Roman Suligowski, Institute of Geography, The Jan Kochanowski University, Kielce, Poland Introduction
In summer months of recent years (1997-2010) in southern Poland area, enormously high rainfalls have occurred, resulting in a number of flash-floods in the upper Odra and Vistula basins. At that time, numerous local floods have been observed also in Kielce Upland. Those floods covered the area of up to several hundred square kilometers.
The analysis of catastrophic rainfall floods demonstrated that in the second half of 20-th century the area of Kielce Upland was one of a few physicogeographical regions of Poland with the highest frequency of local floods (Dobrowolski et al. 2005). Also the investigations of Ciupa (2002a, b) and Prokop (2006) have confirmed that Kielce Upland is an area particularly predisposed for very intensive storms.
Maximum precipitation values are essential input data for hydrological models that calculate maximum flood hydrographs in small river catchments. Specifying the characteristics of maximum rainfalls that could occur in selected catchment in short time steps (for example - 1 h) is substantial for this modelling. Therefore, the analysis of the maximum precipitation characteristics in one hour intervals in Kielce Upland seems to be justified because of the flood risk they cause.
The statistical analysis used precipitation data for the summer months (V-X) from the years 1961-2000, which was obtained from measurements performed in 6 meteorological stations located in the area of interest: Bodzentyn, Kielce-Sukow, Sandomierz, Skroniow, Suchedniow and Swiety Krzyz. Hourly precipitation sums and time of their occurrence were arranged according to Central European Time. Summarized precipitations in one hour intervals were the basis to create hourly precipitation series. Additionally, for all measuring stations, Annual Maximum Series (AMS) were derived, AMS method being widely described in a number of publications (Flood Studies Report 1975, Sevruk and Geiger 1981, Pilon et al. 1991, Koutsoyiannis and Baloutsos 2000, Alexanderson et al.
2001, Bonnin et al. 2006, Deka et al. 2009).
Study area
Kielce Upland is, from the physicogeographical point of view, a macroregion which occupies the area of 6 800 km2, and is a part of Malopolska Upland (Kondracki 2011) (Fig. 1).
Fig. 1. Physicogeographical location of the study area. 1 – precipitation stations (station names listed in table 2.1), 2 – river, 3 – Kielce Upland boundary, 4 – mesoregion The region described is characterized by diverse terrain morphology, forming low or moderate upland hills (Gielniow Hummock, Sandomierz Upland), and plateaus
(Iłża Foothills, Szydłow Plateau, Suchedniow Plateau). In the central and northern part of the macroregion, among the mentioned hills and plateaus, Swietokrzyskie Mountains are situated, with relative heights of 200-300 meters. A characteristic feature of this mountains relief is the existence of many parallel mountain ranges and ridges (dominant directions are WNW–ESE and NW–SE).
Spatial distribution of annual precipitation totals in the region is the result of dominant directions (NW and W) of incoming humid air masses and almost parallel positions of ridges and hills in Swietokrzyskie Mountains. An important role in local air circulation is played by humid, vast, flat-bottomed valleys and surrounding slope areas on their northern and southern sides. This specific terrain morphology and deforested, agriculturally used areas of Sandomierska Upland enhance heat convection and turbulence processes, which lead to rapid development of clouds and rainfall, especially in the late spring period.
In the meteorological stations of Swietokrzyskie Mountains, an apparent hypsometric gradient of rainfall is also observed. Here, the mean annual precipitation totals (1961-2000) reaches 620-680 mm (Biernat et al. 2004), and in the highest stations - above 800 mm (Swiety Krzyz – 823 mm). On the south east side of Swietokrzyskie Mountains lower precipitation totals are observed (Staszow – 543 mm, Klimontow – 572 mm, Sandomierz – 568 mm), regardless the height of the meteorological stations, which could lead to an assumption that there is a rain shadow. Similar annual precipitation totals were recorded in Iłża Foothills: Osowka – 528 mm, Kurzacze – 575 mm (Suligowski et al. 2009).
Results
The average number of hours, in which the rainfall occurred in pluviographic stations localized in Kielce Upland in the summer half-year (May – October) 1961-2000, varied from 7,5% (Sandomierz) to 10,8% (Swiety Krzyz) of total number of hours in this time.
The analysis of pluviographic data sheets has shown that real precipitation duration in this half-year ranged from 4,6 to 6,5% of total number of hours in the half-year (Fig. 2).
Fig. 2. Percentage of number of hours with precipitation and real precipitation duration at the pluviographic stations of Kielce Upland in the warm half-year (1961–2000)
The analysis covered average duration (tsr), average depth (Hsr) and average intensity (Isr) of hourly precipitation (Fig. 3). Additionally, basic characteristics of the analyzed rainfall are presented in Table 1.
