Uncertainty in different precipitation products in the case of two atmospheric river events

April 28, 2021

Alexandre Ramos, a researcher at the Institute Dom Luiz at the University of Lisbon, recently published a paper (Ramos et al., 2021) in Environmental Research Letters with several co-authors including two from CW3E, Anna Wilson and F. Martin Ralph.

This study uses the Frequent Rainfall Observations on GridS (FROGS) database, which includes satellite, ground-based, and reanalysis daily precipitation products on a 1^ox 1^o grid. This is the first time this database has been evaluated using atmospheric rivers (ARs). For the ARs examined here, in two different Mediterranean climates (California and the Iberian peninsula), results indicated that products based on in situ observations were most skilled at obtaining accurate precipitation estimates, while satellites were least skilled (Figure 1). Overall, there remains significant underestimation of precipitation, with mean absolute percentage errors reaching up to 100% in the California AR. This study points out the need to develop higher resolution and accurate gridded products to capture the spatial and temporal properties and variability of precipitation due to ARs.

This study contributes to the goals of CW3E’s 2019-2024 Strategic Plan to support Atmospheric River (AR) Research and Applications, and Monitoring and Projections of Climate Variability and Change, by assessing whether existing precipitation observations are sufficient to understand extreme atmospheric rivers.

Figure 1: Error statistics for precipitation linked to the atmospheric river cases in (a) Portugal, and (b) California. The error measures include bias, MAE, MAPE and RMSE, and were computed pooling together all data for all the groups of the regular gridded products (pool_all), and additionally computing the average observational value for each gridpoint and then compared directly with the regular gridded products values (av). PT and US stand for Portugal and western US, respectively. RE indicates reanalysis products; SG indicates satellite and gauge; SO indicates satellite only products; and GO indicates gauge only. (Figure 6 from Ramos et al., 2021).

Ramos, A.M., Roca, R., Soares, P.M.M., Wilson, A.M., Tigo, R.M. & Ralph, F.M. (2021). Uncertainty in different precipitation products in the case of two atmospheric river events. Environmental Research Letters, 16, 045012, https://doi.org/10.1088/1748-9326/abe25b.