GC23B-01
ENSEMBLES Regional Climate Modeling: A Multi-model Approach Towards Climate Change Predictions for Europe and Elsewhere
Projections of future climate change for Europe even at a country by country level already exist, but are largely building on olders generation of climate change experiments with state-of-the-art climate models of the late 90's or regional climate model experiments carried out via national programs. In 2001 high-resolution (50 km) climate change simulations for an area covering the entire European continent and a substantial part of the North Atlantic were conducted in a coordinated fashion in the EU FP5 project PRUDENCE (http://prudence.dmi.dk) using an array of regional climate models nested in two different general circulation models. The emission scenarios used were the IPCC SRES scenarios A2 and B2, which compared well with the scenarios emphasized in the IPCC Third Assessment Record chapter on regional climate. A large set of 30-year time slice experiments were carried out with all the models involved for periods representing the present (1961-1990) and the future (2071- 2100) in these scenarios. These simulations have during the project and since its closing stages in 2004 been heavily used for a variety of climate change and climate change impact studies taking advantage of the multiplicity of experiments, which allow for an assessment of associated uncertainty measures. In the follow up project ENSEMBLES (http://ensembles-eu.metoffice.com) - an EU Integrated Project under FP6 – a direct collaboration with GCM modelers from the very beginning of the project has allowed for a further advancement in the strategy of combining RCM and GCM models in an optimal manner to better constrain uncertainties related to regional climate change projections. Not only does ESEMBLES utilize a large array of regional climate models, it also involves at least five different GCMs. Resolution in the RCMs are further increased to 25 km and the core of experiments contain a simulation using ‘perfect' boundary conditions from ERA40 (covering 1958 – 2002), and transient experiments with GCM boundaries representing the period 1950 – 2050 (optional until 2100) for the A1B SRES scenario. By focusing on the period up till 2050, the actual choice of emission scenario becomes less important. With this multiplicity of experiments, a statistical approach will be adopted, that intends to constrain climate change in a probabilistic manner, providing the most likely change with probabilistically deduced ranges. In the present paper, we will discuss the general ideas behind the project and assess some of the first analyses performed that will assist in deriving the probabilistic approach.
GC23B-02
The North American Regional Climate Assessment Program (NARCCAP): Overview and Early Results
NARCCAP is an international program that is serving the climate scenario needs of the United States, Canada, and northern Mexico. We are systematically investigating the uncertainties in regional scale projections of future climate and producing high resolution climate change scenarios using multiple regional climate models(RCMs)and multiple global model responses to a future emission scenario, by nesting the RCMs within atmosphere ocean general circulation models (AOGCMs) forced with the A2 SRES scenario, over a domain covering the conterminous US, northern Mexico, and most of Canada. The project also includes a validation component through nesting the participating RCMs within NCEP reanalyses. The basic spatial resolution of the RCM simulations is 50 km. This program includes RCMs that participated in the European PRUDENCE program (HadRM3 and RegCM), the Canadian regional climate model (CRCM) as well as the NCEP regional spectral model (RSM), the NCAR/PSU MM5, and NCAR WRF. Candidate AOGCMs include the Hadley Centre HadCM3, NCAR CCSM, the Canadian CGCM3 and the GFDL model. The resulting climate model runs will form the basis for multiple high resolution climate scenarios that can be used in climate change impacts assessments over North America. High resolution (50 km) global time-slice experiments based on the GFDL atmospheric model and the NCAR atmospheric model (CAM3) have also been produced and will be compared with the simulations of the regional models. There also will be opportunities for double nesting over key regions through which additional modelers in the regional modeling community will be able to participate in NARCCAP. Additional key science issues are being investigated such as the importance of compatible physics in the nested and nesting models. Measures of uncertainty across the multiple runs are being developed by geophysical statisticians. In this overview talk, results from Phase I of the project, the RCM simulations using boundary conditions from NCEP reanalyses, will be presented. In addition, outcomes of a combined modeler and user group meeting for NARCCAP will be discussed. http://www.narccap.ucar.edu
GC23B-03
Functional ANOVA Modeling of Regional Climate Model Experiments
One of the goals of the North American Regional Climate Change Assessment Program (NARCCAP) is to explore uncertainties in regional climate modeling over North America by nesting a set of regional models within a set of global models. As a diagnostic tool to compare model similarities across spatial regions, we propose a functional ANOVA approach, in which we decompose the climate response into a common mean response, effects due to regional model, effects due to global model, and interactions. We model these functional effects using Gaussian process priors, and use the posterior distribution to compare sources of variability in model output. We illustrate the method on an existing data set from the Prudence Project.
GC23B-04
Robustness of Future Changes in Local Precipitation Extremes
Reliable projections of future changes in local precipitation extremes are essential for informing policy decisions regarding mitigation and adaptation to climate change. In this study, we examine the extent to which natural climate variability affects our ability to project the anthropogenically forced component of change in daily precipitation extremes at the local scale. The work uses a three-member ensemble of the Hadley Centre Regional Climate Model HadRM3H and applies a statistical framework to estimate uncertainty due to natural variability on all timescales from daily to multi-decadal. We show that climate noise significantly impacts on our ability to measure robust signals of extreme precipitation change across Europe. In particular, extreme precipitation changes at the grid box level are found to be discernible above climate noise over much of northern and central Europe in winter, but over less than half of Europe in summer. In addition, the ability to quantify the change to within reasonable bounds is largely limited to isolated local regions in northern Europe. In general, where climate noise has a significant component varying on decadal timescales, single 30 year climate change projections are insufficient to infer changes in the extreme tail of the underlying precipitation distribution. Also generally on moving to finer spatial scales and when considering more extreme events, natural variability increases and it becomes increasingly difficult to discern an underlying change. In this context, we demonstrate the need for ensembles of integrations and explore the relative effectiveness of spatial pooling and averaging for generating robust signals of extreme precipitation change. We anticipate that the key conclusions for the HadRM3H climate projection will apply qualitatively to other models and forcing scenarios.
