FIGURE 1.

FIGURE 2.

FIGURE 3.

FIGURE 4.

Values of parameter α for estimating the empirical exceedance probability
| α | Comment | Reference |
|---|---|---|
| 0.4 | Recommended for hydrometeorological data; provides a balanced estimation for both small and large sample sizes | Cunnane (1978) |
| 0.5 | Universal, but performs poorly at the tails (rare events). Frequently used in engineering calculations, but may overestimate probabilities at the distribution tails | Hazen (1914) |
| 0 | Simple and widely used, but may introduce bias | Weibull (1939) |
| 0.3 | Based on Soviet tradition, but often inadequate in mountainous regions | Chegodayev (1955) |
| 0.375 | Used in statistics; closer to the normal distribution | Blom (1958) |
| ≈0.333 | Sometimes applied in scientific publications | Tukey (1962) |
Statistical characteristics of annual precipitation sum data series observed in the period of 2000–2023 by stations
| Statistical test value | Meteorological station | ||||
|---|---|---|---|---|---|
| Almaty | Shymbulak | Mynzhylky | BAL | Kemen | |
| Independence | |U| = 1.5 | |U| = 0.83 | |U| = 0.38 | |U| = 0.24 | |U| = 1.23 |
| Stationarity | |K| = 1.76 | |K| = 1.32 | |K| = 0.74 | |K| = 0.86 | |K| = 0.82 |
| Homogeneity | |W| = 1.01 | |W| = 0.22 | |W| = 1.01 | |W| = 0.72 | |W| = 0.43 |
Probability density functions, equations, and descriptions
| Distribution | Probability formula | Typical use | Advantages | Limitations |
|---|---|---|---|---|
| Gumbel |
| Maxima (annual peak precipitation) | Simple, widely used in hydrology | May underestimate tail behavior (underpredict extremes) |
| Generalized extreme value (GEV) |
| Flexible for maxima with different tail behavior | Accounts for skewness and heavy tails | More complex parameter estimation |
| Log--Pearson Type III |
| Flood and rainfall extremes | Recommended by the U.S. Water Resources Council | Sensitive to sample size and outliers |
| Pearson Type III |
| General hydrologic use | Good fit for varied data with skewness | Assumes continuous positive data |
| Lognormal |
| Precipitation intensities | Suitable for moderately skewed data | Sensitive to zero and near-zero values |
| Normal |
| Not recommended for extremes | Easy to interpret | Poor fit for skewed and extreme event data |
Geographic characteristics of meteorological stations and descriptive statistics of annual precipitation sum data series observed in the period of 2000–2023
| Geographical coordinate | Meteorological station | |||||
|---|---|---|---|---|---|---|
| Almaty | Shymbulak | Mynzhylky | BAL | Kemen | ||
| Latitude (N) | 43°24′ | 43°12′ | 43°08′ | 43°05′ | 43°18′ | |
| Longitude (E) | 76°93′ | 77°08′ | 77°07′ | 76°98′ | 76°96′ | |
| Descriptive statistics of annual precipitation sum | ||||||
| Minimum [mm] | 489 | 687 | 668 | 636 | 615 | |
| Maximum [mm] | 1,010 | 1,480 | 1,240 | 1,320 | 1,360 | |
| Mean (M) [mm] | 678 | 968 | 875 | 866 | 904 | |
| Standard deviation (SD) [mm] | 135 | 196 | 154 | 165 | 179 | |
