Evaluating Biosphere Model Estimates of the Start of the Vegetation Active Season in Boreal Forests by Satellite Observations

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http://hdl.handle.net/10138/175354

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Böttcher , K , Markkanen , T , Thum , T , Aalto , T , Aurela , M , Reick , C H , Kolari , P , Arslan , A N & Pulliainen , J 2016 , ' Evaluating Biosphere Model Estimates of the Start of the Vegetation Active Season in Boreal Forests by Satellite Observations ' Remote sensing , vol. 8 , no. 7 , 580 . DOI: 10.3390/rs8070580

Title: Evaluating Biosphere Model Estimates of the Start of the Vegetation Active Season in Boreal Forests by Satellite Observations
Author: Böttcher, Kristin; Markkanen, Tiina; Thum, Tea; Aalto, Tuula; Aurela, Mika; Reick, Christian H.; Kolari, Pasi; Arslan, Ali N.; Pulliainen, Jouni
Contributor: University of Helsinki, Ecosystem processes/ Jaana Bäck
Date: 2016-07
Language: eng
Number of pages: 31
Belongs to series: Remote sensing
ISSN: 2072-4292
URI: http://hdl.handle.net/10138/175354
Abstract: The objective of this study was to assess the performance of the simulated start of the photosynthetically active season by a large-scale biosphere model in boreal forests in Finland with remote sensing observations. The start of season for two forest types, evergreen needle-and deciduous broad-leaf, was obtained for the period 2003-2011 from regional JSBACH (Jena Scheme for Biosphere-Atmosphere Hamburg) runs, driven with climate variables from a regional climate model. The satellite-derived start of season was determined from daily Moderate Resolution Imaging Spectrometer (MODIS) time series of Fractional Snow Cover and the Normalized Difference Water Index by applying methods that were targeted to the two forest types. The accuracy of the satellite-derived start of season in deciduous forest was assessed with bud break observations of birch and a root mean square error of seven days was obtained. The evaluation of JSBACH modelled start of season dates with satellite observations revealed high spatial correspondence. The bias was less than five days for both forest types but showed regional differences that need further consideration. The agreement with satellite observations was slightly better for the evergreen than for the deciduous forest. Nonetheless, comparison with gross primary production (GPP) determined from CO2 flux measurements at two eddy covariance sites in evergreen forest revealed that the JSBACH-simulated GPP was higher in early spring and led to too-early simulated start of season dates. Photosynthetic activity recovers differently in evergreen and deciduous forests. While for the deciduous forest calibration of phenology alone could improve the performance of JSBACH, for the evergreen forest, changes such as seasonality of temperature response, would need to be introduced to the photosynthetic capacity to improve the temporal development of gross primary production.
Subject: start of season
boreal forest
MODIS
JSBACH
fractional snow cover
NDWI
evergreen needle-leaf forest
deciduous broad-leaf forest
SCOTS PINE FOREST
PHOTOCHEMICAL REFLECTANCE INDEX
GROWING-SEASON
TIME-SERIES
BUD-BURST
SPRING PHENOLOGY
CLIMATE-CHANGE
CONIFEROUS FOREST
CONTINENTAL-SCALE
BIAS CORRECTION
114 Physical sciences
4112 Forestry
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