Bruce Hewitson – University of Cape Town

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

2. 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 Models • Development 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 downscaling • Development and skill  Identifying the “true” scale translation function • Stationarity assessment  How much do future projections transgress historical envelope? • Related problems: • Data representation  model / observation data on appropriate time/space scales • Political access  inter-nation barriers - NWS limitations and poor links with researchers • Formats (paper / electronic)  finding / rescuing “lost” archives, standard data structures • Bandwidth access  (Meta-)data dissemination to broad community

3. AIACC Example: An end-to-end process with dependency on observations at all stages * Acquire GCM Simulations Assess control simulations Quantify skill & uncertainty Develop GCM-based regional scenarios Acquire Observational Data Quality Control Collate to common format Include reanalysis fields * * Assess User Needs Review AIACC projects Integrate GCM and obs data Disseminate via web * * Common multi-GCM / Observational data sets for participants usage Availibility via internet and CD- ROM • Regional Climate Model Simulations • Control simulations with reanalysis forcing • Quantify skill & uncertainty • Simulations with GCM boundary forcing • Long-term for large sub-continental domains • Short-term high resolution on focus domains • Process-based investigations • Empirical downscaling • Downscaling functions from reanalysis data • Quantify skill & uncertainty • Downscaling of GCM simulation data • Initial downscaling to station scale ppt and T • Additional downscaling to impacts variables * * * * Integration and Analysis Inter-GCM comparison -- Inter-RCM comparison -- Regional skill variability -- RCM versus Empirical downscaling Confidence levels and uncertainty of regional scenarios -- tailoring of results to user needs Journal papers -- workshops and training -- inter-institutional visits and internships * *

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

5. 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.

6. Data needs: GCMs / RCMs / downscaling for impacts • … Principal data sources used and problems … • a) Radiosondes and upper air observations • Network declining • Access to archived data problematic • b) Surface precipitation / air temp / stream gauge observations • Network declining or absent • Issues of quality and duration • Access to archived data problematic • c) Satellite derived albedo / radiation / skin temperature / surface winds • Observations increasing – but short data record • Access to archived data problematic • d) Reanalysis data sets • Uncertainty on quality (NCEP / ERA / Truth!) • Regionally dependant problems pre-79 • Access to archived data problematic

7. Data needs: GCMs / RCMs / downscaling for impacts • … Long-term surface observations … 50-yr trend (robust regression) Number of raindays > 2mm in a month

8. Green: 1-day snapshot of station presence Black + Green: Station presence between 1980-2000

9. ~50-100km observational network

10. 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

11. 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!

12. 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 sources • eg: 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

13. 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

14. Eg: Perturbation simulations: Experiment: Desiccation of soil moisture – temperature increases up to 4°C Q: What should the “real” soil moisture be?

16. 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

17. 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 willingess Facilitate an appropriate resource base from governments ------

18. 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 willingess • Facilitate 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