Trends in Greenness and Snow Cover in Alaska’s Arctic National Parks, 2000–2016

David Swanson

doi:10.3390/rs9060514

Abstract

In cold-limited arctic environments, the duration and timing of the snow cover and the vegetation green season have major ecological implications. I monitored the phenology of snow cover and greenness using MODIS Terra satellite data for the years 2000 to 2016 in the 5 National Parks of northern Alaska, USA. Mann-Kendall trend tests showed that the end of the continuous snow season and midpoint of spring green-up became significantly earlier in parts of the study area over the 16-year period. Using the observed relationship between thaw degree-days at Kotzebue, Alaska and dates of snow-off and half green-up in nearby lowland tundra for the 16 years of MODIS data, I reconstructed the dates of snow-off and half green-up from long-term Kotzebue weather records back to 1937. The average snow-off and green-up dates probably became earlier by about 6 days over this 80-year time interval. Remote sensing of fall vegetation senescence and establishment of the snow cover were less reliable than the spring events due to cloudiness and low sun angles. The annual maximum normalized difference vegetation index (NDVI) generally did not increase significantly from 2001 to 2016, except in places where vegetation was recovering from forest fires.

Highlights

The climate of the Arctic has been warming since about 1980 [1] and the timing of spring snow loss has become significantly earlier over the same period [2]
Snow-off prior to May 1 within the study area occurred in some windy tundra
Snow-off prior to May 1 within the study area occurred in some windy tundra area −2

Summary

Introduction

The climate of the Arctic has been warming since about 1980 [1] and the timing of spring snow loss has become significantly earlier over the same period [2]. Parks of northern Alaska, the National Park Service is monitoring vegetation and snow phenology as a part of its long-term monitoring program [7,8,9,10]. Spectroradiometer, [11]) Terra satellite has been providing spectral information with 250 m resolution on a daily basis since the year 2000. These images can be used to determine greenness and snow cover, and allow us to study the magnitude and timing of changes in the seasons at finer spatial and temporal resolution than was possible previously. The purpose of this study is to explore the following questions for the National Parks of northern

Objectives

Results

Conclusion