Heavy precipitation and flooding associated with tropical cyclones are responsible for a large number of fatalities and economic damage worldwide. A study conducted by CMCC researchers addresses the accuracy of observational data sets and reanalysis in representing tropical cyclone associated precipitation trends, with a special focus on the record breaking storm of 2023,  “Freddy”.

Tropical cyclones (TCs) have a significant impact on precipitation trends, to the point that they can cause up to 20% of total yearly precipitation over land and up to 40% over ocean regions depending on where they occur. This makes a reliable quantification of the precipitation amount associated with each past tropical cyclone important if we want to improve our understanding of the footprint of tropical cyclones on the climate.

A new study by the CMCC, which received funding from the European Union’s Horizon 2020 research and innovation programme under the Climate Intelligence (CLINT) project, compares tropical cyclone-related precipitation in various observational and reanalysis datasets, with a particular focus on the record-breaking tropical cyclone Freddy (Southern Indian Ocean, 2023).

“A reliable quantification of the amount of water associated with tropical cyclones plays a pivotal role in helping stakeholders and policy makers anticipate and prepare for these kinds of events that cause major impacts on society and ecosystems,” says CMCC researcher and lead author of the study Enrico Scoccimarro. “In the study we verify the ability of observational data sets and reanalysis in representing tropical cyclone associated precipitation during the historical period, with a special focus on tropical cyclone Freddy, also with the aim of verifying potential trends associated with global warming.”

Tropical cyclone Freddy formed to the northwest of Australia at the beginning of February 2023 and tracked west across the Indian Ocean, making several landfalls, lasting longer than five weeks, and bringing large flooding to parts of Madagascar, Malawi and Mozambique. Upper panel shows accumulated rainfall (based on MSWEP dataset ) and intensity along the TC path, while the lower panels show the total accumulated precipitation as resulting from different datasets. Source: Scoccimarro et al 2024

The results of the study reveal that care should be exercised when using observational datasets for trend analysis due to spurious temporal discontinuities that can occur mainly due to the introduction of additional satellite data sources along the time series. Even more caution should also be taken when using reanalysis products such as ERA5 and MERRA2 for trend analysis over long periods.

Providing a benchmark for future work on the improvement of tropical cyclone associated precipitation representation through AI driven approaches, the study brings to light evidence of the inability of observational and reanalysis products in representing past trends of extremes.

“This suggests that climate models, free to evolve following physical laws only, can be a better tool compared to observations in determining historical trends associated with extreme events such as tropical cyclones and the relative associated precipitation,” says Scoccimarro. “In addition this work characterizes for the first time the record breaking tropical cyclone Freddy, also in terms of associated precipitation within the historical tropical cyclone sample from 1980 onward, when considering TCs making landfall.”

The study is another contribution to the CMCC CLIVAP division’s effort to improve knowledge on extreme event dynamics, further reinforcing the role of the CMCC as a leading center in the investigation of the relationship between extreme events and the climate system.

For more information:

Enrico Scoccimarro, Paolo Lanteri and Leone Cavicchia; 2024; Environ. Res. Lett. 19 064013; DOI 10.1088/1748-9326/ad44b5