Implications of climate change on flow regime affecting Atlantic salmon

International audienceThe UKCIP02 climate change scenarios (2070?2100) suggest that the UK climate will become warmer (an overall increase of 2.5?3°C), with temperature increases being greater in the summer and autumn than in the spring and winter seasons. In terms of precipitation, winters are expected to become wetter and summers drier throughout the UK. The effect of changes in the future climate on flow regimes are investigated for the Atlantic salmon, Salmo salar, in a case study in an upland UK river. Using a hydraulic modelling approach, flows simulated across the catchment are assessed in terms of hydraulic characteristics (discharge per metre width, flow depths, flow velocities and Froude number). These, compared with suitable characteristics published in the literature for various life stages of Atlantic salmon, enable assessment of habitat suitability. Climate change factors have been applied to meteorological observations in the Eden catchment (north-west England) and effects on the flow regime have been investigated using the SHETRAN hydrological modelling system. High flows are predicted to increase by up to 1.5%; yet, a greater impact is predicted from decreasing low flows (e.g. a Q95 at the outlet of the study catchment may decrease to a Q85 flow). Reliability, Resilience and Vulnerability (RRV) analysis provides a statistical indication of the extent and effect of such changes on flows. Results show that future climate will decrease the percentage time the ideal minimum physical habitat requirements will be met. In the case of suitable flow depth for spawning activity at the outlet of the catchment, the percentage time may decrease from 100% under current conditions to 94% in the future. Such changes will have implications for the species under the Habitats Directive and for catchment ecological flow management strategies

Modelling the impacts of projected future climate change on water resources in north-west England

International audienceOver the last two decades, the frequency of water resource drought in the UK, coupled with the more recent pan-European drought of 2003, has increased concern over changes in climate. Using the UKCIP02 Medium-High (SRES A2) scenario for 2070?2100, this study investigates the impact of climate change on the operation of the Integrated Resource Zone (IRZ), a complex conjunctive-use water supply system in north-western England. The results indicate that the contribution of individual sources to yield may change substantially but that overall yield is reduced by only 18%. Notwithstanding this significant effect on water supply, the flexibility of the system enables it to meet modelled demand for much of the time under the future climate scenario, even without a change in system management, but at significant expense for pumping additional abstraction from lake and borehole sources. This research provides a basis for the future planning and management of the complex water resource system in the north-west of England

Hydrological impacts of climate change on the Tejo and Guadiana Rivers

International audienceA distributed daily rainfall?runoff model is applied to the Tejo and Guadiana river basins in Spain and Portugal to simulate the effects of climate change on runoff production, river flows and water resource availability with results aggregated to the monthly level. The model is calibrated, validated and then used for a series of climate change impact assessments for the period 2070?2100. Future scenarios are derived from the HadRM3H regional climate model (RCM) using two techniques: firstly a bias-corrected RCM output, with monthly mean correction factors calculated from observed rainfall records; and, secondly, a circulation-pattern-based stochastic rainfall model. Major reductions in rainfall and streamflow are projected throughout the year; these results differ from those for previous studies where winter increases are projected. Despite uncertainties in the representation of heavily managed river systems, the projected impacts are serious and pose major threats to the maintenance of bipartite water treaties between Spain and Portugal and the supply of water to urban and rural regions of Portugal

Improving bank erosion modelling at catchment scale by incorporating temporal and spatial variability

Bank erosion can contribute a significant portion of the sediment budget within temperate catchments, yet few catchment scale models include an explicit representation of bank erosion processes. Furthermore, representation is often simplistic resulting in an inability to capture realistic spatial and temporal variability in simulated bank erosion. In this study, the sediment component of the catchment scale model SHETRAN is developed to incorporate key factors influencing the spatio-temporal rate of bank erosion, due to the effects of channel sinuosity and channel bank vegetation. The model is applied to the Eden catchment, north-west England, and validated using data derived from a GIS methodology. The developed model simulates magnitudes of total catchment annual bank erosion (617 - 4063 t yr-1) within the range of observed values (211 - 4426 t yr-1). Additionally the model provides both greater inter-annual and spatial variability of bank eroded sediment generation when compared with the basic model, and indicates a potential 61% increase of bank eroded sediment as a result of temporal flood clustering. The approach developed within this study can be used within a number of distributed hydrologic models and has general applicability to temperate catchments, yet further development of model representation of bank erosion processes is required

