Correlations between discharge and meteorological parameters and runoff forecasting from a highly glacierized Himalayan basin

To assess the predictive significance of meteorologica l parameters for forecasting discharge from the Dokriani Glacier basin in the Himalayan region, discharge autocorrelation and correlations between discharge and meteorological factors were investigated on a monthly and a seasonal basis. Changes in correlations between discharge and meteorological variables, lagged by 0-3 days, were determined. Discharge autocorrelation was found to be very high for each individual summer month and for the melt season as a whole. This suggests that a substantial meltwater storage in the glacier, which results in a delayed response of runoff, and therefore discharge, from the highly glacierized basins is very much dependent on the previous day's discharge. A comparison of correlations between discharge and temperature, and discharge and precipitation shows that temperature has a better correlation with discharge during June and September, while precipitation has good correlation with discharge in July and August. Variations in the physical features of the glacier, weather conditions, and precipitation and its distribution with time over the basin account for changes in correlations. To forecast the runoff from the Dokriani Glacier basin, multiple linear regression equations were developed separately for each month and for the whole melt season. A better forecast was obtained using the seasonal regression equation. A comparison of correlations for the Dokriani Glacier with those for the Z'rautt Glacier basin, Switzerland, illustrates that, for both basins, the previous day's discharge (Q,--i) shows maximum autocorrelation throughout the melt period. Whereas a good correlation between discharge and temperature was observed for the Z'mutt Glacier basin for the whole melt period, for the Dokriani Glacier basin it was strong at the beginning and end of the ablation season. Runoff delaying behaviour in the Dokriani Glacier basin is found more prominent than in the Z'mutt Glacier basin early in the melt season. Water storage appears to be less significant in the Dokriani Glacier than in the Z'mutt Glacier towards the end of the ablation season. The strength of correlation between discharge and precipitation is higher for the Dokriani Glacier basin than for the Z'mutt Glacier basin. This is due to higher rainfall in the Dokriani Glacier basin. In general, for both glacier basins, maximum correlation is found between discharge and precipitation on the same day. Corrélations entre débit et variables météorologiques et prévision des débits sur un bassin glaciaire himalayen Résumé Afin d'évaluer la capacité des variables météorologiques à prévoir le débit du bassin du glacier Dokriani (Région de l'Himalaya), on a étudié l'autocorrélation des débits et la corrélation entre débit et variables météorologiques aux échelles mensuelle et saisonnière. Les modifications des corrélations entre débit et variables météoro­ logiques ont été déterminées pour des décalages de 0 à 3 jours. L'autocorrélation des débits s'est révélée très importante pour tous les mois d'été et pour la saison de fonte dans son ensemble. Cela suggère qu'il existe dans le glacier un substantiel stock d'eau de fonte, nourrissant un débit retardé de ce bassin glaciaire qui dépend fortement du débit des jours précédents. Une comparaison des corrélations entre débit et température et entre débit et précipitation s montre que la meilleure corrélation entre débit et température est obtenue en juin et en septembre, alors qu'il s'agit des mois de juillet et d'août pour les précipitations. Les variations des caractéristiques physiques du glacier, le temps, les précipitations et leur distribution sur le bassin au cours du