Cyclone Jasper mostly Affected by Human-driven Climate Change

Press Summary (First published 2024/01/07)

• Low pressure systems similar to that producing the December 2023 cyclone Jasper are locally 0-2 °C warmer and 0-7mm/day drier in the present than they have been in the past.

• The December 2023 cyclone Jasper was a largely unique event.

• Natural climate variability likely played a role in driving the pressure pattern and the associated decrease in precipitation linked to cyclone Jasper, but human-driven climate change may have also contributed. 

Event Description

On the 13th December, cyclone Jasper made landfall in Northern Queensland, Australia. Although its winds had weakened to tropical depression strength, the cyclone stalled over the Cape York Peninsula, causing heavy precipitation over the course of several days in Northern Queensland, until the 19th December. Several locations received cumulated precipitation in excess of 600 mm, including the city of Cairns. Some sites reportedly received over 2000 mm, with a peak precipitation report of 2,252 mm, as of writing yet to be verified. The heavy precipitation led to extensive flooding, with insured damage estimated to amount to several hundred million USD. The hazardous weather caused extensive power outages, the closure of Cairns airport, road closures and one death.

The Surface Pressure Anomalies reveal a weather pattern characterized by a low-pressure system over the Cape York Peninsula. This favoured advection of moist air into Northern Queensland and the resulting heavy precipitation. Temperature Anomalies display negative values over most of the area affected by the heavy precipitation, presumably as a result of the cooling from the precipitation itself. Precipitation Data shows values of around 200 mm cumulated over the three days we consider in the analysis (16th-18th December), considerably lower than on-the-ground measures. The cyclone, which at landfall had tropical depression strength, also caused strong winds along the Queensland coast, as shown in the Windspeed Data. 

Climate and Data Background for the Analysis

The IPCC AR6 WG1 CH11 (p. 1592)  reports a future decrease in tropical cyclones, yet an increase in heavy rainfall intensity in Australia, the latter with medium confidence. The same chapter highlights increased risks for the finance sector from future climate extremes, with medium confidence, and specifically notes that insurance premiums in northern Australia are almost double those in the rest of Australia, and rising, mainly due to cyclone damage (p. 1626).

Our analysis approach rests on looking for weather situations similar to those of the event of interest having been observed in the past. For the December 2023 cyclone Jasper, we have low confidence in the robustness of our approach given the available climate data, as the event is largely unique in the data record.

ClimaMeter Analysis

We analyze here (see Methodology for more details) how events similar to the low-pressure system associated with the December 2023 cyclone Jasper have changed in the present (2000–2021) compared to what they would have looked like if they had occurred in the past (1979–2000) in the region [138°E 155°E 10°S 25°S]. The Surface Pressure Changes show that low-pressure systems have not significantly changed their intensity compared to the past, and may have even locally weakened. Temperature Changes show that similar events are associated with warmer conditions (0-2 °C)  in the present than in the past over much of the analysed region. Examining Precipitation Changes reveals that present events exhibit a decrease in precipitation over parts of Queensland, of up to 6-7 mm/day. Windspeed Changes show that present events lead to generally windier conditions over the western coast of Queensland (2-6 km/h), with calmer conditions in the Gulf of Carpentaria. We find no marked change in the seasonal occurrence of similar events between the past and present periods. Considering the affected urban areas of Townsville, Cairns and Mackay, our analysis finds that they display no marked changes in temperature in the present compared to the past during similar events. All urban areas also tend to receive less precipitation in the present than in the past (4-7 mm/day) during cyclones similar to Jasper. Finally, we find that sources of natural climate variability, notably the Atlantic Multidecadal Oscillation and the Pacific Decadal Oscillation, may have influenced the event. This suggests that the changes we see in the event compared to the past may be due to human-driven climate change, with a contribution from natural variability.

Conclusion

Based on the above, we conclude that low pressure patterns similar to that associated with the December 2023 cyclone Jasper are locally 0-2 °C warmer and 0-7 mm/day drier in the present than they have been in the past. We interpret the December 2023 cyclone Jasper as a largely unique event for which natural climate variability played a role.

Contact Authors

Gabriele Messori, Uppsala University, Sweden📨gabriele.messori@geo.uu.se  🗣️Italian, English, French, Swedish

Davide Faranda, IPSL-CNRS, France  📨davide.faranda@lsce.ipsl.fr  🗣️French, Italian, English