Showing papers in "International Journal of Climatology in 2011"

El Niño/Southern Oscillation behaviour since 1871 as diagnosed in an extended multivariate ENSO index (MEI.ext)

Abstract: El Nino/Southern Oscillation (ENSO) remains the most important coupled ocean–atmosphere phenomenon to cause global climate variability on seasonal to interannual time scales. This paper addresses the need for a reliable ENSO index that allows for the historical definition of ENSO events in the instrumental record back to 1871. The Multivariate ENSO Index (MEI) was originally defined as the first seasonally varying principal component of six atmosphere–ocean (COADS) variable fields in the tropical Pacific basin. It provides for a more complete and flexible description of the ENSO phenomenon than single variable ENSO indices such as the SOI or Nino 3.4 SST. Here we describe our effort to boil the MEI concept down to its most essential components (based on SLP, SST) to enable historical analyses that more than double its period of record to 1871–2005. The new MEI.ext confirms that ENSO activity went through a lull in the early- to mid-20th century, but was just about as prevalent one century ago as in recent decades. We diagnose strong relationships between peak amplitudes of ENSO events and their duration, as well as between their peak amplitudes and their spacing (periodicity). Our effort is designed to help with the assessment of ENSO conditions through as long a record as possible to be able to differentiate between ‘natural’ ENSO behaviour in all its rich facets, and the ‘Brave New World’ of this phenomenon under evolving GHG-related climate conditions. So far, none of the behaviour of recent ENSO events appears unprecedented, including duration, onset timing, and spacing in the last few decades compared to a full century before then. Copyright © 2011 Royal Meteorological Society

The integrated WRF/urban modelling system: development, evaluation, and applications to urban environmental problems

Abstract: To bridge the gaps between traditional mesoscale modelling and microscale modelling, the National Center for Atmospheric Research, in collaboration with other agencies and research groups, has developed an integrated urban modelling system coupled to the weather research and forecasting (WRF) model as a community tool to address urban environmental issues. The core of this WRF/urban modelling system consists of the following: (1) three methods with different degrees of freedom to parameterize urban surface processes, ranging from a simple bulk parameterization to a sophisticated multi-layer urban canopy model with an indoor–outdoor exchange sub-model that directly interacts with the atmospheric boundary layer, (2) coupling to fine-scale computational fluid dynamic Reynolds-averaged Navier–Stokes and Large-Eddy simulation models for transport and dispersion (TD addresses the daunting challenges of initializing the coupled WRF/urban model and of specifying the potentially vast number of parameters required to execute the WRF/urban model; explores the model sensitivity to these urban parameters; and evaluates the ability of WRF/urban to capture urban heat islands, complex boundary-layer structures aloft, and urban plume T&D for several major metropolitan regions. Recent applications of this modelling system illustrate its promising utility, as a regional climate-modelling tool, to investigate impacts of future urbanization on regional meteorological conditions and on air quality under future climate change scenarios. Copyright © 2010 Royal Meteorological Society

Empirical‐statistical downscaling and error correction of daily precipitation from regional climate models

Abstract: Although regional climate models (RCMs) are powerful tools for describing regional and even smaller scale climate conditions, they still feature severe systematic errors. In order to provide optimized climate scenarios for climate change impact research, this study merges linear and nonlinear empirical-statistical downscaling techniques with bias correction methods and investigates their ability for reducing RCM error characteristics. An ensemble of seven empirical-statistical downscaling and error correction methods (DECMs) is applied to post-process daily precipitation sums of a high-resolution regional climate hindcast simulation over the Alpine region, their error characteristics are analysed and compared to the raw RCM results. Drastic reductions in error characteristics due to application of DECMs are demonstrated. Direct point-wise methods like quantile mapping and local intensity scaling as well as indirect spatial methods as nonlinear analogue methods yield systematic improvements in median, variance, frequency, intensity and extremes of daily precipitation. Multiple linear regression methods, even if optimized by predictor selection, transformation and randomization, exhibit significant shortcomings for modelling daily precipitation due to their linear framework. Comparing the well-performing methods to each other, quantile mapping shows the best performance, particularly at high quantiles, which is advantageous for applications related to extreme precipitation events. The improvements are obtained regardless of season and region, which indicates the potential transferability of these methods to other regions. Copyright © 2010 Royal Meteorological Society

A systematic review and scientific critique of methodology in modern urban heat island literature

Abstract: In the modern era of urban climatology, much emphasis has been placed on observing and documenting heat island magnitudes in cities around the world. Urban climate literature consequently boasts a remarkable accumulation of observational heat island studies. Through time, however, methodologists have raised concerns about the authenticity of these studies, especially regarding the measurement, definition and reporting of heat island magnitudes. This paper substantiates these concerns through a systematic review and scientific critique of heat island literature from the period 1950–2007. The review uses nine criteria of experimental design and communication to critically assess methodological quality in a sample of 190 heat island studies. Results of this assessment are discouraging: the mean quality score of the sample is just 50 percent, and nearly half of all urban heat island magnitudes reported in the sample are judged to be scientifically indefensible. Two areas of universal weakness in the literature sample are controlled measurement and openness of method: one-half of the sample studies fail to sufficiently control the confounding effects of weather, relief or time on reported ‘urban’ heat island magnitudes, and three-quarters fail to communicate basic metadata regarding instrumentation and field site characteristics. A large proportion of observational heat island literature is therefore compromised by poor scientific practice. This paper concludes with recommendations for improving method and communication in heat island studies through better scrutiny of findings and more rigorous reporting of primary research. Copyright © 2010 Royal Meteorological Society

