Abstract:An empirical (geo)statistical modelling scheme is developed to address the challenges of modelling the severity and distribution of groundwater droughts given their spatially and temporally heterogeneous nature and given typically highly irregular groundwater level observations in space and time. The scheme is tested using GWL measurements from 948 observation boreholes across the Chalk aquifer (UK) to estimate monthly groundwater drought status from 1960 to 2013. For each borehole, monthly GWLs are simulated … Show more
“…Eight clusters are identified, of which five clusters are located in the Chalk (C1-5) and three in the Permo-Triassic Sandstone (S1-3) ( Figure 1). The spatial distribution of Chalk clusters (C1, C3, C4) is consistent with clusters previously identified by Marchant and Bloomfield (2018). A separate cluster is identified in East Anglia for 5 reference wells (C2).…”
Abstract. Groundwater use affects groundwater storage continuously, as the removal of water changes both short-term and long-term variation in groundwater level. This has implications for groundwater droughts, i.e. a below-normal groundwater level. The impact of groundwater use on groundwater droughts remains unknown. Hence, the aim of this study is to investigate the impact of groundwater use on groundwater droughts adopting a methodological framework that consists of two approaches. The first approach compares groundwater monitoring sites that are potentially influenced by abstraction to uninfluenced sites. Observed groundwater droughts are compared in terms of drought occurrence, magnitude, and duration. The second approach consists of a groundwater trend test that investigates the impact of groundwater use on long-term groundwater level variation. This framework was applied to a case study of the UK. Four regional water management units in the UK were used, in which groundwater is monitored and abstractions are licensed. The potential influence of groundwater use was identified on the basis of relatively poor correlations between accumulated standardised precipitation and standardised groundwater level time series over a 30-year period from 1984 to 2014. Results of the first approach show two main patterns in groundwater drought characteristics. The first pattern shows an increase of shorter drought events, mostly during heatwaves or prior to a long drought event for influenced sites compared to uninfluenced sites. This pattern is found in three water management units where the long-term water balance is generally positive and annual average groundwater abstractions are smaller than recharge. The second pattern is found in one water management unit where temporarily groundwater abstractions exceeded recharge. In this case, groundwater droughts are lengthened and intensified in influenced sites. Results of the second approach show that nearly half of the groundwater time series have a significant trend, whilst trends in precipitation and potential evapotranspiration time series are negligible. Detected significant trends are both positive en negative, although positive trends dominate in most water management units. These positive trends, indicating rising groundwater levels, align with changes in water use regulation. This suggests that groundwater abstractions have reduced during the period of investigation. Further research is required to assess the impact of this change in groundwater abstractions on drought characteristics. The overall impact of groundwater use is summarised in a conceptual typology that illustrates the asymmetric impact of groundwater use on groundwater drought occurrence, duration, and magnitude. The long-term balance between groundwater abstraction and recharge appears to be influencing this asymmetric impact, which highlights the relation between long-term and short-term sustainable groundwater use.
“…Eight clusters are identified, of which five clusters are located in the Chalk (C1-5) and three in the Permo-Triassic Sandstone (S1-3) ( Figure 1). The spatial distribution of Chalk clusters (C1, C3, C4) is consistent with clusters previously identified by Marchant and Bloomfield (2018). A separate cluster is identified in East Anglia for 5 reference wells (C2).…”
Abstract. Groundwater use affects groundwater storage continuously, as the removal of water changes both short-term and long-term variation in groundwater level. This has implications for groundwater droughts, i.e. a below-normal groundwater level. The impact of groundwater use on groundwater droughts remains unknown. Hence, the aim of this study is to investigate the impact of groundwater use on groundwater droughts adopting a methodological framework that consists of two approaches. The first approach compares groundwater monitoring sites that are potentially influenced by abstraction to uninfluenced sites. Observed groundwater droughts are compared in terms of drought occurrence, magnitude, and duration. The second approach consists of a groundwater trend test that investigates the impact of groundwater use on long-term groundwater level variation. This framework was applied to a case study of the UK. Four regional water management units in the UK were used, in which groundwater is monitored and abstractions are licensed. The potential influence of groundwater use was identified on the basis of relatively poor correlations between accumulated standardised precipitation and standardised groundwater level time series over a 30-year period from 1984 to 2014. Results of the first approach show two main patterns in groundwater drought characteristics. The first pattern shows an increase of shorter drought events, mostly during heatwaves or prior to a long drought event for influenced sites compared to uninfluenced sites. This pattern is found in three water management units where the long-term water balance is generally positive and annual average groundwater abstractions are smaller than recharge. The second pattern is found in one water management unit where temporarily groundwater abstractions exceeded recharge. In this case, groundwater droughts are lengthened and intensified in influenced sites. Results of the second approach show that nearly half of the groundwater time series have a significant trend, whilst trends in precipitation and potential evapotranspiration time series are negligible. Detected significant trends are both positive en negative, although positive trends dominate in most water management units. These positive trends, indicating rising groundwater levels, align with changes in water use regulation. This suggests that groundwater abstractions have reduced during the period of investigation. Further research is required to assess the impact of this change in groundwater abstractions on drought characteristics. The overall impact of groundwater use is summarised in a conceptual typology that illustrates the asymmetric impact of groundwater use on groundwater drought occurrence, duration, and magnitude. The long-term balance between groundwater abstraction and recharge appears to be influencing this asymmetric impact, which highlights the relation between long-term and short-term sustainable groundwater use.
