Browsing by Author "Rust, William"

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    A conceptual model for climatic teleconnection signal control on groundwater variability in the UK and Europe
    (Elsevier, 2017-07-22) Rust, William; Holman, Ian P.; Corstanje, Ronald; Bloomfield, John; Cuthbert, Mark
    The ability to predict future variability of groundwater resources in time and space is of critical importance to drought management. Periodic control on groundwater levels from oscillatory climatic systems (such as the North Atlantic Oscillation) offers a potentially valuable source of longer term forecasting capability. While some studies have found evidence of the influence of such climatic oscillations within groundwater records, there is little information on how periodic signals propagate between a climatic system and a groundwater resource. This paper develops a conceptual model of this relationship for groundwater resources in the UK and Europe, based on a review of current research. The studies reviewed here reveal key spatial and temporal signal modulations between climatic oscillations, precipitation, groundwater recharge and groundwater discharge. Generally positive correlations are found between the NAO (as a dominant influence) and precipitation in northern Europe indicating a strong control on water available for groundwater recharge. These periodic signals in precipitation are transformed by the unsaturated and saturated zones, such that signals are damped and lagged. This modulation has been identified to varying degrees, and is dependent on the shape, storage and transmissivity of an aquifer system. This goes part way towards explaining the differences in periodic signal strength found across many groundwater systems in current research. So that an understanding of these relationships can be used by water managers in building resilience to drought, several research gaps have been identified. Among these are improved quantification of spatial groundwater sensitivity to periodic control, and better identification of the hydrogeological controls on signal lagging and damping. Principally, research needs to move towards developing improved predictive capability for the use of periodic climate oscillations as indicators of longer term groundwater variability.
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    Exploring the role of hydrological pathways in modulating multi-annual climate teleconnection periodicities from UK rainfall to streamflow
    (European Geosciences Union, 2021-04-23) Rust, William; Cuthbert, Mark; Bloomfield, John; Corstanje, Ron; Howden, Nicholas; Holman, Ian P.
    An understanding of multi-annual behaviour in streamflow allows for better estimation of the risks associated with hydrological extremes. This can enable improved preparedness for streamflow-dependant services, such as freshwater ecology, drinking water supply and agriculture. Recently, efforts have focused on detecting relationships between long-term hydrological behaviour and oscillatory climate systems (such as the North Atlantic Oscillation – NAO). For instance, the approximate 7 year periodicity of the NAO has been detected in groundwater-level records in the North Atlantic region, providing potential improvements to the preparedness for future water resource extremes due to their repetitive, periodic nature. However, the extent to which these 7-year, NAO-like signals are propagated to streamflow, and the catchment processes that modulate this propagation, are currently unknown. Here, we show statistically significant evidence that these 7-year periodicities are present in streamflow (and associated catchment rainfall), by applying multi-resolution analysis to a large data set of streamflow and associated catchment rainfall across the UK. Our results provide new evidence for spatial patterns of NAO periodicities in UK rainfall, with areas of greatest NAO signal found in southwest England, south Wales, Northern Ireland and central Scotland, and show that NAO-like periodicities account for a greater proportion of streamflow variability in these areas. Furthermore, we find that catchments with greater subsurface pathway contribution, as characterised by the baseflow index (BFI), generally show increased NAO-like signal strength and that subsurface response times (as characterised by groundwater response time – GRT), of between 4 and 8 years, show a greater signal presence. Our results provide a foundation of understanding for the screening and use of streamflow teleconnections for improving the practice and policy of long-term streamflow resource management
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    The importance of non-stationary multiannual periodicities in the North Atlantic Oscillation index for forecasting water resource drought
    (European Geosciences Union (EGU), 2022-05-11) Rust, William; Bloomfield, John P.; Cuthbert, Mark; Corstanje, Ron; Holman, Ian P.