ICOADS Release 2.5: extensions and enhancements to the surface marine meteorological archive

Abstract: Release 2.5 of the International Comprehensive Ocean-Atmosphere Data Set (ICOADS) is a major update (covering 1662–2007) of the world's most extensive surface marine meteorological data collection. Building on extensive national and international partnerships, many new and improved contributing datasets have been processed into a uniform format and combined with the previous Release 2.4. The new data range from early non-instrumental ship observations to measurements initiated in the twentieth century from buoys and other automated platform types. Improvements to existing data include replacing preliminary Global Telecommunication System (GTS) receipts with more reliable, delayed mode reports for post-1997 data, and in the processing and quality control (QC) of humidity observations. Over the entire period of record, spatial and temporal coverage has been enriched and data and metadata quality has been improved. Along with the observations, now updated monthly in near real time, Release 2.5 includes quality-controlled monthly summary products for 2° latitude × 2° longitude (since 1800) and 1° × 1° boxes (since 1960), together with multiple options for access to the data and products. The measured and estimated data in Release 2.5 are subject to many technical changes, multiple archive sources, and historical events throughout the more than three-century record. Some of these data characteristics are highlighted, including known unresolved errors and inhomogeneities, which may impact climate and other research applications. Anticipated future directions for ICOADS aim to continue adding scientific value to the observations, products, and metadata, as well as strengthen the cooperative enterprise through expanded linkages to international initiatives and organisations. Copyright © 2010 Royal Meteorological Society

A review of methods for estimating anthropogenic heat and moisture emissions in the urban environment

Abstract: Energy consumption in the urban environment impacts the urban surface energy budget and leads to the emission of anthropogenic sensible heat and moisture into the atmosphere. Anthropogenic heat and moisture emissions vary significantly both in time and space, and are not readily measured. As a result, detailed models of these emissions are not commonly available for most cities. Furthermore, most attempts to quantify anthropogenic emissions have focused on the sensible heat component, largely ignoring moisture emissions and invoking assumptions—such as the equivalence of energy consumption and anthropogenic sensible heating—which limit the accuracy of the resulting anthropogenic heating estimates. This paper provides a historical perspective of the development of models of energy consumption in the urban environment and the associated anthropogenic impacts on the urban energy balance. It highlights some fundamental limitations of past approaches and suggests a roadmap forward for including anthropogenic heat and moisture in modelling of the urban environment. Copyright © 2010 Royal Meteorological Society

The influence of trees and grass on outdoor thermal comfort in a hot-arid environment

Abstract: The effects of vegetation on human thermal stress in a hot-arid region were tested in two semi-enclosed urban spaces with various combinations of mature trees, grass, overhead shading mesh and paving. The index of thermal stress was calculated hourly from measured meteorological data in the studied sites to evaluate thermal comfort in the different spaces based on radiative and convective pedestrian–environment energy exchanges and sweat efficiency, and expressed on a thermal sensation scale ranging from ‘comfortable’ to ‘very hot’. The efficiency of water use in providing improved comfort was gauged for each of the vegetative landscaping treatments by comparing the total evapotranspiration with the reduction in thermal stress, both expressed in terms of their values in equivalent energy. While conditions in a paved, unshaded courtyard were found to be uncomfortable throughout the daytime hours (with half of these hours defined by severe discomfort), each of the landscape treatments made a clear contribution to improved thermal comfort. With shading, either by trees or mesh, discomfort was reduced in duration by over half and limited in maximum severity when the shading was placed above paving. When combined with grass, both shading mechanisms yielded comfortable conditions at all hours. In both cases, the effect of trees was more pronounced than that of the mesh, but by a small margin. With unshaded grass, ‘hot’ conditions in the courtyard were restricted to a short period in mid-afternoon, a considerable improvement over unshaded paving, attributable mainly to the lower radiant surface temperatures. Copyright © 2010 Royal Meteorological Society

Initial results from Phase 2 of the international urban energy balance model comparison

Abstract: Urban land surface schemes have been developed to model the distinct features of the urban surface and the associated energy exchange processes. These models have been developed for a range of purposes and make different assumptions related to the inclusion and representation of the relevant processes. Here, the first results of Phase 2 from an international comparison project to evaluate 32 urban land surface schemes are presented. This is the first large-scale systematic evaluation of these models. In four stages, participants were given increasingly detailed information about an urban site for which urban fluxes were directly observed. At each stage, each group returned their models' calculated surface energy balance fluxes. Wide variations are evident in the performance of the models for individual fluxes. No individual model performs best for all fluxes. Providing additional information about the surface generally results in better performance. However, there is clear evidence that poor choice of parameter values can cause a large drop in performance for models that otherwise perform well. As many models do not perform well across all fluxes, there is need for caution in their application, and users should be aware of the implications for applications and decision making. Copyright  2010 Royal Meteorological Society

