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Session Overview
107RA: Assessing, modelling, and analysing land use and land management impacts on the Earth system - Part A
Thursday, 25/Apr/2019:
10:45am - 12:15pm

Session Chair: Karlheinz Erb
Session Chair: Julia Pongratz
Location: UniS-A 003
UniS Building, Auditorium A 003, ground floor, 178 seats + 54 seats on gallery on first floor
Session Topics:
What are the visions for the planetary land system?

Session Abstract

Currently, by far more than half of the Earth’s ice-free land surface are managed by humans for the provision of essential resources and services such as food, fibre, energy, and living space for about 7 billion people. These activities affect key processes of the Earth system, including biogeochemical and biophysical properties of the biosphere, and result in daunting sustainability challenges such as climate change or biodiversity loss. A central prerequisite to overcome these sustainability challenges is an improved understanding of the complex and dynamic interactions between the various Earth system components, as well as the various and ubiquitous influence of human activities. Many remaining unknowns, however, relate to the extent and degree of human impacts on the natural components of the Earth system. While a relatively robust body of knowledge exists on the effect of land-cover conversions (i.e. the land-use induced change from one land cover type to another, for example deforestation), land-use activities that result in changes that occur within the same land-cover type (denoted “land management”) remain much less analysed. However, well-established insights, e.g. on the effects of fertilization or harvest activities, have been reinforced by recent evidence, suggesting the magnitude of management impacts to be substantial and of global proportion. Thus, omitting land management in assessing the role of land use in the Earth system may result in substantial difficulties to elucidate spatiotemporal dynamics and patterns of crucial Earth System processes. Furthermore, an improved understanding of management impacts on the Earth system is required to exploit the possibly large potentials of land use in mitigating the sustainability challenges while at the same time avoiding massive trade-offs or target conflicts that may reduce or even overturn the benefits of such strategies. Two interacting impediments are responsible for this at least partial neglect: First, major knowledge gaps exist in our qualitative and quantitative understanding of the biogeochemical and biophysical impacts of land management. Second, substantial data gaps on the magnitude and pattern of various management practices prevail. This session assembles contributions that address these currently prevailing impediments in research from a multitude of disciplinary perspectives and spatio-temporal scales, including Earth System modelling, socioecological accounting or ecological case study research. It presents empirical and conceptual approaches aimed at assessing, modelling and analysing the impacts of land management on various components of the Earth system and will discuss novel approaches and databases. These findings are put into context of land use as a tool to mitigate sustainability challenges such as climate change. A particular focus will be on the trade-offs, but also synergies, that emerge when land-management is employed in such strategies.

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Full talk
ID: 363 / 107RA: 1
107R Assessing, modelling, and analysing land use and land management impacts on the Earth system
Keywords: fertilizer use, cropland management, sustainable food production, crop production efficiency, tele-coupling

Trends in fertilizer use efficiency of the world’s biggest crop producers

Richard Fuchs1, Heera Lee1, Navin Ramankutty2, Bumsuk Seo1, Verena Seufert1, Karina Winkler1, Mark Rounsevell1

1Karlsruhe Institute of Technology, Germany; 2University of Britsh Columbia, Canada

To be able to feed a growing population with changing diets while minimizing the environmental impacts of food production, we need to achieve high yields with more sustainable practices. Given the strong negative environmental impact of fertilizer use, improving fertilizer use efficiency - that is, the ratio of how much fertilizer has to be used for a unit of harvested product - is one of the key steps for moving towards a more sustainable food production system. Here we show the developments in fertilizer use efficiency over the last three decades amongst the ‘Big Five’ crop producers of the world (China, United States, India, Europe (EU28) and Brazil). These five producers account for about 60% of the world’s crop production and 70% of the fertilizer use. For the first time, we disentangled the fertilizer use efficiency per major crop type and per fertilizer type (NPK and manure) using a unique set of international reports. We discuss underlying drivers of increases or decreases in fertilizer use efficiency, such as environmental and agricultural policies, crop diversification or crop usage (food, feed, and biofuel). We traced fertilizer use efficiency to the consumers using agricultural trade data to pinpoint causal relationships of production efficiency, regional water quality, land cover changes and other displacement effects of fertilizer (in)efficiencies. Our results provide new data layers for Earth System Models to quantify the environmental effects of various land management practices in the cropland system.

