Spatial and Temporal Changes in Hydrological Regionalization of Lowland Rivers

Regionalization of the riverine system is a challenging task not only for large-scale basins but also for catchments of regional relevance. Especially, there is a lack of studies related to the regionalization of lowland rivers. Therefore, this study aims to perform the regionalization of lowland rivers based on the example of Lithuanian rivers, using long data series and selected hydrological characteristics. The suggested classification scheme used the estimated proportional contribution of river feeding sources (rainfall, snowmelt, and groundwater) as well as hydrological indicators describing river runoff and its variability (specific annual runoff, coefficient of flow irregularity, and coefficient of variation). K-value clustering algorithms were applied for the hydrological regionalization of Lithuanian rivers. Three hydrological regions were determined: Western, Central and South-eastern. For the rivers of South-eastern region, the groundwater feeding was typical (55% of multiannual runoff). The rivers of Central region were mainly fed by surface sources-rain (47%) and snow (36%). The rivers of Western region were described as rain dependent (62%). These regionalization results were compared with the first hydrological classification established by Jablonskis and Janukeniene (Change of Lithuanian river runoff. Science, Vilnius, 1978). Some catchments in Central region have changed their intra-annual and multiannual flow behaviour. Most of them tended to shift from snow-fed to rain-fed type. The uniqueness of the applied methodology is related to the proposed hydrological characteristics, which allow dividing the lowland rivers into regions. This opens the way to expand the proposed scheme of regionalization to neighbouring countries or regions where lowland rivers are prevalent. [GRAPHICS] .

Automated summary

Regionalization of lowland rivers is performed based on Lithuanian rivers using long data series and selected hydrological characteristics. Three hydrological regions (Western, Central, and South-eastern) are determined, and it is found that some catchments in the Central region have changed their flow behavior.