Changes in near-surface wind speed in China: 1969-2005

Abstract: This study extends upon previous analyses and details near-surface wind speed change in China and its monsoon regions from 1969 to 2005, using a new dataset consisting of 652 stations. Moreover, causes of wind speed changes are examined. Major results show that most stations in China have experienced significant weakening in annual and seasonal mean wind during the study period. The averaged rate of decrease in annual mean wind speed over China is -0.018 ms(-1)a(-1). Decrease in seasonal mean wind differs. The largest rate of decline is in spring at -0.021 ms(-1)a(-1) and the least is in summer at -0.015 ms (1)a (1). Spatially, large declines are found in northern China, the Tibetan Plateau and the coastal areas in east and southeast China, while central and south-central China have the least change in their wind speed. Significant weakening of wind speed has occurred primarily in strong wind categories. Decreases in light wind categories are trivial, and light wind has even increased slightly in parts of central China. These changes indicate reduced fluctuations in wind and wind storms in recent decades, contributing to decreased frequency and magnitude of dust storms. The trivial changes in summer winds in east and southeast China suggest fairly steady monsoon winds over the decades. A main cause of the weakening wind is shown to be the weakening in the lower-tropospheric pressure-gradient force, a result pointing to climate variation as the primary source of the wind speed change. Superimposed on the climate effect is the urban effect. While analysis of winds between urban and rural stations reinstate the urban frictional effect, a peculiar stronger increase in wind at urban stations than at rural stations after the abrupt urbanization since 1990 indicates a new aspect of the urban effect on wind speed. Copyright. (C) 2010 Royal Meteorological Society

Different impacts of El Niño and El Niño Modoki on China rainfall in the decaying phases

Abstract: In this study, we investigate the different impacts of El Nino and El Nino Modoki on China rainfall in their decaying phases. During spring, in the decaying year of El Nino events, there are positive rainfall anomalies south of the Yangtze River, whereas no obvious rainfall signals are found in the same season for the decaying El Nino Modoki. In the subsequent summer season, the wet signal south of the Yangtze River associated with El Nino continues, while suppressed rainfall now appears in the northern Yangtze–Huaihe River region. In contrast, the rainfall is above normal in the region from the Huaihe River to the Yellow River, and below normal in southern China during the summer of the decaying El Nino Modoki events. The distinct China rainfall anomaly is mainly attributed to the difference between the evolution and location of the anomalous western North Pacific (WNP) anti-cyclone associated with El Nino and El Nino Modoki events. For the case of El Nino, the WNP anti-cyclone brings plentiful moisture to southern China; meanwhile it shifts the ridge of sub-tropical high westward in both spring and summer. These tend to induce positive rainfall anomalies in the southern Chinese region. In contrast, due to fast decaying of El Nino Modoki, the anomalous WNP anti-cyclone becomes weak so that there are no significant rainfall anomalies in China. In summer, however, the WNP anti-cyclone re-invigorates possibly associated with a subsequent developing La Nina and extends more northwestward towards the inland region, compared to its El Nino counterpart. The anomalous moisture transport and sub-tropical high activity associated with this WNP anti-cyclone result in different summer rainfall anomalies in China. Copyright © 2010 Royal Meteorological Society

Global to city scale urban anthropogenic heat flux: model and variability

Abstract: The large scale urban consumption of energy (LUCY) model simulates all components of anthropogenic heat flux (QF) from the global to individual city scale at 2.5 × 2.5 arc-minute resolution. This includes a database of different working patterns and public holidays, vehicle use and energy consumption in each country. The databases can be edited to include specific diurnal and seasonal vehicle and energy consumption patterns, local holidays and flows of people within a city. If better information about individual cities is available within this (open-source) database, then the accuracy of this model can only improve, to provide the community data from global-scale climate modelling or the individual city scale in the future. The results show that QF varied widely through the year, through the day, between countries and urban areas. An assessment of the heat emissions estimated revealed that they are reasonably close to those produced by a global model and a number of small-scale city models, so results from LUCY can be used with a degree of confidence. From LUCY, the global mean urban QF has a diurnal range of 0.7–3.6 W m−2, and is greater on weekdays than weekends. The heat release from building is the largest contributor (89–96%), to heat emissions globally. Differences between months are greatest in the middle of the day (up to 1 W m−2 at 1 pm). December to February, the coldest months in the Northern Hemisphere, have the highest heat emissions. July and August are at the higher end. The least QF is emitted in May. The highest individual grid cell heat fluxes in urban areas were located in New York (577), Paris (261.5), Tokyo (178), San Francisco (173.6), Vancouver (119) and London (106.7). Copyright © 2010 Royal Meteorological Society

