Changes in weather extremes: Assessment of return values using high resolution climate simulations at convection-resolving scale (original) (raw)
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Scale dependency of regional climate modeling of current and future climate extremes in Germany
Theoretical and Applied Climatology
A warmer climate is projected for mid-Europe, with less precipitation in summer, but with intensified extremes of precipitation and near-surface temperature. However, the extent and magnitude of such changes are associated with creditable uncertainty because of the limitations of model resolution and parameterizations. Here, we present the results of convection-permitting regional climate model simulations for Germany integrated with the COSMO-CLM using a horizontal grid spacing of 1.3 km, and additional 4.5-and 7-km simulations with convection parameterized. Of particular interest is how the temperature and precipitation fields and their extremes depend on the horizontal resolution for current and future climate conditions. The spatial variability of precipitation increases with resolution because of more realistic orography and physical parameterizations, but values are overestimated in summer and over mountain ridges in all simulations compared to observations. The spatial variability of temperature is improved at a resolution of 1.3 km, but the results are cold-biased, especially in summer. The increase in resolution from 7/4.5 km to 1.3 km is accompanied by less future warming in summer by 1 • C. Modeled future Merja H.
Meteorologische Zeitschrift, 2008
Precipitation data from long-term high-resolution simulations with two regional climate models (CLM and REMO) are evaluated using a climatology based on observations for southwestern Germany. Both models are driven by a present day climate forcing scenario from the global climate model ECHAM5. The climatological evaluation shows a strong seasonal dependence of the model deficiencies. In spring and summer there are relatively small differences between simulation results and observations. But during winter both the regional models and ECHAM5 strongly overestimate the precipitation. The frequency distributions of the model results agree well with observed data. An overestimation of the precipitation at the upwind sides of mountainous areas occurs in the regional simulations. We found that the coupling of the regional models to the driving model is stronger in winter than in summer. Therefore, in winter the large scale model have a larger impact on the performance of the regional simulations. During summer the benefit of regional climate simulations is higher. Zusammenfassung Die vorliegende Arbeit beschreibt die Ergebnisse der Evaluierung des Niederschlags von zwei hoch aufgelösten Simulationen mit den regionalen Klimamodellen CLM und REMO für die Region Südwest-Deutschland. Dazu wurde eine auf Beobachtungen basierende Klimatologie benutzt. Die Randwerte beider regionalen Modelle stammen von dem globalen Klimamodell ECHAM5, welches Antriebsdaten für das zwanzigste Jahrhundert verwendet. Die klimatologische Evaluierung zeigt eine starke jahreszeitliche Abhängigkeit derÜbereinstimmung. Beide regionalen Modelle zeigen geringe Abweichungen zu den Beobachtungen im Frühjahr und Sommer. Im Winter allerdingsüberschätzen sowohl CLM und REMO als auch ECHAM5 die Niederschläge deutlich. Die Häufigkeitsverteilung des Niederschlags stimmt bei den Modellergebnissen gut mit den Beobachtungenüberein. In den regionalen Simulationen tritt einë Uberschätzung der Niederschläge an den windwärts gelegenen Seiten von gebirgigen Regionen auf. Die vorliegende Studie zeigt, dass die Kopplung zwischen regionalem und globalem Modell im Winter stärker ist als im Sommer. Daher hat das Verhalten des globalen Modells im Winter einen größeren Einfluss. Im Sommer ist der Gewinn durch die regionalen Klimasimulationen höher.
Impact on the climate extremes
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14 The influence of the soil moisture initial conditions on climate extreme indices over West Africa 15 is investigated using the fourth generation of Regional Climate Model version 4 (non16 hydrostatic) coupled to the version 4.5 of the Community Land Model (RegCM4-CLM4.5) at 17 25 km spatial resolution. We initialized the control experiments with the reanalysis soil 18 moisture of the European Centre Meteorological Weather Forecast’s reanalysis of the 20th 19 century data (ERA20C), while for the dry and wet experiments, we initialized the soil moisture 20 at the maximum and minimum value over West Africa domain, respectively. For each 21 experiment, an ensemble of five runs are performed for five years (20012005), with soil 22 moisture initial conditions prescribed on June 1 and simulations performed over four months 23 (122 days) from June to September. The performance of RegCM4-CLM4.5 in simulating the 24 ten extreme rainfall and temperature indices used in this study is present...
Evaluation of modeled changes in extreme precipitation in Europe and the Rhine basin
Environmental Research Letters, 2013
In this study, we investigate the change in multi-day precipitation extremes in late winter in Europe using observations and climate models. The objectives of the analysis are to determine whether climate models can accurately reproduce observed trends and, if not, to find the causes of the difference in trends.
