Implications of climate change on flow regime affecting Atlantic salmon

Abstract

The UKCIP02 climate change scenarios (20702100) suggest that the UK climate will become warmer (an overall increase of 2.53 o 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 Q 95 at the outlet of the study catchment may decrease to a Q 85 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.

Regional climate model data used within the SWURVE project – 1: projected changes in seasonal patterns and estimation of PET

“…To produce more plausible PET estimates, a simple regression-based approach was used to recalculate PET for the control and future scenarios. This method assumes that the historic 19611990 monthly relationship between PET and temperature (Walsh and Kilsby, 2007) can be extrapolated to a future climate. To compute the new PET values the following approach was used:…”

“…The coefficients of an empirical Blaney-Criddle equation (Blaney and Criddle, 1950) were derived using historic PET data by Walsh and Kilsby (2007). These were derived using a linear regression of temperature and PET data, (calculated using a Penman-Monteith type formulation) for observed climatic variables in a northwest England catchment in the Lake District region.…”

A predictive typology for characterising hydromorphology

“…Each channel length was then assigned values for the following variables: stream order (shown to relate closely to catchment area (Orr and Walsh, 2007)), floodplain width and specific stream power. Specific stream power (discharge × slope, divided by bankfull width) used slope derived from a 50 m DEM and bankfull discharge was estimated using the hydrological model SHETRAN, which was set-up for the catchment in a previous study (Walsh and Kilsby, 2007). Floodplain width was extracted from national digital maps of the extent of the 1 in 100 year flood (source: Environment Agency).…”

Distinguishing human and climate influences on hydrological disturbance processes in the Columbia River, USA

“…Large freshets may modify habitat structure and distribution and thereby affect salmon year classes (Bottom et al 2005). In contrast, water quality (especially temperature) and shallow water habitat availability decline during dry years without large spring freshets (Walsh and Kilsby 2007), impacts that are exacerbated by human alterations, e.g. diking for flood protection and flow diversion.…”