*2.1. Study Area*

Iran covers an area of about 1.648 million km2, located between 44–64◦ East and 25–40◦ North in the eastern part of the Middle East [31]. The country is bordered by Azerbaijan, Armenia, Turkmenistan, and the Caspian Sea to the north; Afghanistan and Pakistan to the east; Oman Sea and Persian Gulf to the south; and Turkey and Iraq to the west (Figure 1a). The temporal and seasonal distribution of precipitation is governed by the interaction of the tropical air mass from the Red Sea, the Mediterranean low pressure, and the Siberian and western high pressures [31].

**Figure 1.** (**a**) Map of Iran and (**b**) distribution of rain gauges with altitude.

Half of Iran's land surface is mountainous, a quarter is covered by fertile and productive plains, and the final quarter by salty arid desert [32]. Zagros and Alborz are the two main mountainous areas, which are located along the western and northern borders of the country, respectively. These mountain ranges prevent much of the available humidity, mostly initiating from the Mediterranean and Caspian Sea in the West and North of the country, from reaching the interior parts, so singularly govern the spatial patterns of precipitation across Iran [31,33] (Figure 1b). As a result, the central parts of the country and the southwestern areas of the Caspian Sea receive an average of 100 and 1800 mm year-1, respectively [31].

Iran encircles a variety of climates, which range from extremely to subtropical dry in the central to eastern parts of the country, wet to extremely wet in the coastal plains of the Caspian Sea, relatively wet in some western areas, and arid to semiarid zones in the rest of the country [34]. The Mediterranean Synoptic System is the dominant weather system in the country, where the rainy season is from October to April, with a peak in December. The driest month is July.
