Identifying the Imprint of Climate Change on Low-Arctic Rivers from Planform Changes of the Colville River, Alaska

Abstract

The undeniable effect of climate change is prevalent in countless number of natural processes occurring across our planet, particularly within the circumpolar region. These climatic shifts have had an impact on internal and external forces that drive river movement. Hence, channel activities within these regions would, presumably, also change in response. Using the Colville River, situated in northern Alaska, USA, as a study site, the research first identifies the climatological trends occurring within the region. Temperature, precipitation, and discharge from the year 2002 to 2019 are examined to identify how these internal and external factors have changed throughout the years. Additionally, channel activities of two reaches within the river are also calculated within the same period using Landsat data. These variables are then correlated amongst each other to identify how one factor influences the other. Trends are captured on both a continuous (short-term) and a yearly (long-term) timeframe, whereby the continuous timeframe presents the data in a monthly sequential period from 2002 to 2019 while the yearly timeframe compares the data of each month across the years. Finally, the same approach was completed using Planet satellite imageries, where data is available, to verify the result. The findings show an overall increase in temperature primarily during the winter months, increase in frequency of precipitation towards the more recent years, and both an increase and decrease in discharge during the freezing and thawing period, respectively. Furthermore, the calculation shows a strong positive correlation between discharge and temperature (r = 0.63, r2 = 0.39, p-value = 4.64e-17) for the continuous, short-term, timeframe and a relatively strong negative correlation (r = -0.57, r2 = 0.32, p-value = 1.88e-5) for the yearly, long-term, timeframe. The positive correlation between the two variables in the short-term timeframe shows the seasonal relationship between temperature and discharge, whereby as the temperature increases, discharge also increases in response. Interestingly, however, the long-term timeframe suggests that as the temperature increases, discharge decreases in response. This was identified as the effect of climate change that is caused by the increase in temperature during the freezing months. Discharge is starting to take place throughout the year, therefore it is hypothesized that during the thawing months most ice have already melted which results in an overall decrease in discharge during the freezing months. And given the relatively strong positive correlation of discharge and channel activity for the short-term timeframe (Reach A: r = 0.62, r2 = 0.62, p-value = 1.02e-16 and Reach B: r = 0.68, r2 = 0.46, p-value = 2.65e-19), it is expected that channel movement will soon follow such decrease in discharge trend in the long run. These findings suggest that semi-arctic braided rivers, the Colville River in particular, are transitioning to river movements more similar to rivers situated in temperate climate, whereby activity is not only prevalent during the thawing months but will soon be identifiable throughout the year.