## 3 Study Area  
To examine the accuracy of satellite observatory precipitation data in different topographic conditions, we selected four study areas in Iran with diverse topography and within different precipitation zones proposed by [PERSON] [31] (see Figure 1a,b).  
Due to Iran's variable topography and climate conditions, we partitioned the study area to cover provinces such as Kermanshah situated in western Iran. Most of the surface of the province lies within the Zagros Mountains, which forms the western periphery of the Iranian Plateau. Running from southeast to northwest, the nearly parallel broken ridges of the Zagros are highest in the east of the province, and elevation drops progressively towards the west, until the vast plains of Iraq fill the horizon (shown in Figure 1 in zone G5). The climate of the highlands is mild in summer and cold in winter, with heavy snowfall; only the province's western strip belongs to the warm climate. The average temperatures in Kermanshah City are approximately 0 \({}^{\circ}\)C in January and 26 \({}^{\circ}\)C in July. The winds blowing from the Mediterranean Sea carry rainclouds, with an annual precipitation of up to 700 mm in the highlands and about 400 mm at Kermanshah City [32]. The second province, namely Guilan, belongs to zone G8 and includes the northwestern end of the Alborz Mountains and the western part of the Caspian lowlands of Iran. The mountainous belt is cut through by the deep transversal valley of the Sefidrud. To the northwest, the highlands stretch over a continuous watershed and, except for at their northern end, they are over 2000 m high, with three spots over 3000 m. Their eastern and northeastern side is deeply carved by parallel streams flowing down towards the Caspian Sea. Prevailing north-south atmospheric currents, humidified over the Caspian, are forced to a vigorous ascent by the mighty barrier of Alborz and thus are responsible for abundant rainfall on both the plain and the northwestern slope of the mountains. Mean annual precipitation varies between 1200 mm and 1800 mm along the shoreline, decreases towards a sub-humid area in the southwestern corner of the plain, and reaches again very high amounts in the lower part of the mountain, up to 1500-2400 mm including convective rainfall during summer. Bushehr (shown in Figure 1 in zone G4) is just northwest of the Persian Gulf with an arid and subtropical climate. There are two different regions in Bushehr, which are the plains along the Persian Gulf, and the mountain ranges including the Zagros Mountains. Rainfall in autumn and spring usually occurs in the form of convective precipitation, and during the winter in the form of cyclonic storms. The rest of precipitation is in the form of moderate and light rain. Snowfall was unprecedented in this region. The average annual rainfall in Bushehr is approximately 230 mm and the average temperatures are approximately 24 \({}^{\circ}\)C. Tehran (shown in Figure 1 in zone G2), the capital, at the southern slopes of Alborz Mountains with a semi-arid climate, represents the remaining study area. Tehran's climate is largely defined by its geographic location, with the towering Alborz Mountains to its north and the central desert to the south. It can be generally described as mild in spring and autumn, hot and dry in summer, and cold in winter. The highest point of the Tehran province is Damavand peak at an altitude of 5678 m and the lower most area of the province being the plains of Varamin, 790 m above sea level and located to the south-east of the province. The hottest months of the year are from mid-July to mid-September when temperatures average around 28-30 \({}^{\circ}\)C and the coldest months drop to 1 \({}^{\circ}\)C temperature in December to January, and the average annual precipitation is approximately 400 mm, the maximum being during the winter season (see Figure 2a,b).  
Figure 1: (**a**) Spatial distribution of precipitation zones of Iran [31]; and (**b**) Provincial map of Iran and the four selected study regions.