Bruce Hewitson – University of Cape Town

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GCOS 2 nd Report on Adequacy … Perspectives from GCM / RCM modeling, climate downscaling, and developing nations From the view of practicing climate change and variability research in Africa Bruce Hewitson – University of Cape Town Climate change projection: Multi-model mean Δ precipitation 4 of 6 agreement on sign … but which models are correct …

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GCOS 2 nd Report on Adequacy … Perspectives from GCM / RCM modeling, climate downscaling, and developing nations From the view of practicing climate change and variability research in Africa. Bruce Hewitson – University of Cape Town. - PowerPoint PPT Presentation

Transcript of Bruce Hewitson – University of Cape Town

Page 1: Bruce Hewitson – University of Cape Town

GCOS 2nd Report on Adequacy …

Perspectives from GCM / RCM modeling, climate downscaling, and developing nations

From the view of practicing climate change and variability research in AfricaBruce Hewitson – University of Cape Town

Climate change projection: Multi-model mean Δ precipitation

4 of 6 agreement on sign… but which models are correct …

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Data needs: GCMs / RCMs / downscaling for impacts… the key issues …

Baseline Climate Understanding (through analysis and modeling)Historical variability and change what is the envelope and trend?Climate system processes sensitivity to perturbations, feedback processes?

GCM/RCM ModelsDevelopment and tuning What is real?Evaluation and validation What is the systematic bias, process error?Application and Contextualization Where in data space is the model “skillful”?

Empirical downscalingDevelopment and skill Identifying the “true” scale translation functionStationarity assessment How much do future projections transgress historical envelope?

Related problems:Data representation model / observation data on appropriate time/space scalesPolitical access inter-nation barriers - NWS limitations and poor links with researchersFormats (paper / electronic) finding / rescuing “lost” archives, standard data structuresBandwidth access (Meta-)data dissemination to broad community

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AIACC Example: An end-to-end process with dependency on observations at all stages

Acquire GCM SimulationsAssess control simulationsQuantify skill & uncertaintyDevelop GCM-based regional scenarios

Acquire Observational DataQuality ControlCollate to common formatInclude reanalysis fields

Assess User NeedsReview AIACC projectsIntegrate GCM and obs dataDisseminate via web

Common multi-GCM / Observational data sets for participants usageAvailibility via internet and CD- ROM

Regional Climate Model SimulationsControl simulations with reanalysis forcingQuantify skill & uncertaintySimulations with GCM boundary forcing

Long-term for large sub-continental domainsShort-term high resolution on focus domainsProcess-based investigations

Empirical downscalingDownscaling functions from reanalysis dataQuantify skill & uncertaintyDownscaling of GCM simulation data

Initial downscaling to station scale ppt and TAdditional downscaling to impacts variables

Integration and AnalysisInter-GCM comparison -- Inter-RCM comparison -- Regional skill variability -- RCM versus Empirical downscaling

Confidence levels and uncertainty of regional scenarios -- tailoring of results to user needsJournal papers -- workshops and training -- inter-institutional visits and internships

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Temporalresolution

N a tiveo r rec o rd edre so lu tion

Skill oravailableresolution

Nativeor recordedresolution

Skill or availableresolution

Achieving Spatial requirement

Achieving temporal requirements

Spatialresolu tionPoint

resolution

E nve lope ofuser needs

Key issue: delivery of / access to products appropriate to user needs

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Data needs: GCMs / RCMs / downscaling for impacts… Data specifics (ideals) …

Application of models and climate change scenario for impacts assessments:

Necessity to develop/validate for time/space scales of application

Atmospheric dynamics: - On model grid, at sub-daily resolution- Model comparable area averages- 3D atmospheric u,v,q,T- 3D cloud fields- GCMs: 6-12 hourly on ~2.5º grid- RCMs: 6 hourly on 20-50km grid

Surface variables- At time resolutions resolving extremes (eg: for rain rates etc). -(Long term) precipitation and temperature- Land use/cover and albedo- Radiative fluxes at surface and top of atmosphere- Sea Surface Temperatures- Soil moisture- Key vulnerability variables: Stream flow, extremes, etc.

