**Appendix A**

Formulas for calculation of the indices used

**RPI:**

$$\text{RPI} = (\text{P}/\text{P}\_{\text{mean}})^\ast 100\%$$

where:

P—precipitation sum in a certain period (e.g., a month; in mm);

Pmean—mean multi-annual precipitation sum for the same period (e.g., a certain month; in mm).

**Selianinov index:**

K = 10P/Σt,

where:

P—monthly precipitation sum

Σt—sum of mean daily air temperatures; the index is calculated only for the months when mean daily air temperature exceeds 10 ◦C

**EQ:**

EQ = TW/P × 1000

where:

TW—temperature of the warmest month in a year P—annual precipitation total

**FAI:**

$$\text{FAI} = 100 \times \text{ (Jul-Aug)} / \text{(P}\_{\text{(May} \cdot \text{Jul)}} + \text{P}\_{\text{(Jul-Aug)}})$$

where:

T (Jul–Aug)—mean air temperature in July and August;

P (May–Jul)—precipitation total from May to July;

P (Jul–Aug)—precipitation total from July to August.

**MT:**

$$\text{MT} = (\text{T}\_{\text{May}} + \text{T}\_{\text{Jun}} + \text{T}\_{\text{Jul}} + \text{T}\_{\text{Aug}})/4$$

where:

TMay, TJun etc.—mean monthly air temperature for May, June etc. **AI:**

AI = P/(TA + 10)

where:

P—annual precipitation total

TA—mean annual air temperature
