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The Water, Life and Civilisation project: Meteorology Investigating the climate of the Eastern Mediterranean using regional climate models David Brayshaw, Brian Hoskins, Julia Slingo & Emily Black MedCLIVAR meeting, ICTP, Italy, October 2008. CBRL. Talk outline.

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  1. The Water, Life and Civilisation project: MeteorologyInvestigating the climate of the Eastern Mediterranean using regional climate modelsDavid Brayshaw, Brian Hoskins, Julia Slingo & Emily Black MedCLIVAR meeting, ICTP, Italy, October 2008 CBRL

  2. Talk outline • WLC-Meteorology is part of a broader programme at Reading University: • Describe the WLC project more generally • Present an outline of the Meteorology component • Initial results • Plans for the future

  3. EUPHRATES VALLEY Mesopotamian Civilisation 6500 BC JORDAN VALLEY Origin of agriculture, 10,000 BC First towns, 8500 BC NILE VALLEY Egyptian Civilisation, 3500 BC Throughout human history into the present day, and beyond, the scene of economic, social, and political change that is intimately related to the hydrological climate Ancient civilisations in the Middle East and North East Africa Aim: To assess the impact of changes in the hydrological climate on past, present and future societies in the semi-arid regions of the Middle East and North Africa, with a case study of the Jordan Valley

  4. The five sub-projects and their links Climate modelling To describe annual and seasonal changes in climate for the Middle East and North Africa Region, 20,000 BC – AD 2100 Archaeological studies To understand human history within the Jordan Valley, and MENA region as a whole Hydrological modelling To describe the spatial and temporal variations in water flow of the Jordan River system Palaeoenvironmental studies To reconstruct prehistoric, historic and modern landscapes of the Jordan Valley Development studies To understand current and future demands on water usage and supply

  5. The Jordan Valley

  6. Aims of WLC-Meteorology • Produce climate simulations of the Middle East that are of use to the palaeo-science teams in interpreting proxy-records and archaeological evidence over the last 12,000 years • Combine/compare/contrast with regional palaeo-records • Develop understanding of the physical mechanisms involved in such changes • Emily Black working on C21 simulations

  7. Palaeo-modelling design • Two sets of integrations: • “Baseline integrations” • Investigating the impact of (relatively) slow changes in GHG, and insolation • “Event scenarios” and sensitivity tests • Atlantic MOC disruption at 8.2kBP • Green/Wet Sahara • Warm West Pacific

  8. Palaeo-modelling design: The baseline integrations Climate forcings Changed to “past” values Fixed at “modern” values Solar forcing due to orbital changes Land surface properties (fixed at present day) Pre-industrial ocean heat fluxes Green house gas changes Climate models High res. regional model (~50km) Low resolution global models (~300km) Lateral SST HadSM3 HadAM3 HadRM3 boundaries Simulations at: Pre-industrial, 1kBP, 2kBP, 3kBP, 4kBP, 5kBP, 6kBP, 8kBP, 10kBP, 12kBP

  9. Palaeo-modelling design:The “event scenarios” • Palaeorecords indicate spikes and shifts in the regional climate • Profound impact on societies: • For example, increased aridity associated with collapse of Akkadian Empire ~4kBP (Cullen et al., 2000) • Causal mechanisms: • “Natural” variability (which may also change with time) • Specific climate “events” or “shifts” • Model limitations: • Atmosphere only (thermodynamic slab ocean used in global model) • Fixed vegetation scheme • Short run length due to computational cost • Force specific, well known, climate “events” through the surface boundary conditions to examine the extent of the climatic response

  10. The regional modelDJF Mediterranean storm track ERA-40 (1958-2000) Global model Regional model Plot from Kevin Hodge’s webpage Figures show 2-6 day band-pass filtered standard deviation of meridional wind at 500 hPa

  11. The regional modelMAM Mediterranean storm track ERA-40 (1958-2000) Global model Regional model Plot from Kevin Hodge’s webpage Figures show 2-6 day band-pass filtered standard deviation of meridional wind at 500 hPa

  12. Using a regional model: Spatial structurePrecipitation gradients Global model (Pre-industrial control run) ERA-40: January precipitation Regional model (Preindustrial control run)

  13. Changes over the last 12,000 yearsSolar forcing and the seasonal cycle • Warmer summer, colder winter • Seasonal forcing bigger than GHG forcing (typically <1Wm-2 from pre-ind) • Also see “later” seasons in recent millenia Month Latitude Month Cross section at 35oN for each time period (anomalies) ka BP