Urban climatic map studies: a review

Abstract: Since their introduction 40 years ago, worldwide interest in urban climatic map (UCMap) studies has grown. Today, there are over 15 countries around the world processing their own climatic maps, developing urban climatic guidelines, and implementing mitigation measures for local planning practices. Facing the global issue of climate change, it is also necessary to include the changing climatic considerations holistically and strategically in the planning process, and to update city plans. This paper reviews progress in UCMap studies. The latest concepts, key methodologies, selected parameters, map structure, and the procedures of making UCMaps are described in the paper. The mitigation measures inspired by these studies and the associated urban climatic planning recommendations are also examined. More than 30 relevant studies around the world have been cited, and both significant developments and existing problems are discussed. The thermal environment and air ventilation condition within the urban canopy layer (UCL) of the city are important in the analytical processes of the climatic-environmental evaluation. Possible mitigation measures and planned actions include decreasing anthropogenic heat release, improving air ventilation at the pedestrian level, providing more shaded areas, increasing greenery, creating air paths, and controlling building morphologies. Further developments have and will continue to focus on the spatial analysis of human thermal comfort in urban outdoor environments and on the impacts and adaptations of climate change. Mapmakers must continue to share lessons and experiences with city planners and policy makers, especially in the rapidly expanding cities of developing countries and regions. Copyright © 2010 Royal Meteorological Society

Effect of thermal adaptation on seasonal outdoor thermal comfort

Abstract: Thermal perceptions and preferences of individuals outdoors cannot be entirely explained by the energy balance of the human body. They are also affected by psychological and behavioural factors or the so-called thermal adaptation. To examine the effect of thermal adaptation on seasonal outdoor thermal comfort, 1644 interviews with concurrent micrometeorological measurements were conducted outdoors in central Taiwan. Results indicate a deviation of 1.3 °C standard effective temperature (SET*) in neutral temperatures between hot and cool seasons, and a deviation of 1.8 °C SET* in preferred temperature between hot and cool seasons. Additionally, although subjects' temperature and sunshine preferences were highly correlated with SET*, they diverged between seasons for identical SET* exposures in the two seasons. Analysis reveals that people's thermal perceptions were strongly related to the air temperature (Ta) and mean radiant temperature (Tmrt), but not significant to air speed and air humidity. These results demonstrate that thermal adaptation markedly influences seasonal outdoor thermal comfort, knowledge of which may be useful in the planning and design of outdoor environments in hot–humid regions. Copyright © 2010 Royal Meteorological Society

Satellite monitoring of summer heat waves in the Paris metropolitan area

Abstract: Summer warming trends in Western Europe are increasing the incidence, intensity and duration of heat waves. They are especially deadly in large cities owing to population density, physical surface properties, anthropogenic heat and pollutants. In August 2003, for 9 consecutive days, the Paris metropolitan area experienced an extreme heat wave that caused 4867 estimated heat-related deaths. A set of 61 NOAA-AVHRR (advanced very high-resolution radiometer) images and one SPOT-high resolution visible (HRV) image were used to analyse the spatial variations of land surface temperature (LST) over the diurnal cycle during the heat wave. The LST patterns were markedly different between daytime and night-time. A heat island was centred downtown at night, whereas multiple temperature anomalies were scattered in the industrial suburbs during the day. The heat wave corresponded to elevated nocturnal LST compared to normal summers. The highest mortality ratios matched the spatial distribution of the highest night-time LSTs, but were not related to the highest daytime LSTs. LSTs were sampled from images at the addresses of 482 elderly people (half were deceased persons and half were control ones) to produce daily and cumulative minimal, maximal and mean thermal indicators, over various periods of time. These indicators were integrated into a conditional logistic regression model to test their use as heat exposure indicators, based on risk factors. Over the period 1–13 August, thermal indicators taking into account minimum nocturnal temperatures averaged over 7 days or over the whole period were significantly linked to mortality. These results show the extent of the spatial variability in urban climate variables and the impact of night-time temperatures on excess mortality. These results should be used to inform policy and contingency planning in relation to heat waves, and highlight the role that satellite remote sensing can play in documenting and preventing heat-related mortality. Copyright © 2010 Royal Meteorological Society

Changes in temperature and precipitation extremes over the Indo-Pacific region from 1971 to 2005

Abstract: Up-to-date regional and local assessments of changing climate extremes are important to allow countries to make informed decisions on mitigation and adaptation strategies, and to put these changes into a global context. A workshop for countries from the Indo-Pacific region has brought together daily observations from 13 countries for an analysis of climate extremes between 1971 and 2005. This paper makes use of the workshop outcomes and post-workshop analyses to build on previous work in Southeast Asia to update the assessment of changing climate extremes using newly available station data. We utilise a consistent and widely tested methodology to allow a direct comparison of the results with those from other parts of the world. The relationship of inter-annual variability in the climate extremes indices with sea surface temperature (SST) patterns has been investigated with a focus on the influence of the El Nino-Southern Oscillation phenomenon. The results support findings from elsewhere around the globe that warm extremes, particularly at night, are increasing and cold extremes are decreasing. Trends in precipitation extremes are less spatially consistent across the region. © Royal Meteorological Society and Crown Copyright 2010.

