Groundwater Resilience under Extreme Drought

Abstract:

Government guidance suggests that, by 2050, water companies should be resilient to a 1-in-500-year drought, allowing them to maintain supply in all except the most extreme droughts. However, drought is poorly defined with no universally accepted definition. This is because drought is often the result of many complex processes, is not a distinct event, and is usually only recognisable after a period of time. This leads to problems when predicting, quantifying, and assessing the impact and magnitude of drought within the environment. Consequently, how do water companies prepare themselves for an extreme drought when such drought cannot be quantified? Particularly, how do they ensure that groundwater resources are resilient, given the dependence on these resources to provide public water supply? These questions are particularly prevalent due to the predicted changes in climate and the current lack of understanding of how and to what magnitude groundwater resources will be affected.

Global warming has already been shown to affect groundwater droughts in the UK, however its impact on groundwater resources has not been quantified due to the challenges associated with defining groundwater drought onset and termination, as well as the difficulties with identifying how precursor conditions affect the magnitude and duration of groundwater drought. This lack of knowledge makes groundwater resources vulnerable to direct climate change and also to the indirect socioeconomic pressures associated with climate change.

Modelling is an important process in the assessment of the impacts of drought on groundwater, however, the principle focus of climate change research with regards to groundwater has been on assessing the likely direct impacts of a general changes in precipitation and temperature patterns, using a range of modelling techniques such as soil water balance models, empirical models, conceptual models, and distributed models. However, model development has been focusses within specific fields, for example surface hydrology and flooding, groundwater, distribution networks, and water resource systems and the integration of these separate models has been limited. Integrated, physically-based, and spatially distributed models have generally not been used in large sample studies due to their extensive time, data, and computational resource requirements, however they are key to representing surface water-groundwater interactions accurately, which is key in determining how groundwater will be affected by changes in climate, and hence drought.

Subsequently, this research uses SHETRAN, a physically-based, spatially-distributed hydrological model, in a large sample size study of UK river catchments. Through using this model, the aim of this research is to address gaps in knowledge and fully understand the response of groundwater resources to changing climate, the impact of pre-cursor conditions on drought magnitude and duration, and aims to improve the current issue that is the lack of an adequate model that can be used to investigate these issues.