Full talk
ID: 664 / 107RA: 2
107R Assessing, modelling, and analysing land use and land management impacts on the Earth system
Keywords: land use, carbon budget, global modeling, CO2 emissions

Pinning down uncertainties in global CO2 emissions from land use change

Julia Pongratz1,2, Ana Bastos1, Julia Nabel2

1University of Munich, Germany; 2Max Planck Institute for Meteorology, Hamburg, Germany

Land use change and land management are considered a key driver of past and future global climate change – for contributing about a third of anthropogenic CO2 emissions until today, and for playing a key role in achieving net negative emissions under strong mitigation scenarios. Yet estimates of CO2 fluxes associated with land use change and land management even in recent years have an uncertainty of typically +/- 50%. This hampers trust in our understanding of the carbon cycle and of estimates of future sink potentials by land use activities. Understanding why land use change fluxes are so uncertain is therefore an imminent research gap.

Here we review the state of knowledge of differences in land use change fluxes, the relevance of land management in carbon emissions, and the terminological differences of fundamentally different approaches of quantifying these fluxes. We then use BLUE (“bookkeeping of land use emissions”), one of the two bookkeeping models providing the net land use change flux for the annual carbon budget estimates, to investigate in detail the land use dynamics and flux dynamics of time periods and regions that diverge from other estimates. This is particularly relevant as BLUE provides a link between other bookkeeping estimates and process-based land surface model intercomparisons because it shares the same land use reconstruction (the land use harmonization) with the latter. In our analysis we for example show that a substantial part of global emissions in particular in the first part of the 20th century is an overlay of temporarily high emissions from temporary land use activities in individual, often pristine, regions, which permanently degrades the land carbon stocks in the bookkeeping models.

Full talk
ID: 769 / 107RA: 3
107R Assessing, modelling, and analysing land use and land management impacts on the Earth system
Keywords: land surface modeling, land-use change, biomass heat storage

Is the dampening effect of forests on diurnal temperature variations caused by biomass heat storage?

Ronny Meier1, Edouard L. Davin1, David Lawrence2, Sean Swenson2

1ETH Zürich, Switzerland; 2University Corporation for Atmospheric Research (UCAR)

Remote sensing and in-situ observations have revealed a dampened diurnal temperature cycle in forests compared to other land cover types such as grassland at most locations on earth (Lee et al., 2011; Li et al., 2015; Vanden Broucke et al., 2015; Duveiller et al. 2018). This feature is missing in all of the LUCID and CMIP5 climate models (Lejeune et al., 2017). In particular, the origin of the nighttime warming effect by forests is poorly understood up to now. A possible candidate for alleviating these biases are heat storage fluxes in and out of the biomass. These fluxes are observed to reach a diurnal amplitude of up to 100 W/m² (e.g. Dos Michiles et al., 2008) and have therefore the potential to increase nighttime temperatures and decrease daytime temperatures in forests significantly.

We incorporated a biomass heat storage scheme into the state-of-the-art land surface model CLM5.0. Results from global-scale simulations show that, compared to the configuration not including biomass heat storage, nighttime temperatures are increased by more than 1 K in densely forested areas, thereby improving the agreement with remote sensing observations. During daytime, the biomass heat storage induces a reduction of the turbulent heat fluxes leading to a smaller cooling effect.

Overall our results indicate that biomass heat storage is a crucial process that is missing from most current global climate models, with potentially critical implications about their ability to capture the biogeophysical effect of forest changes and forest management, even more so when investigating land use change effects on temperature extremes (e.g. Davin et al., 2014). In a next step, we will investigate how this process affects the dynamics of the boundary layer in simulations that are coupled to the atmosphere.

Davin, E. L., Seneviratne, S. I., Ciais, P., Olioso, A., and Wang, T.: Preferential cooling of hot extremes from cropland albedo management, P. Natl. Acad. Sci. USA, 111, 9757–9761,, 2014.

Dos Michiles, A. A. S. and Gielow, R. (2008). Above-ground thermal energy storage rates, trunk heat fluxes and surface energy balance in a central amazonian rainforest. Agr. Forest Meteorol., 148(6):917–930.

Duveiller, G., Hooker, J., and Cescatti, A. (2018). The mark of vegetation change on earth’s surface energy balance. Nat. Commun., 9(679).

Lee, X., Goulden, M. L., Hollinger, D. Y., Barr, A., Black, T. A., Bohrer, G., Bracho, R., Drake, B., Goldstein, A., Gu, L., Katul, G., Kolb, T., Law, B. E., Margolis, L. H., Meyers, T., Monson, R., Munger, W., Oren, R., Paw U, K. T., Richardson, A. D., Schmid, H. P. Staebler, R., Wofsy, S., and Zhao, L. (2011). Observed increase in local cooling effect of deforestation at higher latitude. Nature, 479:384–387.

Lejeune, Q., Seneviratne, S. I., and Davin, E. L. (2017). Historical land-cover change impacts on climate: Comparative assessment of lucid and cmip5 multimodel experiments. J. Climate, 30:1439–1459.

Li, Y., Zhao, M., Motesharrei, S., Mu, Q., Kalnay, E., and Li, S. (2015). Local cooling and warming effects of forests based on satellite observations. Nat. Commun., 6(6603).

