, with higher sugar concentrations and lower titratable acidity at harvest. Weconclude that these changes in berry composition were significantly influenced by the increasesin temperature over the study period.KEY WORDS: Loire Valley · Climate change · Temperature · Bioclimatic indices ·

Surviving in a warmer world: environmental and genetic responses

Abstract: There are numerous reports in the literature of advancing trends in phenophases of plants, insects and birds attributed to rising temperature resulting from human-driven climate warming. One mechanism that enables a population to respond rapidly to changes in the environ- ment is termed phenotypic plasticity. This plasticity grants a degree of flexibility to enable the tim- ing of developmental stages to coincide with resource availability. If, however, environmental con- ditions exceed the plastic limits of an organism, evolutionary change may be necessary in order to ensure continued survival of their populations. We review evidence for phenotypic plasticity and genetic adaptation in phenological characteristics associated with climatic warming. We focus this review on examples from trees, insects and birds. We found many reports of direct observations of phenotypic plasticity but fewer studies providing conclusive evidence of genetic adaptation. Evi- dence for changes in genes linked with adaptive traits associated with a warming climate was stronger in insects, that have a relatively short life-cycle, than in longer-lived birds and trees. Fur- ther research is required to identify both appropriate long-term data sets for a range of species and traits and suitable analytical methods, which will permit the study of the complex interaction between phenotypic plasticity and genetic adaptation of organisms and their populations in response to climatic change.

Effects of seasonal cycle fluctuations in an A1B scenario over the Euro-Mediterranean region

Abstract: We analysed the downscaling of an A1B scenario simulation for the Euro-Mediterranean area performed with a regional earth system model by focusing on long-term variations in the seasonal cycle of key impact indicators (surface temperature, hydrological cycle). The output of the regional model was compared with the driving global simulation (ECHAM5/MPI-OM) and with available observations. Our objective was to highlight the potential additional information end-users may access by using a high-resolution regional coupled system in place of the corresponding coarser global driver. In the regional downscaling, the large sea surface temperature (SST) bias simulated by the global driver is partially reduced, and SST spatial patterns are in better agreement with those observed in the reference climatology, thereby supporting the tenet that coupling the atmosphere with a high-resolution interactive ocean over small areas characterized by complex orography may improve specific aspects of regional climate modelling. A more accurate description of orography produces in the regional model a narrower identification of the effects of a warmer climate on intense precipitation events and on other key environmental indicators, such as the extension of snow cover and the aridity index. An example of the effect of climate variability on river discharge is also presented for a medium/small catchment basin in northern Italy, the Po River, which responds both to variations in rainfall rates and to the amount of snowfall over the Alps. In contrast with the gross underestimation of the global driver, regional simulation produces a reasonable estimate of the observed average discharge (1500 m3 s−1) and of its seasonal variability, which provides a reliable baseline for societal impact studies.

Lepidopteran species differ in susceptibility to winter warming

Abstract: Predicting assemblage-level impacts of climate change requires knowledge of among-species variation in susceptibility to warming. Increased winter temperatures intuitively reduce cold stress for overwintering ectotherms, but can decrease fitness by increasing consumption of energy reserves. We kept overwintering stages of the butterflies Papilio glaucus, P. troilus (Papilionidae), and Erynnis propertius (Hesperiidae) under current temperatures and conditions simulating a 4°C increase in mean temperature, and compared mass, water, energy reserves (lipid, protein and carbohydrate content), and, in E. propertius and P. troilus, post-winter development time, adult size, and mortality. All 3 species lost mass over winter, more so during warm winters. Erynnis propertius lost more mass than either Papilio. Warm winters increased energy reserve depletion in E. propertius, but had no effect on energy reserves of either Papilio. Warming reduced development time, but did not affect mortality or adult size of P. troilus. Mortality in E. propertius was uniformly high preventing assessment of treatment effects on survival, development, or adult size. The observed overwinter mass loss by E. propertius and P. troilus was predominantly due to water loss; thus we conclude that mass loss is not an appropriate measurement of energy drain in insects, rather body composition should be measured directly. Thus, P. glaucus and P. troilus have low vulnerability to winter warming, while E. propertius shows some vulnerability. Measuring the impact of winter warming on many species will enable the identification of species traits that predict vulnerability, and facilitate identification of clades particularly susceptible to winter warming.

