Intercomparison of daily and monthly precipitation estimates from NASA POWER, CHIRPS and ERA5-Land over Accra, Ghana

Gridded precipitation products are widely used where long, complete gauge records are unavailable, but products built from different observations and models need not agree at the spatial and temporal scales required for local applications. This study intercompares NASA POWER, CHIRPS v2 and ERA5-Land precipitation at a common point over Accra, Ghana (5.6037 N, 0.1870 W) for 1 January 1982 to 31 December 2024. The analysis uses 15,706 complete daily records from each product. ERA5-Land total precipitation required a documented one-day date relabelling because ECMWF accumulations valid at 00 UTC represent the preceding 24 hours; the 31 December 2024 value was completed from the 1 January 2025 00 UTC source record. Pairwise agreement was assessed at daily, monthly and annual scales using mean difference, mean absolute error, root mean square error, Pearson correlation and Spearman rank correlation. Wet-day frequency, wet-day intensity, annual Rx1day and Rx5day were also compared, with wet-day threshold and ERA5-Land timing sensitivity tests. Mean annual totals were 1173.5 mm for NASA POWER, 730.3 mm for CHIRPS and 832.9 mm for ERA5-Land. Daily Pearson correlations were 0.355-0.415, whereas monthly correlations were 0.741-0.847. At a 1 mm/day threshold, wet-day frequencies were 62.2%, 22.8% and 52.2%, respectively. Correct ERA5-Land date alignment increased its daily Pearson correlation with NASA POWER from 0.231 to 0.415 and with CHIRPS from 0.153 to 0.355. The three products reproduce a similar broad seasonal cycle but differ substantially in rainfall amount, event frequency and daily extremes. These differences are product characteristics, not accuracy rankings, because no independent rain-gauge reference is used.