Urban Water Security and Hydro-Climatic Trends: The Case of Krakow (Poland)

In 2018, over half of the world’s population lived in urban areas, and this figure is expected to continue to increase over the next 25 years. Water security in growing urban areas is becoming increasingly important. Current global warming can pose additional challenges for sustainable water resource management. In this study, the city of Krakow (Poland) and its water supply system were considered. The MK and Spearman tests were used to detect trends in the studied data and the residuals from the Ensemble Empirical Mode Decomposition (EEMD) method. The analyses indicate that for 1971–2020, significant increasing trends (p < 0.05) in annual air temperature (0.36–0.46 °C/decade) were accompanied by significant trends in annual precipitation, with differences in direction and intensity (approx. −8 and 30 mm/decade). Similarly, significant trends in annual river flow for the two main sources of drinking water for Krakow (the Raba and Rudawa rivers) differed in both direction and intensity (0.51 m∙s−1 and −0.05 m∙s−1, respectively). The study also examined trends for individual months of the year, which largely explained the observed annual trends. Furthermore, the results of cross-correlation and autocorrelation analyses suggest that the identified decreasing trend in the Rudawa flow may be partly related to the significantly reduced underground recharge in the Rudawa catchment. The information obtained in this work can be used for more realistic and sustainable water resource management and urban-water-security planning.