From Minutes to Millennia: Transient Responses in Groundwater Systems

在全球范围内，地下水是抽取淡水总量的三分之一。在许多环境中，在少雨或无雨期间，天然地下水的排放维持着流向河流、湖泊和湿地的基流。尽管这些对人类福祉和水生生态系统的重要贡献，但由于缺乏关于气候和地下水关系的研究，严重限制了政府间气候变化专门委员会（IPCC）在其第三和第四次评估报告中评估地下水与气候变化之间相互作用的能力。迄今为止进行的大多数气候变化影响研究都将地下水系统模拟为100年预测窗口内的时间快照（2020年代、2050年代）。对这些系统的瞬态（时变）响应进行的研究很少，对涉及偶发性和非常长期变化的计算挑战性问题的研究就更少了。此外，大多数地下水模型继续使用时间平均观测值（代表假定的稳态条件）或短时间瞬态数据（例如抽水试验）进行校准，因此，长期预测的不确定性很高。本研究将利用瞬态建模来探索地下水系统的动力学，以便更好地理解含水层对气候压力的响应，这些气候压力在短时间和长时间框架内（从几分钟到几千年）起作用，并试图通过对瞬态数据集的模型校准来更好地约束适合区域尺度水文地质研究的水力特性范围。将获得有关系统对控制含水层响应的参数的敏感性的重要见解，从而有助于量化未来预测中的不确定性。正如加拿大科学院理事会2009年关于“加拿大地下水可持续管理”的报告所指出的那样，这一贡献对于确定地下水资源的可持续性以及建立适当的监测网络以检测变化至关重要。

Globally, groundwater is the source of one third of all freshwater withdrawals. In many environments, natural groundwater discharges sustain baseflow to rivers, lakes and wetlands during periods of low or no rainfall. Despite these vital contributions to human welfare and aquatic ecosystems, a paucity of studies on the relationship between climate and groundwater severely restricted the ability of the Intergovernmental Panel on Climate Change (IPCC) to assess the interactions between groundwater and climate change in both its third and fourth assessment reports. Most climate change impact studies conducted to date have modeled groundwater systems as a snapshot in time (2020s, 2050s) over a 100-year projection window. Little research has been undertaken on the transient (time-varying) responses of these systems, and even less on the computationally challenging problems involving episodic and very long-term change. Moreover, most groundwater models continue to be calibrated using time-averaged observations (representing assumed steady-state conditions) or short-duration transient data (e.g. pumping tests) and, therefore, the uncertainty in long-term predictions is high. This research will explore the dynamics of groundwater systems using transient modeling in order to better understand aquifer responses to climate stresses that act over short and long time frames, from minutes to millennia, and attempt to better constrain the range of hydraulic properties suitable for regional-scale hydrogeological studies through model calibration to transient datasets. Significant insight will be gained concerning the sensitivity of the system to the parameters that control the aquifer response, and thus, aid in quantifying the uncertainty in future projections. This contribution is crucial for determining the sustainability of the groundwater resource as noted by the Council of Canadian Academies' report in 2009 on "The Sustainable Management of Groundwater in Canada" and for establishing appropriate monitoring networks to detect change.