Urban Water Security Research Alliance

Transcription

1 Urban Water Security Research Alliance Drought Frequency and Duration Projections for South East Queensland David Kent, Wenju Cai, Kim Nguyen Climate and Water 29 September 2010

2 Outline Previous projections Downscaled variables Downscaled drought projections Recent past Future Attribution

3 Outline Previous projections Downscaled variables Downscaled drought projections Recent past Future Attribution

4 Previous projections Climate Change in Australia, BoM & CSIRO, Rainfall Temperature Pot. Evap.

5 Previous projections Drought Exceptional Circumstances, CSIRO & BoM, 2008

6 Kirono and Kent, 2010 Previous projections Percent SEQ in drought Rainfall Reconnaissance Drought Index Ensemble containing fewer, better performing models

7 Previous projections All based on broad scale data Don t capture topography Limited data available for some variables Particularly, little data available on shorter timescales Therefore: downscaling

8 Outline Previous projections Downscaled variables Downscaled drought projections Recent past Future Attribution

9 Downscaled variables Cubic Conformal Atmospheric Model (CCAM) Global atmospheric model with a non-uniform grid Highest resolution over eastern Australia (~20 km) Outputs large set of variables at daily or sub-daily frequency ~ 800 MB per modelled month for 130 years = 1.3 TB per experiment

10 Downscaled variables Projected change by 2050 under high emissions Rainfall % change Pot. Evap. % change Downscaled from CSIRO Mk3.5

11 Outline Previous projections Downscaled variables Downscaled drought projections Recent past Future Attribution

12 Downscaled drought projections Palmer Drought Severity Index Simple water balance model, proxy to soil moisture conditions Driven by monthly rainfall, temperature Modified to use the downscaled potential evaporation data instead of deriving an approximation from rainfall and temperature Index with range of around -6 (severe water deficiency) to +6 (abnormally wet) Calibrated against as normal conditions

13 Recent past Downscaled drought projections Observed

14 Downscaled drought projections PDSI identifies the recent drought events Supply volume of SEQ s three largest dams Observed PDSI Note earlier end date. All model realisations underestimate the observed incidence of drought (particularly the most recent decade)

15 Downscaled drought projections

16 Downscaled drought projections Percent time in drought Mean drought duration % time Mean duration (months) 100 csiro_mk3_0 csiro_mk3_0 80 csiro_mk3_5 gfdl_cm2_1 miroc3_2_medres 60 mpi_echam5 40 csiro_mk3_0 csiro_mk3_0 csiro_mk3_5 gfdl_cm2_1 miroc3_2_medres mpi_echam Centre of time period Centre of time period Large inter-model uncertainty Uncertainty increases with time All agree on increased proportion of time in drought conditions All agree on increased duration

17 Outline Previous projections Downscaled variables Downscaled drought projections Recent past Future Attribution

18 Attribution PDSI is water balance based Index is proxy for the moisture departure (d) for a particular month (i): d i Pˆ i P Pˆ f i i ( PET, antecedent conditions) The above is modified to account for the relative importance of a moisture departure for a particular climate What drives the moisture deficiency? Produce the index based on: 1. climatological rainfall 2. climatological potential evaporation i i

19 Stationary potential evaporation Attribution

20 Stationary Rainfall Attribution

21 Attribution Projected change by 2050 under high emissions Rainfall % change Pot. Evap. % change Downscaled from CSIRO Mk3.5

22 Concluding Remarks Consistent with previous, broad scale projections All models project increased frequency and duration of drought events Large inter-model uncertainty of scale of increase All models underestimate recent drought events Models project an increase in drought duration and total proportion of time under drought conditions Primarily driven by projected temperature and evaporation increases

23 Thank you CSIRO Marine & Atmospheric Research David Kent Support Scientist Phone: David.Kent@csiro.au Web: