Abstract
The study applied the method of hydrological season identification in a time series of river total and base flows and in groundwater levels. The analysis covered a series of daily measurements from the period 2008–2017 in nine catchments located in different geographical regions of Poland. The basis of the classification of hydrological seasons, previously applied for river discharges only, was the transformation of the original variables into a series reflecting three statistical features estimated for single-name days of a year from a multiyear: average value, variation coefficient, and autocorrelation coefficient. New variables were standardized and after hierarchical clustering, every day of a year had a defined type, valorizing three features which refer to quantity, variability, and the stochastic nature of total and base river flow as well as groundwater stage. Finally, sequences of days were grouped into basic (homogenous) seasons of different types and transitional seasons including mixed types of days. Analysis indicated determinants of types, length, and frequency of identified hydrological seasons especially related to river regime, hydrogeological and hydrometeorological conditions as well as physiographical background were directly influenced by geographical location. Analysis of the co-occurrence of the same types of hydrological seasons allowed, in some catchments, periods of synchronic alimentation (groundwater and base flow, mainly in the cold half-year) and water shortages (all three components, mainly in the warm half-year) to be identified.
Highlights
River discharge and groundwater stage are characterized by seasonal variability which is determined by the cyclic changeability of precipitation and evapotranspiration during a year
In a mountainous catchment, high flow variability and significant precipitation alimentation are expected, in a lake catchment flow smoothing and the lake basin retention capacity plays important role in hydrological regime whereas a lowland catchment will be prone to development of severe hydrological droughts
It is worth noting that in the study published by Jokiel and Tomalski [33], in a group of 25 water gauges located in major Polish rivers (Vistula and Oder), a very similar number of types was identified—22
Summary
River discharge and groundwater stage are characterized by seasonal variability which is determined by the cyclic changeability of precipitation and evapotranspiration during a year. As a result, during a year, more predictable periods of particular flow phases occurrence appear (e.g., summer floods, autumn low-flows, spring snowmelt). Identification of such periods in a catchment allows hydrological seasons to be defined. Progress in terms of methodology, quality, and availability of hydrometrical data produces a huge set of measures and procedures used to describe the seasonality of river flows. This set is constantly enriched with new proposals. Widely applied to various components of the hydrological cycle, refer to seasonality index and seasonal time of concentration [4], seasonality coefficient [5], or central of mass data [6]
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