GC23B-05
Land/atmosphere Coupling Methodology and Regional Climate Downscaling --- A Study Using the JIFRESSE WRF/SSiB Model
Land-atmosphere interactions play a crucial role in determining regional climate. To examine the impact of land surface processes on seasonal predictions, we use the Weather Research and Forecast (WRF) model to examine to what extent land surface models and land/atmosphere coupling methods have an impact on seasonal predictions. WRF experiments are designed to run with different choices of land models and coupling methods. The variables under evaluations include precipitation, 2-meter temperature, 200 mb and 850 mb winds, and other land surface parameters. Results from our experiments indicate that land/atmosphere coupling has a significant impact on seasonal predictions. The present study shows a proper coupling between the land surface and atmospheric planetary boundary layer is important in regional climate models (RCMs). However, the coupling problem remains largely unexplored and undiagnosed due to complex processes involved across a range of scales. We illustrate that different coupling methodologies are one of the prime sources producing different downscaling capabilities in RCMs. The land/atmosphere interaction includes exchanges of fluxes of momentum, latent heat, and sensible heat, which are affected by atmospheric stability and land surface conditions. A proper coupling process should cover all these aspects coherently and completely. The coupling strategy in the UCLA JIFRESSE (Joint Institute for Regional Earth System Science and Engineering, a collaboration with JPL) WRF/SSiB (Simplified Simple Biosphere) model will be discussed in this presentation. In particular, our approach will be compared with a number of traditional approaches, such as Louis" parameterization, where the total aerodynamic resistance including both neutral and non-neutral parts is only a function of the Richardson number without a full consideration of vegetation presence. A series of tests using the summer 1998 case have been conducted to quantitatively evaluate the impact of coupling methodology. We show that it has substantial impact on precipitation and large-scale circulation, such as the 200mb wind, on monthly and seasonal scales. We also illustrate that a proper coupling between land and atmosphere greatly enhances the WRF/SSiB's ability in accurately simulating North American regional climate features. Finally, the impact of land surface initial conditions on downscaling will be addressed.
GC23B-06
Land surface coupling in regional climate simulations of tropical monsoon systems
Simulations with the ICTP Regional Climate Model version 3 coupled to the Common Land Model version 3 (RegCM3-CLM3) show significant improvement in the simulation of summer monsoon precipitation and temperature. A ten-year simulation (1992-2001) over Europe and northern Africa driven by reanalysis boundary conditions indicates that timing and magnitude of the African monsoon more closely match observations when a new land surface scheme is implemented. The RegCM3-CLM3 improves the timing of the monsoon advance and retreat across the Guinean Coast and reduces the precipitation bias in the Sahel and Northern Africa. As a result, simulated temperatures are higher, thereby reducing the cool temperature bias noted in northern Africa in RegCM3. The complex treatment of soil in CLM3 leads to a more accurate representation of interannual soil moisture and land surface albedo in RegCM3-CLM, which may lead to the strong land-atmosphere feedback.
GC23B-07
Climate Downscaling Using a Mesoscale Model on a Hemispheric Grid
Under a project funded by the Defense Threat Reduction Agency (DTRA), we have developed a system to downscale global reanalysis fields to a high resolution global grid, to be used within DTRA's Hazard Prediction Assessment Capability, a decision support system used for responding to releases of hazardous material into the atmosphere. The proposed system uses MM5 (with both observation and grid nudging) run on two hemispheric grids centered on the poles, and later merged to produce a seamless global product at an effective resolution 45 km for 1979 to 2005. In this presentation we will discuss preliminary results from the verification of the dynamic and thermodynamic fields at the global and regional scale, and discuss the challenges associated with running such a computationally expensive and data-extensive system.
GC23B-08
A Coupled Regional Climate Modelling System for the Mediterranean Area: Results From the Control Simulation.
Nested limited-area atmospheric models have proven their ability in resolving small features that are missing in global-scale climate simulations. At present fully coupled regional climate models are being developed, so that the interactions among the components of the climate system (i.e. ocean, atmosphere, biosphere and sea-ice) are explicitly simulated. Such models are expected to improve the reliability of climate scenario simulations over complex regions such as the Mediterranean area, which is subject both to the influence of global scale dynamics (e.g. disturbances in the mid- latitudes, strength and meridional extension of the Hadley circulation), and to the effects of local physical processes (complex topography, local evaporation). We present results from the control simulation performed with a novel coupled system for regional climate modelling. The Protheus system consists of the RegCM (atmospheric model), the MITgcm (ocean model), coupled via OASIS3. We have performed the control simulations with the ERA40 reanalysis as lateral boundary condition for the atmospheric model. We have employed the same dataset to supply the surface boundary condition to a stand- alone version of the ocean model. We focus our analysis on the main differences between the stand-alone configurations of the single model components and the fully coupled system.