Quantifying field-scale effects of elevated carbon dioxide concentration on crops

Abstract: Climate change will affect crop growth and agricultural production worldwide. Crop production will be affected not only by modified rainfall patterns, increased air temperatures and changes in evaporative demand, but also elevated atmospheric CO2 concentrations ((CO2)). This study used meta-analytic techniques to quantify field-scale effects of elevated (CO2) (mainly 541 to 620 µmol mol �1 ) on agricultural crops in free air CO2 enrichment (FACE) conditions. Overall, crops benefit from elevated (CO2) by improving water productivity (+23% for biomass production and +27% for yield production), which is achieved through production increases in biomass (+15% for aboveground biomass) and yield (+16%), in combination with a decrease in seasonal evapotranspiration (-5%). Increased root:shoot ratios (+24%) indicate a more than proportional stimulation of belowground biomass production. Less critical, yet statistically significant are changes in canopy development rate and in phenology. Certain statistically significant differences existed between C3 and C4 crops, and between levels of environmental stress (nitrogen and water availability). Once the effect of elevated (CO2) is well understood and quantified, crop modellers can investigate the interactions with other climatic factors, providing better estimates of potential impacts on food production.

Modeling climate change effects on winter ski tourism in Andorra

Abstract: Mountain regions have been identified as especially vulnerable areas to climate change. Changes in snowfall, glacier retreat and shifts in biodiversity amount and distribution are some examples of the sensitivity of mountain ecosystems. Moreover, in many mountain economies, reliable snow cover plays a key role as an important resource for the winter tourism industry, the main income source and driving force of local development in such regions. This study presents a georeferenced agent-based model to analyze the climate change impacts on the ski industry in Andorra and the effect of snowmaking as future adaptation strategy. The present study is the first attempt to analyze the ski industry in the Pyrenees region and will contribute to a better understanding of the vulnerability of Andorran ski resorts and the suitability of snowmaking as potential adaptation strategy to climate change. This study projects a reduction on the ski season length and the drop of the number of skiers especially in the lowest elevation ski resort of this region. Moreover, this work indicates that snowmaking cannot completely solve the problem of ensuring snow cover at low elevation ski resorts and should be considered as a suitable short-term strategy, but not as a sustainable long-term adaptation strategy. The resulting model can be used as a planning support tool to help local stakeholders understand the vulnerability and potential impacts of climate change and in the decision-making process of designing and developing appropriate sustainable adaptation strategies to future climate variability.

Modelling the effects of climate change on air quality over Central and Eastern Europe: concept, evaluation and projections

Abstract: Modelling the effects of climate change on air quality over Central and Eastern Europe: concept, evaluation and projections Katarzyna Juda-Rezler, Magdalena Reizer, Peter Huszar, Bernd C. Kruger, Prodromos Zanis, Dimiter Syrakov, Eleni Katragkou, Wojciech Trapp, Dimitris Melas, Hristo Chervenkov, Ioannis Tegoulias, Tomas Halenka 1Faculty of Environmental Engineering, Warsaw University of Technology, 00-653 Warsaw, Poland 2Department of Meteorology and Environment Protection, Charles University, 180 00 Prague, Czech Republic 3Institute of Meteorology, University of Natural Resources and Life Sciences, 1190 Vienna, Austria 4Department of Meteorology and Climatology, Aristotle University of Thessaloniki, 54124 Thessaloniki, Greece 5Department of Air and Water Pollution, National Institute of Meteorology and Hydrology, 1784 Sofia, Bulgaria 6Laboratory of Atmospheric Physics, Aristotle University of Thessaloniki, 54124 Thessaloniki, Greece 7Air Protection Unit of Ekometria, 80-299 Gdansk, Poland 8National Institute of Meteorology and Hydrology, Branch Plovdiv, 4000 Plovdiv, Bulgaria