Vanden Broucke, S., Luyssaert, S., Davin, E. L., Janssens, I., and van Lipzig, N. (2015). New insights in the capability of climate models to simulate the impact of luc based on temperature decomposition of paired site observations. J. Geophys. Res.-Atmos., 120:5417–5436.

Full talk
ID: 476 / 107RA: 4
107R Assessing, modelling, and analysing land use and land management impacts on the Earth system
Keywords: land use, land cover, carbon, climate, uncertainty

Land use and land cover distribution is a primary determinant of global carbon cycle projections and regional temperature projections

Alan Vincent Di Vittorio1, Xiaoying Shi2, Ben Bond-Lamberty3, Kate Calvin3, Andrew Jones1

1Berkeley Lab, United States of America; 2Climate Change Science Institute, Oak Ridge National Lab; 3Joint Global Change Research Institute, Pacific Northwest National Lab

Earth System Models (ESMs) project future global change based on historical and current conditions and projected greenhouse gas emissions and Land Use and Land Cover Change (LULCC). As climate change is closely related to changes in atmospheric CO2 concentration and local conditions, it is important for these models to accurately project carbon cycle dynamics and LULCC. A previous comparison of 11 ESMs demonstrates a reasonable mean projection for 2005 CO2 concentration, but with a 12 ppmv standard deviation of values. Efforts to reduce this variability and improve future projections have focused on fine scale biogeochemical processes rather than contextual conditions such as land cover distribution. However, using the integrated Earth System Model (iESM) we have shown that uncertainty in land conversion assumptions leading to a 5.1 M km2 difference in global forest area generates a 6 ppmv uncertainty range, which is 50% of the inter-model variability in historically projected 2005 CO2 concentration. This uncertainty in 2005 land cover distribution affects the global carbon and regional climate into the future in an RCP4.5 simulation. The iESM LULCC CO2 concentration uncertainty in 2005 increases by 50% to 9 ppmv in 2094, and the 2005 uncertainty in terrestrial carbon stock increases from 26 PgC to 33 PgC. This initial forest cover difference also generates differences in 2005-2094 average annual regional surface temperature projections ranging from -0.6 to 0.7 °C, with the largest average seasonal difference in Dec-Jan-Feb ranging from -1.27 to 1.13 °C. Furthermore, differences in regional surface temperature projections also range from -0.3 to 0.6 °C due to spatial redistribution of similar global forest area and ~1 M km2 difference in shrubland, when comparing the maximum forest and default cases. These results highlight the importance of accurately characterizing land use and land cover and its uncertainty in global change analysis.

Full talk
ID: 543 / 107RA: 5
107R Assessing, modelling, and analysing land use and land management impacts on the Earth system
Keywords: GHG mitigation; carbon sequestration; bioenergy; short rotation coppice; reforestation

Combatting climate change through land conversion: Carbon benefits from bioenergy plantations vs. natural succession

Kalt Gerald, Lauk Christian, Haberl Helmut, Mayer Andreas, Theurl Michaela C., Erb Karl-Heinz

University of Natural Resources and Life Sciences (BOKU), Austria

Short rotation biomass plantations are often considered as holding vast potentials for future global bioenergy supply. In contrast to raising removals from forests, purpose-grown biomass does not interfere with forest carbon (C) stocks. Provided that agricultural land can be diverted from food and feed production without impairing food security, energy plantations on current agricultural land appear as a beneficial option in terms of renewable, climate-friendly energy supply. However, instead of cultivating energy plantations, land could also be allowed to regrow natural vegetation and thus acting as a long-term C sink which also results in climate benefits. We compare the C sink strength of natural succession on arable land with the C mitigation effects of plantation-based bioenergy. Using geographically explicit data on global cropland distribution among climate and ecological zones, regionally specific C accumulation rates are calculated using IPCC default methods and values. C savings from bioenergy are given for a range of displacement factors, acknowledging the varying efficiency of bioenergy routes and technologies in fossil fuel displacement. We assume a uniform spatial pattern for natural succession and bioenergy plantations, and the considered timeframes range from 30 to 100 years. For many parameter settings – in particular long timeframes and high displacement factors – bioenergy yields higher cumulated savings than succession. Still, if woody biomass displaces natural gas or fossil transport fuels, natural succession is the superior alternative for timeframes up to 30 and 50 years, respectively. The results show that energy plantations can only be more effective in C mitigation than succession during the first half of the 20th century if bioenergy efficiently displaces fossil C. Freeing land for natural succession is a worthwhile short- to medium-term mitigation measure that has many co-benefits but is also associated with the risk of C stock losses (i.e. emissions) due to disturbances or land conversion at a later time.

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