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

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

JORDAN VALLEY

Origin of agriculture, 10,000 BC

First towns, 8500 BC

NILE VALLEY

Egyptian

Civilisation,

3500 BC

EUPHRATES VALLEY

Mesopotamian Civilisation

6500 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

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

Ancient civilisations in the Middle East and North East Africa

Palaeoenvironmental studies

To reconstruct prehistoric, historic and modern landscapes of the

Jordan Valley

Archaeological studies

To understand human history within the Jordan Valley, and MENA region

as a whole

Development studiesTo understand current and future

demands on water usage and supply

Hydrological modelling

To describe the spatial and temporal variations in water

flow of the Jordan River system

Climate modellingTo describe annual and seasonal changes in climate for the Middle East and North Africa

Region, 20,000 BC – AD 2100

The five sub-projects and their links

The Jordan Valley

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

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

Palaeo-modelling design: The baseline integrations

HadSM3 HadAM3 HadRM3

Land surface properties

(fixed at present day)

Green house gas changes

Solar forcing due to orbital

changes

Pre-industrial ocean heat fluxes

Climate forcings

Lateral

boundaries

SST

Climate models

Simulations at:

Pre-industrial, 1kBP, 2kBP, 3kBP, 4kBP, 5kBP, 6kBP, 8kBP, 10kBP, 12kBP

Fixed at “modern” valuesChanged to “past” values

Low resolution global models (~300km)High res. regional

model (~50km)

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

The regional modelDJF Mediterranean storm track

Plot from Kevin Hodge’s webpage

ERA-40 (1958-2000) Global model

Regional model

Figures show 2-6 day band-pass filtered standard deviation of meridional wind at 500 hPa

The regional modelMAM Mediterranean storm track

Plot from Kevin Hodge’s webpage

ERA-40 (1958-2000)

Figures show 2-6 day band-pass filtered standard deviation of meridional wind at 500 hPa

Global model

Regional model

Global model (Pre-industrial control run)

Regional model (Preindustrial control run)

ERA-40: January precipitation

Using a regional model: Spatial structurePrecipitation gradients

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

ka BP

Mo

nth

Latitude

Mo

nth

Cross section at 35oN for each time period (anomalies)

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 anomalyDecember-February

Precipitation anomalyOctober-June

Changes during the last 2kaBP: Surface air temperature anomalies

Cooler spring-early summer and warmer late summer/early autumnSeasons shift, coastal lag

Jan-Apr

May-Aug

Sep-Dec

“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

“Event” modelling:Green Sahara/Wet Sahara

Figures from Braconnot et al (2007)

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

“Event” modelling:Green Sahara/Wet Sahara

From Nick Drake’s webpage: http://uk.geocities.com/morris.drake@btinternet.com/

Possible simulations:

1. Control 6kBP simulation

2. 6kBP + imposed Green Sahara

3. 6kBP + imposed “Wet” Sahara (green and open lakes)

4. 6kBP + enhanced tropical SST gradients

5. Combined (3)+(4)?

Use regional model to examine impact on Mediterranean storm track

“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)

“Event” modelling: MOC shutdown

• 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 warmer colder

Sea ice

DJF surface temperature change

(MOC off – MOC on)

“Event modelling”: MOC shutdownStorm tracks and the mean flow

Control: storm track (BPF MSLP)

Hosed: storm track (BPF MSLP) Hosed: U @ 250 hPa

Control: U @ 250 hPa

For Atlantic storm tracks, see Brayshaw et al (under review, JClim)

Dramatic changes in mid-latitude storm tracks and jet structure but insufficient resolution to confidently assess the impacts on Mediterranean storm track

Other work:Downscaling for hydrology

• Comparing with rain-gauge style data

Rain gauge data

Model simulations

PDF of rain on rain day

Fitted gamma functions/histogram

Probability of rain:

Markov chains

Pr(Rain|Rain) Pr(Rain|NoRain)

Statistical model

Synthetic rainfall time

seriesHydrology models etc

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)

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

Any questions?

Contact:

– d.j.brayshaw@reading.ac.uk

– www.waterlifecivilisation.org