Trend detection of annual and seasonal rainfall in Calabria (Southern Italy)

Abstract: In order to investigate the behaviour of climatic and hydrological variables, several statistical and stochastic techniques are currently applied to time series. In the present study a statistical analysis of annual and seasonal precipitation has been performed over 109 cumulated rainfall series with more than 50 years of data observed in a region of Southern Italy (Calabria). Trend analyses have been made by using both nonparametric (Mann–Kendall test) and parametric (linear regression analysis) procedures. The long historical series of monthly rainfall data employed in this work have been previously processed through a pre-whitening (PW) technique in order to reduce the autocorrelation of rainfall series and its effects on outcomes of trend detection. The application of the above mentioned procedures has shown a decreasing trend for annual and winter–autumn rainfall and an increasing trend for summer precipitation. Moreover the Mann–Whitney test has been used to evidence the possible change points in the data. The higher percentages of rainfall series show possible year changes during decade 1960–1970 for almost all of the temporal aggregation rainfall. Copyright © 2009 Royal Meteorological Society

Comparison of ERA-40, ERA-Interim and NCEP/NCAR reanalysis data with observed surface air temperatures over Ireland

Abstract: Surface air temperatures modelled by ERA-40, ERA-Interim and (NCEP)/(NCAR) reanalysis (NNRP-1) have been compared with observations at 11 synoptic stations in Ireland over the period 1989–2001. The three reanalysis datasets show good agreement with the observed data and with each other. Slopes of the least-squares line to scatter plots of reanalysis data versus observational data show small differences between the three reanalyses, with ERA-40, ERA-Interim and NNRP-1 slopes ranging between (0.79–1.06) ± 0.01, (0.83–1.01) ± 0.01 and (0.76–0.98) ± 0.01, respectively. Summary statistics and the monthly mean temperatures over the 1989–2001 period showed that the reanalyses were significantly warmer in winter than the observations, which resulted in best fit lines with slopes consistently less than unity. ERA-Interim was slightly better than both ERA-40 and NNRP-1 at modelling winter temperatures and it had higher correlation coefficients with the observations. All three reanalyses use different grid sizes and types. Subsequent regridding of the ERA-Interim and NNRP-1 data to the ERA-40 grid showed that the grid difference had no significant influence on the results. Comparison of ERA-Interim and NNRP-1 data with the air temperatures at four marine buoys around the Irish coast for the period 2001–2005 showed that the reanalyses modelled colder winter temperatures than the observations; resulting in best fit lines with slopes consistently greater than unity. The slopes for NNRP-1 and ERA-Interim at the marine buoys, respectively, averaged 1.09 ± 0.04 and 1.10 ± 0.05 while the slopes at the four land stations over the same period averaged 0.87 ± 0.02 and 0.89 ± 0.02, respectively. We believe that this pattern results from the difference in the treatment of land and sea surfaces in the reanalysis datasets. Copyright © 2010 Royal Meteorological Society

Future climate of the Caribbean from a regional climate model

Abstract: Scenarios of rainfall and temperature changes for the period 2071–2100 under the A2 and B2 Special Report on Emissions scenarios are examined using the Hadley Centre Providing Regional Climates for Impacts Studies regional climate model. The model simulates ‘present-day’ (1979–1990) rainfall and temperature climatologies reasonably well, capturing the characteristic bimodality of Caribbean rainfall and the boreal summer maximum and winter minimum temperatures. Seasonal spatial patterns are also reproduced, but rainfall amounts are underestimated over the northern Caribbean island masses, including Cuba, Jamaica, Hispaniola and Puerto Rico. Temperatures over the region are also overestimated by 1–3 °C. For the period 2071–2100, temperatures are projected to increase across the region by 1–4 °C for all months irrespective of the scenario. The rainfall response varies with season with one of the more robust changes being an intensification of a gradient pattern in November–January, in which the northern Caribbean (i.e. north of 22°N) gets wetter and the southern Caribbean gets drier. There is also a robust June–October drying signal. The results point to changes in the regional circulation patterns due to the human-induced climate change and warrants further investigation. Copyright © 2010 Royal Meteorological Society

A new tool for monthly precipitation analysis in Spain: MOPREDAS database (monthly precipitation trends December 1945–November 2005)

Abstract: A new monthly precipitation database has been developed for conterminous provinces in Spain by exploiting the total amount of data available at Spanish Meteorological Agency (AEMET, formerly INM). The new MOPREDAS (monthly precipitation database of Spain) database has been constructed by using all 6821 original data series that have been recorded for at least 10 years. These provide a total of 2670 complete, homogeneous series for the period 1946–2005, and are the most complete and extensive monthly precipitation dataset available in Spain at present. MOPREDAS has been created with the aim of analysing the behaviour of precipitation in the conterminous provinces of Spain, and to help validate the downscaling of climate models on a detailed spatial level. To this end, the station data were also interpolated on a regular grid, at 1/10 of degree of resolution, over the whole Spain. Trend analysis confirms great spatial and temporal variability in the behaviour of precipitation across Spain. The monthly precipitation trends vary from month to month, from coherent spatial trend patterns in March, June (both with a general and significant negative trend) and October (general positive trends), to highly regionalized trend patterns in July (with positive trends in north-west and mainly negative in the remainder), February and April (positive and negative trends in the south-east, respectively). These results suggest that both global and local factors affect the spatial distribution of trends in the Iberian Peninsula. Mountain ranges seem to be the most significant geographical factor in determining the spatial distribution of monthly trends on a detailed, sub-regional spatial scale. These results show that it is possible to accurately delineate the areas affected by different precipitation trends if a dense spatial database is available. Copyright © 2010 Royal Meteorological Society

Spatial distribution of recent rainfall trends in Spain (1961–2006)

