Search

In recent years, opportunities have opened up to develop and validate glacier models in regions that have previously been infeasible due to observation and/or computational constraints, due to the availability of globally-capable glacier evolution modelling codes and spatially-extensive geodetic validation data. The glaciers in the tropical Andes represent some of the least observed and modelled glaciers in the world, making their trajectories under climate change uncertain. Studies to date, have typically adopted empirical models of the surface energy balance and ice flow to simulate glacier evolution under climate change, but these may miss important non-linearities in future glacier mass changes. We combine two globally-capable modelling codes that provide a more physical representation of these processes: i) JULES which solves the full energy balance of snow and ice; and ii) OGGM which solves a flowline representation of the shallow ice equation to simulate ice flow. JULES-OGGM is applied to over 500 tropical glaciers in the Vilcanota-Urubamba basin in Peru and is evaluated against available glaciological and geodetic mass balance observations to assess the potential for using the modelling workflow to simulate tropical glacier evolution over decadal timescales. We show that the JULES-OGGM model can be parameterised to capture decadal (2000–2018) mass changes of individual glaciers, but that limitations of the JULES prognostic snow model prevent accurate replication of observed surface albedo fluctuations. We conclude that this inhibits the robustness of extrapolating the JULES parameters across multiple glaciers. When driven with statistically-downscaled climate change projections, the JULES-OGGM simulations indicate that, contrary to point-scale energy balance studies, sublimation plays a very minor role in glacier evolution at the basin scale and does not bring about significant non-linearities in the glacier response to climate warming. The ensemble mean simulation estimates that total glacier mass will decrease to 17 % and 6 % of that in 2000 by 2100 for RCP4.5 and RCP8.5 respectively which is more conservative than estimates from some other global glacier models. [ABSTRACT FROM AUTHOR]

Hydrological drought is a serious issue globally, which is likely to be amplified by 21st century climate change. In the UK, the impacts of changes in river flow and groundwater drought severity in a future of climate change and higher water demand are potentially severe. Recent publication of a new nationally consistent set of river flow and groundwater level projections (the eFLaG dataset), based on state-of-the-art UKCP18 climate projections, offers a unique opportunity to quantitatively assess future UK hydrological drought susceptibility. The dataset includes a transient, multi-model ensemble of hydrological projections driven by a single regional climate model (RCM), with a 12-member perturbed-parameter ensemble, for 200 catchments and 54 boreholes spanning a period from 1961 to 2080. Assessment of a baseline period (1989–2018) shows that the RCM-driven projections adequately reproduce observed river flow and groundwater level regimes, improving our confidence in using these models for assessment of future drought. Across all hydrological models and most catchments, future low river flows are projected to decline consistently out to 2080. Drought durations, intensities and severities are all projected to increase in most (over 90 %, pooling across different drought characteristics) UK catchments. However, the trajectory of low groundwater levels and groundwater drought characteristics diverges from that of river flows. Whilst groundwater levels at most (> 85 %) boreholes are projected to decline (consistent with river flows), these declines are relatively modest (< 10 % reduction) in transient low groundwater levels by 2080, and, in fact, six show moderate increases. Groundwater drought characteristics in the far future (2050–2079) are often similar to those of the baseline (1989–2018), with only 33 % of boreholes showing an increase (towards worsening drought) of more than 10 % for drought severity (48 % of boreholes for drought intensity). Interestingly, for some boreholes, droughts are projected to be more prolonged and severe in the near future (2020–2049) before returning to shorter durations and lower severity in the far future. A number of explanatory factors for this divergence between river flow and groundwater are discussed. The sensitivity to seasonal changes in precipitation and potential evapotranspiration is proposed as a principal driver of divergence because low river flows are more influenced by shorter-term rainfall deficits in the summer half-year, whilst groundwater drought appears to be offset somewhat by the wetter winter signal in the RCM projections. Our results have important implications for water management, demonstrating a widespread increase in river flow drought severity and diminishing low flows that could have profound societal and environmental impacts unless mitigated. Furthermore, the divergence in projections of drought in river flows and groundwater levels brings into question the balance between surface and subsurface water resources. The projected contrast in fortunes of surface and subsurface water resources identified for the UK may be replicated in other parts of the world where climate projections suggest a shift towards drier summers and wetter winters. [ABSTRACT FROM AUTHOR]