Effects of land use changes on climate in the Greater Horn of Africa

Abstract: The relationships between historical land use transformations and spatio-temporal patterns of precipitation and temperature over the Greater Horn of Africa (GHA) were examined based on Landsat satellite observations for the years 1986, 1995, and 2000 and regional climate model simulations in the period 1991−2000. The satellite-derived land use/cover classification shows increased conversion of large portions of forests over the GHA to agriculture, par ticularly in Kenya, with land (acreage) under crops increasing from 6.55% in 1986 to almost 18% by the year 2000. Sensitivity experiments performed with regional climate model, Version 4 (RegCM4), indicate that expanding agriculture into forested areas led to a modest reduction in monthly rainfall totals and also may be contributing to notable shifts in moisture convergence zones and centers of rainfall maxima. Student’s t-test at a 0.1 significant level showed a decrease in precipitation and an increase in surface temperature around the lake region when surface vegetation cover is converted to agricultural land cover type. Conversely, under the assumption that large sections of croplands are converted to forest, the simulations resulted in a modest increase in precipitation and a reduction of surface temperature around the lake region, changes that are significant at the 0.1 confidence level. A substantial trade-off in the components of the surface energy balance between sensible heat flux (SHF) and latent heat flux (LHF) was observed for the different conversion types. Under the assumption of reforestation, both SHF and LHF increased. The increase in SHF was almost twice that of LHF. On the other hand, when land cover types were converted to agricultural types, SHF decreased, while LHF did not show any significant change.

Climate change scenarios and potential impacts on water availability in northern Mexico

Abstract: The climate predictability tool (CPT) is often used to statistically downscale the Intergovernmental Panel on Climate Change scenarios presented in the Fourth Assessment Report. The CPT reduces systematic errors and interpolates to a higher spatial resolution grid. Monthly means of surface temperature and precipitation from around 20 climate models for 4 greenhouse gas emission scenarios were downscaled for Mexico. Transfer functions are constructed using the 1900−1970 period and evaluated for the 1971−1999 period, examining the CPT ability to reproduce the observed climatology and trends in temperature and precipitation. The CPT-downscaled ensembles of climate change projections are considered adequate since, after correcting systematic biases in climate models, the observed climatology and trends in temperature and precipitation for the 1971−1999 period compare well with the observed data from the Climate Research Unit at 50 × 50 km resolution. The ensemble of downscaled climate change scenarios for the 2000−2099 period is then used to estimate some potential impacts of global warming over Mexico, mostly in water-related sectors. Results show that increases in temperature may be larger in the northwestern than in the northeastern part of the country. Precipitation scenarios project large probabilities of decreases in rainfall over northwestern Mexico, with potential reductions as large as 30%, which correspond to a standard precipitation index of around −1, i.e. a moderate drought. Drought of this magnitude may also bring the vegetation into a state of severe water stress and make it prone to forest fires. The combined effect of increased temperature and precipitation reductions could lead to reduced water availability over northwestern Mexico, especially along the USA−Mexico border region after the 2050s.

Climate sensitivity of a millennium-long pine chronology from Albania

Abstract: Considerable progress has been made in assessing European climate variations of the last millennium, but little is known about the Mediterranean region and particularly its eastern part including the Balkan Peninsula. This area, however, will be particularly vulnerable to a predicted temperature increase and precipitation decrease, likely resulting in amplified drought extremes and episodes. Here we present a well-replicated composite tree-ring width chronology of millennial length from Albania, Balkan Peninsula. The Pinus heldreichii Christ dataset contains 302 series from 217 living and dead trees from 3 high-elevation sites, and spans the years 968–2008. Signal strength and growth–climate relationships were investigated using subsets according to location, age class, and growth level, as well as differently detrended chronology versions. Growth comparisons amongst the 3 sites’ chronologies, between age classes and between growth-rate groups reveal an overall strong common signal. Growth–climate relationships over the last 100 yr, however, indicate that tree-ring formation does not depend on one single dominant factor, but rather on various combinations of summer precipitation and temperature resulting in temporally varying drought sensitivity. Our results emphasize a mixed and variable climate signal, corresponding with findings from other P. heldreichii sites across the Balkan Peninsula and Southern Italy.

