Małgorzata Kijowska-Strugała

Abstract

Ongoing changes in climate (increases in air temperature, changes in the distribution of precipitation over the year) exert an influence on the genesis of watercourse supply, as expressed in relation to the three sources represented by rain, snowmelt and groundwater. In that context, to the work detailed here had as its aim the spatial and temporal determination of the structure (and trends) characterising winter hydrological half‑year runoff from selected river catchments in the Western Carpathians, in the assumed circumstances of a changing climate and growing anthropopressure. To ensure adequate characterisation of the situation, the study took in four drainage basins, representing both the Beskid Mountains as such (in the catchments of the Soła and Osława), as well as their Foothills (in the catchments of the Skawinka and Stobnica). It was in relation to these four watercourses that the nature of the supply was determined over the 40‑year (1981‑2020) period, in regard to mean daily flows in the profiles closing the selected catchments. Interpretation of the nature of supply was made possible by meteorological data concerning precipitation totals and types, thickness of snow cover and air temperature. Mean values for winter half‑year precipitation totals (P_WHY) ranged from 226.5 mm (Skawinka) to 440.6 mm (Soła). The share of annual total precipitation (P_A) accounted for by P_WHY ranged on average from 30.1% (Skawinka) to 43.9% (Soła). The average winter half‑year totals for snowfall (SF) in the study period ranged from 104.8 mm (Skawinka) to 313.4 mm (Soła). It was thus in the latter two catchments that the extreme shares of overall precipitation in the winter hydrological half‑year accounted for by snowfall were to be found, at 30.9% and 43.7% respectively. Average values for runoff in the winter half‑year (H_WHY) ranged from 150.3 mm (in the Skawinka catchment) to 348.8 mm (in the Osława catchment), while the share of annual outflow (H_A) accounted for by H_WHY averaged between 50.9% (Soła) and 60.4% (Stobnica). The 1981‑2020 period was not found to be characterised by any statistically significant directions of change in H_WHY, though negative H_WHY trends could be noted for all the catchments studied in regard to the years since 2000, with the range of relevant values being 4‑7 mm∙year^‑1. The 4 catchments showed a diversity of dominant sources of supply in H_WHY. In the case of the Soła, it was supply by snowmelt that took the largest (40.1%) share, while in the Osława supply by rainfall prevailed (at 38.0%), and in the Skawinka supply by groundwater (on 43.4%). The catchment of the Stobnica featured more or less equal shares of alimentation by precipitation and ground supply (at around 36‑38% in each case). All 4 catchments manifested declines over time in snowmelt‑induced runoff, albeit with these ranging from 0.3 mm∙yr^‑1 (Skawinka) to 1.2 mm∙yr^‑1 (Soła), while the role of supply involving groundwater is seen to be on the increase by between 0.17 mm∙yr^‑1 (Skawinka) and 1.04 mm∙yr^‑1 (Osława). In addition, the trend for increase in ground supply was found to be several times more distinct in the catchments of the Beskids as such, compared with their foothills, with marked spatial differentiation being the feature. In the catchments present in the foothills, the increase in ground supply proved similar, regardless of location.

Changes in land cover can be regarded as affecting the magnitudes of values for the α runoff coefficient for the WHY. Average values were lower in the foothills catchments: Stobnica (64%) and Skawinka (67%). In the catchments located in the Beskids per se, the average a values proved to be higher, with differences between catchments also greater (Soła on 72% and Osława on 94%).The negligible change over the study period when it came to the Skawinka catchment could be related to a 5‑fold increase in built‑up areas, even as the most‑major reduction in the runoff coefficient noted in the catchment of the Stobnica, was attributable to a reduction in the share of arable land from 61.0% (in 1990) to 46.4% (in 2018), with a concomitant increase in forest cover from 32.1 to 43.4%. Study of the α runoff coefficient attributable to rain revealed regional variations. While a downward trend characterised the eastern part of the research area (i.e. the Stobnica and Osława catchments), the trend was upward in the western part (where the Soła is located). It was notable how a downward trend for values of the α runoff coefficient either arose or intensified in all catchments across the 1999‑2020 sub‑period. Furthermore, the whole 40‑year study period did witness a downward trend for values of the coefficient for runoff attributable to snowfall in all 4 catchments, with this intensifying further in the 1999‑2020 sub‑period (hence in the same way as with the coefficient for rain‑related runoff).

The research results presented here attest to progressive increases in air temperature affecting precipitation types and totals, and thus also activity as regards the differentforms of watercourse supply in water. To this extent the working hypothesis established gained confirmation empirically, with demonstrably declining magnitudes and shares of river runoff accounted for by the thawing of snow and ice.

Keywords: snowfall, river runoff, winter hydrological half-year, Western Carpathians

Witold Bochenek [witold.bochenek@zg.pan.krakow.pl], Instytut Geografii i Przestrzennego Zagospodarowania im. S. Leszczyckiego PAN
Małgorzata Kijowska-Strugała [mkijowska@zg.pan.krakow.pl], Institute of Geography and Spatial Organization Polish Academy of Sciences 38-311 Szymbark 430: Poland

Citation

APA: Bochenek, W., & Kijowska-Strugała, M. (2022). Zmiany w strukturze odpływu wody ze zlewni karpackich w półroczu hydrologicznym zimowym w latach 1981‑2020. Przegląd Geograficzny, 94(4), 503-519. https://doi.org/10.7163/PrzG.2022.4.5
MLA: Bochenek, Witold, and Kijowska-Strugała, Małgorzata. "Zmiany w strukturze odpływu wody ze zlewni karpackich w półroczu hydrologicznym zimowym w latach 1981‑2020". Przegląd Geograficzny, vol. 94, no. 4, 2022, pp. 503-519. https://doi.org/10.7163/PrzG.2022.4.5
Chicago: Bochenek, Witold, and Kijowska-Strugała, Małgorzata. "Zmiany w strukturze odpływu wody ze zlewni karpackich w półroczu hydrologicznym zimowym w latach 1981‑2020". Przegląd Geograficzny 94, no. 4 (2022): 503-519. https://doi.org/10.7163/PrzG.2022.4.5
Harvard: Bochenek, W., & Kijowska-Strugała, M. 2022. "Zmiany w strukturze odpływu wody ze zlewni karpackich w półroczu hydrologicznym zimowym w latach 1981‑2020". Przegląd Geograficzny, vol. 94, no. 4, pp. 503-519. https://doi.org/10.7163/PrzG.2022.4.5