Hydrogeological map of Lower Saxony 1: 50 000 — Average monthly groundwater formation 1961-1990 in April, method mGROWA22

The map shows the mean monthly groundwater formation for the month of April in the 30-year period 1961-1990. 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 These are the potential evaporation calculated on the basis of FAO grass reference evaporation (DWD, unpublished) and precipitation based on the REGNIE product (Rauthe et al, 2013) corrected by Richter (Judge, 1995).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1961-1990年30年间4月的月均地下水形成量（groundwater formation）。 地下水是一种可自我更新的可再生自然资源。下萨克森州（Lower Saxony）的入渗降水是地下水补给的主要来源，可使储水岩层中的地下储水量得到补充。冬季的地下水形成量尤为充沛，因为此时土壤中的大部分降雨会渗入地下；而在较为温暖的季节，多数降水会直接在地表蒸发或被植物吸收。 新增地下水形成量的空间分布范围广泛，其影响因素包括降水与蒸发的空间分布、土壤特性、土地利用方式（植被覆盖状况、地表硬化程度）、地表地形、人工排水措施、地下水位以及近地表岩层的性质。由于下萨克森州内这些参数在极小空间尺度内便存在显著差异，因此地下水形成量也会出现较大的横向波动。 若要量化新增地下水形成量，可采用多种测算方法。本次公开的地图展示了经分区标定的月均地下水形成量，其计算采用了mGROWA方法（即"月尺度大型水平衡"（monthly large-scale water balance）的缩写）。mGROWA模型由于利希研究中心（Forschungszentrum Jülich）与LBEG合作开发，用于大型水平衡模拟（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新的输入数据，旨在为水资源管理规划与取水审批流程提供最新的数据库支撑。 本次研究所用的气候输入数据，源自德国气象局（German Weather Service）实测并经空间插值处理的逐日、逐月气候观测资料。 其中包括基于FAO参考蒸散发（FAO grass reference evaporation）计算得到的潜在蒸散发（DWD，未公开），以及经Richter修正（Judge，1995）的、基于REGNIE数据集（REGNIE product）的降水数据。为实现更精准的区域化处理，研究采用双线性插值法将降水与潜在蒸散发这两项气候输入参数降尺度至100×100米的网格，以供mGROWA22模型使用。