Quantification of kettel hole impacts on regional water balance under changing drought and wet conditions

Majid Taie Semiromi1, Christoph Merz1
1 AG Tieflandhydrologie und Wassermanagement, Leibniz Zentrum für Agrarlandschaftsforschung (ZALF), Müncheberg

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Kettle holes are typical landscape features of the young pleistocene moraine regions in Northern Europe and Northern America. In the northeast of Germany, kettle holes, which are broadly populated on an area of 38,000 km2 with a density up to 40 per km2, are estimated to a range of numbers from 150,000 to 300,000.  Due to their great abundance, their interaction with the adjoining shallow groundwater system and possibly with the river network, they can have profound implications for the regional hydrological cycle. This is particularly of paramount importance when the characterization of kettle holes’s influence on the regional water balance under a changing climate, witnessed by recurrent drought and wet conditions, is concerned.

To that end, an integrated hydrological model approach for younger Pleistocene  regions will be presented based on a coupling of hydrological surface-subsurface models with deterministic groundwater models, namely SWAT (Soil and Water Assessment Tool) with  MODFLOW (Modular Three Dimensional Finite-Difference Groundwater Flow Model). The geographical position and geometrical properties of the kettle holes are assigned across the application area (Qillow catchment in the Uckermark region, NE Germany), using LAK3 Package of MODFLOW. Afterwards, the Standardized Precipitation-Evapotranspiration Index (SPEI) will be computed for the observation period according to the historical data record of the meteorological variables (e.g. precipitation, evapotranspiration, temperature) available for the application area. Then, drought and wet periods will be identified for the observation period according to the standard severity classes defined for SPEI. To clearly detect the hydrological influence of the kettle holes under drought and wet conditions, the coupled SWAT-MODFLOW model will be run under two scenarios: (1) the watershed with kettle holes (activation of the LAK3 package in the coupled model) and (2) watershed without kettle holes (deactivation of the LAK3 package in the coupled model). Ultimately, the model scenarios will be forced by the meteorological variables (e.g. daily min and max temperature and precipitation) of the drought/wet conditions identified already by SPEI. Thus, water balance components of the watershed, including evapotranspiration, soil moisture, recharge, streamflow discharge and kettle hole-aquifer interactions can be compared and assessed under both scenarios and in response to different drought/wet severities.