Heat Wave Episodes Research Articles

Expected impacts of climate change on extreme climate events

An overview of the expected change of climate extremes during this century due to greenhouse gases and aerosol anthropogenic emissions is presented. The most commonly used methodologies rely on the dynamical or statistical downscaling of climate projections, performed with coupled atmosphere–ocean general circulation models. Either of dynamical or of statistical type, downscaling methods present strengths and weaknesses, but neither their validation on present climate conditions, nor their potential ability to project the impact of climate change on extreme event statistics allows one to give a specific advantage to one of the two types. The results synthesized in the last IPCC report and more recent studies underline a convergence for a very likely increase in heat wave episodes over land surfaces, linked to the mean warming and the increase in temperature variability. In addition, the number of days of frost should decrease and the growing season length should increase. The projected increase in heavy precipitation events appears also as very likely over most areas and also seems linked to a change in the shape of the precipitation intensity distribution. The global trends for drought duration are less consistent between models and downscaling methodologies, due to their regional variability. The change of wind-related extremes is also regionally dependent, and associated to a poleward displacement of the midlatitude storm tracks. The specific study of extreme events over France reveals the high sensitivity of some statistics of climate extremes at the decadal time scale as a consequence of regional climate internal variability.

Investigating the Independent and Synergistic Effects of Heat Waves and Air Pollution on Health: The EuroHEAT Project

ISEE-861 Objective: The increased mortality associated with heat-wave episodes has been well documented in many studies. An interesting aspect is the role of air pollution in this relationship. Within the EuroHEAT project, the potential confounding by air pollution variables and interaction between heat waves and air pollution was investigated using data from nine European cities for the period 1990–2004. Material and Methods: For the analysis we used a GEE modeling approach. City specific analysis by cause of death and age group was performed for the summer months (June–August). Estimates were combined in a second stage analysis. Results: Heat wave effects on total natural mortality are not confounded by NO2, SO2, and CO levels. However, if the models are not adjusted for PM and ozone, the heat wave effects are overestimated. In particular, when adjusting for PM10, estimates are reduced by about 30% and when adjusting for ozone they are reduced by about 15%–25% (more reduced for the younger, less for the elderly). The effects of heat waves on total natural mortality are larger during high ozone days, but this is less evident for those older than 85. Thus on low ozone days, the existence of a heat wave is associated with 10% increase in mortality, whilst on high ozone days it is associated with 13% increase. When fixed effects models are used the interaction is statistically significant for all ages and the age groups 0 to 64 and 75 to 84. Similarly, the effects of heat wave days on mortality are larger during high PM10 days (for those over 85 years a 13% increase in mortality associated with low PM10 days is observed, whilst a 19% is observed on high PM10 days), and the interaction term is significant for all ages, 74 to 85 and >85. Conclusions: Concluding, ozone and particles concentrations have an active role in the heat wave mortality relationship which must not been overlooked.

The Definition of Heat-Wave Within the European Project “Improving Public Health Responses to Heat” (EuroHEAT)

ISEE-562 Objective: Many studies have documented an increase in mortality associated to high temperatures and during heat wave episodes. To date, a standardized definition of heat wave has not been formulated. Throughout the literature different temperature variables have been considered to define a heat wave, including daily mean, maximum or minimum values, and more complex measures such as composite and biometeorological indexes. One of the aims of the EuroHEAT project was to study the impact of heat on mortality during heat waves in nine European cities (Athens, Barcelona, Budapest, London, Milan, Munich, Paris, Rome, and Valencia). Maximum apparent temperature (Tappmax), an index of thermal discomfort based on air temperature and dew point temperature, was chosen as exposure variable. Materials and Methods: For the summer period (June-August) heat waves were defined as days in which Tappmax exceeds the threshold (90th percentile of Tappmax for each month) for at least 2 days and continues as long as Tappmax is higher than its median value and minimum temperature (Tmin) exceeds its threshold (90th percentile of Tmin for each month). Minimum temperatures were specifically included to account for high night time temperatures that were observed especially in the Mediterranean cities during the 2003 heat wave, which from a preliminary analysis seemed to better depict the increase in mortality during heat episodes. Furthermore, to fully characterize each heat episode the duration, intensity, and time interval between different heat waves were also included. Results: Despite a large heterogeneity, results show the strongest effect on mortality for heat waves of a long duration and high intensity (up to 3 times) in most cities, while the first heat wave of summer had the greatest impact only in few cities. Conclusions: A heat wave definition is a milestone in the investigation of heat-related mortality.

