Climate-driven changes in UK river flows

Hannaford, Jamie

doi:10.1177/0309133314536755

Cited by 116 publications

(123 citation statements)

References 69 publications

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“…River flows and autumn-winter flooding have increased since the 1960s, especially in the north and west of Britain (Hannaford 2015), thereby increasing the potential for fluvial disturbance. However, neither the variability in long term flow nor the increase in annual flood frequency could explain variation in the amount of sediment deposited.…”

Section: Environmental Impact Of Invasive Alien Plants and Sediment Dmentioning

confidence: 99%

“…However, invasive alien plants (IAPs) benefit from these same properties and commonly use riparian zones as corridors for dispersal (Naiman and Decamps 1997). Meteorological and river level data for the UK point to a recent and ongoing increase in runoff, resulting in a greater frequency of high-flow events in autumn and winter, especially in the north and west (Hannaford 2015). Combined with disturbance by sediment deposition this may facilitate colonisation and establishment of IAPs, thus potentially impacting native vegetation and the overall functioning of riparian ecosystems (Richardson et al 2007).…”

Section: Introductionmentioning

confidence: 99%

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Invasion legacy effects versus sediment deposition as drivers of riparian vegetation

2017

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Riparian zones are formed by interactions between fluvio-geomorphological processes, such as sediment deposition, and biota, such as vegetation. Establishment of invasive alien plant (IAP) species along rivers may influence vegetation dynamics, evidenced as higher seasonal or inter-annual fluctuations in native plant diversity when IAP cover is high. This could impact the overall functioning of riparian ecosystems. Conversely, fine sediment deposited in riparian zones after floods may replenish propagule banks, thus supporting recruitment of native species. The interactive effects of invasion and fine sediment deposition have hitherto, however, been ignored. Vegetation surveys across rivers varying in flow regime were carried out over 2 years to assess changes in community composition and diversity. Artificial turf mats were used to quantify over-winter sediment deposition. The viable propagule bank in soil and freshly deposited sediment was then quantified by germination trials. Structural Equation Models were used to assess causal pathways between environmental variables, IAPs and native vegetation. Greater variation in flow increased the cover of IAPs along riverbanks. An increased in high flow events and sediment deposition were positively associated with the diversity of propagules deposited. However, greater diversity of propagules did not result in a more diverse plant community at invaded sites, as greater cover of IAPs in summer reduced native plant diversity. Seasonal turnover in the above-ground vegetation was also accentuated at previously invaded sites, suggesting that a legacy of increased competition in previous years, not recent sediment deposition, drives above-ground vegetation structure at invaded sites. The interaction between fluvial disturbance via sediment deposition and invasion pressure is of growing importance in the management of riparian habitats. Our results suggest that invasion can uncouple the processes that contribute to resilience in dynamic habitats making already invaded habitats vulnerable to further invasions.

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Section: Environmental Impact Of Invasive Alien Plants and Sediment Dmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Invasion legacy effects versus sediment deposition as drivers of riparian vegetation

2017

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“…In addition, the UK natural resources of freshwater (Watts et al, 2015), soils (Reynolds et al, 2013;Bellamy et al, 2005) and vegetation (Berry et al, 2002;Hickling et al, 2006;Norton et al, 2012) are changing. The UK is experiencing new environmental stresses on the land and water systems through changes in temperature and river flows (Crooks and Kay, 2015;Watts et al, 2015;Hannaford, 2015), which are part of a widespread global pattern of temperature increase and circulation changes (Watts et al, 2015).…”

Section: Introductionmentioning

confidence: 99%

Trends in atmospheric evaporative demand in Great Britain using high-resolution meteorological data

Robinson

Blyth

Clark

et al. 2017

Hydrol. Earth Syst. Sci.

