Repeatability cycles of river discharges: can we identify discharge patterns? a case study of the south morava river (serbia)

Water scarcity, unequal access to water resources, and the impact of climate change on water availability are among the major global environmental concerns. As dynamic and vulnerable water subjects, rivers are constantly exposed to the pressure of natural conditions variability (primarily climatic) and direct anthropogenic influences. Therefore, it is necessary to investigate river regime dynamics over longer periods to adapt the water management sector, and human demands to any observed variations in river discharge. Observing the periodicity or cyclicity of the occurrence of certain discharge values is an important topic of modern physical geography and hydrology research. Statistics and hydrologic modelling provide great opportunities for observing cyclicality and forecasting future trends. The aim of this paper is to indicate the importance of specific statistical methods of autocorrelation and spectral analysis to study the repeatability of mean annual and maximum discharges. The South Morava River in Serbia (HS: Mojsinje, Korvingrad, Grdelica) has been selected as a case study. The obtained results (period: 1924-2021) indicated the significant cyclicity of mean annual discharges, especially pronounced at the upstream hydrological station Grdelica (3.5-year cycle) and downstream hydrological station Mojsinje (19.5-year cycle). These cyclicities are mostly influenced by variations in the amount of precipitation received from the upper part of the river basin (R > 0.6). In contrast, no regular cycles of maximum annual discharge values were determined in the studied period. The obtained results can be important for future detailed geographic and hydrologic studies as well as for the development of strategies and plans in the field of water management, environmental protection, spatial planning, prevention of floods and droughts, etc.