Hydro-economic consequences of climate change in the upper Rio Grande

Abstract: Social, economic, and environmental systems in arid regions are vulnerable to dis- ruptions in water supplies that are likely to accompany future climate changes. With a particular focus on the Rio Grande in New Mexico, this paper uses a hydro-economic model to integrate plausible changes in population and climate over the coming 70 yr. Specifically, projections of regional population growth are combined with alternative climate scenarios in order to simulate changes in streamflows, water supplies, and water demands within a framework that economizes water use. The study uses 3 climate change scenarios across 2 distinct future time periods to model runoff, water supply, and water demand changes, and estimate the economic and water-use consequences. Specifically, temperature and precipitation scenarios were generated using results from 3 general circulation models (GCMs), namely, HadCM3 (Hadley Centre for Climate Predic- tion and Research Met Office), CSIRO (Commonwealth Scientific and Industrial Research Orga- nization of Australia), and the GFDL0 (Geophysical Fluid Dynamics Laboratory of the National Oceanic and Atmospheric Administration), all of which were driven by the A1B emissions scenario from the Intergovernmental Panel on Climate Change's Special Report on Emissions Scenarios. The WATBAL hydrologic model and the Rio Grande hydro-economic model were used to model the hydrologic and economic consequences, respectively. Findings indicate that agricultural water users could be most affected by curtailed deliveries and higher water scarcity. Municipal water users are likely to face higher delivery costs as competition for scarce surface water supplies rises; however, groundwater supplies provide an effective buffer for many of the municipal systems and help ameliorate price spikes.

Regional climate feedback of anthropogenic aerosols over Europe using RegCM3

Abstract: Τhe regional climate model RegCM3 coupled with aerosols is used in this study to investigate the direct shortwave effect of anthropogenic aerosols on the regional European climate over a 12 yr period (1996–2007). Aerosol feedback induced small changes in the yearly averaged near-surface temperature over Europe during this period and the greatest negative temperature difference of −0.2°C was observed over the Balkan Peninsula. The field of aerosol-induced near-surface temperature anomalies is not spatially collocated with the field of aerosol radiative forcing as the spatial correlation coefficient is only 0.24. A characteristic of the aerosol-induced changes on near-surface temperature is a dipole pattern in which cooling occurs south of the latitudinal zone from 50 to 55° N and warming occurs northwards. This characteristic dipole pattern of changes in temperature is also seen at higher atmospheric levels but the signal weakens at higher altitudes. A characteristic in the aerosol-induced changes in atmospheric circulation is a negative anomaly of the zonal westerly wind of 500 hPa in the latitudinal belt between 45 and 55° N, which is consistent with a dipole pattern in geopotential heights that consists of an anticyclonic anomaly north of approx. 55° N and cyclonic anomaly south of approx. 45° N. The greatest aerosol-induced negative lower troposphere temperature anomaly over the Balkan Peninsula is associated with the collocated greatest cyclonic anomaly. This reveals the important role of the aerosol-induced circulation changes for the pattern of the temperature anomalies and explains the poor correlation between the patterns of aerosol-induced temperature changes and aerosol radiative forcing. Because the aerosol-induced changes in temperature and atmospheric circulation are at the limits of statistical significance, the present regional climate modelling study indicates there is a limited feedback on the European climate related to the direct shortwave effect of European anthropogenic aerosols.

Dynamical downscaling of rainfall and temperature over the Arabian Peninsula using RegCM4

