248
E. Tomaszewski and M. Kozek
Fig. 12.11 Seasonal concentration date of hydrological drought in Poland (1985–2014). CI – index
of concentration date of hydrological drought: 1 – 1–15 November, 2 – 16–31 December, 3 – 16–31
July, 4 – 1–15 August, 5 – 16–31 August, 6 – 1–15 September, 7 – 16–30 September, 8 – 1–15
October, 9 – 16–31 October; 10 – CI changes in larger transit rivers (outside the map scale), the
legend colour according to the periods: 1–9; C – frequency coefficient of the seasonal concentration
date, IS – seasonality index of hydrological drought
occurrence of river low flows in the region as well as recession and renewal of water
resources. The only exceptions are the Soła and a section of the upper Vistula, where
water management activities in the Soła cascade and the Goczałkowice Reservoir
lower SI down to 33–35%.
Typical concentration date of hydrological drought in the Sudeten rivers precedes
that in the Carpathian watercourses by ca. 15 days. However, mean CI in the rivers
of the Kłodzko Valley, the Karkonosze Mountains, and the Kaczawskie Mountains
falls in the second half of September, thus suggesting a higher contribution of winter
low flows than in the other watercourses of the region. A delay in the seasonal
concentration date in the Nysa Kłodzka due to the effects of the Otmuchów and Nysa
reservoirs is also clearly visible. These effects are strong enough to cause a similar
E. Tomaszewski and M. Kozek
Fig. 12.11 Seasonal concentration date of hydrological drought in Poland (1985–2014). CI – index
of concentration date of hydrological drought: 1 – 1–15 November, 2 – 16–31 December, 3 – 16–31
July, 4 – 1–15 August, 5 – 16–31 August, 6 – 1–15 September, 7 – 16–30 September, 8 – 1–15
October, 9 – 16–31 October; 10 – CI changes in larger transit rivers (outside the map scale), the
legend colour according to the periods: 1–9; C – frequency coefficient of the seasonal concentration
date, IS – seasonality index of hydrological drought
occurrence of river low flows in the region as well as recession and renewal of water
resources. The only exceptions are the Soła and a section of the upper Vistula, where
water management activities in the Soła cascade and the Goczałkowice Reservoir
lower SI down to 33–35%.
Typical concentration date of hydrological drought in the Sudeten rivers precedes
that in the Carpathian watercourses by ca. 15 days. However, mean CI in the rivers
of the Kłodzko Valley, the Karkonosze Mountains, and the Kaczawskie Mountains
falls in the second half of September, thus suggesting a higher contribution of winter
low flows than in the other watercourses of the region. A delay in the seasonal
concentration date in the Nysa Kłodzka due to the effects of the Otmuchów and Nysa
reservoirs is also clearly visible. These effects are strong enough to cause a similar