Wildfire particulate matter in Europe during summer 2003: meso-scale modeling of smoke emissions, transport and radiative effects

Abstract. The present study investigates effects of wildfire emissions on air quality in Europe during an intense fire season that occurred in summer 2003. A meso-scale chemistry transport model CHIMERE is used, together with ground based and satellite aerosol optical measurements, to assess the dispersion of fire emissions and to quantify the associated radiative effects. The model has been improved to take into account a MODIS-derived daily smoke emission inventory as well as the injection altitude of smoke particles. The simulated aerosol optical properties are put into a radiative transfer model to estimate (off-line) the effects of smoke particles on photolysis rates and atmospheric radiative forcing. We have found that the simulated wildfires generated comparable amounts of primary aerosol pollutants (130 kTons of PM2.5, fine particles) to anthropogenic sources during August 2003, and caused significant changes in aerosol optical properties not only close to the fire source regions, but also over a large part of Europe as a result of the long-range transport of the smoke. Including these emissions into the model significantly improved its performance in simulating observed aerosol concentrations and optical properties. Quantitative comparison with MODIS and POLDER data during the major fire event (3–8 August 2003) showed the ability of the model to reproduce high aerosol optical thickness (AOT) over Northern Europe caused by the advection of the smoke plume from the Portugal source region. Although there was a fairly good spatial agreement with satellite data (correlation coefficients ranging from 0.4 to 0.9), the temporal variability of AOT data at specific AERONET locations was not well captured by the model. Statistical analyses of model-simulated AOT data at AERONET ground stations showed a significant decrease in the model biases suggesting that wildfire emissions are responsible for a 30% enhancement in mean AOT values during the heat-wave episode. The implications for air quality over a large part of Europe are significant during this episode. First, directly, the modeled wildfire emissions caused an increase in average PM2.5 ground concentrations from 20 to 200%. The largest enhancement in PM2.5 concentrations stayed, however, confined within a 200 km area around the fire source locations and reached up to 40 μg/m³. Second, indirectly, the presence of elevated smoke layers over Europe significantly altered atmospheric radiative properties: the model results imply a 10 to 30% decrease in photolysis rates and an increase in atmospheric radiative forcing of 10–35 W m−2 during the period of strong fire influence throughout a large part of Europe. These results suggest that sporadic wildfire events may have significant effects on regional photochemistry and atmospheric stability, and need to be considered in current chemistry-transport models.

Models for mortality associated with heatwaves: update of the Portuguese heat health warning system

AbstractIn Portugal a Heat Health Watch Warning exists since 1999—the íCARO Surveillance System. It is a system for monitoring heatwaves with potential impacts on population's morbidity and mortality, which is set in motion every year between May and September. This system was based on a model for the relation between heat and mortality calibrated with the district of Lisbon data for the big heatwaves of June 1981 and July 1991.The occurrence of 2003's big heatwave brought opportunity for updating existing models.The fact that this heatwave has been particularly long and had characteristics that were not described in the previously known heatwave episodes also allowed the chance to investigate the mechanism of the relation between occurrence of extreme heat and mortality.The aim of this work was to update the existing íCARO model and contribute to increase the knowledge on the phenomena of the heatwave's impact on mortality.Thus, four models were assayed, that represent four distinct proposals for reference temperature's thresholds and in the generalization of the main used variable accumulated thermal overcharge (ATO).All the assayed models showed a good adaptation to the observed mortality data for the district of Lisbon for the three known big heatwaves.It is concluded that the rational generalized accumulated thermal overload (GATO) adapts well to the relation between heat and mortality. The best model was chosen as the one that considered a dynamic threshold that follows the ascending phase of the temperatures of summer until reaching its maximum level in the end of the month of August remaining thereafter constant until the end of the summer, thus recurring to a rational of population's adaptation to heat, contrarily to what happens to air temperatures that decrease at end of the summer. Copyright © 2007 Royal Meteorological Society

Contribution of land‐atmosphere coupling to recent European summer heat waves

Most of the recent European summer heat waves have been preceded by a pronounced spring precipitation deficit. The lack of precipitation and the associated depletion of soil moisture result in reduced latent cooling and thereby amplify the summer temperature extremes. In order to quantify the contribution of land‐atmosphere interactions, we conduct regional climate simulations with and without land‐atmosphere coupling for four selected major summer heat waves in 1976, 1994, 2003, and 2005. The coupled simulation uses a fully coupled land‐surface model, while in the uncoupled simulation the mean seasonal cycle of soil moisture is prescribed. The experiments reveal that land‐atmosphere coupling plays an important role for the evolution of the investigated heat waves both through local and remote effects. During all simulated events soil moisture‐temperature interactions increase the heat wave duration and account for typically 50–80% of the number of hot summer days. The largest impact is found for daily maximum temperatures during heat wave episodes.