Abstract: Annual, seasonal and monthly rainfall trends from 1961 to 2006 period were analysed in this study by applying various statistical tools to data from 553 Spanish weather stations. The magnitude of the trends was derived from the slopes of the regression lines using the least squares method, while the statistical significance was determined using the non-parametric Mann-Kendall test. Geostatistical interpolation techniques were applied to generate rainfall trend surfaces. Combining classic trends tests and spatially interpolated precipitation permits the spatio-temporal visualization of detected trends. Updated trends reveal that rainfall is generally decreasing in January, February, March, April, and June. Around 61, 44 and 12% of the whole territory is evidencing significant negative trends in February, June and March, respectively. Significant precipitation decreases are also noted in more than 28% of Spain in summer and winter. On the contrary, rainfall is significantly increasing in October in more than 21% of Spain and areas mainly located in north-western areas. May, August, September and autumn also show significant positive trends in the period 1961–2006, although the percentages are lower than for negative trends. Finally, the annual precipitation is significantly decreasing in 11% of the territory. Copyright © 2010 Royal Meteorological Society

Assessing trends in extreme precipitation events intensity and magnitude using non-stationary peaks-over-threshold analysis: a case study in northeast Spain from 1930 to 2006

Abstract: Most applications of the extreme value (EV) theory have assumed stationarity, i.e. the statistical properties of the process do not change over time. However, there is evidence suggesting that the occurrence of extreme events is not stationary but changes naturally, as it has been found for many other climate variables. Of paramount importance for hazard analysis is whether the observed precipitation time series exhibit long-term trends or cycles; such information is also relevant in climate change studies. In this study, the theory of non-stationary extreme value (NSEV) analysis was applied to data series of daily precipitation using the peaks-over-threshold (POT) approach. A Poisson/generalized Pareto (P/GP) model, in which the model parameters were allowed to vary linearly with time, was fitted to the resulting series of precipitation event's intensity and magnitude. A log-likelihood ratio test was applied to determine the existence of trends in the model parameters. The method was applied to a case study in northeast Spain, comprising a set of 64 daily rainfall series from 1930 to 2006. Statistical significance was achieved in less than 5% of the stations using a linear non-stationary model at the annual scale, indicating that there is no evidence of a generalized trend in extreme precipitation in the study area. At the seasonal scale, however, a significant number of stations along the Mediterranean (Catalonia region) showed a significant decrease of extreme rainfall intensity in winter, while experiencing an increase in spring. Copyright © 2010 Royal Meteorological Society

Recent trends of mean and extreme precipitation in Korea

Abstract: The spatial and temporal variability of precipitation in Korea were investigated using 183 weather station data for 1973–2005. A set of 16 indices that represent mean and extreme values of precipitation data were estimated using daily precipitation data, linear and spatial trend relationships of the indices were analysed using the Mann–Kendall test and Moran's I test statistic, respectively. Results demonstrate that annual precipitation data have a significant positive trend and there is a strong spatial relationship in their variability. The increase of annual precipitation is mainly associated with the increase of frequency and intensity of heavy precipitation during summer season. However, precipitation during spring and winter seasons had a decreasing trend. This variation of precipitation is likely to increase flood and drought risk. It means that the increase of annual precipitation should not be helpful for water resources management but could be a burden to river management and dam operation in Korea. Copyright © 2010 Royal Meteorological Society

Trends in temperature, diurnal temperature range and sunshine duration in Northeast India

Abstract: Trends in maximum (Tmax), minimum (Tmin) and mean (Tmean) temperatures; diurnal temperature range (DTR = Tmax − Tmin); and sunshine duration at eight sites in Northeast (NE) India were investigated. Three sites observed decreasing trends in DTR corresponding to annual, seasonal (pre-monsoon and monsoon) and monthly (September) time scales. On the other hand, DTR increases were also observed at other three sites in monsoon and post-monsoon seasons as well as in the months of June, October and December. The sites showing DTR decreases (increases) witnessed either increasing trends in Tmin (Tmax) or decreasing trends in Tmax (Tmin), with Tmax (Tmin) showing either no trend or increasing at a smaller rate than Tmin (Tmax). Temperature remained practically trendless in winter and pre-monsoon seasons over NE India. However, temperature increases were observed in monsoon and post-monsoon seasons. Decreasing trends in sunshine duration were observed mainly on annual, seasonal (winter and pre-monsoon) and monthly (January, February and March) time scales. Concomitant decreases in sunshine duration may be one of the potential causes of the observed DTR decreases over NE India. Copyright © 2010 Royal Meteorological Society

