Changes in hydrological extremes and climate variability in the Severn Uplands

Hydrological extremes within the UK have increased in intensity, frequency and<br/>persistence over recent years and are predicted to increase in variability throughout the 21st<br/>century. Past and future changes in hydrological extremes relative to climate change were<br/>investigated within Severn Uplands, a climate sensitive catchment. Using the Mann-<br/>Kendall trend detection test, time-series analysis over a 30-year period revealed a<br/>significant increase in winter and autumn precipitation and a decrease in summer<br/>precipitation. The analysis of flow time-series indicated an increase in winter and July<br/>flows and a decrease in spring flows. Changes in climate variability over the same period<br/>showed increases in air temperature and SST, and a reduction in snow cover. Climate<br/>variables were found to largely correlate with hydrological extremes which were<br/>characteristic of certain weather types and largely influenced by the NAO.<br/><br/>To model future flows within the Severn Uplands a hydrological model (HEC-HMS) was<br/>used to simulate hydrological processes. The extreme hydrological event of November-<br/>December 2006 was used to calibrate the model. The difference between using radar and<br/>gauge precipitation data to drive the model was quantified. Radar data resulted in the<br/>smallest prediction accuracy followed by gauge-corrected radar data (corrected using the<br/>mean-field bias where gauge rainfall was interpolated using cokriging) and then gauge<br/>precipitation which had the largest prediction accuracy. Model accuracy was sufficient<br/>using the gauge corrected radar and gauge precipitation data as inputs, so both were altered<br/>for future predictions to investigate the propagation of uncertainty. Predicted changes in<br/>temperature and precipitation by the UKCIP02 scenarios were used to alter the baseline<br/>extreme event to predict changes in peak flow and outflow volume. Both radar- and gaugedriven<br/>hydrological modelling predicted large flow increases for the 21st century with<br/>increases up to 8% by the 2020s, 18% by the 2050s and 30% by the 2080s. Discrepancies<br/>between predictions were observed when using the different data inputs.

Name dc:type.qualificationname

Ph.D.

Level dc:type.qualificationlevel

doctoral

Grantor dc:publisher.institution

University of Southampton

Year dc:date.issued

2009

Author dc:creator

• Biggs, Eloise M.

Advisor dc:contributor.advisor

• Atkinson, Peter M