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History of modifications

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Version Date Description of modification Chapters / Sections 1 22/03/2019 initial All 1.1 26/03/2020 Previous assessment extended to first 4 three-monthly delivery batched of ICDR; GPCP–NIMROD comparison included; PACRAIN comparison extended (atoll-only); Literature review extended All 1.2 08/03/2021 Previous assessment extended to ICDR deliveries until 09/2020 (12/2019 where TMPA decommissioning limits the joint GPCP/TMPA/ERA5 analysis) Reference for KPI assessment from 01/2020 (new subsections 2.2.1.1.x) 1, 2

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table1 table1

Table 1: Basic statistics for the differences between the GPCP and the reference datasets for the temporal coverage of both the TCDR and the ICDR, i.e. the black and blue curves in Figure 4E,F. For the minimum and maximum differences, those GPCP fields that have only zeros and missing values (Section 2.1) and which thus result in a spatial average of zero are discarded. The minimum and maximum differences, the mean, the quantiles (2.5%, median, 97.5%), and the RMS deviations are in mm/d. The RMS is with respect to the mean value. The unit of the slopes is mm/d/decade. In the second to last column, we give the percentage of values that meet the initial target requirement for the KPI accuracy of 0.3 mm/d.

The significantly larger average precipitation in ERA5 compared to GPCP will be analysed in detail in Sections 2.2.2, in which spatial patterns are compared, and 2.2.3, in which the dependence on latitude is briefly discussed.

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Table 2: Basic statistics for the differences between the GPCP and the reference datasets for the temporal coverage of the TCDR (until 12/2017), i.e. the datasets shown as black and blue curves in Figure 4E,F until 12/2017. For the minimum and maximum differences, those GPCP fields that have only zeros and missing values (Section 2.1) and which thus result in a spatial average of zero are discarded. The minimum and maximum differences, the mean, the quantiles (2.5%, median, 97.5%), and the RMS deviations are in mm/d. The RMS is with respect to the mean value. The unit of the slopes is mm/d/decade. In the second to last column, we give the percentage of values that meet the initial target requirement for the KPI accuracy of 0.3 mm/d.

Stability in this context is the absolute slope of a linear regression of the timeseries of differences in spatially averaged values. All absolute values remain below the initial performance target of 0.034 mm/d/dec (last column in Table 2).

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Table 3: Number of per time slice and per grid cell comparisons shown in the histograms of Figure 8, as well as the mean and RMS deviation (in mm/d each).

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Figure 8: Histograms of differences between the GPCP datasets and the respective reference datasets. The differences are computed for every available time step and every GPCP grid cell. Table 3 lists statistics of these distributions. The histogram bins are 0.5 mm/d wide. 

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table4 table4

Table 4: Results of the per-time slice and per-grid cell comparison of GPCP and NIMROD. Listed are the numbers of available data pairs (i.e. grid cells and times for which GPCP and NIMROD are available simultaneously), as well as the mean, 2.5- and 97.5 percentiles, RMS deviation, and – in the case of the monthly product – mean GPCP uncertainty (in mm/d each).

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Figure 11: Temporal evolution of spatially averaged values from the GPCP and NIMROD datasets, and respective differences, for the monthly (A) and daily (B) products. Similar to the temporal means (Figure 10), a grid cell only contributes to the spatial average at a given time, if both the GPCP and the NIMROD product are available at that time in that grid cell (see the varying number of contributing grid cells at the bottom of each sub-figure).

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Table 5: Statistics of the GPCP/PACRAIN comparison as shown in Figure 12 and Figure 13 (rows labelled as 'all'). All values are differences between the respective GPCP product, averaged over all grid cells in which PACRAIN stations are available at a given time, and the respective PACRAIN average over all available stations at a given time. Minimum, maximum, and mean values as well as the RMS deviation from the mean value and the mean GPCP uncertainty are in mm/d. Also included are rows where the statistics are given for the subset of temporal instances where a minimum number of PACRAIN stations is exceeded, and for the separate atoll-only comparison where only the subset of PACRAIN stations situated in atolls and the respective GPCP grid cells have been averaged for each time step. Note that these latter '> n PACRAIN stations' rows (with n=100, n=120) provide the statistics to a sub-set of the timeseries to which the 'all' rows provide respective statistics (i.e., filtering out specific points in time, depending on overall station availability), whereas the 'atoll stations only' provide statistics to the separate timeseries that is compiled by averaging over a smaller amount of stations and GPCP grid cells in the first place (i.e., filtering out specific stations/grid cells). Consequently, it is not contradictory that the numbers of values are equal in the 'all' and 'atoll stations only' rows, and that minimum/maximum values are lower/higher in the 'atoll stations only' rows.

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Comparison with OceanRAIN

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You, Q.; Min, J.; Zhang, W. et al., 2015: Comparison of multiple datasets with gridded precipitation observations over the Tibetan Plateau. Clim. Dyn., 45:791. https://doi.org/10.1007/s00382-014-2310-6.

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This document has been produced in the context of the Copernicus Climate Change Service (C3S). The activities leading to these results have been contracted by the European Centre for Medium-Range Weather Forecasts, operator of C3S on behalf of the European Union (Delegation agreement signed on 11/11/2014). All information in this document is provided "as is" and no guarantee or warranty is given that the information is fit for any particular purpose. The users thereof use the information at their sole risk and liability. For the avoidance of all doubt, the European Commission and the European Centre for Medium-Range Weather Forecasts have no liability in respect of this document, which is merely representing the author's view.

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