Future East Coast Lows

We have improved our ability to model ECLs now and into future. Climate change may affect the intensity, frequency and duration of ECLs with implications for coastal erosion, inundation, flooding, storm-water infrastructure and water security.

Research findings 

ECL activity may change in the future and this should be considered by coastal and water managers 

Climate modelling projects a decrease in the number of small to moderate ECLs in the cool season with little change in these storms during the warm season. However extreme ECLs in the warmer months may increase in number but extreme ECLs in cool seasons may not change. 

Projected changes in ECLs into the future are smaller than the natural variability we see in ECLs from the historical record. This means that ‘planning for the past’ in addition to the future will enhance risk management by accounting for the broader range of ECL variability and associated risk. Risk analysis should consider the storminess of the 1600-1900 period. 

ESCCI-ECL Project Results

Projections of future ECL frequency and intensity along the NSW coast

Although they can be damaging ECLs are relatively small, short-lived storms, and Global Climate Models (GCMs) tend to under-predict their frequency and duration. This project sought to capture the full ECL climatology and project future changes in ECL frequency and intensity (with confidence estimates) through robust regional climate modelling.

Regional Climate Models (RCMs) were used to simulate the climate of the east coast at high enough spatial and temporal resolutions to capture ECL development and intensification. The RCMs were also ‘nested’ in GCM simulations to produce high resolution projections of the future east coast climate, including changes in the frequency and intensity of ECLs. The Weather Research and Forecasting (WRF) model, a dynamical regional climate model, was selected to model ECL events. This model was found to be effective in simulating temperature and rainfall in NSW, and to reasonably represent the local topography and coastal processes. Three RCMs, comprising WRF with three different physics schemes, were applied within the NSW and ACT Regional Climate Modelling (NARCliM) Project to downscale projections from four GCMs for three 20-year periods: 1990-2009 (base case), 2020-2039 (near future) and 2060-2079 (far future). Changes in the frequency, duration and intensity of ECLs were assessed by comparing projections for the near and far future periods with the base case period.

Different automated ECL tracking methods were applied to detect ECLs, with the intensity thresholds set to identify 22 ECLs per year for the base case to coincide with the average annual number of events identified through earlier subjective analysis. All methods applied detected the majority of severe ECLs, but had different seasonal accuracies making it useful to consider results from all methods when drawing conclusions.

Data from this study are being incorporated into projections of water levels in reservoirs and other stores as part of ESCCI-ECL Project 5. The results of Project 2 can also be combined with those of Projects 3 and 4 to estimate the coastal impact of sea level rise and storm surges.

Future work will attempt to project future changes in ECL sub-types, due to studies of past ECLs finding that the type of event significantly affects the extent, location and seasonality of associated impacts. Specific attention will be paid to ECLs resulting in rainfall, wind and wave impacts on the land.

References

Evans J, Ekström M, Ji F (2012) Evaluating the performance of a WRF physics ensemble over South-East Australia. Climate Dynamics 39:1241–1258. doi: 10.1007/s00382-011-1244-5.

Pepler, A.S., A. Di Luca, L. Alexander, J.P. Evans, F. Ji and S. Sherwood (2014) Impact of identification method on the inferred characteristics and variability of Australian East Coast Lows. Monthly Weather Review. http://dx.doi.org/10.1175/MWR-D-14-00188.1.

Ji, F., J.P. Evans, D. Argueso, L. Fita and A. Di Luca (2015) Using large-scale diagnostic quantities to investigate change in East Coast Lows. Clim Dyn 1–11. doi: 10.1007/s00382-015-2481-9.

Pepler, A., L. Alexander and J.P. Evans (2015) Zonal winds and southeast Australian rainfall in climate models. Climate Dynamics, accepted 16 March 2015.

Di Luca, A., J.P. Evans, A.S. Pepler, L. Alexander and D. Argueso (2014) Resolution sensitivity of cyclone climatology over eastern Australia using five reanalysis products. Journal of Climate, accepted 29 June 2015.

Gilmore, J., J.P. Evans, S.C. Sherwood, M. Ekstrom and F. Ji (2015) Extreme Precipitation in WRF during the Newcastle East Coast Low of 2007. Theoretical and Applied Climatology, accepted 29 June 2015.

Di Luca, A., J.P. Evans, A. Pepler, L.V. Alexander and D. Argueso (2015) Evaluation of East Coast Lows in the NARCliM Regional Climate Model ensemble. Submitted to Australian Meteorological and Oceanographic Journal.