Gerd Schädler

Evaluation of forest snow processes models (SnowMIP2)

Thirty-three snowpack models of varying complexity and purpose were evaluated across a wide range of hydrometeorological and forest canopy conditions at five Northern Hemisphere locations, for up t ...

Evaluation of the precipitation for South-western Germany from high resolution simulations with regional climate models

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 south-western 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.

Comparison of Soil Hydraulic Parameterizations for Mesoscale Meteorological Models

Abstract Soil water contents, calculated with seven soil hydraulic parameterizations, that is, soil hydraulic functions together with the corresponding parameter sets, are compared with observational data. The parameterizations include the Campbell/Clapp–Hornberger parameterization that is often used by meteorologists and the van Genuchten/Rawls–Brakensiek parameterization that is widespread among hydrologists. The observations include soil water contents at several soil depths and atmospheric surface data; they were obtained within the Regio Klima Projekt (REKLIP) at three sites in the Rhine Valley in southern Germany and cover up to 3 yr with 10-min temporal resolution. Simulations of 48-h episodes, as well as series of daily simulations initialized anew every 24 h and covering several years, were performed with the “VEG3D” soil–vegetation model in stand-alone mode; furthermore, 48-h episodes were simulated with the model coupled to a one-dimensional atmospheric model. For the cases and soil types consi...

High-resolution sensitivity studies with the regional climate model COSMO-CLM

This paper presents sensitivity studies with the regional climate model COSMO-CLM for southwest Germany and the period from 1991 to 2000. The influence of horizontal resolution (7 km and 14 km) and driving data (ERA-40 and NCEP reanalysis data) on simulation results are assessed and a suitable simulation setup for high-resolution simulations is derived by using varying domain sizes, soil moisture initialization, physical parameterizations and numerical schemes. The use of ERA-40 reanalyses as driving data yields better overall results for temperature and precipitation than the use of NCEP reanalysis data. Increase in the horizontal resolution leads to better simulation results compared to observations. The choice of driving data has a larger impact on simulation results than changing resolutions, physical parameterizations, numerical schemes or initial soil water contents for simulations of this area.

Determination of precipitation return values in complex terrain and their evaluation.

To determine return values at various return periods for extreme daily precipitation events over complex orography, an appropriate threshold value and distribution function are required. The return values are calculated using the peak-over-threshold approach in which only a reduced sample of precipitation events exceeding a predefined threshold is analyzed. To fit the distribution function to the sample, the L-moment method is used. It is found that the deviation between the fitted return values and the plotting positions of the ranked precipitation events is smaller for the kappa distribution than for the generalized Pareto distribution. As a second focus, the ability of regional climate models to realistically simulate extreme daily precipitation events is assessed. For this purpose the return values are derived using precipitation events exceeding the 90th percentile of the precipitation time series and a fit of a kappa distribution. The results of climate simulations with two different regional climate models are analyzed for the 30-yr period 1971–2000: the so-called consortium runs performed with the climate version of the Lokal Modell (referred to as the CLM-CR) at 18-km resolution and the Regional Model (REMO)–Umweltbundesamt (UBA) simulations at 10-km resolution. It was found that generally the return values are overestimated by both models. Averaged across the region the overestimation is higher for REMO–UBA compared to CLM-CR.

Sensitivity of Heavy Precipitation Forecasts to Small Modifications of Large-Scale Weather Patterns for the Elbe River

Abstract Extreme flood events are caused by long-lasting and/or intensive precipitation. The detailed knowledge of the distribution, intensity, and spatiotemporal variability of precipitation is, therefore, a prerequisite for hydrological flood modeling and flood risk management. For hydrological modeling, temporal and spatial high-resolution precipitation data can be provided by meteorological models. This study deals with the question of how small changes in the synoptic situation affect the characteristics of extreme forecasts. For that purpose, two historic extreme precipitation events were hindcasted using the Consortium for Small Scale Modeling (COSMO) model of the German Weather Service (DWD) with different grid resolutions (28, 7, and 2.8 km), where the domains with finer resolutions were nested into the ones with coarser resolution. The results show that the model is capable of simulating such extreme precipitation events in a satisfactory way. To assess the impact of small changes in the synopti...

Analysis of the connection between precipitation and synoptic scale processes in the Eastern Mediterranean using self-organizing maps

This study examines the connection between precipitation in Israel and synoptic-scale weather patterns in the Eastern Mediterranean. Using the method of self-organizing maps (SOM), a classification of synoptic systems is established which separates weather situations with from those without precipitation and identifies synoptic systems causing extreme rainfall. It is shown that by using appropriate parameter settings the method is able to retrieve the typical synoptic patterns of the Eastern Mediterranean and to provide the claimed separation of the clusters concerning the precipitation.

Soil moisture impacts on convective indices and precipitation over complex terrain

The impact of soil moisture on convective precipitation, convective indices, surface energy balance components, and near-surface meteorological variables is analysed for seven intensive observation periods of the Convective and Orographically induced Precipitation Study (COPS) conducted in summer 2007 using a non-hydrostatic limited-area atmospheric prediction model. The control runs are compared to sensitivity experiments under dry (-25 %) and wet (+25 %) initial soil moisture conditions. In the wet experiment, surface fluxes produce moister and cooler boundary layers with increased equivalent potential temperatures. Furthermore, the lifting condensation level and the level of free convection are lowered for all analysed regions, even under different synoptic controls. The comparison of boundary-layer and mid-tropospheric forcing regimes reveal that the impact of soil moisture on the atmosphere is not systematically higher for boundary-layer forcing. Whereas the Bowen ratio exhibits a clear dependence on soil moisture conditions, the impact on precipitation is complex and strongly depends on convective inhibition. A considerable, but non-systematic dependence of convective precipitation on soil moisture exists in the analysed complex orography. The results demonstrate the high sensitivity of numerical weather prediction to initial soil moisture fields.

A Comparison of Continuous Soil Moisture Simulations Using Different Soil Hydraulic Parameterizations for a Site in Germany

Abstract Continuous time series of soil water content over a period of more than 9 months for a midlatitude sandy loam soil covered by grass are calculated with the Campbell and the van Genuchten soil hydraulic functions and the Clapp–Hornberger, Cosby et al., and Rawls–Brakensiek parameter sets. The results are compared with soil water content observed at several soil depths, and the water balance components are evaluated. The Campbell soil hydraulic functions are often used by meteorologists, whereas the van Genuchten functions are widespread among hydrologists. The simulations are performed with the “VEG3D” soil–vegetation model in stand-alone mode forced by on-site meteorological observations. The soil water content and meteorological observations were obtained within the Regional Climate Project (REKLIP) at a site in the Rhine valley in southern Germany with 10-min temporal resolution. Apart from the different soil hydraulic functions and parameter sets, the effects of different lower boundary condit...

Modelling Near Future Regional Climate Change for Germany and Africa

The scope of regional climate simulations carried out at the Institute for Meteorology and Climate Research (IMK) of Karlsruhe Institute of Technology (KIT) using the regional climate model (RCM) COSMO-CLM (CCLM) has been extended during the last years. From the focus first on Southwest Germany the area of interest has then been extended to the whole of Germany for the assessment of changes in flood risk for medium and small mountainous river catchments (CEDIM project: www.cedim.de), and within the frame of CORDEX (Coordinated Regional climate Downscaling Experiment, http://wcrp.ipsl.jussieu.fr/SF_RCD_CORDEX.html) also to the whole African continent. CORDEX aims to provide a framework to evaluate and benchmark RCMs and to design a set of experiments to produce climate projections for use in impact and adaption studies and as input to the IPCC 5th Assessment Report (AR5).