A stochastic rainfall model for the assessment of regional water resource systems under changed climatic condition

International audienceA stochastic model is developed for the synthesis of daily precipitation using conditioning by weather types. Daily precipitation statistics at multiple sites within the region of Yorkshire, UK, are linked to objective Lamb weather types (LWTs) and used to split the region into three distinct precipitation sub-regions. Using a variance minimisation criterion, the 27 LWTs are clustered into three physically realistic groups or ?states'. A semi-Markov chain model is used to synthesise long sequences of weather states, maintaining the observed persistence and transition probabilities. The Neyman-Scott Rectangular Pulses (NSRP) model is then fitted for each weather state, using a defined summer and winter period. The combined model reproduces key aspects of the historic precipitation regime at temporal resolutions down to the hourly level. Long synthetic precipitation series are useful in the sensitivity analysis of water resource systems under current and changed climatic conditions. This methodology enables investigation of the impact of variations in weather type persistence or frequency. In addition, rainfall model statistics can be altered to simulate instances of increased intensity or proportion of dry days for example, for individual weather groups. The input of such data into a water resource model, simulating potential atmospheric circulation changes, will provide a valuable tool for future planning of water resource systems. The ability of the model to operate at an hourly level also allows its use in a wider range of hydrological impact studies, e.g. variations in river flows, flood risk estimation etc. Keywords: water resources; climate change; impacts; stochastic rainfall model; Lamb weather types</p

A Detailed Cloud Fraction Climatology of the Upper Indus Basin and Its Implications for Near-Surface Air Temperature*

implications for near surface air temperature. Journal of Climate 2015, 28(9)

Quantifying and Mitigating Wind‐Induced Undercatch in Rainfall Measurements

Despite the apparent simplicity, it is notoriously difficult to measure rainfall accurately because of the challenging environment within which it is measured. Systematic bias caused by wind is inherent in rainfall measurement and introduces an inconvenient unknown into hydrological science that is generally ignored. This paper examines the role of rain gauge shape and mounting height on catch efficiency (CE), where CE is defined as the ratio between nonreference and reference rainfall measurements. Using a pit gauge as a reference, we have demonstrated that rainfall measurements from an exposed upland site, recorded by an adjacent conventional cylinder rain gauge mounted at 0.5 m, were underestimated by more than 23% on average. At an exposed lowland site, with lower wind speeds on average, the equivalent mean undercatch was 9.4% for an equivalent gauge pairing. An improved-aerodynamic gauge shape enhanced CE when compared to a conventional cylinder gauge shape. For an improved-aerodynamic gauge mounted at 0.5 m above the ground, the mean undercatch was 11.2% at the upland site and 3.4% at the lowland site. The mounting height of a rain gauge above the ground also affected CE due to the vertical wind gradient near to the ground. Identical rain gauges mounted at 0.5 and 1.5 m were compared at an upland site, resulting in a mean undercatch of 11.2% and 17.5%, respectively. By selecting three large rainfall events and splitting them into shorter-duration intervals, a relationship explaining 81% of the variance was established between CE and wind speed

The blue-green path to urban flood resilience

Abstract Achieving urban flood resilience at local, regional and national levels requires a transformative change in planning, design and implementation of urban water systems. Flood risk, wastewater and stormwater management should be re-envisaged and transformed to: ensure satisfactory service delivery under flood, normal and drought conditions, and enhance and extend the useful lives of ageing grey assets by supplementing them with multi-functional Blue-Green infrastructure. The aim of the multidisciplinary Urban Flood Resilience (UFR) research project, which launched in 2016 and comprises academics from nine UK institutions, is to investigate how transformative change may be possible through a whole systems approach. UFR research outputs to date are summarised under three themes. Theme 1 investigates how Blue-Green and Grey (BG + G) systems can be co-optimised to offer maximum flood risk reduction, continuous service delivery and multiple co-benefits. Theme 2 investigates the resource capacity of urban stormwater and evaluates the potential for interoperability. Theme 3 focuses on the interfaces between planners, developers, engineers and beneficiary communities and investigates citizens’ interactions with BG + G infrastructure. Focussing on retrofit and new build case studies, UFR research demonstrates how urban flood resilience may be achieved through changes in planning practice and policy to enable widespread uptake of BG + G infrastructure.EPSR