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Data needs: GCMs / RCMs / downscaling for impacts… Principal data sources used and problems …

a) Radiosondes and upper air observationsNetwork decliningAccess to archived data problematic

b) Surface precipitation / air temp / stream gauge observationsNetwork declining or absentIssues of quality and durationAccess to archived data problematic

c) Satellite derived albedo / radiation / skin temperature / surface windsObservations increasing – but short data recordAccess to archived data problematic

d) Reanalysis data setsUncertainty on quality (NCEP / ERA / Truth!)Regionally dependant problems pre-79Access to archived data problematic

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Data needs: GCMs / RCMs / downscaling for impacts… Long-term surface observations …

50-yr trend (robust regression)

Number of raindays > 2mm in a month

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Green: 1-day snapshot of station presence

Black + Green: Station presence between 1980-2000

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~50-100km observational network

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Data needs: GCMs / RCMs / downscaling for impacts… Long-term surface observations …

Serious problems with data coverage not appropriate to regional climate gradients

Quality control poor (Sunday/Monday problem)

Non-homogeneous data sets, widely differing (cryptic) data formats with variable user-skill in data management (eg: NCAR formats, GRIB, etc)

“Lost” data – hardcopy in diverse (unknown?) institutional archives

Almost insurmountable bureaucratic / political barriers to accessing data

Network bandwidth in Developing nations extremely inadequate

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Data needs: GCMs / RCMs / downscaling for impacts… Long-term surface observations …

Serious problems with data coverage not appropriate to regional climate gradients

Quality control poor (Sunday/Monday problem)

Non-homogeneous data sets, widely differing (cryptic) data formats with variable user-skill in data management (eg: NCAR formats, GRIB, etc)

“Lost” data – hardcopy in diverse (unknown?) institutional archives

Almost insurmountable bureaucratic / political barriers to accessing data

Network bandwidth in Developing nations extremely inadequate

GCOS: addresses these in principal, but ….- Capacity: resources for developing nation to collate / process archives- Politics: How to break through inter-agency and inter-nation barriers- Communication: Facilitating access by the research community- Bandwidth: Internet in developing nations not adequate for data access!

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Data needs: GCMs / RCMs / downscaling for impacts… Free atmosphere variables / boundary fields …

Dependency on radiosondes, satellites, reanalysis data sets

Declining radiosonde network – seriously absent in most developing nations

Issues of comparing data of different character derived from different sourceseg: satellite vs radiosonde vs model area averages

Question of reanalysis skill in data sparse regions, esp. prior to 1979 in SH

GCOS: addresses these in principal, but ….- Data access: problematic, especially for nationally held archives- Reanalysis data – quantification of error / skill in data spare regions- Reanalysis access – eg: ERA 40 not affordable by developing nations- Bandwidth: developing nation internet currently not adequate!

Land cover / SST / and other spatially continuous boundary fields

GCOS: addresses these in principal, but ….- Bandwidth a problem

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Eg: Perturbation simulations:

Experiment: 20% change in land surface albedo (within natural variability), can generate a temperature anomaly of 1°C

Q: notable difference to reanalysis: is the baseline of model correct, or reanalysis due to absence of constraining observations?

Dynamics driving perturbation response related to moisture flux – yet strong baseline moisture flux disagreement between NCEP/ERA

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Eg: Perturbation simulations:

Experiment: Desiccation of soil moisture – temperature increases up to 4°C

Q: What should the “real” soil moisture be?

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Summary issues and questions

Process based investigations:A need for quantified error / skill of reanalysis data

Eg: NCEP Reanalysis I and ERA15 have marked differences in moisture flux over central and southern Africa – what is the baseline for model evaluation?

The historical envelope:Proactively addressing regionally-held data (in developing nations), quality controlled, integration with existing archives?

Data access for researchers:Significant barriers exist between the research community and the operational network / data archiving centers:

Meta data not available, access procedures problematic, even finding data! What more be done than simply “urging” (GCOS term) nations to cooperate.

Infrastructural limitations on data dissemination:Beyond western developed nations, capacity to download or even store data is woefully inadequate

Data massaging: Compiling data sets appropriate to end user needs

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GCOS 2nd Report on Adequacy …

Shortcomings in observing network … … but secondary to issues of access

Adequacy in principal, inadequacy in practice

Fundamental constraints: Financial resources and political willingessFacilitate an appropriate resource base from governments

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GCOS 2nd Report on Adequacy …

Shortcomings in observing network … … but secondary to issues of access

Adequacy in principal, inadequacy in practice

Fundamental constraints: Financial resources and political willingessFacilitate an appropriate resource base from governments

------Strengthen statements relating to barriers to accessing data:

- Sharing of data / barriers between archives and researchers- Proactively communicating metadata (perhaps modeled on the DDC) - Facilitating dissemination / addressing bandwidth in developing nations- Reanalysis data – financial barriers!

Data products appropriate to endusers in the research community- Adding conversion activities to existing archiving procedures

Tropical regions, and 3D atmosphere data, especially moisture - Special focus need for understanding climate processes, model skill assessment