Dependency of summer lake inflows and precipitation on spring SOI

Abstract Inflows to South Island, New Zealand lakes deriving from snowmelt are quantified using a water balance approach and are shown to be between 8% and 24% of annual inflow. A snow accumulation index calculated from climatological data using a snowpack simulation model confirms the general pattern of the year-to-year variability of these estimates. Previous work has shown that summer inflows tend to be relatively low in years when the El Nino Southern Oscillation phenomenon is in a positive phase (i.e. La Nina). We show that this patter is also evident in records of precipitation around the catchments, particularly where precipitation exceeds 1000 mm/yr. Variance of inflows and precipitation appears to be dependent on the magnitude of the SOI. Snowmelt increases somewhat in La Nina years, and this may relate to a general trend for warmer temperatures in these years. A relative absence of La Nina conditions for 1976–1994 may be partially responsible for a significant increase in mean lake inflows over the period 1978–1994.