Influence of meteorological drought on environmental flows in mountain catchments

Abstract

This study investigates the course of atmospheric drought to the response of the water resources availability taking into account the constraints arising from the need to maintain adequate environmental flows (e-flow) releases. For that purpose, eight catchments of southern Poland, namely, Skawa and Dunajec sub-basins (i.e., upper Vistula basin), were considered as study cases. The analysis was carried out as follows: trend analysis of streamflow rate and mean annual precipitation; determination of e-flows using the following methods: 25% mean multi-year flow (25%MAF), the minimum acceptable flow determined by Kostrzewa's method (Qn), the median of monthly mean flows (Qmed), flow with a guarantee of 90% (Q90%), and minimum mean 7-day flow with a recurrence period of 2 years (7Q2). The standardized precipitation index (SPI) and normal precipitation index (PNI) were used as meteorological drought indices to determine the relationship between meteorological drought and e-flow releases. The results revealed a lack of significant trends in annual precipitation and a significantly decreasing trend of streamflow rate in the Skawa sub-basin. For the Dunajec sub-basin, the significantly decreasing trend in streamflow was detected only for Biała; a significant increasing trend was for Biała and Sękówka catchments. The highest values of e-flows were obtained for Qmed and the lowest for 7Q2. The SPI values resulting from the multi-year analysis show that most of the period was dominated by meteorological drought. According to PNI values, the dominant period was normal years. Extremely wet years were found sporadically and were triggered by extremely high precipitation over southern Poland, like in 2010. The results demonstrate that the highest correlations between the SPI, PNI, and e-flows were obtained for 25%MAF and Qmed. Moreover, results exhibited a weak correlation between SPI, PNI values, streamflow rate, and a medium to high correlation for e-flows. The findings from this study showed that SPI and PNI indices could be a helpful tool in water resources management and planning, especially in predicting the influence of droughts on the e-flows deficit.