Correlation Analysis of Mackenzie River Discharge and NDVI Relationship

Abstract

. This study, based on the analyses of long-term discharge and Normalized Difference Vegetation Index (NDVI) data, revealed a strong seasonal consistency between NDVI and discharge over the Mackenzie River Basin in Canada. The flow–NDVI association is particularly strong in the early growing season (May to the 1st half of June). During this period, discharge rapidly rises and reaches the peak, whereas NDVI increases around the 1st half of May and reaches the maximum at the 2nd half of July. In the mid- and late summer, both discharge and NDVI decline gradually. Correlation analyses identify 2 sensitive periods, i.e., May to June and the 2nd half of July to the 1st half of September, when NDVI significantly responds to discharge variations. In the first period, the half-month NDVI highly correlates to the 1st half of May discharge, indicating that spring flow has a strong influence on vegetation growth in the early growing season. Spatially, almost all of the basin shows a high correlation, except Mackenzie and the Rocky Mountains and the region near the eastern edge of the basin. For the 2nd period, from the 2nd half of July to the 1st half of September, the NDVI relates closely to discharge with lags of 0–5 half-months. Trends analyses suggest river discharge increased during 1982 to 2006 in most seasons except summer. The NDVI trends during the growing season (May to September) clearly correspond to discharge changes. Examination of extreme flow years and corresponding NDVI conditions over the basin also reveal that a lower runoff was associated with a lower basin NDVI with an earlier maximum, whereas the higher flow was linked with a higher NDVI and a longer growing season.