Regional climate modelling in the future. Ralf Döscher, SMHI, Sweden

Transcription

1 Regional climate modelling in the future Ralf Döscher, SMHI, Sweden

2 The chain Global H E H E C ( m 3/s ) Regional downscaling 120 adam 3 C HAM 4 adam 3 C HAM 4 trl A2 A2 B2 B J F M A M J J A S O N D Impact, climate services and conclusions for vulnerability and adaptation

3 CORDEX Coordinated Regional climate Downscaling Experiment Outcomes: RCMs better serve regional climate information needs Ensembles allow for the description of the regional uncertainty from RCM and GCM Added value for conditions of variable orography, landsea and other contrasts, capturing, short-duration and extreme events. Large-scale and time-averaged fields, over smooth terrain are not much affected Issues: boundaries, integration of regions,... Relies on the abilities of GCMs

4 Higher resolution in RCMs tends to increase extreme precipitation intensity (in line with observations)

5 Status and ongoing development RCMs (and GCMs) are evolving Updated physics and dynamics Increased resolution for routinely running models RCMs (10-25 km, continental domains) compared to typical GCMs ( km) Cutting edge resolutions: Most GCMs still do not resolve regional scale land and orography variability, which shapes regional climate GCMs towards 20 km, RCMs (or local models) down to 1 km: convection permitting (or resolving) more realistic performance in regions with variable orography, contrasts, as well as extreme events. The value of downscaling for impact application is increasing with resolution, e.g. hydrological impact of watersheds in mountainous regions. The RCM community formulates new goals towards higher resolution (1-2 km) and more complete ensemble downscaling.

6 Challenges for regional climate modelling Model scales need to be further synchronized with impact scales, which are local Better representation and projection of extremes Studies on regional processes and forcing, designed to give actionable value. e.g CORDEX Flagship Pilot Studies: Extrem precipitation events in South America; convective phenomena, impact of land use change in Europe; role of natural and anthropogenic aerosol in the med area; role of air-sea coupling and small scale ocean processes in the Mediterranean. Regional Earth System Models for a more complete understanding of regional and local change in response to climate change. Understanding feed-back mechanisms due to LULC and aerosols Inter-domain homogenization of coordinates projections in Atlas-like products Definition and documentation of added value to be broadened from the increase in skill by downscaling to increase of user value (which varies very much with user sector and application type.) Outreach and services: Distillation of climate information: Results need to be conveyed in a comprehensible way, using different sources, addressing regional and local issues. Two-way exchange with users.

7 Regional ESM components add value RCMs coupled to regional ocean, sea ice and dynamic vegetation, lakes are incorporating more sources of local-to-regional scale coupled feedback, and user value. e.g. Coupled ocean and sea ice: Coupled lake model: high res atmosphere forcing for ocean-standalone studies of e.g. ocean bio-chemistry in the changing Baltic detail of SST and airsea interaction under strong wind conditions in the Mediterranean. improved precipitation and circulation features for the western North Pacific, and improved coastal effects I the Baltic Process studies on gas exchange lake effects have been captured for Europe, North American Great Lakes, African Great Lakes. In the African case, thermal differences between the lake and the surrounding land affect diurnal and seasonal temperature variability, enhanced precipitation due to induced local circulation. Coupled dynamic vegetation: Feedbacks enhance the warming trend over the Scandinavian Mountains due to forest expansion in a warming climate and subsequent reduction of the albedo, Allows to quantify land-based albedo feedback (additional winter and spring warming) and evapotranspiration feedback (summertime cooling), methane release effects for the Arctic under climate change.

8 Regional ESM in the Arctic: methane (a) The monthly CH4 fluxes from 1961 to 2080 (b) The change of the CH4 flux between the recent and the future periods. Values are for the wetland fraction of the study area only. Zhang et al. 2013

9 RCMs in the light of future GCM development Higher res GCMs are desirable for RCM downscaling due to remote drivers of regional change The visionary 1 km convection-resolving GCM needs exascale supercomputing, anticipated in the 2020's. Short integrations, difficult tuning, possible model diversity Fully available maybe 2030 Until full availability, RCMs are needed for 1 km and coarser studies, projections, services Even with 1 km GCMs, RCMs for user-targeted and local ESM studies

10 RCMs and GCMs RCMs as test cases and forerunners for future high resolution GCMs More scale sensitive parameterizations of convection and clouds for a range of scales. Formulations can be used in both GCMs and RCMs and would allow for more consistent results throughout scales Biases and other shortcomings can be dealt with in different suitable set-ups, regionally and globally Regionally focussing grids Common data infrastructure including data streams from the global to the regional modelling

11 RCMs in km resolution to unlock the expected benefits for new studies into future changes in local-scale severe weather, extremes, short-term events Radar Kendon et al. 2012

12 Intensity and duration of precipitation Period: Observations: 30-min automatic gauge RCM data: - 30-min precipitation from RCA model with ERA40 boundary - resolutions 50, 25, 12.5, 6.25 km grid boxes Intensity (mm/hour) Intensity (mm/hour) Stockholm Malmö Duration (hours) From Jonas Olsson, SMHI

13 A major rain event on the 31/ in Malmö

14 Accumulated precipitation 31/ ( ) Operational NWP forecast (HARMONIE) from the 30th of August (2,5 km grid spacing) Precipitation from weather radar Kjellström et al. (2014), GEWEX Newsletter

15 Precipitation over the Alps in HARMONIE-Climate (HCLIM) Improvements for increasing resolution better physics Lindstedt and Lind, SMHI Daily cycle

16 HARMONIE-Climate (HCLIM), non-hydrostatic RCM catching extreme events Maximum observed precipitation 200 mm/day, station in Western Crete, 17th Oct. HCLIM (unlike coarser models) represents extreme event.

17 Approaching the urban scale Domain: 240x240 km2 1 km resolution Urban SIS, a Copernicus project, with Stockholm as pilot city Stakeholders: Stockholm municipality and water company Based on 1 km climate simulations and more detailed land use data. Important: to resolve intra-city gradients Focus: consistent ECVs for urban planning, with Air quality applications Hydrological applications

18 Better numerics and codes Discretization should be of high order to most efficiently using computer resources (for a given accuracy) Apply principles of proven accuracy and stability, even for boundary conditions and interfaces (e.g. Method of Manufactured Solutions, MMS) Better optimization of parameterizations (tuning) Higher standards for model documentation, model verification and tuning Open code (for transparency and more efficient community engagement) Modular code

19 Well-Posed and Accurate Boundary Conditions for Regional Climate Modelling Better solution exact solution Current typical solution Regional model codes rely on the formulation of boundary conditions, which in many cases involve radiation boundary conditions in combination with a nudging procedure. Improvements are seen in treating the boundary value problem in a well-posed and stable way. Modern difference approximations yield an almost skew-symmetric differentiation matrix yielding only boundary terms, exactly mimicking the continuous boundary value problem.

20 Summary RCMs will get better in adding value to GCMs (extremes, short term events...) offer to support high res GCM development as forerunners for 2030's GCMs allow for regional process and ESM studies is today and will be the primary source for climate services on regional and local level Will benefit from parallel efforts of higher resolving GCMs km scale resolution in local-regional domains for better synchronization with impact scales Regional system models

21 The End