Studies of 21st-Century Precipitation Trends Over West Africa

Abstract: West Africa includes a semi-arid zone between the Sahara Desert and the humid Gulf of Guinea coast, approximately between 10 N and 20 N, which is irrigated by summer monsoon rains. This article refers to the region as the Sahel. Rain-fed agriculture is the primary sustenance for Sahel populations, and severe droughts (in the 1970s and 1980s), therefore, have devastating negative societal impacts. The future frequency of Sahel droughts and the evolution of its hydrological balance are therefore of great interest. The article reviews 10 recent research studies that attempt to discover how climate changes will affect the hydrology of the Sahel throughout the 21st century. All 10 studies rely on atmosphere ocean global climate model (AOGCM) simulations based on a range of greenhouse gas emissions scenarios. Many of the simulations are contained in the Intergovernmental Panel on Climate Change archives for Assessment Reports #3 and #4. Two of the studies use AOGCM data to drive regional climate models. Seven studies make projections for the first half of the 21st century and eight studies make projections for the second half. Some studies make projections of wetter conditions and some predict more frequent droughts, and each describes the atmospheric processes associated with its prediction. Only one study projects more frequent droughts before 2050, and that is only for continent-wide degradation in vegetation cover. The challenge to correctly simulate Sahel rainfall decadal trends is particularly daunting because multiple physical mechanisms compete to drive the trend upwards or downwards. A variety of model deficiencies, regarding the simulation of one or more of these physical processes, taints models climate change projections. Consequently, no consensus emerges regarding the impact of anticipated greenhouse gas forcing on the hydrology of the Sahel in the second half of the 21st century.

Potential changes in outdoor thermal comfort conditions in Gothenburg, Sweden due to climate change: the influence of urban geometry

Abstract: Quantitative information about outdoor thermal comfort, on various temporal and spatial scales, is required to design better cities and mitigate heat problems not only in warm but also in temperate climates. The overall objective of this study is to explore the augmentation of global/regional climate changes by urban features such as geometry in a compact mid-rise high-latitude city (Gothenburg). The magnitude of spatial and temporal variations of intra-urban mean radiant temperatures (T(mrt)) is quantified using the SOLWEIG (SOlar and LongWave Environmental Irradiance Geometry) model. Hourly time resolution, statistically downscaled meteorological data, based on the ECHAM5-GCM under the A1B emission scenario is used to simulate changes in T(mrt) and physiologically equivalent temperature (PET) at the 2080-2099 time horizon. Results show that urban geometry causes large intra-urban differences in T(mrt), on hourly, daytime and yearly time scales. In general, open areas are warmer than adjacent narrow street canyons in summer, but cooler in winter. According to the ECHAM5-based scenario, the daytime T(mrt) will increase by 3.2 degrees C by the end of this century. This is 0.4 degrees more than simulated increase in air temperature (2.8 degrees C) and is mainly a result of decreases in summer cloudiness. Occasions of strong/extreme heat stress are expected to triple. This equates to 20-100 h a year, depending on geometry. Conversely, the number of hours with strong/extreme cold stress decreases by 400-450 h. Furthermore, the number of hours with no thermal stress increases by 40-200 h a year. The study confirms the potential for using geometry to mitigate daytime thermal stress. A densely built structure mitigates extreme swings in T(mrt) and PET, improving outdoor comfort conditions both in summer and in winter. Furthermore, it highlights the importance of including information on either T(mrt) or thermal comfort in climate scenarios to describe the combined effects of changes in multiple climate variables and to more realistically measure the impact on humans. Copyright. (C) 2010 Royal Meteorological Society (Less)

Fine-resolution (25 m) topoclimatic grids of near-surface (5 cm) extreme temperatures and humidities across various habitats in a large (200 × 300 km) and diverse region

Abstract: The development of fine-resolution climate grids is an important priority in explaining species' distributions at the regional scale and predicting how species may respond to variable and changing climates. Recent studies have demonstrated advantages of producing these grids using large networks of inexpensive climate loggers, as the resulting grids can capture local climatic variations over a range of environments. In this study we extend these methods to develop innovative fine-resolution (25 m) climate grids for a large region (∼200 × 300 km) of New South Wales, Australia. The key aspects of these grids is that they: (1) are based on near-surface (5 cm) observations to better reflect where many species live; (2) cover a wide variety of habitats including forests, woodlands and grasslands so that they are broadly applicable; (3) include both temperature and humidity, the latter of which has often been neglected in similar studies; (4) are developed using a variety of climate-forcing factors rather than relying only on elevation and geographic location; and (5) they focus on the extreme temperatures and humidities regardless of when these occur. Analyses showed that elevation was the dominant factor explaining mild temperatures (low maximums, high minimums), but cold air drainage, distance from coast, canopy cover and topographic exposure had more effect on the extreme maximum and minimum temperatures. Humidities were predominately determined by distance to coast, elevation, canopy cover and topography; however, the relationships were nonlinear and varied in both shape and effect size between dry and moist extremes. Extreme climates occur under specific weather conditions, and our results highlight how averaging climates over seasons or periods of consecutive days will include different weather patterns and obscure important trends. Regional-scale climate grids can potentially be further improved through a better understanding of how the effects of different climate-forcing factors vary under different weather conditions. Copyright © 2011 Royal Meteorological Society