    Drought forecasting and early warning systems for water resource extremes are increasingly important tools in water resource management in Europe where increased population density and climate change are expected to place greater pressures on water supply. In this context, the North Atlantic Oscillation (NAO) is often used to indicate future water resource behaviours (including droughts) over Europe, given its dominant control on winter rainfall totals in the North Atlantic region. Recent hydroclimate research has focused on the role of multiannual periodicities in the NAO in driving low frequency behaviours in some water resources, suggesting that notable improvements to lead-times in forecasting may be possible by incorporating these multiannual relationships. However, the importance of multiannual NAO periodicities for driving water resource behaviour, and the feasibility of this relationship for indicating future droughts, has yet to be assessed in the context of known non-stationarities that are internal to the NAO and its influence on European meteorological processes. Here we quantify the time–frequency relationship between the NAO and a large dataset of water resources records to identify key non-stationarities that have dominated multiannual behaviour of water resource extremes over recent decades. The most dominant of these is a 7.5-year periodicity in water resource extremes since approximately 1970 but which has been diminishing since 2005. Furthermore, we show that the non-stationary relationship between the NAO and European rainfall is clearly expressed at multiannual periodicities in the water resource records assessed. These multiannual behaviours are found to have modulated historical water resource anomalies to an extent that is comparable to the projected effects of a worst-case climate change scenario. Furthermore, there is limited systematic understanding in existing atmospheric research for non-stationarities in these periodic behaviours which poses considerable implications to existing water resource forecasting and projection systems, as well as the use of these periodic behaviours as an indicator of future water resource drought.
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    Long-range hydrological drought forecasting using multi-year cycles in the North Atlantic Oscillation
    (Elsevier, 2024-09) Rust, William; Bloomfield, John P.; Holman, Ian
    With global temperatures, populations and ecological stressors expected to rise, hydrological droughts are projected to have progressively severe economic and environmental impacts. As a result, hydrological drought forecasting systems have become increasingly important water resource management tools for mitigating these impacts. However, high frequency behaviours in meteorological or atmospheric conditions often limit the lead times of hydrological drought forecasts to seasonal timescales, either through poorer performance of multi-year meteorological forecasts or the lack of multi-year lags in atmosphere-hydrology systems. By contrast, low frequency behaviours in regionally important teleconnection systems (such as the North Atlantic Oscillation, NAO) offer a novel way to forecast hydrological drought at longer lead times. This paper shows that, by using a data-driven modelling approach, long-term behaviours within the NAO can be skilful predictors of hydrological drought conditions at a four-year forecasting horizon. Multi-year semi-periodic patterns in the NAO were used to forecast regional groundwater drought coverage in the UK (proportion of groundwater boreholes in drought), with the greatest forecast performance achieved for longer duration droughts, and for hydrogeological regions with longer response times. Model errors vary from 14 % (proportion of boreholes, (MAE)) in flashy hydrological regions or short droughts (<3 months), to 2 % for longer duration droughts (>8 months). Model fits of r2 up to 0.8 were produced between simulated and recorded regional drought coverage. As such our results show that teleconnection indices can be a skilful predictor of hydrological drought dynamics at multi-year timescales, opening new opportunities for long-lead groundwater drought forecasts to be integrated within existing drought management strategies in Europe and beyond.
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    Nao control on multi-annual periodicities in water resources and their utility for managing water resource extremes.
    (Cranfield University, 2021-08) Rust, William; Holman, Ian P.; Corstanje, Ronald
    Water scarcity and the hazard of drought impacts millions of people worldwide, highlighting the need for robust water resource management. Forecasting of water resources (i.e., groundwater and streamflow) aids in the planning and preparedness for water resource extremes which, in turn, can help mitigate their societal and economic impacts. With the effects of climate change expected to exacerbate certain water resource extremes, there is increased pressure to develop improved ways to estimate future water resource behaviour. Hydrometeorological conditions in Europe are modulated by the North Atlantic Oscillation with important multiannual periodicities. Existing studies have shown that the NAO can drive multiannual periodicity behaviour in water resources and influence the timing of water resource extremes such as drought. As such, it has been discussed in hydroclimate literature that these multiannual relationships may have some utility in water resource forecasting applications. However, a systematic assessment of the relationship between the NAO and wide-scale water resources, at multiannual periodicities, has yet to be undertaken for large water resource datasets. Therefore, there is limited information to develop significant relationships between catchment properties and water resource response to multiannual NAO periodicity (e.g., magnitude, or lags), which may be of value in forecasting applications. The aim of this PhD thesis is to assess the feasibility of a relationship between the NAO and water resource variables, at multiannual periodicities, for indicating water resource behaviour (including extremes), at seasonal to multiannual timescales. This has been achieved using large hydrological datasets in the UK and the wavelet transform to characterise periodicities in these records and the NAOI. This research demonstrates that a significant and wide-spread ~7-year periodicity is exhibited by most UK water resources and has a significant relationship with the NAOI. Research presented here show that the degree of influence of this ~7-year periodicity is considerable, affecting groundwater median regional groundwater level anomalies by up to 0.71sd, and median regional streamflow anomalies by up to 0.55sd. These anomalies are also comparable to the projected effects of climate change on UK water resources. Findings demonstrate that there are notable non-stationarities of this multiannual NAO periodicity and its relation to UK water resource variables, with the ~7-year periodicity detected in water resources only being dominant since the 1970s. This has important implications for the applicability of existing water resource forecasting systems that have utilized data from this period (of a relatively stationarity frequency structure). Findings also demonstrate a second non-stationarity between the NAO and European rainfall, producing considerable uncertainties in the detection of lags between multiannual NAO periodicities and water resource response. At present, there is limited atmospheric research to explain these modes of non-stationarity in the NAO and their influence on water resources, which poses a substantial challenge to the application of these multiannual periodicities in water resource forecasting systems. Future cross-discipline work between atmospheric and hydrological sciences may be needed to account for these non-stationaries, and to better understand how the relationship between multiannual NAO periodicities and water resource response may be used in the forecasting of water resource behaviours.
