UK Hydrological Bulletin: May - July 2013

After the hydrological pyrotechnics of last year, runoff patterns were more subdued through the first half of 2013, but temperatures were seasonally very unusual: an exceptionally hot July followed a notably cool spring. River flows and aquifer replenishment were generally within the normal range through the spring and early summer and overall water resources remained healthy. However, the persistence of high pressure during most of July — with an associated prolonged heatwave — changed the complexion of the landscape and the arid conditions triggered sustained river flow recessions. By mid-July heat stress had become a significant health issue, the parched soils were impacting on agriculture and fire risk in the countryside had increased markedly; there was also significant ecological stress as headwater streams dried up. Although, overall reservoir stocks, and groundwater resources, remained well within the normal summer range, heatwave-related surges in water demand stretched water treatment and distribution capacities. Late July witnessed a further transformation: heavy rainfall and intense thunderstorms terminated lengthy sequences of rainless days in most areas, disruptive flash flood events were very common and, approaching month-end, flood alerts were widespread across northern Britain