Climatology of Mediterranean cyclones using the ERA‐40 dataset

Abstract: The generation of cyclone climatologies has recently received a renewed interest. Cyclones are closely related to the climate of certain regions, and thus, their variability is one of the key points in current climate research. The Mediterranean is a region with high density of cyclones, but due to its location and its particular morphology, cyclones are subject to large spatial and seasonal variability. Moreover, some cyclones are related to hazardous weather events, in particular, heavy precipitation and strong winds. Improved knowledge of Mediterranean cyclones would contribute to the improvement of the forecasts of such damaging events. In this study, objective detection and tracking algorithms are used on the ERA-40 reanalysis to derive a climatology of surface cyclones for the Mediterranean region. The detection algorithm is also applied at various vertical levels, characterizing the three-dimensional structure of the cyclones, and allowing to derive their vertical thickness. The relatively high spatial resolution, but mainly the long period (45 years) makes the ERA-40 reanalysis especially suitable for the generation of a cyclone climatology. The aim of this study is twofold. First, a detailed description of the Mediterranean surface cyclones is obtained. This includes the spatial and seasonal variability and some of their main individual features, like the intensity, size, vertical thickness and life cycle. Moreover, some regions with a large cyclogenetic frequency are studied in detail. Second, the results of the present climatology are compared with many other studies. The qualitative comparison indicates a general agreement with most of previous climatologies. However, as a consequence of the ERA-40 resolution, the comparison with high-resolution cyclone datasets shows a shortcoming related to the detection of small cyclones. Nevertheless, it is concluded that the current climatology depicts a comprehensive view of the synoptic and sub-synoptic cyclonic activities in the Mediterranean. Copyright © 2010 Royal Meteorological Society

An examination of urban heat island characteristics in a global climate model

Abstract: A parameterization for urban surfaces has been incorporated into the Community Land Model as part of the Community Climate System Model. The parameterization allows global simulation of the urban environment, in particular the temperature of cities and thus the urban heat island. Here, the results from climate simulations for the AR4 A2 emissions scenario are presented. Present-day annual mean urban air temperatures are up to 4 °C warmer than surrounding rural areas. Averaged over all urban areas resolved in the model, the heat island is 1.1 °C, which is 46% of the simulated mid-century warming over global land due to greenhouse gases. Heat islands are generally largest at night as evidenced by a larger urban warming in minimum than maximum temperature, resulting in a smaller diurnal temperature range compared to rural areas. Spatial and seasonal variability in the heat island is caused by urban to rural contrasts in energy balance and the different responses of these surfaces to the seasonal cycle of climate. Under simulation constraints of no urban growth and identical urban/rural atmospheric forcing, the urban to rural contrast decreases slightly by the end of the century. This is primarily a different response of rural and urban areas to increased long-wave radiation from a warmer atmosphere. The larger storage capacity of urban areas buffers the increase in long-wave radiation such that urban night-time temperatures warm less than rural. Space heating and air conditioning processes add about 0.01 W m−2 of heat distributed globally, which results in a small increase in the heat island. The significant differences between urban and rural surfaces demonstrated here imply that climate models need to account for urban surfaces to more realistically evaluate the impact of climate change on people in the environment where they live. Copyright © 2010 Royal Meteorological Society

Urban warming in Japanese cities and its relation to climate change monitoring

Abstract: This article briefly reviews urban warming studies in Japan, where many of the stations established by the beginning of the 20th century are located in cities that have undergone rapid industrialization. The recorded rate of temperature increase is a few degrees per century in large cities and tends to be larger at night than during the daytime. In some cities, the increase in annual extreme minimum temperature exceeds 10 °C century−1. On the other hand, recent numerical studies have revealed widespread urban warming around Tokyo and other megacities during afternoons of the warm season as a result of extensive urbanization that enhances daytime surface heating. An analysis using data from the dense Automated Meteorological Data Acquisition System network has shown that an urban bias in recent temperature trends is detectable not only in densely inhabited areas but also at slightly urbanized sites with 100–300 people km−2, indicating the need for careful assessment of the background climate change. There is also some evidence of microscale effects on observed temperature, as revealed by an analysis of the relationship between trends in temperature and wind speed. Copyright © 2010 Royal Meteorological Society

Spatial variations of climate indices in Turkey

Abstract: The present study explores the spatial variability of the continentality, oceanity and aridity indices in Turkey. Climatic indices are diagnostic tools used to describe climatic conditions and the state of a climate system. In this study, four indices were calculated using the climatic data from 229 meteorological stations in Turkey. The nature of the indices expresses general climatic features such as continentality, marine influences and aridity. The climatic indices used here are the Johansson Continentality (JC) Index, the Kerner Oceanity Index (KOI), the De Martonne Aridity Index (IDM) and the Pinna Combinative (PV) Index. Furthermore, aridity characteristics in Turkey have been examined using the two separate periods (1960–1990 and 1991–2006). To assess the temperature and precipitation patterns in Turkey, the climatic indices were calculated by using monthly temperature and precipitation for the period 1960–2006. According to the results of the KOI, marine climates characteristics were dominant in the Black Sea region than in its Aegean and Mediterranean region. The JC index is used for the climatic classification between continental and oceanic climates. The continental effect was found across 25% of the country. The maximum continentality with a score of 71.5 has been found in the eastern Anatolia. Furthermore, semi-dry areas were increasing in the 1991–2006 period compared to 1960–1990. A significant correlation was found between the values of the JC index and the KOI. The JC index gives reasonable results for Turkey. The continental effect was found across 25% of the country. This analysis may be of benefit for the explanation of landscape characteristics and the rational utilization of water resources, agriculture and energy scenarios for the region in many areas of Turkey. Copyright © 2010 Royal Meteorological Society