“…A number of studies have described major episodes of hydrological drought, including groundwater drought, in the UK since the 19th century (Marsh et al, 2007;Lloyd-Hughes et al, 2010;Bloomfield and Marchant, 2013;Folland et al, 2015;Marchant and Bloomfield, 2018) and the societal impacts of those droughts (Taylor et al, 2009;Lange et al, 2017). Marsh et al (2007) identified seven episodes of major hydrological droughts in England and Wales between 1890 and 2007 using ranked rainfall deficiency time series and analysis of long river flow and groundwater level time series (Marsh et al, 2007, Table 2) as follows: 1890-1910 (known as the "Long Drought"), 1921-1922, 1933-1934, 1959, 1976, 1990-1992and 1995-1997 noted that of these major droughts all but one, the drought of 1959, had sustained and/or severe impacts on groundwater levels.…”
Section: Climate and Drought Contextmentioning
confidence: 99%
“…All the major droughts typically had large geographical footprints extending over much of England and Wales as well as over parts of north-western Europe (Lloyd-Hughes and Saunders, 2002;Lloyd-Hughes et al, 2010;Fleig et al, 2011;Hannaford et al, 2011). However, regional variations in drought intensities were present within and between the major drought events as a function of spatial differences in driving meteorology and catchment and aquifer properties (Marsh et al, 2007;Bloomfield and Marchant, 2013;Bloomfield et al, 2015;Marchant and Bloomfield, 2018).…”
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
1Â 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
30âm 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.
“…Groundwater monitoring is essential to groundwater management and provides fundamental information regarding the long-term sustainability and status of an aquifer (Reghunath et al, 2005;Taylor & Alley, 2001). However, groundwater-level measurements are typically irregularly collected and have many spatial and temporal gaps in the record which presents challenges in understanding spatial and temporal changes and stresses to the system (Marchant & Bloomfield, 2018;Oikonomou et al, 2018;Varouchakis & Hristopulos, 2013). In some cases, spatial and temporal data gaps can lead to limited analysis.…”
Section: Introductionmentioning
confidence: 99%
“…Oikonomou et al (2018) use an exogenous seasonal autoregressive integrated moving average stochastic model and ensemble smoother for predicting water table levels and filling in data gaps. Others studies model groundwater levels and deal with missing data by using higher spatial and/or temporally more frequent data sets, such as remotely sensed data from the GRACE satellites (Mukherjee & Ramachandran, 2018;Sun, 2013), impulse response functions to relate precipitation to groundwater levels (Marchant & Bloomfield, 2018;von Asmuth et al, 2002), machine learning using artificial neural networks (Daliakopoulos et al, 2005;Sahoo et al, 2017), and interpolation methods that use secondary variables to improve estimation in sparsely sampled areas (Desbarats et al, 2002;Passarella et al, 2017;Peterson et al, 2011). Interpolation techniques are commonly used to transform point measurements at groundwater wells to groundwater surfaces across an aquifer.…”
Groundwater monitoring is fundamental to understanding system dynamics, trends in storage, and the longâterm sustainability of an aquifer. Waterâlevel data are the key source of information used to understand the response. However, groundwaterâlevel data are often irregularly sampled, leading to temporal gaps in the record, and are not adequately distributed spatially across an aquifer. This presents challenges when spatially interpolating potentiometric surfaces and creating groundwater maps due to data availability. We present a spatiotemporal kriging methodology to improve spatial and temporal confidence in groundwaterâlevel predictions at unsampled locations. The spaceâtime data set consists of a trend and residual component modeled with a linear regression and utilize a sumâmetric model to represent spatiotemporal covariances. The Arapahoe aquifer is used as a case study to demonstrate the benefits of spatiotemporal kriging over spatial kriging across a sparsely gauged and irregularly sampled aquifer. The Arapahoe aquifer is a major source of water for many residents along the Rocky Mountain Front Range in Colorado. The results show superior performance of spatiotemporal kriging to predict groundwater levels over the traditional spatial kriging. Spatiotemporal kriging represents realistic temporal and spatial changes in water levels and avoids some of the problems inherent to spatial kriging. This study demonstrates the power of spatiotemporal kriging to help inform system dynamics in irregularly sampled aquifers.
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