GroMoPo Metadata for Chennai FEFLOW model

The objective of this study is to assess the impact of climate change induced rainfall, sea level rise, and urbanization on a fragile coastal aquifer. This study was carried out in one such an aquifer located in Southeast India. Downscaled climate projection was carried out using the regional climate model (RCM) with seven ensembles and the best matching ensemble for the study area has been taken to quantify the rainfall in future. The changes in land use and land cover were estimated using remote sensing techniques, and background information on sea level rise at local and regional scale were investigated. Numerical simulation of groundwater in this isolated coastal aquifer was carried out to understand the responses of the groundwater level to downscaled projected rainfall, sea level rise, expected urbanization, and their combinations until the year 2050. The RCM-projected rainfall shows a decline in the groundwater level and shrinking of the freshwater lens. However, the prediction for change in the groundwater level combined with sea level rise minimizing a decline in the groundwater level. The rapid changes in land use and land cover pattern as inferred by change detection were extended and examined in the aquifer's future characteristics by increasing and decreasing groundwater pumping with RCM-projected rainfall recharge and with sea level rise. The results without considering sea level rise show that the aquifer undergoes degradation even if pumping is reduced by 10%. The simulation with sea level rise shows that the aquifer behaves better in maintaining freshwater lens even with 10% increase in groundwater pumping. Sea level rise prevents the availability of the freshwater lens by reducing groundwater decline caused by the reduced RCM-projected rainfall and predicted groundwater demand. Huge variation and seasonal fluctuation in the volume of outflow to the sea is noticed between north and south. Also, reduced outflow against a range of sea level rise confirms that the sea level rise in the study area will lessen the volume of outflow, will reduce the groundwater decline, and will allow an increase in groundwater level. On the other hand, the shrinking of area will decrease the freshwater volume and occurrence of reduced groundwater gradient against sea level rise will increase the possibility of seawater intrusion to pumping. The present study confirms that even with RCM-projected decrease in rainfall recharge, the increase in the sea level will help to prevent groundwater decline in this aquifer by controlling an elevation of the groundwater level. Meanwhile, it is reducing the volume of freshwater and increasing the possibility of further seawater intrusion. Hence, it is recommended to reduce the groundwater pumping from this aquifer.

本研究旨在评估气候变化引发的降雨变化、海平面上升以及城市化作用对脆弱滨海含水层的影响。本研究以印度东南部的一处滨海含水层为研究对象开展工作。采用包含7个集合成员的区域气候模型（Regional Climate Model，RCM）开展降尺度气候预测，并选取研究区匹配度最优的集合成员以量化未来降雨情势。本研究采用遥感技术估算土地利用与土地覆被变化，并调研了局地及区域尺度的海平面上升背景信息。本研究对该孤立滨海含水层开展地下水流数值模拟，以明晰2050年之前地下水位对降尺度预测降雨、海平面上升、预期城市化及其综合作用的响应机制。区域气候模型预测的降雨结果显示，地下水位将出现下降，淡水透镜体（freshwater lens）也会发生萎缩。然而，结合海平面上升的地下水位变化预测结果表明，地下水位的下降幅度将得到抑制。本研究通过变化检测方法获取了土地利用与土地覆被格局的快速变化特征，并结合区域气候模型预测的降雨补给量与海平面上升情景，通过调整地下水开采量（增减开采），对含水层未来特征展开推演与分析。未考虑海平面上升的模拟结果显示，即便将地下水开采量降低10%，含水层仍会发生退化。加入海平面上升的模拟结果则表明，即便地下水开采量增加10%，含水层仍能较好地维持淡水透镜体的规模。海平面上升通过缓解由区域气候模型预测的降雨减少与预估地下水需水量增长所引发的地下水位下降，保障了淡水透镜体的可利用性。研究区南北向的入海径流量存在显著差异与季节性波动。此外，针对不同海平面上升情景的入海径流量缩减结果证实，研究区的海平面上升将降低入海径流量，减缓地下水位下降，并推动地下水位回升。另一方面，含水层面积的萎缩将减少淡水储量；而海平面上升背景下地下水位坡降的降低，则会增加抽水井遭受海水入侵（seawater intrusion）的风险。本研究证实，即便区域气候模型预测的降雨补给量有所减少，海平面上升仍可通过调控地下水位高程，缓解该含水层的地下水位下降问题。但与此同时，海平面上升也会缩减淡水储量，并进一步提升海水入侵的风险。因此，本研究建议降低该含水层的地下水开采量。