The average summer temperature at that station is 5.4 o C , which leads the linear model to predict 3.56 m of ablation. There are four months with temperatures above the melting point, for a total of 527 positive degree-days. The runoff predicted by the six model combinations is compared, in Table 3, to observations at the few stations which provide that information. The underestimation of runoff at ETH Camp is linked to the downwelling shortwave radiation being slightly too small, the excess runoff at Nordbogletscher is due to the model's mid-summer air temperatures being slightly too warm. The largest discrepancies between these two model combinations occurs at Camp 4 and the absence of ablation measurements at that station does not allow any inferences from this difference.
Units are cm .
As the melt zone expands, the firn thickness which has to be brought to the melting point before any runoff can occur increases. The bulk of the extra energy would thus go at first into forming superimposed ice layers within the firn before any runoff could begin to take place. An error of 2 o C on the climate model's part leads to a difference of 1 m in the predicted ablation. This is an accuracy which regional climate predictions have yet to attain. This discrepancy highlights the danger of relying on a single model input, temperature, to calculate runoff.