Land surface phenology in the highland pastures of montane Central Asia: Interactions with snow cover seasonality and terrain characteristics

• Published in: Remote sensing of environment Vol. 240; p. 111675
• Main Authors: Tomaszewska, Monika A., Nguyen, Lan H., Henebry, Geoffrey M.
• Format: Journal Article
• Language: English
• Published: New York Elsevier Inc 01-04-2020; Elsevier BV
• Subjects: Aridity; Climate change; Climatic conditions; Correlation; Correlation analysis; Degree-days; Elevation; Global climate; Growing season; Kyrgyzstan; Land surface temperature; Landsat; Landsat satellites; MODIS; Normalized difference vegetative index; Pasture; Phenology; Remote sensing; Seasonal variations; Slopes; Snow; Snow cover; Snowmelt; Surface temperature; Sustainability; Terrain; Terrain effects; Vegetation; Vegetation index; Central Asia; Kyrgyzstan; Climate change; MODIS; Kyrgyzstan; Landsat; Terrain effects
• ISSN: 0034-4257; 1879-0704
• DOI: 10.1016/j.rse.2020.111675

Many studies have shown that high elevation environments are among very sensitive to climatic changes and where impacts are exacerbated. Across Central Asia, which is especially vulnerable to climate change due to aridity, the ability of global climate projections to capture the complex dynamics of mountainous environments is particularly limited. Over montane Central Asia, agropastoralism constitutes a major portion of the rural economy. Extensive herbaceous vegetation forms the basis of rural economies in Kyrgyzstan. Here we focus on snow cover seasonality and the effects of terrain on phenology in highland pastures using remote sensing data for 2001–2017. First, we describe the thermal regime of growing season using MODerate Resolution Imaging Spectrometer (MODIS) land surface temperature (LST) data, analyzing the modulation by elevation, slope, and aspect. We then characterized the phenology in highland pastures with metrics derived from modeling the land surface phenology using Landsat normalized difference vegetation index (NDVI) time series together with MODIS LST data. Using rank correlations, we then analyzed the influence of four metrics of snow cover seasonality calculated from MODIS snow cover composites—first date of snow, late date of snow, duration of snow season, and the number of snow-covered dates (SCD)—on two key metrics of land surface phenology in the subsequent growing season, specifically, peak height (PH; the maximum modeled NDVI) and thermal time to peak (TTP; the amount of growing degree-days accumulated during modeled green-up phase). We evaluated the role of terrain features in shaping the relationships between snow cover metrics and land surface phenology metrics using exact multinomial tests of equivalence. Key findings include (1) a positive relationship between SCD and PH occurred in over 1664 km2 at p < 0.01 and 5793 km2 at p < 0.05, which account for >8% of 68,881 km2 of the pasturelands analyzed in Kyrgyzstan; (2) more negative than positive correlations were found between snow cover onset and PH, and more positive correlations were observed between snowmelt timing and PH, indicating that a longer snow season can positively influence PH; (3) significant negative correlations between TTP and SCD appeared in 1840 km2 at p < 0.01 and 6208 km2 at p < 0.05, and a comparable but smaller area showed negative correlations between TTP and last date of snow (1538 km2 at p < 0.01 and 5188 km2 at p < 0.05), indicating that under changing climatic conditions toward earlier spring warming, decreased duration of snow cover may lead to lower pasture productivity, thereby threatening the sustainability of montane agropastoralism; and (4) terrain had a stronger influence on the timing of last date of snow cover than on the number of snow-covered dates, with slope being more important than aspect, and the strongest effect appearing from the interaction of aspect and steeper slopes. In this study, we characterized the snow-phenology interactions in highland pastures and revealed strong dependencies of pasture phenology on timing of snowmelt and the number of snow-covered dates.
•Modeled LSP in pastures at 30 m using 17 years of Landsat and MODIS data•Prevalent trend of increasing peak NDVI in highland pastures 2001–2017•Later snowmelt date and more snow covered dates increased peak NDVI•Slope was more important than aspect on linkages between snow cover & LSP.