Effects of spring breakup on microscale air temperatures

ABSTRACT. The effects of spring breakup on microscale air temperatures in the Mackenzie River delta were investigated by means of intervention analysis. Small but statistically significant increases in temperatures were detected for some areas within the delta nd appeared to be related to ice breakup events in nearby channels and lake systems. The magnitude of the temperature increase appeared to b correlated with the severity of winter conditions p d i n g breakup and with the rate at which breakup progressed. The relative irnportanw'8f changes in surface albedo and river heat in-put in causing air temperature ises is discussed. Temperature increases due to breakup are smalt in com&nson to seasonal warming trends and diur-nal temperature fluctuations. Key words: Mackenzie River, delta, breakup, climate, air temperature, intervention analysis, time-series RÉSUMÉ. Les effets de la debacle printani&re sur les temperatures microclimatiques de l'air observks dans le delta du fleuve Mackenzie ont et6 6tudiCs par une analyse d'intervention. Des augmentations de temfirature minimes mais nhmoins statistiquement signifwatives furent d6tectks dans certaines egions du delta et semblent &res apparent & aux tvenements de la d6bZlcle se produisant dans les syst&mes avoisants de canaux et de lacs. L'amplitude des augmentations de tempCrature semble varier en fonction de la &vErit6 des conditions hivernales prkedant la d6Mcle et en fonc-tion de la vitesse avec laquelle la dCbicle s'est produite. L'importance relative des changements de I'albedo superficiel et d l'apport calorifique des eaux fluviales est aussi discutk. Les augmentations de temphture rbultant des phhomknes associC h la dCb6cle sont minimes quand comparets aux rkhauffement saissonier et aux fluctuations diurnales de temphture