Regional Differences in Spatiotemporal Drought Characteristics in Great Britain

Abstract

Despite being one of the most damaging natural hazards, droughts and their spatiotemporal dynamics are typically not well understood. Great Britain, which is the focus of this work, has experienced many major drought episodes in the past, causing a range of socioeconomic and environmental impacts. Here, we apply a recently developed technique to identify and characterise past droughts, using space-time connectivity to extract events from a monthly gridded precipitation dataset covering 1862–2015, without imposing fixed geographical boundaries or time-frames. For each grid cell, the data was aggregated into four new time series using moving averages over 3-, 6-, 12- and 24-month windows. These reflect a range of response times for different types of drought impacts. Drought events were then extracted for each time window separately. In order to assess regional differences in drought characteristics, each extracted drought was assigned to one of three regions: the South-East (SE), the North-West (NW) and a “Transition” region in-between them. A frequency analysis of drought characteristics (duration, area, intensity and severity) highlighted differences between regions: for short and medium accumulation periods (3, 6, and 12 months), short and less severe droughts are more frequent in the NW than in the SE, whereas long, spatially extended and more severe droughts are more frequent in the SE than in the NW. However, for long accumulation periods (24 months), fewer differences are observed between the NW and the SE. In the “Transition” region, severe droughts are less frequent than in the other two regions. A timeline of historic drought events detected by our method included the vast majority of known drought events from previous studies, with a few additional ones, and we shed important new light on the relative severity of these historical drought episodes. Finally, an analysis of the spatial coherence between regions showed that the most extreme drought events presented little spatial coherence, whereas less severe droughts tend to be more spatially coherent. This has important implications for water resources planning and drought management strategies, particularly given the increasing emphasis on inter-regional water transfers as a potential solution in situations of extreme drought.

Projected changes in droughts and extreme droughts in Great Britain strongly influenced by the choice of drought index

“…6 and Fig. 7) agrees with Tanguy et al (2021) that the most extreme droughts tend to be less spatially coherent, so more localised, than when all droughts are considered. A projected increase in the extent of drought and extreme drought was also found by Rahiz and New (2013) using UKCP09 and the DSI6.…”

The importance of non-stationary multiannual periodicities in the NAO index for forecasting water resource extremes

“…Some of this variance may be due to changing storage dynamics within a catchment over time (Rust et al, 2014;Beverly and Hocking, 2012), but also the introduction of red noise from reconstructing from nonsignificant wavelets. This also explains the increased variance seen in aquifer groups characterised by higher autocorrelation (e.g., Sandstone) (Bloomfield and Marchant, 2013), and the relatively low variance seen in streamflow records which often have lower autocorrelation when compared to groundwater level (Hannaford et al, 2021). While this can be minimised by calculating phase difference from significant wavelets only, we have shown in the previous section that the significance between the NAO and water resources and multiannual periodicities is also subject to notable non-stationarity.…”

“…Furthermore, prior to this mode of behaviour, an approximate 16-year periodicity predominated the water resource extremes record that did not covary with NAOI. Previous studies have associated a minimum in this 16-year cycle in water resources with the wide-scale 1976 drought (Rust et al, 2019) Multiple studies have noted a marked change in European hydrological drought trends since the 1970s, often in the context of the ongoing effects of climate change on water resources (Tanguy et al 2021;Rodda and Marsh, 2011;Bloomfield et al, 2019). These impacts vary depending on the water resource and region but can include changing drought frequency (Spinoni et al, 2015;Bloomfield et al, 2019;Chiang et al, 2021), severity (Hanel et al, 2018;Bloomfield et al, 2019), and increasing divergence of drought characteristic across Europe (Cammalleri et al, 2020).…”

eFLaG: enhanced future FLows and Groundwater. A national dataset of hydrological projections based on UKCP18

“…Spatially coherent projections are needed to address the spatio-temporal dynamics of droughts (e.g. Tanguy et al 2021) and how these may change in future and what this may mean for water resources planningwhere, in practice, water resources management plans often involve transfers between regions (e.g. Murgatroyd et al 2021).…”