THE INFLUENCE OF VARIABLE WEATHER PATTERNS ON RIVER WATER QUANTITY AND QUALITY REGIMES

There is growing awareness as to the potential sensitivity of hydrolog ical systems to climate change. In particular long-term changes in pre cipitation variability will have consequences for runoff regimes and t hence solute transport. By utilizing the Lamb's Weather Type register in conjunction with observed 24 h rainfall totals it was possible to d etermine daily precipitation event probabilities and magnitudes for ei ght dominant synoptic classes. The stochastic rainfall series thus gen erated were then used to drive a robust hydrochemical model of an expe rimental catchment in the East Midlands, UK. The model results indicat e that the frequencies of flood and drought are dependent upon the syn optic scenario, and especially the historical prevalence of both the a nticyclonic and cyclonic patterns. Given that there have been marked f luctuations in the annual frequencies of these classes since the mid-n ineteenth century, long-term variations in the severity and incidence of extreme flows may be anticipated. Clearly this will have major impl ications for the episodic export and dilution of solutes, sediments an d microorganisms originating from both pristine and polluted hydrosyst ems.