Soil Moisture–Atmosphere Interactions during the 2003 European Summer Heat Wave
TL;DR: The role of land surface-related processes and feedbacks during the record-breaking 2003 European summer heat wave is explored with a regional climate model in this article, where sensitivity experiments are performed by perturbing spring soil moisture in order to determine its influence on the formation of the heat wave.
Abstract: The role of land surface–related processes and feedbacks during the record-breaking 2003 European summer heat wave is explored with a regional climate model. All simulations are driven by lateral boundary conditions and sea surface temperatures from the ECMWF operational analysis and 40-yr ECMWF ReAnalysis (ERA-40), thereby prescribing the large-scale circulation. In particular, the contribution of soil moisture anomalies and their interactions with the atmosphere through latent and sensible heat fluxes is investigated. Sensitivity experiments are performed by perturbing spring soil moisture in order to determine its influence on the formation of the heat wave. A multiyear regional climate simulation for 1970–2000 using a fixed model setup is used as the reference period. A large precipitation deficit together with early vegetation green-up and strong positive radiative anomalies in the months preceding the extreme summer event contributed to an early and rapid loss of soil moisture, which exceeded the multiyear average by far. The exceptionally high temperature anomalies, most pronounced in June and August 2003, were initiated by persistent anticyclonic circulation anomalies that enabled a dominance of the local heat balance. In this experiment the hottest phase in early August is realistically simulated despite the absence of an anomaly in total surface net radiation. This indicates an important role of the partitioning of net radiation in latent and sensible heat fluxes, which is to a large extent controlled by soil moisture. The lack of soil moisture strongly reduced latent cooling and thereby amplified the surface temperature anomalies. The evaluation of the experiments with perturbed spring soil moisture shows that this quantity is an important parameter for the evolution of European heat waves. Simulations indicate that without soil moisture anomalies the summer heat anomalies could have been reduced by around 40% in some regions. Moreover, drought conditions are revealed to influence the tropospheric circulation by producing a surface heat low and enhanced ridging in the midtroposphere. This suggests a positive feedback mechanism between soil moisture, continental-scale circulation, and temperature.
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TL;DR: In this paper, the authors provide a synthesis of past research on the role of soil moisture for the climate system, based both on modelling and observational studies, focusing on soil moisture-temperature and soil moistureprecipitation feedbacks, and their possible modifications with climate change.
3,402 citations
Cites background from "Soil Moisture–Atmosphere Interactio..."
...Nonetheless, both in global (Haarsma et al., 2009) and regional climate simulations (Pal and Eltahir, 2003; Fischer et al., 2007a), possible effects of soil moisture on pressure systems during droughts were also recently documented....
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...…impact near-surface climate, and have been shown in particular to be relevant for the occurrence of extreme hot temperatures and heat waves (e.g. Durre et al., 2000; Seneviratne et al., 2006a; Fischer et al., 2007a,b; Diffenbaugh et al., 2007; Zhang et al., 2009; Jaeger and Seneviratne, in press)....
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...There are some indications that such an effect played a possibly important role for the European 2003 heat wave (Fischer et al., 2007a; Teuling and Seneviratne, 2008)....
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TL;DR: In this paper, the authors discuss the environmental drivers of phenology, and the impacts of climate change on phenology in different biomes, and assess the potential impact on these feedbacks of shifts in phenology driven by climate change.
1,522 citations
TL;DR: In this paper, a set of high-resolution regional climate simulations reveals consistent geographical patterns in these changes, with the most severe health impacts in southern European river basins and along the Mediterranean coasts.
Abstract: Climate-change projections suggest that European summer heatwaves will become more frequent and severe during this century. An analysis of a set of high-resolution regional climate simulations reveals consistent geographical patterns in these changes, with the most severe health impacts in southern European river basins and along the Mediterranean coasts. Climate-change projections suggest that European summer heatwaves will become more frequent and severe during this century1,2,3,4, consistent with the observed trend of the past decades5,6. The most severe impacts arise from multi-day heatwaves, associated with warm night-time temperatures and high relative humidity. Here we analyse a set of high-resolution regional climate simulations and show that there is a geographically consistent pattern among climate models: we project the most pronounced changes to occur in southernmost Europe for heatwave frequency and duration, further north for heatwave amplitude and in low-altitude southern European regions for health-related indicators. For the Iberian peninsula and the Mediterranean region, the frequency of heatwave days is projected to increase from an average of about two days per summer for the period 1961–1990 to around 13 days for 2021–2050 and 40 days for 2071–2100. In terms of health impacts, our projections are most severe for low-altitude river basins in southern Europe and for the Mediterranean coasts, affecting many densely populated urban centres. We find that in these locations, the frequency of dangerous heat conditions also increases significantly faster and more strongly, and that the associated geographical pattern is robust across different models and health indicators.
