Multi-scale assessment of interactions between surface water and groundwater fluxes in hard rock, water limited environment

This is a PhD research dataset by S M Tanvir Hassan, Water Resources Department of the Faculty of Geo-information Science and Earth Observation (ITC), University of Twente, The Netherlands. The abstract of the research outcome is as follows: The multi-scale assessment of surface-groundwater interactions in hard rock (granite), water limited environments was carried out first in the ~80 km2 Sardon catchment and finally in a small, 7.6 ha Trabadillo study area (Western Spain). Three different thematic studies (Chapters 2-4) had been carried out applying various techniques including: field data acquisition, automated monitoring, remote sensing and integrated hydrological modelling using GSFLOW code. Chapter 2 addresses the assessment of dynamics of surface-groundwater interactions at the Sardon catchment scale; the main findings were: (1) intense groundwater exfiltration; (2) groundwater flow characterized by short groundwater flow-path and short residence time; (3) declining trend of catchment groundwater outflow; and (4) large variability of infiltration influenced by land cover type. That impact of land cover upon dynamics of surface-groundwater interactions triggered expansion of further research in Chapters 3 and 4, but also underpinned some hardcoded deficiencies of GSFLOW, related to formulation of driving forces. That initiated the study in Chapter 3, addressing spatiotemporal tree rainfall interception loss (Ei). Experimental measurements of Ei on selected evergreen Quercus ilex and deciduous Quercus pyrenaica oaks were carried out during two years and spatiotemporally upscaled into two homogeneous (1 ha) plots and into the entire Sardon catchment; the main findings were: (1) yearly Ei was larger in wet than in dry hydrological years but if reflected as percent of rainfall, then it was opposite; (2) Ei of Quercus ilex trees were larger than of Quercus pyrenaica but for the catchment scale Ei, it was opposite, because of much larger catchment population of the latter; (3) catchment Ei was primarily dependent on tree density and species type. The Chapter 4 focusses on simulating surface-groundwater interactions at very fine grid (5x5 m) and at temporal daily resolution, using 20-year time-series observation to assess the net recharge dependence upon land cover type expressed through hydrological terrain units (hydrotopes). The findings of this study confirmed all findings of the Chapter 2, adding the following: (1) hydrotope-dependent variability of water fluxes; (2) non-negligible grass interception; and (3) much lower net recharge under tree than grass hydrotopes, meaning more trees, less water resources.

本数据集由荷兰特文特大学地理信息科学与地球观测学院（ITC）水资源系的S M Tanvir Hassan构建，源自其博士研究。研究成果的摘要如下：
研究首先在面积约80 km²的萨尔东（Sardon）流域开展硬岩（花岗岩）、水分受限环境下地表水-地下水交互作用的多尺度评估，最终在西班牙西部面积7.6 ha的特拉巴迪略（Trabadillo）小型研究区完成全部研究。
第2至第4章共开展3项专题研究，应用了包括野外数据采集、自动监测、遥感以及采用GSFLOW代码的集成水文建模在内的多种技术手段。
第2章聚焦萨尔东流域尺度下的地表水-地下水交互作用动态评估，主要研究结论包括：（1）存在强烈的地下水渗出现象；（2）地下水流动具有流程短、驻留时间短的特征；（3）流域地下水径流量呈下降趋势；（4）入渗过程的变异性受土地覆盖类型的显著影响。
土地覆盖对地表水-地下水交互作用动态的影响，不仅推动了第3、4章的后续研究，同时也暴露了GSFLOW在驱动力表征方面存在的固有缺陷。这一问题催生了第3章的研究，该章针对树木降雨截留损失（Ei）的时空分布特征展开。研究团队在两年时间内，对选定的冬青栎（Quercus ilex）和西班牙栓皮栎（Quercus pyrenaica）开展了Ei的原位观测，并将观测结果从空间尺度上推至两个1 ha的均质地块以及整个萨尔东流域。该章主要结论包括：（1）湿润水文年的年Ei总量高于干旱水文年，但以降雨占比表征时则恰好相反；（2）冬青栎的Ei高于西班牙栓皮栎，但在流域尺度下的整体Ei则呈现相反结果，原因在于流域内西班牙栓皮栎的种群规模远大于冬青栎；（3）流域整体Ei主要受树木密度与物种类型影响。
第4章聚焦采用日时间分辨率、5×5 m的精细网格，利用20年的时间序列观测数据，模拟地表水-地下水交互作用，以评估净补给量与通过水文地形单元（hydrotopes）表征的土地覆盖类型之间的相关性。本研究的结论验证了第2章的全部发现，并补充了以下内容：（1）水通量存在依赖于水文地形单元的变异性；（2）草本植被截留效应不可忽视；（3）树木覆盖的水文地形单元下的净补给量远低于草本覆盖的水文地形单元，即树木覆盖率越高，区域水资源量越少。