Changes in groundwater drought associated with anthropogenic warming

Abstract

Abstract. Here we present the first empirical evidence for changes in groundwater drought associated with anthropogenic warming in the absence of long-term changes 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 show that precipitation deficits are the main control on groundwater drought formation and propagation. However, long-term changes in groundwater drought are shown to be associated with anthropogenic warming over the study period. These include increases in the frequency and intensity of individual groundwater drought months, and increases in the frequency, magnitude and intensity of episodes of groundwater drought, as well as an increasing tendency for both longer episodes of groundwater drought and for an increase in droughts of less than 1 year in duration. We also identify a transition from a 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 of long-term changes in precipitation deficits, 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 30 m in the Chalk means that ET should not be limited by precipitation at either site. 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, anthropogenic warming may widely effect changes to groundwater drought characteristics in temperate environments.

Global GRACE Data Assimilation for Groundwater and Drought Monitoring: Advances and Challenges

“…Groundwater drought, defined as below‐normal groundwater storage (Mishra & Singh, ), is mainly driven by long‐term precipitation deficit (Bloomfield et al, ; Eltahir & Yeh, ; Li et al, ). Bloomfield et al () also showed that thick capillary fringes in the unsaturated zone may have played a role in the increase in groundwater drought frequency in a warming world. These studies suggest that both climate and hydrogeological conditions may influence the evolution of groundwater drought.…”

Evapotranspiration depletes groundwater under warming over the contiguous United States

“…Despite these findings, the extent to which temperature and water availability will control ecosystem function in the future remains uncertain 4,5 . A recent study noted an increase in groundwater droughts coincident with hot periods in the 21st century (as opposed to only dry periods) and inferred that this shift was likely do to evaporative shifts with warming 6 . Higher temperatures increase evaporative demand, but how much this will induce moisture deficits and evaporative stress, as opposed to increased evapotranspiration, is partially dependent on climate [7][8][9] .…”

Analysis of the impact of hydraulic properties and climate change on estimations of borehole yields

“…This study used an idealised borehole in the Chalk of south-east England (Figure 2). Previous work has shown that in England climate change has already increased the frequency and intensity of groundwater droughts (Bloomfield et al, 2019) and is likely to result in future reductions in recharge and groundwater levels both on an annual basis and during seasonal minima (Jackson et al, 2015;Jackson et al, 2011;Watts et al, 2015). An idealised site was chosen as (1) the purpose of this research is to illustrate the methodology, and this ensures the approach is generic and can be applied across a range of future real-world examples from different types of fractured aquifers, and…”