Abstract
Abstract. The English Lowlands is a relatively dry, densely populated region in the south-east of the UK in which water is used intensively. Consequently, parts of the region are water-stressed and face growing water resource pressures. The region is heavily dependent on groundwater and particularly vulnerable to long, multi-annual droughts primarily associated with dry winters. Despite this vulnerability, the atmospheric drivers of multi-annual droughts in the region are poorly understood, an obstacle to developing appropriate drought management strategies, including monitoring and early warning systems. To advance our understanding, we assess known key climate drivers in the winter half-year (October–March) and their likely relationships with multi-annual droughts in the region. We characterise historic multi-annual drought episodes back to 1910 for the English Lowlands using various meteorological and hydrological data sets. Multi-annual droughts are identified using a gridded precipitation series for the entire region, and refined using the Standardized Precipitation Index (SPI), Standardized Streamflow Index (SSI) and Standardized Groundwater level Index (SGI) applied to regional-scale river flow and groundwater time series. We explore linkages between a range of potential climatic driving factors and precipitation, river flow and groundwater level indicators in the English Lowlands for the winter half-year. The drivers or forcings include El Niño–Southern Oscillation (ENSO), the North Atlantic tripole sea surface temperature (SST) pattern, the Quasi-Biennial Oscillation (QBO), solar and volcanic forcing and the Atlantic Multi-decadal Oscillation (AMO). As expected, no single driver convincingly explains the occurrence of any multi-annual drought in the historical record. However, we demonstrate, for the first time, an association between La Niña episodes and winter rainfall deficits in some major multi-annual drought episodes in the English Lowlands. We also show significant (albeit relatively weak) links between ENSO and drought indicators applied to river flow and groundwater levels. We also show that some of the other drivers listed above are likely to influence English Lowlands rainfall. We conclude by signposting a direction for this future research effort.
Highlights
From 2010 until early 2012, a protracted drought affected much of the central and southern UK
Temperature could be influential in increasing the likelihood of snowfall as opposed to rainfall, which could confound links between the atmospheric drivers we have identified and precipitation, river flow and groundwater deficits
While water storage in snow/ice during the cold season can be a major influence on hydrological drought in parts of Europe, generally, snowfall is limited in the English Lowlands
Summary
From 2010 until early 2012, a protracted drought affected much of the central and southern UK. While there has been a considerable research effort, no known studies have explored close to the full range of likely climate drivers of winter half-year rainfall in the English Lowlands, nor examined how these drivers manifest themselves in multi-annual meteorological droughts and propagate through to hydrological and hydrogeological systems. Given these knowledge gaps, key objectives of this study are to. – conduct a preliminary examination of the links between these drivers and drought indicators to search for causal connections and point the way to future studies
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