Hydrological drought is a serious issue globally which is likely to be amplified by 21st 10 century climate change. In the UK, the impacts of changes in river flow and groundwater drought severity in a future of climate change and higher water demand are potentially severe. Recent publication of a new nationally-consistent set of river flow and groundwater level projections based on state-of-the-art UKCP18 climate projections offers a unique opportunity to quantitatively assess future UK hydrological drought susceptibility. The dataset includes a transient, multi-model ensemble of hydrological 15 projections driven by a single regional climate model (RCM) for 200 catchments and 54 boreholes spanning a period from 1961 to 2080. Assessment of a baseline period (1989-2018) shows that the RCM-driven projections adequately reproduce observed river flow and groundwater level regimes, improving our confidence in using these models for assessment of future drought. Across all hydrological models and most catchments, future low river flows are projected to decline consistently out to 2080. Drought durations, intensities and severities are all projected to increase in most UK catchments. However, the 20 trajectory of low groundwater levels and groundwater drought characteristics diverge from those of river flows. Whilst groundwater levels at most boreholes are projected to decline (consistent with river flows), the majority of boreholes show <10% reduction in transient low groundwater levels by 2080 and eight show moderate increases. Groundwater drought characteristics in the far future (2050-2079) are often similar to those of the baseline (1989-2018), and in some instances droughts are projected to be most prolonged and severe in the near future (2020-2049). A number of explanatory factors for 25 this divergence are discussed. The sensitivity to seasonal changes in precipitation and potential evapotranspiration is proposed as a principal driver of divergence because low river flows are more influenced by shorter-term rainfall deficits in the summer half-year, whilst groundwater drought appears to be offset somewhat by the wetter winter signal in the RCM projections. Our results have fundamental importance for water management, demonstrating a widespread increase in river flow drought severity and diminishing low flows that could have profound societal and environmental impacts unless 30 mitigated. Furthermore, the divergence in projections of drought in river flows and groundwater levels brings into question the balance between surface and subsurface water resources. The projected contrast in fortunes of surface and subsurface water resources identified for the UK may be replicated in other parts of the world where climate projections suggest a shift towards drier summers and wetter winters. [ABSTRACT FROM AUTHOR]

Unsustainable exploitation of groundwater in northwestern India has led to extreme but spatially variable depletion of the alluvial aquifer system in the region. Mitigation and management of groundwater resources require an understanding of the drivers behind the pattern and magnitude of groundwater depletion, but a regional perspective on these drivers has been lacking. The objectives of this study are to (1) understand the extent to which the observed pattern of groundwater level change can be explained by the drivers of precipitation, potential evapotranspiration, abstraction, and canal irrigation, and (2) understand how the impacts of these drivers may vary depending on the underlying geological heterogeneity of the system. We used a transfer function-noise (TFN) time series approach to quantify the effect of the various driver components in the period 1974–2010, based on predefined impulse response functions (θ). The dynamic response to abstraction, summarized by the zeroth moment of the response M 0, is spatially variable but is generally large across the proximal and middle parts of the study area, particularly where abstraction is high but alluvial aquifer bodies are less abundant. In contrast, the precipitation response is rapid and fairly uniform across the study area. At larger distances from the Himalayan front, observed groundwater level rise can be explained predominantly by canal irrigation. We conclude that the geological heterogeneity of the aquifer system, which is imposed by the geomorphic setting, affects the response of the aquifer system to the imposed drivers. This heterogeneity thus provides a useful framework that can guide mitigation efforts; for example, efforts to decrease abstraction rates should be focused on areas with thinner and less abundant aquifer bodies. [ABSTRACT FROM AUTHOR]

The flow regime of glacier-fed rivers are sensitive to climate change due to strong climate-cryosphere-hydrosphere interactions. Previous modelling studies have foccused on projecting changes in annual and seasonal flow magnitude, but neglect other changes in river flow regime that could also have socio-economic and environmental impacts. This study employs a more comprehensive, signature-based analysis of climate change impacts on the river flow regime for the deglaciating Virkisá river basin in southern Iceland. 25 metrics (signatures) are derived from 21st century projections of river flow time-series to evaluate changes in different characteristics (magnitude, timing and variability) of river flow regime over sub-daily to decadal timescales. The projections are produced by a model chain that links numerical models of climate and glacio-hydrology. Five components of the model chain including the emission scenario, numerical climate model, downscaling procedure, snow/ice melt model and runoff-routing model are perturbed to propagate their uncertainties through to the river discharge projections. The signature-based analysis indicates that glacier-fed rivers will exhibit changes in the magnitude, timing and variability of river flows over a range of timescales in response to climate change. For most signatures there is high confidence in the sign of change, but the magnitude of change is uncertain and varies substantially across the different signatures. A decomposition of the projection uncertainties using analysis of variance (ANOVA) shows that all five perturbed model chain components contribute to projection uncertainty, but their relative contributions vary across the signatures (characteristic and timescale) of river flow. Signature-based decompositions of projection uncertainty can be used to better design impact studies to provide more robust projections. [ABSTRACT FROM AUTHOR]

Describes studies designed to examine the optimal breathing rate, obtain maximum heart rate variation, demonstrate the value of the measurement as a diagnostic test for autonomic neuropathy and examine the causes of death of patients with cardiac denervation. Less optimal breathing rate in diabetics with autonomic neuropathy; Consideration of impaired heart rate variation as the earliest sign of diabetic neuropathy.