Demonstrating the impact of integrated drought policies on hydrological droughts

Abstract

Abstract. Managing water-human systems in times of water shortage and droughts is key to avoid overexploitation of water resources, particularly for groundwater, which is a crucial water resource during droughts sustaining both environmental and anthropogenic water demand. Drought management is often guided by drought policies to avoid crisis management and to actively introduce management strategies during droughts. However, the impact of drought management strategies on hydrological droughts is rarely assessed. In this study, we present a newly developed socio-hydrological model, simulating feedbacks between water availability and managed water use over three decades. Thereby, we aim to assess the impact of drought policies on both surface water and groundwater droughts. We tested this model in an idealised catchment based on climate data, water resource management practices, and drought policies in England. The model includes surface water storage (reservoir), groundwater storage for a range of hydrogeological conditions and optional imported surface water or groundwater. These modelled water sources can all be used to satisfy anthropogenic and environmental water demand. We tested four aspects of drought management strategies: 1) increased water supply, 2) restricted water demand, 3) conjunctive water use, and 4) maintained environmental flow requirements by restricting groundwater abstractions. These four strategies were evaluated in separate and combined scenarios. Results show mitigated droughts for both streamflow and groundwater droughts in scenarios applying conjunctive use, particularly in low groundwater storage systems. In high groundwater storage systems, maintaining environmental flows reduces hydrological droughts most. Scenarios increasing or restricting water demand have an opposing effect on droughts, although these scenarios are in balance when combined at the same time. Most combined scenarios reduce the severity and occurrence of hydrological droughts given an incremental dependency on imported water that satisfies up to a third of the total anthropogenic water demand. The necessity for importing water shows the considerable pressure on water resources and the delicate balance of water-human systems during droughts that calls for short-term and long-term sustainability targets within drought policies.

How is Baseflow Index (BFI) impacted by water resource management practices?

“…There are often large uncertainties in the underlying streamflow data used to estimate BFI (Coxon et al, 2015), but these are difficult to characterize across large samples of catchments, and uncertainty estimates are not available for all the CAMELS-GB catchments (Coxon et al, 2020b). However, BFI typically has lower uncertainty compared with other hydrological signatures, as it is based on temporal averaging (Westerberg and McMillan, 2015), and only typically small differences in the BFI estimates are observed in the present study based on the two methods of estimate (Fig. 3).…”

“…5,7,and 8). Water resources in England have been well-regulated within the context of the European Water Framework Directive and Daughter Directives (European Commission, 2000), and a wide range of sophisticated schemes and measures are used to manage low flow and drought, including conjunctiveuse schemes, low-flow alleviation schemes, and hands-off flow measures (Clayton et al, 2008;Shepley et al, 2009;Agnew et al, 2000;Hutchinson et al, 2012;Wendt et al, 2020Wendt et al, , 2021. Conjunctive-use schemes use combined management of groundwater and surface water abstractions to maintain ecological flows, while low-flow alleviation schemes and hands-off flow measures are used in England to constrain the amount of water that is abstracted from groundwater and rivers, with abstractions being reduced or stopped at a given low-flow trigger level.…”