EFFECTS OF CLIMATE VARIABILITY ON RIVERS: CONSEQUENCES FOR LONG TERM WATER QUALITY ANALYSIS

The influence of the El Nino Southern Oscillation (ENSO) climate pattern on physical and chemical characteristics of surface waters at 77 river sites throughout New Zealand over the period 1989 2001 was investigated. The Southern Oscillation Index was used to characterize ENSO, and to examine the effect of climate variability on flow and water-quality variables, simple linear regression was performed of each variable on the Southern Oscillation Index for each site. Results suggested increasing flows in the north and decreasing flows in the south, and the pattern observed for river water temperature matched known ENSO effects on air temperature and sea-surface temperature around New Zealand. The temperature variation appeared to be relatively independent of rainfall flow variation. Variation in rainfall/flow associated with the Southern Oscillation Index was related to the patterns observed for conductivity, water clarity/turbidity, and total phosphorus levels, but no correlation was found with nitrogen species, dissolved reactive P, BOD, and river color.