837 citations
TL;DR: A longer growing season as a result of climate change will in turn affect climate through biogeochemical and biophysical effects, and the magnitude and sign of this effect are unknown but depend on water availability and regional characteristics.
Abstract: Climate warming has advanced the biological spring and delayed the arrival of biological winter ( 1 , 2 ). These changes in the annual cycle of plants and the lengthening of the green-cover season have many consequences for ecological processes, agriculture, forestry, human health, and the global economy ( 3 ). Studies on vegetation-atmosphere interactions ( 4 ) and particularly on the impact of leaf emergence on climate ( 5 – 9 ) suggest that the phenological shifts in turn affect climate. The magnitude and sign of this effect are unknown but depend on water availability and regional characteristics.
693 citations
References
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TL;DR: Observations and the model show that present-day heat waves over Europe and North America coincide with a specific atmospheric circulation pattern that is intensified by ongoing increases in greenhouse gases, indicating that it will produce more severe heat waves in those regions in the future.
Abstract: A global coupled climate model shows that there is a distinct geographic pattern to future changes in heat waves. Model results for areas of Europe and North America, associated with the severe heat waves in Chicago in 1995 and Paris in 2003, show that future heat waves in these areas will become more intense, more frequent, and longer lasting in the second half of the 21st century. Observations and the model show that present-day heat waves over Europe and North America coincide with a specific atmospheric circulation pattern that is intensified by ongoing increases in greenhouse gases, indicating that it will produce more severe heat waves in those regions in the future.
3,391 citations
"Soil Moisture–Atmosphere Interactio..." refers background in this paper
...These patterns are often characterized by quasi-stationary 500-hPa height anomalies that dynamically produce subsidence, clear skies, light winds, warm-air advection, and prolonged hot conditions at the surface (Kunkel et al. 1996; Palecki et al. 2001; Xoplaki et al. 2003; Meehl and Tebaldi 2004)....
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...Several model studies suggest that events such as the 2003 summer heat wave will become more frequent, more intense, and longer lasting in the future (S04; Beniston 2004; Meehl and Tebaldi 2004; Vidale et al. 2007)....
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TL;DR: In this paper, a two-dimensional, time-dependent cloud model was used to simulate a moderate intensity thunderstorm for the High Plains region, where six forms of water substance (water vapor, cloud water, cloud ice, rain, snow and hail) were simulated.
Abstract: A two-dimensional, time-dependent cloud model has been used to simulate a moderate intensity thunderstorm for the High Plains region. Six forms of water substance (water vapor, cloud water, cloud ice, rain, snow and hail, i.e., graupel) are simulated. The model utilizes the “bulk water” microphysical parameterization technique to represent the precipitation fields which are all assumed to follow exponential size distribution functions. Autoconversion concepts are used to parameterize the collision-coalescence and collision-aggregation processes. Accretion processes involving the various forms of liquid and solid hydrometeors are simulated in this model. The transformation of cloud ice to snow through autoconversion (aggregation) and Bergeron process and subsequent accretional growth or aggregation to form hail are simulated. Hail is also produced by various contact mechanisms and via probabilistic freezing of raindrops. Evaporation (sublimation) is considered for all precipitation particles outsi...
3,300 citations
"Soil Moisture–Atmosphere Interactio..." refers methods in this paper
...Its physical package includes a mass flux scheme for convection (Tiedtke 1989), Kessler-type microphysics (Kessler 1969; Lin et al. 1983), a land surface scheme (Dickinson 1984), and a soil thermal model (Jacobsen and Heise 1982)....
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TL;DR: In this paper, a simple spectral cloud ensemble was proposed to provide realistic values of the thermal forcing by convection under various synoptic conditions, such as tropical penetrative convection, tradewind cumuli, and extratropical organized convection.
