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
Outline Previous projections Downscaled variables Downscaled drought projections Recent past Future Attribution
Outline Previous projections Downscaled variables Downscaled drought projections Recent past Future Attribution
Previous projections Climate Change in Australia, BoM & CSIRO, 2007 2 0 3 0 2 0 5 0 2 0 7 0 Rainfall Temperature Pot. Evap.
Previous projections Drought Exceptional Circumstances, CSIRO & BoM, 2008
Kirono and Kent, 2010 Previous projections Percent SEQ in drought Rainfall Reconnaissance Drought Index Ensemble containing fewer, better performing models
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
Outline Previous projections Downscaled variables Downscaled drought projections Recent past Future Attribution
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
Downscaled variables Projected change by 2050 under high emissions Rainfall % change Pot. Evap. % change Downscaled from CSIRO Mk3.5
Outline Previous projections Downscaled variables Downscaled drought projections Recent past Future Attribution
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 1971-2000 as normal conditions
Recent past Downscaled drought projections Observed 1971-2007
Downscaled drought projections PDSI identifies the recent drought events Supply volume of SEQ s three largest dams 1994-2010 http://www.seqwater.com.au/public/dam-levels Observed PDSI 1994-2007. Note earlier end date. All model realisations underestimate the observed incidence of drought (particularly the most recent decade)
2010-2100 Downscaled drought projections
Downscaled drought projections Percent time in drought Mean drought duration 80.00 140 70.00 120 % time 60.00 50.00 40.00 30.00 20.00 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_echam5 10.00 20 0.00 0 1990 2032 2078 1990 2032 2078 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
Outline Previous projections Downscaled variables Downscaled drought projections Recent past Future Attribution
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
Stationary potential evaporation Attribution
Stationary Rainfall Attribution
Attribution Projected change by 2050 under high emissions Rainfall % change Pot. Evap. % change Downscaled from CSIRO Mk3.5
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
Thank you www.urbanwateralliance.org.au CSIRO Marine & Atmospheric Research David Kent Support Scientist Phone: +61 3 9239 4552 Email: David.Kent@csiro.au Web: www.csiro.au/cmar