Abstract: We use the International Centre for Theoretical Physics’ (ICTP) regional climate model (RegCM4) nested in the European Community−Hamburg atmospheric model (ECHAM5) and the European Centre for Medium-Range Weather Forecasts’ (ECMWF) 40-yr reanalysis (ERA40) data to perform and analyze multi-decadal present-day climate simulation over the Arabian Peninsula. Mean climatology, annual cycle, and interannual variability of rainfall and temperature are compared to observational data. The results show that, while ECHAM5 and ERA40 exhibit drier and warmer biases, RegCM4 simulates higher rainfall intensity and lower warm temperatures, providing a more realistic spatial distribution of these variables over the region. This originates from a more reasonable simulation of specific humidity, wind fields, and geopotential heights compared to the driving field. Annual cycles over the northern Arabian Peninsula (NAP) are better captured by RegCM4 than by ECHAM5, while, over the south (SAP), annual cycles mostly follow the driving field. This suggests that the annual cycle over the NAP is driven by regional processes represented by the internal regional climate model dynamics and physics, and, over the SAP sub-region, the influences of large-scale conditions induced by boundary forcing are dominant. Both RegCM4 and ECHAM5 exhibit similar performance in terms of variance over the low-variability region (SAP); however, the regional climate model outperforms the driving global climate model for the high-variability region (NAP). Therefore, although dynamical downscaling offers some improvements regarding climatology and the annual cycle, it has mixed benefits in terms of interannual variability.

Rio Grande and Rio Conchos water supply variability over the past 500 years

Abstract: The Rio Grande is a major source of water for parts of Mexico and the USA. The 2 main source regions for the Rio Grande system are the San Juan Mountains of the southern Rocky Mountains and the Sierra Madre Occidental in Mexico, which is the headwaters for the Rio Con- chos, the largest tributary of the Rio Grande. Precipitation and streamflow from these 2 source regions are largely independent of each other; winter snowpack is the dominant contributor to the annual streamflow north of the USAMexico border, and the North American monsoon is a key factor in the Rio Conchos basin. Reconstructions of water year (OctoberSeptember) streamflow for a gauge in the upper Rio Grande, 1508�2002, and of OctoberJuly precipitation in the Rio Con- chos watershed region, 1649�1993, also indicate a lack of correlation between the 2 basins over century time scales. Despite this lack of correlation, periods of concurrent multiyear drought have occurred over the past 4 centuries, most notably in the 1770s, 1890s and 1950s. These rare concur- rent droughts in the upper Rio Grande and Rio Conchos source regions may arise from large-scale forcing out of the Pacific Ocean and will be relevant to the binational planning of these water resources, which serve a large and growing population of users.

Tourism demand and atmospheric parameters: non-intrusive observation techniques

Abstract: In this study, we used images from webcam cameras and Argus video systems to examine how the behaviour of sun and beach tourists in Spain was influenced by the meteorological weather conditions. We applied a qualitative visual count method, which involved creating a bank of images and undertaking a classification of the density of use at each observation point. Thus, each image was assigned a density-of-use level. These results were then correlated with a range of meteorological variables and the physiological equivalent temperature (PET). Atmo spheric conditions do have an impact on the behaviour of sun and beach tourists, and our study shows that the density of use of the beaches in Spain is controlled by solar radiation (the aesthetic facet) and the maximum temperature and PET (the comfort facet). The optimal thresholds of these meteorological variables for going to the beach were as follows: a maximum temperature between 28.83 and 31°C; a maximum PET between 34.5 and 38.8°C; a percentage of solar radiation at 13:00 h of at least 50%; a wind speed at 13:00 h of <8 m s−1 (or, at the most, <10 m s−1); and no rainfall or, at the most, <1 mm d−1 or a rainfall event with a duration of <60 min. The application of these thresholds for determining the degree of use of beaches during the year should lead to more accurate forecasts of the calendar of the tourist season and ensure that the basic tourist resources provided for beach tourism are managed more effectively during these periods, including the provision of services and safety facilities.

Temperature trends in Hong Kong from a seasonal perspective

Abstract: We examined the seasonal trends of mean and extreme temperatures in Hong Kong using data from 1885−2010. The analysis revealed that the daily maximum temperature (TMax), daily mean temperature (TMean), and daily minimum temperature (TMin) of Hong Kong had a sig- nificant long-term increasing trend in all 4 seasons and that the warming trend was more promi- nent in winter and spring. The relatively higher rate of increase in temperatures in winter and spring could be attributed to local urbanization effects and the weakening of the East Asian winter monsoon in the last few decades. For extreme indices, we observed a significant increase in the hot indices (TN90p and TX90p) and a significant decrease in the cold indices (TX10p and TN10p) in all seasons. The seasonal variations in the heating and cooling degree-days (HDD and CDD) also indicated that CDD in spring, summer, and autumn had a significant increasing trend, while HDD in spring, autumn and winter had a decreasing trend. Analysis of the hot and cool periods in Hong Kong showed a significant decreasing (increasing) trend in the number of cool (hot) days. Also, the cool (hot) period has become shorter (longer) over the last century.

