On the Importance of High-Resolution Time Series of Optical Imagery for Quantifying the Effects of Snow Cover Duration on Alpine Plant Habitat

Jean-Pierre Dedieu,Philippe Choler,Vincent Vionnet,Pascal Sirguey,Sylvain Bigot,Bradley Carlson

doi:10.3390/rs8060481

Abstract

We investigated snow cover dynamics using time series of moderate (MODIS) to high (SPOT-4/5, Landsat-8) spatial resolution satellite imagery in a 3700 km2 region of the southwestern French Alps. Our study was carried out in the context of the SPOT (Take 5) Experiment initiated by the Centre National d’Etudes Spatiales (CNES), with the aim of exploring the utility of high spatial and temporal resolution multispectral satellite imagery for snow cover mapping and applications in alpine ecology. Our three objectives were: (i) to validate remote sensing observations of first snow free day derived from the Normalized Difference Snow Index (NDSI) relative to ground-based measurements; (ii) to generate regional-scale maps of first snow free day and peak standing biomass derived from the Normalized Difference Vegetation Index (NDVI); and (iii) to examine the usefulness of these maps for habitat mapping of herbaceous vegetation communities above the tree line. Imagery showed strong agreement with ground-based measurements of snow melt-out date, although R2 was higher for SPOT and Landsat time series (0.92) than for MODIS (0.79). Uncertainty surrounding estimates of first snow free day was lower in the case of MODIS, however (±3 days as compared to ±9 days for SPOT and Landsat), emphasizing the importance of high temporal as well as high spatial resolution for capturing local differences in snow cover duration. The main floristic differences between plant communities were clearly visible in a two-dimensional habitat template defined by the first snow free day and NDVI at peak standing biomass, and these differences were accentuated when axes were derived from high spatial resolution imagery. Our work demonstrates the enhanced potential of high spatial and temporal resolution multispectral imagery for quantifying snow cover duration and plant phenology in temperate mountain regions, and opens new avenues to examine to what extent plant community diversity and functioning are controlled by snow cover duration.

Highlights

IntroductionMountain regions are privileged areas for water and energy exchanges
Topographic heterogeneity within 250 m pixels led to discrepancy between ground-based measurements of snow melt-out and Normalized Difference Snow Index (NDSI) observed by MODIS
Through ground validation and comparison with moderate resolution products, our study demonstrates the utility of high-resolution time series imagery for mapping snow cover duration in alpine environments

Summary

Introduction

Mountain regions are privileged areas for water and energy exchanges. The seasonal evolution of the snow pack is a key parameter influencing regional climate [2], water resource budgets [3], and ecosystem functioning and structure [4]. Within the context of global climate change [1,5], temperature rise in the European. Alps has been pronounced and accompanied by rising snow lines and earlier melt-out dates [6,7]. Recent studies show that a continuous winter snow pack is becoming increasingly rare in Alpine catchments below 1200 m above sea level (a.s.l.) [8], snow cover duration above 2000 m a.s.l

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