Yukon River Discharge-NDVI Relationship

Similar to the Mackenzie River, a strong seasonal consistency between NDVI and discharge exists for Yukon River. The flow-NDVI association is particularly strong before June, discharge rapidly rises and reaches the peak the 1st half of June, while the NDVI in the period of April to June increases fastest and reaches the maximum in July. In the mid and late summer, both discharge and NDVI decline gradually. Similarly, two sensitive periods while NDVI significantly correlates to discharge variations were also found in this region. May to June is key time of vegetation relates to discharge, the NDVI on 2nd half of May and 1st half of June is significantly correlated to the 1st half of May discharge mainly in midstream zone. August is another sensitive period, the 2nd half of August NDVI closely related to the synchronous and previous half-month discharge. River discharge decreased during growing season except in May from 1982 to 2013 in Yukon Basin. The significant decrease about 8–15% of the average flow, but a significant increase with a trend above 34.2% occurred in May. The NDVI trends during the growing season from May to September almost inversely correspond to discharge changes with a weak increments about 5% of the mean NDVI. In addition, examination of extreme flow years and corresponding NDVI conditions also reveals that low runoff year was associated with a lower basin NDVI with an earlier maximum, while the higher flow year was linked with a higher NDVI and a longer growth season. It may imply the better water supply with higher flow in the spring will induce a higher vegetation production.