*2.5. Method*

#### Performance Evaluation of SPPs GPM IMERG

The homogeneity of the rain gauge measurements was verified through the nonparametric CUSUM test using the TREND program (https://toolkit.ewater.org.au/Tools/ TREND, accessed on 11 October 2022). TREND is designed to facilitate statistical analysis of trends, changes and randomness in hydrological and time series data [27]. Missing data were filled in using the random forest method incorporated in the MICE (Generates Multivariate Imputations by Chained Equations) package for the R project [28]. Homogeneity was checked with monthly data after filling in the missing data [29,30].

Comparisons between IMERG and rain gauges were performed using a pixel-topoint approach as performed in previous studies [14]. This is based solely on observed precipitation measurements.

In effect, three continuous statistical metrics were used to evaluate performance (Table 1). These metrics aim to quantitatively compare the performance of IMERG measurements with rain gauge measurements. The evaluations were performed with different temporal variations, that is, daily, monthly and annual. The lack of rain gauge measurements in some areas of the LTB could limit the ability to fully evaluate IMERG measurements.


**Table 1.** Statistical performance metrics.

*S* is the satellite measurement; *O* the rain gauge measurement; *S* and *O* denote the mean values of *S* and *O* respectively; *n* indicates the number of data pairs.
