Abstract
Instrumental data show that the groundwater and lake levels in Northeast Germany have decreased over the past decades, and this process has accelerated over the past few years. In addition to global warming, the direct influence of humans on the local water balance is suspected to be the cause. Since the instrumental data usually go back only a few decades, little is known about the multidecadal to centennial-scale trend, which also takes long-term climate variation and the long-term influence by humans on the water balance into account. This study aims to quantitatively reconstruct the surface water areas in the Lower Havel Inner Delta and of adjacent Lake Gülpe in Brandenburg. The analysis includes the calculation of surface water areas from historical and modern maps from 1797 to 2020. The major finding is that surface water areas have decreased by approximately 30% since the pre-industrial period, with the decline being continuous. Our data show that the comprehensive measures in Lower Havel hydro-engineering correspond with groundwater lowering that started before recent global warming. Further, large-scale melioration measures with increasing water demands in the upstream wetlands beginning from the 1960s to the 1980s may have amplified the decline in downstream surface water areas.
Highlights
This study aims to quantitatively reconstruct the human impact on changes in surface water areas and groundwater levels within the Lower Havel River Region in Germany’s Federal State of Brandenburg
Havel River Region (Figure 1) represents the western part of the Brandenburg glacial area [36], which consists of gently undulating till plains, sandy valley fills with covering dunes and hilly terminal moraines [37]
In the Holocene, large areas of peat began to form on the sandy deposits of the glacial valleys, which ended with fen formation in the late Holocene [38,39,40]
Summary
Droughts in Lowland River Floodplains and Peatlands. Lowland river floodplains and Central European peatlands are especially sensitive to increasing drought periods in the context of global warming [1,2,3,4,5,6,7]. In addition to the current global warming which constitutes an indirect human effect [11], direct human impacts via hydro-engineering and land reclamation measures have been discussed as potential factors [12]. The extensive drainage works and groundwater regulation measures from the 1960s to the 1980s and water-sapping pine monocultures have been mentioned in this context [13,14]. Scenarios suggest that water availability will continue to deteriorate significantly in the future [15]
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