A cyclone climatology of the British‐Irish Isles 1871–2012

Abstract

ABSTRACT:The British-Irish Isles (BI) lie beneath the North Atlantic storm track year-round and thus are impacted by the passage of extra-tropical cyclones. Given recent extreme storminess and projections of enhanced winter cyclone activity for this region, there is much interest in assessing the extent to which the cyclone climate of the region may be changing. We address this by assessing a 142-year (1871-2012) record of cyclone frequency, intensity and 'storminess' derived from the 20th Century Reanalysis V2 (20CR) dataset. We also use this long-term record to examine associations between cyclone activity and regional hydroclimate. Our results confirm the importance of cyclone frequency in driving seasonal precipitation totals which we find to be greatest during summer months. Cyclone frequency and storminess are characterized by pronounced interannual and multi-decadal variability which are strongly coupled to atmospheric blocking in the Euro-Atlantic region, but we detect no evidence of an increasing trend. We observe an upward trend in cyclone intensity for the BI region, which is strongest in winter and consistent with model projections, but promote caution interpreting this given the changing data quality in the 20CR over time. Nonetheless, we assert that long-term reconstruction is helpful for contextualizing recent storminess and for identifying emerging changes in regional hydroclimate linked to cyclones.

A hydrogeomorphic assessment of twenty‐first century floods in the UK

“…As well as milder/wetter winters characterized by fewer rain‐on‐snow floods, reduced late twentieth century upland flooding is also related to an unusual run of positive summer NAO index values, strong negative rainfall anomalies and a marked decline in summer cyclonic flow. The latter is especially marked between 1961 and 1990 (Matthews et al, ) and corresponds with a reduction in heavy upland rainfall provided by cyclonic weather types (Burt and Horton, ; Burt and Ferranti, ). Such consistently positive summer NAO values have not been recorded in the last 150 years and tree‐ring reconstructions indicate they were last experienced in the early sixteenth century (Figure c; Folland et al, ; Linderholm et al, ).…”

“…Negative summer NAO index values indicate a southerly displacement of the north Atlantic storm track and cyclones towards the UK. Note that the probability of a cyclone over the British Isles is highest during late summer (Matthews et al, ), giving the potential for slow moving torrential downpours and boulder‐berm generation (Foulds et al, ). Positive summer NAO index values are associated with drier, warmer and sunnier weather in the UK and northwest Europe. Although usually drier than average, −NAO winters are often snowy, which increases the likelihood of severe rain‐on‐snow floods as polar or continental air masses are displaced by mild and wet Atlantic air masses (i.e.…”

Persistence of Hydrometeorological Droughts in the United Kingdom: A Regional Analysis of Multi-Season Rainfall and River Flow Anomalies

“…The years 1988The years , 1989The years and 1990 were also noteworthy at the time for being the warmest in the Central England Temperature series (Marsh and Monkhouse, 1993). Earlier drought periods in the 1970s were remarkable for the quiescence of summer cyclones (Matthews et al, 2015). Nonetheless, care must be taken when interpreting long-run, low-flow sequences because of their susceptibility to local artificial influences such as river regulation, effluent returns, water storage, or groundwater abstraction (in the case of the Wensum).…”

A systematic assessment of drought termination in the United Kingdom

“…Further research is required to assess the extent to which changes in these and other synoptic drivers might be influencing the seasonality of drought terminations in the UK. For instance, Matthews et al (2016) report relatively low frequencies of summer cyclones in the period 1961-1990 but a marked resurgence in counts since the 1990s.…”