Downscaling of weather generator parameters to quantify hydrological impacts of climate change

Abstract: A major obstacle in quantifying the hydrological impacts of climate change is the mismatch between the coarse resolution of climate model outputs (general circulation models and regional climate models) and the fine resolution requirements of hydrological models. This research presents a statistical downscaling approach combining the attributes of both the stochastic weather generator (WG) and the change factor (CF) method to overcome this problem. It is further compared against the commonly used CF method in terms of quantifying the hydrological impacts of climate change over the next century for a Canadian watershed (Quebec Province). Both downscaling methods suggested increases in winter (November−April) discharge and decreases in summer (June−October), especially for those downscaled by the WG-based method. The WG-based method predicted higher peak discharges than the CF method. The 2 downscaling methods suggested significantly different increases in annual and seasonal discharges, particularly for low flows. Hydrology results show that precipitation and temperature variability play a very important role in the runoff generating process, and that neglecting to address this variability can lead to biased results. In particular, the WG-based method has a significant advantage in simulating low flows because it takes into account the change of precipitation occurrence. The results also outline the uncertainty linked to the choice of a downscaling method.

Reducing overdispersion in stochastic weather generators using a generalized linear modeling approach

Abstract: Stochastic weather generators are commonly used to simulate time series of daily weather, especially minimum (Tmin) and maximum (Tmax) temperature and amount of precipitation. Recently, generalized linear models (GLM) have been proposed as a convenient approach to fit- ting weather generators. One limitation of weather generators is a marked tendency to underesti- mate the observed interannual variance in monthly, seasonal, or annual total precipitation and mean temperature, termed the 'overdispersion' phenomenon. In this study, aggregated statistics, consisting of seasonal total precipitation and mean Tmin and Tmax, are introduced as additional covariates into the GLM weather generator. With an appropriate degree of smoothing of these aggregated statistics, this approach is shown to virtually eliminate overdispersion when applied to 2 sites, Pergamino and Pilar, in the Argentine Pampas. The addition of these covariates does not distort the performance of the weather generator in other respects, such as annual cycles in the probability of precipitation and in the mean Tmin and Tmax. For seasonal total precipitation, the reduction in overdispersion is partially attributable to a corresponding reduction in the overdisper- sion of the frequency of precipitation occurrence, as well as to apparent temporal trends or 'regime' shifts. For seasonal mean Tmin and Tmax, the reduction in overdispersion is largely due to temporal trends on an interannual time scale.

Influence of atmospheric modes of variability on a deep lake south of the Alps

Abstract: Limnological measurements and winter air temperatures recorded in a deep lake south of the Alps (Lake Garda) have been analysed and related to temporal variations in 5 telecon- nection patterns, i.e. the East Atlantic pattern (EA), the Eastern Mediterranean Pattern (EMP), the North Atlantic Oscillation (NAO), the Scandinavia pattern (SCAND) and the East Atlantic/West Russia Pattern (EA/WR). The EA and EMP played a significant role in winter in the large-scale atmospheric circulation over the Mediterranean region. Positive and negative EA, and negative and positive EMP phases were closely connected with the development of mild and harsh winters, respectively. In turn, harsh winters had a strong positive impact on the development of diatoms in spring and cyanobacteria in summer and autumn. These modifications were controlled through a linked chain of factors, which included lower winter lake water temperatures, deep lake circula- tion episodes, and higher replenishment of epilimnetic phosphorus at spring overturn. This work demonstrates the existence of a strong connection between large-scale climatic fluctuations over the Mediterranean area and the temporal variations in the limnological characteristics of the large lakes located between the Alps and the northern border of the Mediterranean region. Conversely, the NAO, SCAND and EA/WR did not show any relationship with the winter climate and the limnological characteristics of Lake Garda.