Spatiotemporal variations of alpine climate, snow cover and phenology

Transcription

1 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

2 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

3 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?

4 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

5 Asam et al., Spatiotemporal variations of alpine climate, snow cover and phenology 5 DATA Monthly mean NDVI Start of Season [Alps, , 250 m] Snow Cover Duration Snow Cover Area [Alps, , 250 m]

6 Asam et al., Spatiotemporal variations of alpine climate, snow cover and phenology 6 DATA Monthly mean NDVI Start of Season [Alps, , 250 m] Snow Cover Duration Snow Cover Area [Alps, , 250 m] Temperature Precipitation Relative humidity Radiation & Day length Wind & air pressure [South Tyrol, , 16-days mean/sums, 2 km]

7 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

8 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

9 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

10 Asam et al., Spatiotemporal variations of alpine climate, snow cover and phenology 10 RESULTS Start of Season spatial patterns

11 Asam et al., Spatiotemporal variations of alpine climate, snow cover and phenology 11 RESULTS Start of Season topography & land cover patterns

12 RESULTS Start of Season temporal trend Adjusted R-squared: 0.23 *** On average 2.7 days earlier SOS / 10 years 28 June m m: days / 10 years 1400 m m: days/ 10 years 2600 m m: -2.7 days/ 10 years Asam et al., Spatiotemporal variations of alpine climate, snow cover and phenology 12

13 Asam et al., Spatiotemporal variations of alpine climate, snow cover and phenology 13 RESULTS Snow cover duration spatial patterns

14 Asam et al., Spatiotemporal variations of alpine climate, snow cover and phenology 14 RESULTS Snow cover area & duration temporal trends

15 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

16 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

17 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

18 Asam et al., Spatiotemporal variations of alpine climate, snow cover and phenology 18 RESULTS Vegetation & Climate cross correlations

19 Asam et al., Spatiotemporal variations of alpine climate, snow cover and phenology 19 RESULTS Vegetation & Climate cross correlations Percentage of all pixels Altitude [km]

20 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

21 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

22 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

23 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)

24 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

25 THANK YOU! CONTACT US Eurac Research Institute for Earth Observation Drususallee/Viale Druso Bozen/Bolzano T info@eurac.edu 28 June 2017 Asam et al., Spatiotemporal variations of alpine climate, snow cover and phenology 25