Aerosol extinction in a remote continental region of the Iberian Peninsula during summer

Summer in Évora (38°34′N, 7°54′W), Portugal, is described in terms of aerosol properties of extinction of the solar radiation. We create a data set composed of (1) cloud‐screened half‐day averaged values of aerosol optical thickness (AOT) measured at 7 wavelengths by both a CIMEL Sun/sky‐photometer and a YES shadowband radiometer and (2) half day averaged values of aerosol scattering coefficient (ASC) measured at the surface level at two wavelengths by a TSI nephelometer. Spectral dependence of both AOT and ASC gives the column and the surface Ångström exponents, αC and αS, respectively. Measurements are acquired in both 2002 and 2003 summers. Back trajectories are computed. A statistical study of the data set provides thresholds in AOT and αC for a classification of the days. The classification is applied with success to the case study of the 2003 summer heat wave episode and is generalized to the whole data set. In 23% of the cases, the turbidity in Évora is very low, with AOT441 < 0.12 and AOT873 < 0.04. The air mass origin is the North Atlantic Ocean at 700 and 970 hPa. In 31% of the cases, the turbidity is high. Increase of AOT is due to forest fire emissions, originating in the Iberian Peninsula, with 0.30 < AOT441 < 1.10 and αC > 1.2, and to desert dust plumes transported from North Africa within 72 to 120 hours at 700 hPa, with 0.10 < AOT873 < 1.10 and 0.1 < αC < 1.0. The vertical profile is highly variable, and several cases of aerosol mixing in the column are identified. The duration of the aerosol episode during the 2003 summer heat wave is 16 days, which is exceptionally long.

Atmospheric aerosols during the 2003 heat wave in southeastern Spain II: Microphysical columnar properties and radiative forcing

The columnar properties of atmospheric aerosol (size distributions, single scattering albedo and asymmetry parameter) are investigated based on sun/sky photometer measurements obtained during August 2003 at Granada (37.18°N, 3.58°W, 680 m a.s.l.), southeastern Spain. Also, we compute and analyze the average aerosol radiative forcing under two different atmospheric situations that occurred during the heat wave event that affected Western Europe during first half of August 2003: intrusions of desert dust and episodes of European–Mediterranean (EUR–MED) air masses influence, both combined with the impact of the intense biomass burning due to the multiple forest fires that affected southern Europe during this period. Interpretation of the results obtained in these analyses has been done using key synoptic aspects evidenced in a previous paper. The results showed that during the heat wave episode and under the different air masses influence the fine particle concentration was more important than that obtained after this event. In the situation of EUR–MED influence the single scattering albedo decreased sharply with wavelength from 0.91±0.02 at 440 nm to 0.83±0.04 at 1020 nm. These values are similar to those obtained by other authors for urban-industrial particles and biomass burning aerosols. The single scattering albedo reported during the dust events (0.87±0.02 at 670 nm) was lower than that obtained using AERONET data characterizing pure desert dust, and did not show the spectral variation indicated in the literature, indicating the possible combination of dust, urban-industrial particles and biomass burning aerosols. Estimates of the local direct aerosol radiative forcing in the 400–700 nm wavelength range were obtained both at ground level and at the top of atmosphere (TOA). The daily radiative forcing efficiencies at the surface ranged between −78.2 and −73.4 W m −2 whereas they were between −19.4 and −14.5 W m −2 at TOA. Aerosol radiative forcing efficiencies at the surface and TOA were slightly larger for EUR–MED case than for desert dust episode. Nevertheless, the daily atmospheric radiative forcing efficiencies obtained in the both cases were similar, about 59 W m −2, indicating that during desert dust episode dust was mixed with considerable amounts of absorbing aerosols.

How exceptional was the early August 2003 heatwave in France?

The summer of 2003 was characterised by exceptionally warm weather in Europe with the average temperature exceeding that of any previous summer over the last 500 years. The seasonal 2003 summer temperature for central Europe was beyond the historical distribution range and could bear a closer resemblance with climate change scenarios for late XXI century. Nevertheless, it was the heatwave that occurred between the 1st and the 15th of August 2003 that had a major impact in excessive mortality rates throughout Europe, with catastrophic amplitude in France. Here we show, on a daily basis, when and where the magnitude and spatial extent of this heatwave episode has surpassed previous historical maxima, and that this episode is associated with an equally maximum blocking pattern over western Europe. Finally we show that surface and low troposphere air temperature anomalies are particularly well associated with the increased mortality rates in France.

Systematic Errors of the ECMWF Operational Model over Tropical Africa

Abstract Five-day forecasts using the high-resolution T213L31 Operational Global Spectral Model of the European Centre for Medium-Range Weather Forecasts and associated analyses for summer 1995 are compared in this study to assess the model drift. It is shown here that there is extensive model warming of the lower troposphere especially over the Sahel (+7.5°C) and cooling of the middle troposphere in the tropical Southern Hemisphere. The surface heat wave episode diagnosed by the Climate Prediction Center in summer 1995 was severely overestimated (11°C). A likely cause of this major error is the inaccuracy of convection and boundary layer parameterizations in the case of extreme events. It is found that the model overestimates upper-level subtropical westerlies (+3 m s−1), low-level monsoon winds, and the Hadley circulation. The African easterly jet is weaker in the model than observed probably because initial easterly zonal wind errors evolve rapidly leading to underestimation of the jet at medium range....