  14. Changes during the last 12kaBP Changes in surface air temperature and precipitation in palaeo simulations for the target region Anomalies expressed w.r.t preindustrial 1 and 2 standard deviations shown Surface air temperature anomaly December-February Precipitation anomaly October-June

  15. Changes during the last 2kaBP: Surface air temperature anomalies Jan-Apr May-Aug Sep-Dec Cooler spring-early summer and warmer late summer/early autumn Seasons shift, coastal lag

  16. “Event” modelling:Green Sahara/Wet Sahara From Nick Drake’s webpage: http://uk.geocities.com/morris.drake@btinternet.com/ In early-mid Holocene evidence for large palaeo-lakes in North Africa (e.g. Lake Megachad, Drake and Bristow, 2006). Dessicated in a relatively abrupt shift ~4-6kyBP Also evidence of much increased vegetation in the earlier Holocene

  17. “Event” modelling:Green Sahara/Wet Sahara • GCMs: Northward shift and intensification of the ITCZ at 6kBP • Connected to stronger NH summer insolation, stronger monsoonal flows and changes in tropical SST gradients (e.g. PMIP2, Braconnot et al 2007) • Amplified by vegetation feedbacks Figures from Braconnot et al (2007)

  18. “Event” modelling:Green Sahara/Wet Sahara Possible simulations: Control 6kBP simulation 6kBP + imposed Green Sahara 6kBP + imposed “Wet” Sahara (green and open lakes) 6kBP + enhanced tropical SST gradients Combined (3)+(4)? From Nick Drake’s webpage: http://uk.geocities.com/morris.drake@btinternet.com/ Use regional model to examine impact on Mediterranean storm track

  19. “Event” modelling: 8.2kBP event • Widespread evidence for a “spike” in palaeorecords around ~8,000 years ago • Cause believed to be bursting of ice dams holding back glacial lake Agassiz in NE America • “Put very simply, a really big flood happened … from Laurentide-dammed lakes … [at] an age of about 8.47ka” (Alley and Agustsdottir, 2005) • Disrupts MOC in North Atlantic • Some relevance to future MOC weakening (“it is very likely that the Atlantic MOC will slow down during the 21st century”, IPCC 4AR) Summary of climate anomalies associated with 8.2kBP event From Alley and Agustsdottir (2005)

  20. “Event” modelling: MOC shutdown DJF surface temperature change (MOC off – MOC on) • MOC shutdown experiments • HadCM3 “hosing” simulation under pre-industrial conditions (Vellinga and Wu, 2008) • Using SST data to tune slab models and repeat experiments using HadSM3/HadRM3 • Focus on impacts upon Mediterranean storm track • Sensitivity to background state • 8,000 years BP • Pre-industrial conditions Sea ice warmer colder

  21. “Event modelling”: MOC shutdownStorm tracks and the mean flow Control: storm track (BPF MSLP) Control: U @ 250 hPa Dramatic changes in mid-latitude storm tracks and jet structure but insufficient resolution to confidently assess the impacts on Mediterranean storm track Hosed: storm track (BPF MSLP) Hosed: U @ 250 hPa For Atlantic storm tracks, see Brayshaw et al (under review, JClim)

  22. Other work:Downscaling for hydrology • Comparing with rain-gauge style data Model simulations Rain gauge data Probability of rain: Markov chains Pr(Rain|Rain) Pr(Rain|NoRain) PDF of rain on rain day Fitted gamma functions/histogram Statistical model Synthetic rainfall time series Hydrology models etc

  23. Future work:TRACK diagnostics • Kevin Hodges’ TRACK diagnostics • Track density • Storm intensity • Genesis density • Lysis density • Feature density • Lifetime • Speed • Growth/decay rates • Using Vorticity 500 hPa (3h) and a range of 6h data • See Hoskins and Hodges (2002)

  24. Summary • Regional model greatly improves spatial detail in the Eastern Mediterranean • Simulations run for a range of time periods: 2100AD to 12kBP • Future work will focus on physical mechanisms: • Understanding changes in storm track (e.g., using TRACK) • Sensitivity tests (8.2ky event, Green Sahara, Warm West Pacific) • Investigating downscaling, and possibly forward modelling of Oxygen isotopes

  25. Contact: d.j.brayshaw@reading.ac.uk www.waterlifecivilisation.org Any questions?

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