Intercomparison of modis albedo retievals and in situ measurements across the global fluxnet network
Cescatti, A. ; Marcolla, B. ; Santhana Vannan, S.K. ; Roman, J.Y. ; Moors, E.J. - \ 2012
Remote Sensing of Environment 121 (2012). - ISSN 0034-4257 - p. 323 - 334.
reflectance distribution function - broad-band albedo - surface albedo - boreal forests - climate-change - vegetation - products - feedbacks - validation - instrument
Surface albedo is a key parameter in the Earth's energy balance since it affects the amount of solar radiation directly absorbed at the planet surface. Its variability in time and space can be globally retrieved through the use of remote sensing products. To evaluate and improve the quality of satellite retrievals, careful intercomparisons with in situ measurements of surface albedo are crucial. For this purpose we compared MODIS albedo retrievals with surface measurements taken at 53 FLUXNET sites that met strict conditions of land cover homogeneity. A good agreement between mean yearly values of satellite retrievals and in situ measurements was found (r2 = 0.82). The mismatch is correlated with the spatial heterogeneity of surface albedo, stressing the relevance of land cover homogeneity when comparing point to pixel data. When the seasonal patterns of MODIS albedo are considered for different plant functional types, the match with surface observations is extremely good at all forest sites. On the contrary, satellite retrievals at non-forested sites (grasslands, savannas, croplands) underestimate in situ measurements across the seasonal cycle. The mismatch observed at grassland and cropland sites is likely due to the extreme fragmentation of these landscapes, as confirmed by geostatistical attributes derived from high resolution scenes.
Research priorities in land use and land-cover change for the Earth System and Integrated Assessment Modelling
Hibbard, K. ; Janetos, A. ; Vuuren, D. van; Pongratz, J. ; Rose, S. ; Betts, R. ; Herold, M. ; Feddema, J. - \ 2010
International Journal of Climatology 30 (2010)13. - ISSN 0899-8418 - p. 2118 - 2128.
carbon-cycle feedbacks - global vegetation models - climate-change - atmospheric co2 - surface albedo - 21st-century - nitrogen - increase - impacts - energy
This special issue has highlighted recent and innovative methods and results that integrate observations and modelling analyses of regional to global aspect of biophysical and biogeochemical interactions of land-cover change with the climate system. Both the Earth System and the Integrated Assessment modeling communities recognize the importance of an accurate representation of land use and land-cover change to understand and quantify the interactions and feedbacks with the climate and socio-economic systems, respectively. To date, cooperation between these communities has been limited. Based on common interests, this work discusses research priorities in representing land use and land-cover change for improved collaboration across modelling, observing and measurement communities. Major research topics in land use and land-cover change are those that help us better understand (1) the interaction of land use and land cover with the climate system (e.g. carbon cycle feedbacks), (2) the provision of goods and ecosystem services by terrestrial (natural and anthropogenic) land-cover types (e.g. food production), (3) land use and management decisions and (4) opportunities and limitations for managing climate change (for both mitigation and adaptation strategies)
CO2 and albedo climate impacts of extratropical carbon and biomass plantations
Schaeffer, M. ; Eickhout, B. ; Hoogwijk, M. ; Strengers, B. ; Vuuren, D.J. van; Leemans, R. ; Opsteegh, T. - \ 2006
Global Biogeochemical Cycles 20 (2006). - ISSN 0886-6236 - 15 p.
land-cover changes - intermediate-complexity - northern-hemisphere - decadal variability - surface albedo - model - system - sensitivity - vegetation - forest
We explored the climate impacts for two land-use change scenarios, aimed at mitigating the buildup of greenhouse gases in the atmosphere. Using the integrated assessment model IMAGE 2.2, we found that the large-scale implementation in the extratropics of either carbon-sequestration or modern-biomass plantations decreases the CO2 concentration with 70-80 ppmv by the year 2100 compared to a nonmitigation baseline. In a coupled land/atmosphere/ocean/sea-ice model this moderates global warming over the 21st century by 10%. However, the carbon-sequestration option raises the absorption of solar radiation due to a lower albedo compared to the scenario involving modern-biomass plantations (for biofuels production). The albedo-induced difference in global mean temperature is as large as the mitigation by CO2 changes in the two scenarios compared to the baseline. Further, an atmospheric circulation change in the carbon-plantation scenario weakens the supply of moisture from the oceans to North Africa and central Eurasia. In our model this decreases annual mean precipitation over North Africa by up to 10% and further increases summer temperatures over Eurasia. These findings lead us to conclude that other climate impacts than just CO2 changes have to be taken into account when discussing climate-change mitigation options that involve land-use changes