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    Non‐stationary control of the NAO on European rainfall and its implications for water resource management
    (Wiley, 2021-02-19) Rust, William; Bloomfield, John P.; Cuthbert, Mark O.; Corstanje, Ron; Holman, Ian P.
    Water resource forecasting generally centres on understanding hydrological variability over coming months or years, so that water managers can prepare for extremes such as droughts or floods (Chang & Guo, 2020; Hao et al., 2018). Some forecasting systems seek to project further into the future to allow long‐term planning of infrastructure and resilience to extremes and climate change (Svensson et al., 2015). These systems can rely directly or indirectly on outputs from Global Climate Models (GCMs; such as gridded reanalysis datasets) to forecast hydrological conditions (Bhatt & Mall, 2015; Ionita & Nagavciuc, 2020). In the North Atlantic region, in particular Western Europe, the North Atlantic Oscillation (NAO) is used as an indicator for hydrometeorological conditions given its leading control on winter rainfall totals (Hurrell & Deser, 2010; Scaife et al., 2008, 2014). A dipole of pressure anomalies over the North Atlantic, the NAO's positive phase (greater than average pressure gradient; NAO+) results in wetter conditions in northwest Europe with dryer conditions in southwest Europe (Rust et al., 2018; Trigo et al., 2004). Its negative phase (weaker than average pressure gradient; NAO−) results in the inverse effect on rainfall (Folland et al., 2015; and as shown by the correlation coefficients in Figure 1). Given this relationship, and, considering the role of winter rainfall variability in groundwater drought development (e.g., reduced winter recharge) and generation of late winter/early spring floods, the NAO offers a potential explanatory variable when understanding the behaviour of some hydrological extremes.
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    Understanding the potential of climate teleconnections to project future groundwater drought
    (European Geosciences Union, 2019-08-08) Rust, William; Holman, Ian P.; Bloomfield, John; Cuthbert, Mark; Corstanje, Ronald
    Predicting the next major drought is of paramount interest to water managers globally. Estimating the onset of groundwater drought is of particular importance, as groundwater resources are often assumed to be more resilient when surface water resources begin to fail. A potential source of long-term forecasting is offered by possible periodic controls on groundwater level via teleconnections with oscillatory ocean–atmosphere systems. However, relationships between large-scale climate systems and regional to local-scale rainfall, evapotranspiration (ET) and groundwater are often complex and non-linear so that the influence of long-term climate cycles on groundwater drought remains poorly understood. Furthermore, it is currently unknown whether the absolute contribution of multi-annual climate variability to total groundwater storage is significant. This study assesses the extent to which multi-annual variability in groundwater can be used to indicate the timing of groundwater droughts in the UK. Continuous wavelet transforms show how repeating teleconnection-driven 7-year and 16–32-year cycles in the majority of groundwater sites from all the UK's major aquifers can systematically control the recurrence of groundwater drought; and we provide evidence that these periodic modes are driven by teleconnections. Wavelet reconstructions demonstrate that multi-annual periodicities of the North Atlantic Oscillation, known to drive North Atlantic meteorology, comprise up to 40 % of the total groundwater storage variability. Furthermore, the majority of UK recorded droughts in recent history coincide with a minimum phase in the 7-year NAO-driven cycles in groundwater level, providing insight into drought occurrences on a multi-annual timescale. Long-range groundwater drought forecasts via climate teleconnections present transformational opportunities to drought prediction and its management across the North Atlantic region.