*The choice of the statistical index*

The Standardized Precipitation Index (SPI), developed by [22], is used in this study to characterize meteorological droughts. It has advantages in terms of statistical consistency and the ability to describe both short-term and long-term drought impacts through different time scales [22]. The development of this index is based solely on the use of rainfall as a baseline data to determine wet and dry periods, and to specify their duration and intensity. The probabilistic nature of the SPI index allows it to be comparable between different sites [23].

*Standardized Precipitation Index*

The standardized precipitation index (SPI) [22,24] was developed to quantify the rainfall deficit for multiple time scales that will reflect the impact of drought on the availability of different types of water resources over a given period. It is expressed as follows (Equation (1)):

$$\text{SPI} = (\text{Pi} - \text{Prn}) \text{/S} \tag{1}$$

Pi: Total rainfall over year i (mm); Pm: Average precipitation over the period 1953–2015 (mm); S: Standard deviation of precipitation over the period 1953–2015 (mm).

According to [22], a drought occurs when the SPI is consecutively negative and its value reaches an intensity of −1 or less and ends when the SPI becomes positive. A drought classification is performed according to the SPI values (Table 2).

**Table 2.** Classification of drought sequences according to Standardized Precipitation Index (SPI) [22].

