water Article Spatial Differentiation of the Maximum River Runoff Synchronicity in the Warta River Catchment, Poland Adam Perz * , Leszek Sobkowiak and Dariusz Wrzesi ´nski Institute of Physical Geography and Environmental Planning, Adam Mickiewicz University, Krygowskiego 10, 61-680 Pozna´n,Poland;
[email protected] (L.S.);
[email protected] (D.W.) * Correspondence:
[email protected] Received: 8 May 2020; Accepted: 19 June 2020; Published: 23 June 2020 Abstract: Based on daily flows recorded in the period 1971–2010, the synchronous occurrence of the annual (AMAXq), winter (WMAXq), and summer (SMAXq) maximum specific runoffs in 39 sub-catchments of the Warta River catchment (WRC) in Poland was analyzed. First, trends in the flows were detected using the non-parametric Mann–Kendall (M-K) test. Then, the degree of the synchronous and asynchronous occurrences of the maximum specific runoffs (MAXq) in respective sub-catchments in relation to the Gorzów Wielkopolski gauge closing the WRC was calculated. Finally, the reasons for the detected spatial and temporal differences were discussed. The study revealed a noticeable variability of the analyzed parameters. The highest synchronicity of AMAXq and WMAXq in relation to the closing Gorzów Wielkopolski gauge was revealed in the man-made Ko´scia´nskiand Mosi´nskicanals and in the sub-catchments of the Note´c,Wełna, and lower Prosna rivers. While compared to AMAXq and WMAXq, the summer maxima showed relatively lower degrees of synchronicity, an increase in the synchronous occurrence of SMAXq in the southern part of WRC, and a decrease in its central part were identified. It was concluded that the stronger synchronicity of WMAXq resulted from the nival regime of the investigated rivers.