Tellus A, 2008
A B S T R A C T Time-slices of eight global climate model (GCM) response simulations of the IPCC IS92a, CMIP2, SRES A2, B2 and A1B greenhouse gas scenarios have been downscaled using the HIRHAM atmospheric regional climate model (RCM). (UiO). The resulting ensemble covers a range of future climate realizations from different global models, different greenhouse gas scenarios and natural climate variability. In order to present trends in statistical parameters including extreme events and their return periods, the downscaled response data are combined as an ensemble of equally valid possible realizations. The combined statistics is obtained after adjustments accounting for (i) different set-ups of the respective GCMs in producing the control climate and (ii) the variable range of time between the control and scenario periods. We find that annual extreme events of daily precipitation and wind speed in the control climate become more frequent in the scenario period over large areas in Northern Europe. The variability in the regional result appears sensitive to the phase of the Scandinavian pattern.
On the role of domain size and resolution in the simulations with the HIRHAM region climate model
Climate Dynamics, 2013
We investigate the simulated temperature and precipitation of the HIRHAM regional climate model using systematic variations in domain size, resolution and detailed location in a total of eight simulations. HIRHAM was forced by ERA-Interim boundary data and the simulations focused on higher resolutions in the range of 5.5-12 km. HIRHAM outputs of seasonal precipitation and temperature were assessed by calculating distributed model errors against a higher resolution data set covering Denmark and a 0.25°resolution data set covering Europe. Furthermore the simulations were statistically tested against the Danish data set using bootstrap statistics. The results from the distributed validation of precipitation showed lower errors for the winter (DJF) season compared to the spring (MAM), fall (SON) and, in particular, summer (JJA) seasons for both validation data sets. For temperature, the pattern was in the opposite direction, with the lowest errors occurring for the JJA season. These seasonal patterns between precipitation and temperature are seen in the bootstrap analysis. It also showed that using a 4,000 9 2,800 km simulation with an 11 km resolution produced the highest significance levels. Also, the temperature errors were more highly significant than precipitation. In similarly sized domains, 12 of 16 combinations of variables, observation validation data and seasons showed better results for the highest resolution domain, but generally the most significant improvements were seen when varying the domain size.
Here we present the first multi-model ensemble of regional climate simulations at kilometer-scale horizontal grid spacing over a decade long period. A total of 23 simulations run with a horizontal grid spacing of ∼ 3 km, driven by ERA-Interim reanalysis, and performed by 22 European research groups are analysed. Six different regional climate models (RCMs) are represented in the ensemble. The simulations are compared against available high-resolution precipitation observations and coarse resolution (∼ 12 km) RCMs with parameterized convection. The model simulations and observations are compared with respect to mean precipitation, precipitation intensity and frequency, and heavy precipitation on daily and hourly timescales in different seasons. The results show that kilometer-scale models produce a more realistic representation of precipitation than the coarse resolution RCMs. The most significant improvements are found for heavy precipitation and precipitation frequency on both daily and hourly time scales in the summer season. In general, kilometer-scale models tend to produce more intense precipitation and reduced wet-hour frequency compared to coarse resolution models. On average, the multi-model mean shows a reduction of bias from ∼ −40% at 12 km to ∼ −3% at 3 km for heavy hourly precipitation in summer. Furthermore, the uncertainty ranges i.e. the variability between the models for wet hour frequency is reduced by half with the use of kilometer-scale models. Although differences between the model simulations at the kilometer-scale and observations still exist, it is evident that these simulations are superior to the coarse-resolution RCM simulations in the representing precipitation in the present-day climate, and thus offer a promising way forward for investigations of climate and climate change at local to regional scales.
Climate Research, 2006
A simple method is tested for scaling climate-extreme results from high resolution regional climate models (RCMs) to time-periods and emission scenarios for which the RCMs have not been run. The 30 yr mean relationships between indicators of extremes (IoEs) and annual mean daily maximum temperature (T xa) are investigated. Such relationships from the UK Met Office Hadley Centre RCM HadRM3P, along with temperatures from the global climate model HadCM3, are used to scale IoEs to other time periods and scenarios. This is tested for selected indicators of heatwave and drought over Europe for the period 1961-2099. Curvature is demonstrated in the relationships between these quantities and T xa. Such non-linearities are shown to have a large potential effect on how these climate extremes are likely to evolve during the century, as well as their sensitivity to emissions. A broad picture of possible changes in European heatwave and drought severity is presented. For drought over the Mediterranean and western Europe, a very clear positive curvature in the relationship between drought length and annually averaged temperature is found. (This feature is also common in a brief study of 6 other RCMs.) It suggests a rapid increase in drought length towards the end of the century, and a strong sensitivity to the emission scenario. Extended summer dry spells are projected to become a much more regular feature of western European climates. For European heatwaves, we find a slightly earlier onset of increases in heatwave severity and a reduced sensitivity to emission scenarios than might be expected from a more straightforward interpretation of the Hadley Centre model results. This is linked with extreme dryness occurring at high summer in all years by the end of the century, but was not evident in the 6 other RCMs studied. Based on these results, suggestions are made for choices of future RCM experiments.