Abstract:
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.