Spatiotemporal variations of alpine climate, snow cover and phenology S. Asam, M. Callegari, M. Matiu, G. Fiore, L. De Gregorio, A. Jacob, A. Menzel, C. Notarnicola, M. Zebisch
Asam et al., Spatiotemporal variations of alpine climate, snow cover and phenology 2 INTRODUCTION Timing and magnitude of phenological events rely on climate variability Mountain ecosystems are fragile environments and assumed to be sensitive to climate changes High complexity of abiotic influences on phenology Snow cover and snow melt particularly relevant Few studies on alpine phenology & snow, no alpinewide pixel-wise analysis available
Asam et al., Spatiotemporal variations of alpine climate, snow cover and phenology 3 QUESTIONS What are the spatio-temporal patterns of plant phenology and its drivers in the Alps? How does the relationship between climate, snow and plant growth change in different altitude ranges? What is the combined influence of climate and snow on vegetation phenology?
Asam et al., Spatiotemporal variations of alpine climate, snow cover and phenology 4 OBJECTIVES Joint analysis of alpine-wide MODIS vegetation & snow metrics and climate data Detection of patterns and trends with regard to altitude Identification the relationships between phenology and its drivers under varying site conditions
Asam et al., Spatiotemporal variations of alpine climate, snow cover and phenology 5 DATA Monthly mean NDVI Start of Season [Alps, 2000 17, 250 m] Snow Cover Duration Snow Cover Area [Alps, 2000 17, 250 m]
Asam et al., Spatiotemporal variations of alpine climate, snow cover and phenology 6 DATA Monthly mean NDVI Start of Season [Alps, 2000 17, 250 m] Snow Cover Duration Snow Cover Area [Alps, 2000 17, 250 m] Temperature Precipitation Relative humidity Radiation & Day length Wind & air pressure [South Tyrol, 2004 2013, 16-days mean/sums, 2 km]
Asam et al., Spatiotemporal variations of alpine climate, snow cover and phenology 7 METHODS Alpine scale Pixel-wise correlations (n= 18 years) inter-annual influence of SCD lag effects Month - Month Different month combinations SNOW COVER DURATION time series NDVI time series years Periods - month combinations
Asam et al., Spatiotemporal variations of alpine climate, snow cover and phenology 8 METHODS South Tyrol scale Single parameter cross- correlation (Pearson) intra-annual seasonality -4 : 4 (< 2 month lags) Correlation
Asam et al., Spatiotemporal variations of alpine climate, snow cover and phenology 9 METHODS South Tyrol scale Single parameter cross- correlation (Pearson) intra-annual seasonality -4 : 4 (< 2 month lags) Correlation Multivariate correlation of deseasonalized* NDVI, SCD, altitude, HLI, and climate variables (50/50 training/test) Combined influence of climate Interactions dndvi si = β 0 + β 1 dscd si + β 2 dtmean si + β 3 drad si + β 4 WinterSCD si + β 5 Altidtude s + β 6 HLI s + Altitude s (γ 1 dscd si + γ 2 dtmean si + γ 3 drad si + γ 4 WinterSCD si ) + HLI s (δ 1 dscd si + δ 2 dtmean si + δ 3 drad si + δ 4 WinterSCD si ) + ε si Main effects * penalized cyclic splines
Asam et al., Spatiotemporal variations of alpine climate, snow cover and phenology 10 RESULTS Start of Season spatial patterns
Asam et al., Spatiotemporal variations of alpine climate, snow cover and phenology 11 RESULTS Start of Season topography & land cover patterns
RESULTS Start of Season temporal trend Adjusted R-squared: 0.23 *** On average 2.7 days earlier SOS / 10 years 28 June 2017 200 m - 1000 m: -1.45 days / 10 years 1400 m - 2200 m: -0.68 days/ 10 years 2600 m - 3000 m: -2.7 days/ 10 years Asam et al., Spatiotemporal variations of alpine climate, snow cover and phenology 12
Asam et al., Spatiotemporal variations of alpine climate, snow cover and phenology 13 RESULTS Snow cover duration spatial patterns