The values of all three mentioned rainfall characteristics were very similar. Apparent divergence in rainfall duration emerged only in addition to the average (from 35 to 4 min) and median (35-50 min). Noticeable divergence occurred also between the highest observed precipitation depth (36,0-61,9 mm) and intensity (1,045-2,500 mm·min-1). The analysis of the average duration of hourly precipitation showed the lowest values in Bodzentyn and Sandomierz. The highest value (above 45 minutes) was recorded in Swiety Krzyz.
A. B.
C.
Fig. 3. Average: precipitation duration tsr
(min), precipitation depth Hsr (mm) and hourly precipitation intensity Isr (mm·min−1) at the pluviographic stations of Kielce Upland in the warm half-year (1961–2000)
Extremely high one hour rainfall occurred on 17.07.1965 in Swiety Krzyz (61,9 mm) and on 15.07.1995 in Skroniow (48,0 mm). Both of those storms took place in the afternoon and were the result of cold weather fronts moving in the axis of cyclonic furrows.
In all measuring stations 75% of hourly precipitation did not exceed 1,2 mm (Table 1).
Relatively short time of precipitation duration (tsr) in Bodzentyn station have found its confirmation in the highest average precipitation intensity. The lowest one hour rainfall intensity 0,029 mm·min−1 occurred in Suchedniow (Table 1). The absolute maximum of rainfall intensity was recorded in Bodzentyn – it was a short, 5-minute storm (9.09.1968).
Distribution of maximum precipitation arranged in series of 1 hour to 24 hours duration showed regularity. The average depth of maximum hourly precipitation (Hsr) apparently increased with the rainfall duration (t) in all measuring stations, especially in Sandomierz. This relation was described by the exponential equation:
Hsr, N = A0 · tB0 where:
A0, B0 – regression coefficient R2–determination coefficient α – significance level
Course of the curves was illustrated in Fig. 4, obtained values of regression coefficient were arranged in Table 2. High values of determination coefficient (R2), ranging from 0,982 (Kielce-Sukow) to 0,999 (Skroniow), at the significance level α = 0,01, showed high reliance of these variables.
Table 1. Statistical characteristics of hourly precipitation in the pluviographic stations of Kielce Upland in the warm half-year (1961–2000)
Precipitation characteristics
Statistical characteristics
Bodzentyn Kielce- Suków Sandomier z Skroniów Suchednió w Święty Krzyż
Duration
Table 2. Values of regression coefficient (A0, B0) and determination coefficient (R2) of average depth of maximum hourly precipitation as a duration function in the pluviographic
stations of Kielce Upland in the warm half-year (1961–2000)
Pluviometric stations A0 B0 R2 α
In addition, distribution of the absolute maximum of hourly precipitation depths in all analyzed duration time periods in individual measuring points was variable.
Admittedly, absolute maximums of hourly precipitation had a tendency to rise with the time duration, but this process was not regular (Fig. 5).
Summary
Hourly precipitation distribution in the function of time showed the existence of two different groups of measuring stations. In the first one, an apparent rise of the maximum hourly precipitation depth was noticeable in the first hours of rainfall duration, while later this process was weakened. To this group belong: Bodzentyn (rise up to 6 hours), Kielce-Sukow and Suchedniow (rise up to 3 hours). Measurements from Suchedniow were a phenomenon, where the maximum 3-hour precipitation depth was the same as for the 18-hour one. The second group of stations, with close to rectilinear distribution of analyzed relation, was formed by: Skroniow and Sandomierz. After a relatively levelized distribution of the maximum precipitation depths in first hours of rainfall duration,
starting from 6 hours in Skroniow and from 12 hours in Sandomierz, an apparent rise up to 24 hours is visible. By contrast, in Swiety Krzyz station, the lowest growth of precipitation depth, up to 10 hours of rainfall duration, was the result of the biggest observed hourly precipitation depth in this point (61,9 mm). In the analyzed period of 1961-2000, only in two described measuring stations 24-hour precipitation sum exceeded 100 mm.
Fig. 4. Average maximum hourly precipitation depths Hsr, N (mm) as a function of precipitation
duration t (h) in the meteorological and hydrometeorological stations of Kielce Upland
in the warm half-year (1961–2000)
Fig. 5. Absolute maximum hourly precipitation depths Hmax, N (mm) of
precipitation duration t (h) in the pluviographic stations of Kielce Upland in
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ЛАНДШАФТНО-ЭКОЛОГИЧЕСКИЙ ПОДХОД В ИЗУЧЕНИИ ГЕОХИМИЧЕСКИХ ОСОБЕННОСТЕЙ ГОРНЫХ ПОЧВ
Григорьева Е.А.1, Нестеров Е.М.2
1 ГБОУ СОШ №10 с углубленным изучением химии, г. Санкт-Петербург
2 РГПУ им. А.И. Герцена, г. Санкт-Петербург