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Abstract. Observations of climate are often available on very different spatial scales from observations of the natural environments and resources that are affected by climate change. In order to help bridge the gap between these scales using modelling, a new dataset of daily meteorological variables was created at 1 km resolution over Great Britain for the years 1961-2012, by interpolating coarser resolution climate data and including the effects of local topography. These variables were used to calculate atmospheric evaporative demand (AED) at the same spatial and temporal resolution. Two functions that represent AED were chosen: one is a standard form of potential evapotranspiration (PET) and the other is a derived PET measure used by hydrologists that includes the effect of water intercepted by the canopy (PETI). Temporal trends in these functions were calculated, with PET found to be increasing in all regions, and at an overall rate of 0.021 ± 0.021 mm day −1 decade −1 in Great Britain. PETI was found to be increasing at a rate of 0.019 ± 0.020 mm day −1 decade −1 in Great Britain, but this was not statistically significant. However, there was a trend in PETI in England of 0.023 ± 0.023 mm day −1 decade −1 . The trends were found to vary by season, with spring PET increasing by 0.043 ± 0.019 mm day −1 decade −1 (0.038 ± 0.018 mm day −1 decade −1 when the interception correction is included) in Great Britain, while there is no statistically significant trend in other seasons. The trends were attributed analytically to trends in the climate variables; the overall positive trend was predominantly driven by rising air temperature, although rising specific humidity had a negative effect on the trend. Recasting the analysis in terms of relative humidity revealed that the overall effect is that falling relative humidity causes the PET to rise. Increasing downward short-and longwave radiation made an overall positive contribution to the PET trend, while decreasing wind speed made a negative contribution to the trend in PET. The trend in spring PET was particularly strong due to a strong decrease in relative humidity and increase in downward shortwave radiation in the spring.

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“…There are also a number of studies (e.g. Tekleab et al, 2013;Gebremicael et al, 2013;Wang et al, 2015;Hannaford, 2015;Saraiva-Okello et al, 2015) who found that changes in rainfall are not sufficient to explain the trends in the streamflow.…”

Section: Introductionmentioning

confidence: 99%

Temporal and spatial changes of rainfall and streamflow in the Upper Tekezē–Atbara river basin, Ethiopia

Gebremicael

Mohamed

Zaag

et al. 2017

Hydrol. Earth Syst. Sci.

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Abstract. The Upper Tekezē-Atbara river sub-basin, part of the Nile Basin, is characterized by high temporal and spatial variability of rainfall and streamflow. In spite of its importance for sustainable water use and food security, the changing patterns of streamflow and its association with climate change is not well understood. This study aims to improve the understanding of the linkages between rainfall and streamflow trends and identify possible drivers of streamflow variabilities in the basin. Trend analyses and changepoint detections of rainfall and streamflow were analysed using Mann-Kendall and Pettitt tests, respectively, using data records for 21 rainfall and 9 streamflow stations. The nature of changes and linkages between rainfall and streamflow were carefully examined for monthly, seasonal and annual flows, as well as indicators of hydrologic alteration (IHA).The trend and change-point analyses found that 19 of the tested 21 rainfall stations did not show statistically significant changes. In contrast, trend analyses on the streamflow showed both significant increasing and decreasing patterns. A decreasing trend in the dry season (October to February), short season (March to May), main rainy season (June to September) and annual totals is dominant in six out of the nine stations. Only one out of nine gauging stations experienced significant increasing flow in the dry and short rainy seasons, attributed to the construction of Tekezē hydropower dam upstream this station in 2009. Overall, streamflow trends and change-point timings were found to be inconsistent among the stations. Changes in streamflow without significant change in rainfall suggests factors other than rainfall drive the change. Most likely the observed changes in streamflow regimes could be due to changes in catchment characteristics of the basin. Further studies are needed to verify and quantify the hydrological changes shown in statistical tests by identifying the physical mechanisms behind those changes. The findings from this study are useful as a prerequisite for studying the effects of catchment management dynamics on the hydrological variabilities in the basin.

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Climate-driven changes in UK river flows

Cited by 116 publications

References 69 publications

Invasion legacy effects versus sediment deposition as drivers of riparian vegetation

Invasion legacy effects versus sediment deposition as drivers of riparian vegetation

Trends in atmospheric evaporative demand in Great Britain using high-resolution meteorological data

Temporal and spatial changes of rainfall and streamflow in the Upper Tekezē–Atbara river basin, Ethiopia

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