Abstract
A range of in situ, satellite and reanalysis products on a common daily 1° × 1° latitude/longitude grid were extracted from the Frequent Rainfall Observations on Grids database to help facilitate intercomparison and analysis of precipitation extremes on a global scale. 22 products met the criteria for this analysis, namely that daily data were available over global land areas from 50°S to 50°N since at least 2001. From these daily gridded data, 10 annual indices that represent aspects of extreme precipitation frequency, duration and intensity were calculated. Results were analysed for individual products and also for four cluster types: (i) in situ, (ii) corrected satellite, (iii) uncorrected satellite and (iv) reanalyses. Climatologies based on a common 13-year period (2001–2013) showed substantial differences between some products. Timeseries (which ranged from 13 years to 67 years) also highlighted some substantial differences between products. A coefficient of variation showed that the in situ products were most similar to each other while reanalysis products had the largest variations. Reanalyses however agreed better with in situ observations over extra-tropical land areas compared to the satellite clusters, although reanalysis products tended to fall into ‘wet’ and ‘dry’ camps overall. Some indices were more robust than others across products with daily precipitation intensity showing the least variation between products and days above 20 mm showing the largest variation. In general, the results of this study show that global space-based precipitation products show the potential for climate scale analyses of extremes. While we recommend caution for all products dependent on their intended application, this particularly applies to reanalyses which show the most divergence across results.
Highlights
Precipitation indices are widely used in the climate literature to assess global and regional trends in precipitation extremes (e.g. Alexander et al 2006, Donat et al 2013, Sillmann et al 2013, Zhou et al 2016)
Overall extreme precipitation indices in reanalyses tend to be less spatially consistent than the in situ and satellite datasets with, for example, tropical Africa being very wet in some reanalyses and much drier in others
We conclude that taken on global average products can appear reasonably similar in terms of their spatial patterns but in terms of the range of values of precipitation extremes over space and time they can have quite different forms
Summary
Precipitation indices (e.g. annual wettest day, consecutive dry days, days above 20 mm) are widely used in the climate literature to assess global and regional trends in precipitation extremes (e.g. Alexander et al 2006, Donat et al 2013, Sillmann et al 2013, Zhou et al 2016). While indices limit some inferences regarding the full distribution of daily data, they offer a mechanism to increase the quality and amount of data that can be shared among researchers to examine extremes (e.g. Alexander 2016, Alexander et al 2019 (in this Focus Collection)). Most of the literature to-date has been primarily focused on in situ data because this has offered a sufficiently long record to determine climate-scale trends spatial coverage is limited. Some satellite records are reaching several decades long, potentially making them suitable for long-term global assessment (Roca et al 2019, others). Reanalysis products are available that have been assessed for their
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