2.2.2. Ground-Based Precipitation

The ground-based precipitation data were obtained from the I.R. IRAN Meteorological Organization (IRIMO). IRIMO is responsible for recording hourly and daily precipitation and quality control is carried out before releasing recorded data to the user's community across the country [33]. This dataset is considered as the most reliable precipitation data source in Iran [31].

Although these data are freely available for research purposes, the data are not available online and should be obtained in person. In total, 403 meteorological synoptic stations were under operation across the country, of which only 370 stations had at least one year of daily records and were selected for this study. Perfectly, 368 and 349 of the selected stations had at least two and three years of daily records for the studied period, respectively, between April 2014 and December 2017. While GPM IMERG data were historically complete (without missing data), the selection of this period is attributed to the availability of both satellite and rain gauge precipitation datasets. Figure 1b shows the distribution of the synoptic stations throughout the country.

#### *2.3. Evaluation Processes and Indices*

#### 2.3.1. Data Preparation

The GPM IMERG products that cover the entire country from 1 April 1 2014 to 31 December 2017 at daily and monthly time scales and 0.1◦ × 0.1◦ (about 11 km on the equator) resolution were acquired. The RT-H5 file format, in which RT refers to real-time and H5 denotes an HDF5 file, was converted to the ASCII format and all days were stacked by a written algorithm in R programming language. The precipitation was converted to mm day−<sup>1</sup> for all IMERG products for the purpose of consistency with ground-based data. As for the point (rain-gauges) to pixel (IMERG products) comparison, each IMERG pixel corresponding to single rain gauge locations was extracted. The extracted IMERG data and the corresponding rain gauge data for daily and monthly time scales were then used in the analyses.
