## 2 Material and Methods  
### Study Area and Rainfall Data  
The study area encompassed the central and southern portions of the state of Goias, in the Brazilian midwestern region (Figure 1). The study region is characterized by tropical savanna climate, with a dry season spanning from April to September and a wet season between October and March. Temperatures range from 17 \({}^{\circ}\)C to 31 \({}^{\circ}\)C, whilst the mean annual rainfall amounts vary from 1100 to 1800 mm. As for topography, important altimetric variations are observed, particularly in the northeastern portion of the study area, and the relief can be characterized from smooth to wavy [38].  
Daily rainfall data were retrieved from 50 gauging stations operated by the Brazilian Agency of Water and Sanitation (ANA) (Table 1). These stations, which comprised periods of record of at least 30 years, are located in the southeastern region of the state of Goias (Figure 1). A simplified data quality check was performed for excluding those years with more than 20% of missing data (which indirectly defined the periods of record utilized in the calibration of the models) and those with mean annual rainfall lower than 1000 mm and larger than 2500 mm, which were deemed unreasonable in the study area on the basis of previous research [38].  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & **ANA Code** & **Station** & **Longitude** & **Latitude** & **Altitude** & **Mean Annual** \\  & & & & & **(m)** & **Rainfall (mm)** \\ \hline
1 & 1548003 & Pirenopolis & \(-48.966\) & \(-15.855\) & 768 & 1627 \\
2 & 1648001 & Ponte Alta Anapolis & \(-48.6\) & \(-16.143\) & 883 & 1433 \\
3 & 1649000 & Anicuns & \(-49.943\) & \(-16.465\) & 657 & 1334 \\
4 & 1649001 & Aragoi\(\dot{\rm a}\)nia & \(-49.452\) & \(-16.912\) & 878 & 1538 \\
5 & 1649004 & Goianapolis & \(-49.02\) & \(-16.516\) & 1007 & 1485 \\
6 & 1649006 & Inhumas & \(-49.495\) & \(-16.347\) & 746 & 1078 \\
7 & 1649009 & Ouro Verde de Goi\(\dot{\rm a}\)s & \(-49.198\) & \(-16.219\) & 1077 & 1569 \\
8 & 1649010 & Palmeiras de Goi\(\dot{\rm a}\)s & \(-49.929\) & \(-16.803\) & 605 & 1249 \\
9 & 1649012 & Trindade & \(-49.488\) & \(-16.661\) & 781 & 1280 \\
10 & 1650000 & Cacheira de Goias & \(-50.649\) & \(-16.669\) & 763 & 1376 \\
11 & 1650001 & Corrego do Ouro & \(-50.557\) & \(-16.298\) & 565 & 1341 \\
12 & 1650002 & Isrraelandia & \(-50.906\) & \(-16.316\) & 411 & 1481 \\
13 & 1650003 & Turvania & \(-50.133\) & \(-16.609\) & 637 & 1476 \\
14 & 1651000 & Caiaponia & \(-51.799\) & \(-16.95\) & 700 & 1382 \\
15 & 1651001 & Iporáá & \(-51.083\) & \(-16.428\) & 605 & 1650 \\
16 & 1748004 & Marzagão & \(-48.683\) & \(-17.983\) & 812 & 1438 \\
17 & 1749000 & Edeía (Alegrete) & \(-49.93\) & \(-17.341\) & 590 & 1278 \\
18 & 1749001 & Fazenda Boa Vista & \(-49.691\) & \(-17.106\) & 550 & 1459 \\
19 & 1749002 & Jovi\(\dot{\rm a}\)nia & \(-49.626\) & \(-17.809\) & 845 & 1485 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Rainfall gauging stations utilized in the study.  
Figure 1: Study area and location rainfall gauging stations utilized in this study.  
For assessing the predictive abilities of the regression-based models for filling daily missing data, 6 gauging stations were randomly selected from the ensemble as testing sites (Figure 1). Next, a complete water year of data, spanning from 1 September 2016 to 31 August 2017, was discarded, and the corresponding estimates were obtained with the MLR and the SLR models, as explained in Section 2.3, and imputed in the original time series. We note that this water year was selected for analyses because, along the interval in which the ground-based information overlapped the IMERG-GPM product (i.e., from 2014 onwards), this was the only period in which no missing data were verified at the \"donor\" sites utilized for both simple and multiple linear regression. A similar reasoning was utilized for the monthly time scale. We note, however, that the neighbor gauging stations utilized as \"donor\" sites may be different for these distinct time scales.