Publication Date:
2018-06-21
Description:
Here we present the first empirical evidence for changes in groundwater droughts associated with anthropogenic warming in the absence of significant long-term trends in precipitation. Analysing standardised indices of monthly groundwater levels, precipitation and temperature, using two unique groundwater level data sets from the Chalk aquifer, UK for the period 1891 to 2015, we describe an increase in both the frequency and intensity of groundwater drought months, and an increase in frequency, duration and intensity of episodes of groundwater drought since 1891 associated with anthropogenic warming. We also identify a transition from coincidence of episodes of groundwater drought with precipitation droughts at the end of the 19th century, to an increasing coincidence with both precipitation droughts and with hot periods in the early 21st century. In the absence either of long-term changes in precipitation deficits during episodes of groundwater drought or long-term changes in the occurrence and intensity of consecutive dry winters, we infer that the changing nature of groundwater droughts is due to changes in evapotranspiration (ET) associated with anthropogenic warming. We note that although the water tables are relatively deep at the two study sites, a thick capillary fringe of at least 30m in the Chalk means that ET should not be limited by precipitation at either site; that ET may be supported by groundwater through major episodes of groundwater drought; and, hence, long-term changes in ET associated with anthropogenic warming may drive long-term changes in groundwater drought phenomena in the Chalk aquifer. Given the extent of shallow groundwater globally, this phenomenon may be widespread in temperate environments.
Print ISSN:
1812-2108
Electronic ISSN:
1812-2116
Topics:
Geography
,
Geosciences
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