SHORT-TERM AND MEDIUM-TERM TRENDS IN THE HYDROMETEOROLOGY OF THE CENTRAL SOUTHERN ALPS, NEW-ZEALAND

Short-and-medium term trends in the hydrometeorology of the central So uthern Alps are examined with the aim of developing monthly and season al inflow forecasting models for alpine hydro lakes. Both ambient air temperature and precipitation are considered principal components in t he generation of inflows. These two meteorological variables display b oth strong annual cycles and longer term fluctuations which are linked to the influence of different synoptic circulation systems and their regional impact, through such mechanisms as the ENSO phenomenon. Recen t investigations have indicated that negative phases of ENSO tend to d elay the onset of the spring melt season and to result in drought cond itions within the central Southern Alps. Such conditions during 1991 a nd 1992 were compounded by a global increase in atmospheric turbidity following two large volcanic eruptions, and contributed to a national energy crisis in New Zealand during the 1992 winter. Both seasonal and monthly empirically derived inflow models are assessed incorporating temperature, precipitation and circulation parameters to predict inflo ws. Although inflows for these time-scales correlate strongly with pre cipitation, temperature and atmospheric circulation for the same perio d, predicted inflows one season or month in advance did not. This supp orts the need for much shorter term monitoring of meteorological condi tions within such alpine catchments. In addition, there also appears t o be a need for quantifying inflows generated from the present long-te rm retreat of major eastern alpine glaciers, which also make a signifi cant contribution to lake inflows.