Asam et al., Spatiotemporal variations of alpine climate, snow cover and phenology 14 RESULTS Snow cover area & duration temporal trends
RESULTS SCD NDVI correlations - spatial & temporal patterns % significantly correlated pixels of all vegetated pixels Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec 28 June 2017 Asam et al., Spatiotemporal variations of alpine climate, snow cover and phenology 15
Asam et al., Spatiotemporal variations of alpine climate, snow cover and phenology 16 RESULTS SCD NDVI correlations, time lags Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Asam et al., Spatiotemporal variations of alpine climate, snow cover and phenology 17 METHODS South Tyrol scale Single parameter cross- correlation (Pearson) intra-annual seasonality -4 : 4 (< 2 month lags) Correlation Multivariate correlation of deseasonalized* NDVI, SCD, altitude, and climate variables (50/50 training/test) Combined influence of climate Interactions dndvi si = β 0 + β 1 dscd si + β 2 dtmean si + β 3 drad si + β 4 WinterSCD si + β 5 Altidtude s + β 6 HLI s + Altitude s (γ 1 dscd si + γ 2 dtmean si + γ 3 drad si + γ 4 WinterSCD si ) + HLI s (δ 1 dscd si + δ 2 dtmean si + δ 3 drad si + δ 4 WinterSCD si ) + ε si Main effects * penalized cyclic splines
Asam et al., Spatiotemporal variations of alpine climate, snow cover and phenology 18 RESULTS Vegetation & Climate cross correlations
Asam et al., Spatiotemporal variations of alpine climate, snow cover and phenology 19 RESULTS Vegetation & Climate cross correlations Percentage of all pixels Altitude [km]
Asam et al., Spatiotemporal variations of alpine climate, snow cover and phenology 20 METHODS South Tyrol scale Single parameter cross- correlation (Pearson) intra-annual seasonality -4 : 4 (< 2 month lags) Correlation Multivariate correlation of deseasonalized* NDVI, SCD, altitude, HLI, and climate variables (50/50 training/test) Combined influence of climate Interactions dndvi si = β 0 + β 1 dscd si + β 2 dtmean si + β 3 drad si + β 4 WinterSCD si + β 5 Altidtude s + β 6 HLI s + Altitude s (γ 1 dscd si + γ 2 dtmean si + γ 3 drad si + γ 4 WinterSCD si ) + HLI s (δ 1 dscd si + δ 2 dtmean si + δ 3 drad si + δ 4 WinterSCD si ) + ε si Main effects * penalized cyclic splines
Asam et al., Spatiotemporal variations of alpine climate, snow cover and phenology 21 RESULTS Vegetation & Climate multivariate correlations 30% of NDVI variations Oct-May explained Varying influence in different altitudes Decreasing influence Varying influence throughout the year
Asam et al., Spatiotemporal variations of alpine climate, snow cover and phenology 22 CONCLUSIONS (1/3) What are the spatio-temporal patterns of plant phenology and its drivers in the Alps? Clear patterns in vegetation and snow metrics related to topography Trends towards earlier SOS & less SCA/ shorter SCD
Asam et al., Spatiotemporal variations of alpine climate, snow cover and phenology 23 CONCLUSIONS (2/3) How does the relationship between climate, snow and plant growth change in different altitude ranges? Negative relationship of Jan Apr NDVI to SCD of preceding months sensitivity of green-up to snow accumulation and melt Positive relationship between winter SCD and late summer NDVI lagged water storage effect? Snow important phenology driver at > 1000 m (in South Tyrol) Time lags differ according to altitude (< 1.5 month)
Asam et al., Spatiotemporal variations of alpine climate, snow cover and phenology 24 CONCLUSIONS (3/3) What is the combined influence of climate and snow? SCD and Temperature have highest influence Combined climate ~ NDVI influence varies throughout the year and for altitudes Combined climate ~ topography explains approx. 30% of NDVI variations Oct-May
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