GroMoPo Metadata for Central Kalahari Basin integrated hydrological model

Distributed numerical models, considered as optimal tools for groundwater resources management, have always been constrained by availability of spatio-temporal input data. This problem is particularly distinct in arid and semi-arid developing countries, characterized by large spatio-temporal variability of water fluxes but scarce ground-based monitoring networks. That problem can be mitigated by remote sensing (RS) methods, which nowadays are applicable for modelling not only surface-water but also groundwater resources, through rapidly increasing applications of integrated hydrological models (IHMs). This study shows implementation of various RS products in the IHM of the Central Kalahari Basin (similar to 200 Mm(2)) multi-layered aquifer system, characterized by semi-arid climate and thick unsaturated zone, both enhancing evapotranspiration. The MODFLOW-NWT model with UZF1 package, accounting for variably saturated flow, was set up and calibrated in transient conditions throughout 13.5 years using borehole hydraulic heads as state variables and RS-based daily rainfall and potential evapotranspiration as driving forces. Other RS input data included: digital-elevation-model, land-use/land-cover and soils datasets. The model characterized spatio-temporal water flux dynamics, providing 13-year (2002-2014) daily and annual water balances, thereby evaluating groundwater-resource dynamics and replenishment. The balances showed the dominant role of evapotranspiration in restricting gross recharge to only a few mm yr(-1) and typically negative net recharge (median,-1.5 mm yr(-1)), varying from -3.6 (2013) to +3.0 (2006) mm yr(-1) (rainfall of 287 and 664 mm yr(-1) respectively) and implying systematic water-table decline. The rainfall, surface morphology, unsaturated zone thickness and vegetation type/density were primary determinants of the spatio-temporal net recharge distribution.分布式数值模型作为地下水资源管理的最优工具，长期以来一直受限于时空输入数据的可获取性。该问题在干旱半干旱发展中国家尤为突出：这些地区水通量时空变异性极强，但地面监测网络却十分匮乏。遥感（Remote Sensing，RS）技术可有效缓解这一难题。随着综合水文模型（Integrated Hydrological Models，IHMs）的应用快速普及，如今遥感不仅可用于地表水模拟，还能通过集成水文模型支撑地下水资源模拟。本研究将多款遥感产品应用于卡拉哈里盆地中部多层含水层系统的综合水文模型中，该盆地面积约200 Mm²，属半干旱气候且发育厚包气带，二者均会强化蒸散发过程。本研究构建了搭载UZF1模块的MODFLOW-NWT模型，该模型可模拟变饱和渗流过程；并以钻孔水头作为状态变量，以基于遥感获取的日降水量与潜在蒸散发作为驱动因子，在13.5年的瞬态条件下完成了模型率定。其余遥感输入数据集还包括数字高程模型、土地利用/土地覆盖数据以及土壤数据集。该模型刻画了水通量的时空动态特征，生成了2002-2014年共13年的日尺度与年尺度水量平衡结果，借此评估了地下水资源动态与补给特征。水量平衡结果显示，蒸散发在限制总补给量方面起到主导作用，使得总补给量仅为数毫米每年；净补给量通常为负值（中位数为-1.5毫米每年），波动范围为-3.6（2013年）至+3.0（2006年）毫米每年（对应两年的年降水量分别为287毫米与664毫米），这意味着区域地下水位整体呈下降趋势。降水量、地表形态、包气带厚度以及植被类型与密度，是控制净补给量时空分布的主要影响因素。