RELATIONSHIPS BETWEEN TEMPERATURE AND ABLATION ON THE TASMAN GLACIER, MOUNT COOK NATIONAL-PARK, NEW-ZEALAND

Ablation-stake measurements carried out between 1985 and 1987 show seasonal changes in glacier ablation at two altitudes, which are correlated with air temperature measured at Mount Cook village. Temperature variation explains 88% of the variability in ablation at 960 m altitude and 71% at 1360 m, indicating that estimation of ablation can be made with reasonable confidence and convenience from off-site temperature records. The empirical temperature-ablation relation is extended to predict ablation at all altitudes. The relationship allows reconstruction of nineteenth century ablation conditions at one site, and indicates that mean mid-summer ablation has increased from 63 mm/d to 88 mm/d since A.D. 1890. Of this, 60% has been due to regional warming and 40% to glacier thinning. Prediction of future mid-summer ablation under a warming climate indicates a mean ablation rate of up to 18 mm/d above 1986 values for a 1 degrees C warming, and up to 40 mm/d for a 2 degrees C warming. If meltwater production increases in proportion to ablation rate, meltwater discharges would increase by 20-25% and 40-50% for these two warmer climate scenarios. More likely, glacier area will reduce and the increased meltwater discharge will be a transient phase preceding reduced melt-generated runoff.