Hydrogeological map of Lower Saxony 1: 50 000 — Average monthly groundwater formation 1981-2010 in January, method mGROWA22

The map shows the mean monthly groundwater formation for the month of January in the 30-year period 1981-2010. Groundwater is a raw material that can regenerate and renew itself. The main supplier for the groundwater supply is precipitation water leaking in Lower Saxony. It ensures that the groundwater deposits of the storage rocks are replenished in the underground. The groundwater formation is particularly high in winter, as at this time a large part of the rainfall in the soil is leaking. In the warmer seasons, on the other hand, much of the precipitation already evaporates on the surface or is absorbed by plants. The new groundwater formation is widely distributed in different areas. It depends on the distribution of precipitation and evaporation, the characteristics of the soil, the land use (growth, degree of sealing), the relief of the land surface, the artificial drainage by drainage, the groundwater fluid level and the properties of the near-surface rocks. Since these parameters differ significantly in the smallest space in Lower Saxony, groundwater formation is also subject to large lateral fluctuations. In order to determine the new groundwater formation, there are different methods. The available maps show the area-differentiated designation of the mean groundwater formation, which was calculated using the mGROWA method (short for “monthly large-scale water balance”). The model mGROWA was developed for the large-scale simulation of the water balance at Forschungszentrum Jülich in cooperation with the LBEG (Herrmann et al. 2013) and updated methodically for Lower Saxony since 2016. In addition, a series of new input data has been used to provide an up-to-date data base for water management planning and water approval procedures. As climatic input data, daily and monthly measured and subsequently spatially interpolated climate observation data from the German Weather Service were used. These are the potential evaporation calculated on the basis of FAO grass reference evaporation (DWD, unpublished) and precipitation based on the REGNIE product (Rauthe et al, 2013) corrected by Richter (Judge, 1995). For better regionalisation, the climatic input parameters precipitation and potential evaporation with bilinear interpolation were scaled down to a 100 x 100 m grid for mGROWA22.本地图展示了1981-2010年30年气候基准期内1月份的平均月地下水补给量。 地下水是一种可自我更新、循环再生的自然资源。下萨克森州（Lower Saxony）的地下水补给主要来源于入渗降水，该部分降水可补充地下储水岩层中的地下水储量。 冬季地下水补给量尤为充沛，因为此时土壤中的大部分降雨会发生入渗。 而在较为温暖的季节，大部分降水会直接在地表蒸发，或被植物吸收利用。 新增地下水补给量在多个区域广泛分布。 其影响因素包括降水与蒸发的空间分布、土壤特性、土地利用状况（植被覆盖度、地表封闭程度）、地表地形起伏、人工排水工程、地下水位以及近地表岩层的物性特征。 由于下萨克森州内上述参数在极小空间尺度内便存在显著差异，因此地下水补给量也会出现较大的横向波动。 为测算新增地下水补给量，学界已开发出多种方法。 本次公开的地图展示了经区域差异化标注的平均地下水补给量，其计算采用了mGROWA方法（全称为“monthly large-scale water balance”，即月尺度大规模水平衡模型）。 mGROWA模型由于利希研究中心（Forschungszentrum Jülich）与LBEG合作开发，用于大规模水平衡模拟（Herrmann等，2013），并自2016年起针对下萨克森州进行了系统性更新。 此外，本次研究还采用了一系列全新的输入数据，可为水资源管理规划与取水许可审批流程提供最新的数据库支撑。 气候输入数据采用了德国气象局（DWD, Deutscher Wetterdienst）提供的实测逐日、逐月气候观测数据，经空间插值处理后得到。 该数据包括基于FAO参考作物蒸发蒸腾量（FAO grass reference evaporation）计算得到的潜在蒸发量（DWD，未公开数据），以及经Richter（Judge，1995）校正、基于REGNIE产品（Rauthe等，2013）得到的降水量数据。 为实现更精准的区域化处理，研究人员采用双线性插值法将降水与潜在蒸发量这两项气候输入参数降尺度至100×100米的网格分辨率，以适配mGROWA22模型。