| Coefficient of variation (CV) | 0.198 | 0.202 | 0.176 | 0.190 | 0.198 | |
| Skewness (γ1) | 0.995 | 1.34 | 0.739 | 1.12 | 0.632 | |
| Kurtosis coefficient (γ2) | 3.24 | 4.19 | 2.87 | 3.60 | 2.88 | |
| Data length [year] | 2000–2023 (24 years) | 2001–2023 (23 years) | 2000–2023 (24 years) | 2000–2023 (24 years) | 2000–2023 (24 years) | |
Design rainfall intensities for return periods of 1%, 2% and 10% calculated by selected empirical probability functions applied to precipitation annual sum time series in meteorological stations of Almaty city
| Meteorological station | Design rainfall for return periods calculated by selected probability distribution functions [mm] | ||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| exp. | GEV | normal | lognormal | gamma | |||||||||||
| 10% | 2% | 1% | 10% | 2% | 1% | 10% | 2% | 1% | 10% | 2% | 1% | 10% | 2% | 1% | |
| Almaty | 936 | 1,250 | 1,390 | 851 | 1,020 | 1,090 | 851 | 955 | 991 | 849 | 983 | 1030 | 845 | 964 | 1,010 |
| Shymbulak | 1,350 | 1,820 | 2,030 | 1,210 | 1,480 | 1,590 | 1,220 | 1,370 | 1,420 | 1,210 | 1,400 | 1,470 | 1,210 | 1,380 | 1,440 |
| Mynzhylky | 1,160 | 1,500 | 1,650 | 1,070 | 1,260 | 1,330 | 1,070 | 1,190 | 1,230 | 1,070 | 1,230 | 1,280 | 1,070 | 1,200 | 1,250 |
| BAL | 1,180 | 1,570 | 1,730 | 1,080 | 1,310 | 1,410 | 1,080 | 1,200 | 1,250 | 1,070 | 1,230 | 1,290 | 1,070 | 1,210 | 1,270 |
| Kemen | 1,300 | 1,780 | 1,990 | 1,140 | 1,330 | 1,400 | 1,130 | 1,270 | 1,320 | 1,140 | 1,330 | 1,400 | 1,130 | 1,290 | 1,350 |
Comparison of the analysis for the meteorological station based on AIC, BIC, P(Mi|x), χ2 test, and p-value criteria
| Meteorological station | Parameter | Probability distribution type | ||||
|---|---|---|---|---|---|---|
| exp. | GEV | normal | lognormal | gamma | ||
| Almaty | AIC | 305.7 | 304.2 | 306.4 | 303.2 | 304.0 |
| BIC | 308.1 | 307.7 | 308.7 | 305.6 | 306.3 | |
| P(Mi|x) | 11.2 | 13.4 | 8.2 | 39.9 | 27.1 | |
| χ2 | 9.2 | 2.8 | 7.5 | 5.1 | 5.1 | |
| p | 0.05 | 0.41 | 0.11 | 0.27 | 0.27 | |
| Shymbulak | AIC | 311.4 | 307.2 | 311.0 | 306.9 | 309.2 |
| BIC | 313.7 | 310.6 | 313.3 | 309.2 | 310.2 | |
| P(Mi|x) | 4.5 | 21.1 | 5.5 | 43.4 | 25.3 | |
| χ2 | 7.1 | 2.8 | 4.7 | 1.6 | 3.4 | |
| p | 0.13 | 0.41 | 0.32 | 0.80 | 0.48 | |
| Mynzhylky | AIC | 310.0 | 312.2 | 312.8 | 310.8 | 311.2 |
| BIC | 312.4 | 315.7 | 315.2 | 313.1 | 313.6 | |
| P(Mi|x) | 37.4 | 7.1 | 9.2 | 25.8 | 20.4 | |
| χ2 | 8.6 | 4.0 | 2.8 | 4.5 | 4.5 | |
| p | 0.07 | 0.26 | 0.58 | 0.33 | 0.33 | |
| BAL | AIC | 315.1 | 312.8 | 316.0 | 312.5 | 313.4 |
| BIC | 317.4 | 316.3 | 318.4 | 314.9 | 315.8 | |
| P(Mi|x) | 10.9 | 18.8 | 6.7 | 38.9 | 24.5 | |
| χ2 | 12.7 | 5.7 | 1.6 | 5.1 | 5.1 | |
| p | 0.01 | 0.12 | 0.79 | 0.27 | 0.27 | |
| Kemen | AIC | 326.0 | 320.3 | 320.2 | 318.5 | 318.5 |
| BIC | 328.3 | 323.9 | 322.5 | 320.8 | 320.8 | |
| P(Mi|x) | 0.9 | 8.6 | 16.9 | 39.3 | 34.1 | |
| χ2 | 11.0 | 6.3 | 4.00 | 8.0 | 6.3 | |
| p | 0.02 | 0.09 | 0.40 | 0.08 | 0.17 | |