Abstract: Observational studies indicate that a mass flux approach may provide a realistic framework for cumulus parameterization in large-scale models, but this approach, through the introduction of a spectral cloud ensemble, leads normally to rather complex schemes. In this paper the question is addressed whether much simpler schemes can already provide realistic values of the thermal forcing by convection under various synoptic conditions. This is done through verifying such a scheme first on data from field experiments for periods of tropical penetrative convection (GATE, Marshall Islands), tradewind cumuli (ATEX, BOMEX) and extratropical organized convection (SESAME-79) and then in a NWP model. The scheme considers a population of clouds where the cloud ensemble is described by a one-dimensional bulk model as earlier applied by Yanai et al. in a diagnostic study of tropical convection. Cumulus scale downdrafts are included. Various types of convection are represented, i.e., penetrative convection in c...
3,296 citations
"Soil Moisture–Atmosphere Interactio..." refers methods in this paper
...Its physical package includes a mass flux scheme for convection (Tiedtke 1989), Kessler-type microphysics (Kessler 1969; Lin et al....
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...Its physical package includes a mass flux scheme for convection (Tiedtke 1989), Kessler-type microphysics (Kessler 1969; Lin et al. 1983), a land surface scheme (Dickinson 1984), and a soil thermal model (Jacobsen and Heise 1982)....
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TL;DR: It is found that an event like that of summer 2003 is statistically extremely unlikely, even when the observed warming is taken into account, and it is proposed that a regime with an increased variability of temperatures (in addition to increases in mean temperature) may be able to account for summer 2003.
Abstract: Instrumental observations1,2 and reconstructions3,4 of global and hemispheric temperature evolution reveal a pronounced warming during the past ∼150 years. One expression of this warming is the observed increase in the occurrence of heatwaves5,6. Conceptually this increase is understood as a shift of the statistical distribution towards warmer temperatures, while changes in the width of the distribution are often considered small7. Here we show that this framework fails to explain the record-breaking central European summer temperatures in 2003, although it is consistent with observations from previous years. We find that an event like that of summer 2003 is statistically extremely unlikely, even when the observed warming is taken into account. We propose that a regime with an increased variability of temperatures (in addition to increases in mean temperature) may be able to account for summer 2003. To test this proposal, we simulate possible future European climate with a regional climate model in a scenario with increased atmospheric greenhouse-gas concentrations, and find that temperature variability increases by up to 100%, with maximum changes in central and eastern Europe.
2,660 citations
"Soil Moisture–Atmosphere Interactio..." refers background in this paper
...With mean summer [June– August (JJA)] temperatures exceeding the 1961–90 mean by about 3°C over large areas and by over 5°C regionally (Schär et al. 2004, hereafter S04), it was very likely the hottest European summer over the past 500 yr (Luterbacher et al. 2004)....
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TL;DR: In this article, the authors consider simplification based on the observation that the parameters governing the degree of anisotropy are small, and propose a simplification approach for the problem of a planetary boundary layer subject to a diurnally varying surface heat flux or surface temperature.
Abstract: Turbulence models centered on hypotheses by Rotta and Kolmogoroff are complex. In the present paper we consider systematic simplifications based on the observation that parameters governing the degree of anisotropy are small. Hopefully, we shall discern a level of complexity which is intuitively attractive and which optimizes computational speed and convenience without unduly sacrificing accuracy. Discussion is focused on density stratified flow due to temperature. However, other dependent variables—such as water vapor and droplet density—can be treated in analogous fashion. It is, in fact, the anticipation of additional physical complexity in modeling turbulent flow fields that partially motivates the interest in an organized process of analytical simplification. For the problem of a planetary boundary layer subject to a diurnally varying surface heat flux or surface temperature, three models of varying complexity have been integrated for 10 days. All of the models incorporate identical empirica...
2,410 citations
"Soil Moisture–Atmosphere Interactio..." refers methods in this paper
...Vertical diffusion and turbulent fluxes in the atmosphere are parameterized by a flux gradient approach of the Beljaars and Viterbo (1998) type in the surface layer and Mellor and Yamada (1974) type in the boundary layer....
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...Vertical diffusion and turbulent fluxes in the atmosphere are parameterized by a flux gradient approach of the Beljaars and Viterbo (1998) type in the surface layer and Mellor and Yamada (1974) type in the boundary layer....
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