5th iLEAPS Science Conference Abstracts - A1

Abstracts – Session A1

Land-use change in a warming world: interactions between climate and socio-ecological systems, and implications for land-based climate change mitigation

A101 - ORAL-0089: Synergies and trade-offs between ecosystem service indicators in afforestation and bioenergy land-use scenarios

Almut Arneth, Andreas Krause, Anita Bayer, Thomas Pugh, Peter Anthoni, Benjamin Bodirski, Jonathan Doelman, Florian Humpenöder, Alex Popp, Stefan Olin, Elke Stehfest

Land management for carbon storage is an indispensable concept of climate change mitigation discussions because of its potential to remove carbon dioxide from the atmosphere, and its contribution to reduce carbon dioxide emissions from ecosystems. However, the feasibility of mitigation projects needs to be assessed also with respect to broader ecological impacts. Here, we used projections of future land-use (LU) for different land-based mitigation options from two land-use models and evaluate their effects on ecosystem function and ecosystem service indicators, using a global dynamic vegetation model. The socio-economic setting in all land-use scenarios is based on SSSP2/RCP2.6. A cumulative carbon removal target of ~130 Gt C by the end of the 21st century was assumed to be either achievable via growth of bioenergy crops combined with CCS, or via avoided deforestation and afforestation. We compared these scenarios to a reference scenario without land-based mitigation and analyzed the simulations with the aim to assess synergies and trade-offs across a range of ecosystem service indicators. In our mitigation simulations carbon removal by year 2099 were lower than the removal simulated by the land-use models. Other ecosystem service indicators were influenced heterogeneously both positively and negatively, with large variability across regions and land-use scenarios. Avoided deforestation and afforestation led to an increase in evapotranspiration and enhanced emissions of biogenic volatile organic compounds, and to a decrease in albedo, runoff, and nitrogen loss. Also crop production decreased in the afforestation scenario as a result of reduced crop area. Bioenergy-based climate change mitigation was projected to affect less area globally than in the forest expansion scenarios, and resulted in less pronounced changes in most ecosystem service indicators than forest-based mitigation, but included a decrease in crop production, nitrogen loss and biogenic volatile organic compounds emissions.
 

A102 -ORAL-0117: The limits to global-warming mitigation by terrestrial carbon removal with biomass plantations

Lena Boysen, Dieter Gerten, Wolfgang Lucht, Vera Heck

The feasibility of biomass plantations (BPs) is still very uncertain in terms of carbon sequestration, subsequent utilization and environmental and social consequences. Still, they are utilized in most of the current mitigation scenarios that stay around or below 2°C global warming by 2100. We here give an overview of terrestrial carbon dioxide removal (tCDR) potentials and trade-offs with other actors on land by analyzing a set of possible BP scenarios incombination with different levels of emission pathways simulated by a biogeochemical process model. These scenarios range from systematic and rather far-fetched assumptions of large-scale conversion of agricultural and/or natural land over strict constraints on land availability to a sophisticated transient socio-economic mitigation scenario.
 
We show that the option space for tCDR is likely limited. tCDR is not a viable option to delay, stop or even reverse climate change if mitigation efforts in the near-term future are insufficient or fail completely and would induce severe trade-offs for food production and natural ecosystems. The needs for increasing food production on crop and pasture areas for a growing world population and the conservation of ecosystems would likely limit the land availability for BPs and thus, substantially reduce the potential for tCDR to 10-100GtC. Strictly following the land-use patterns of the mitigation scenario RCP2.6 to avoid such conflicts would still require strong increases in irrigation and highly efficient carbon processing and storage to guarantee success. Emissions and biogeophysical effects from land conversion and management of BPs are the main drivers for reducing the effectiveness of tCDR and should therefore be accounted for in the land selection process for BPs. Still, tCDR in selected places, forest conservation and restoration as well as smart and sustainable land management could still lead to substantial carbon removal on land.

A103 - ORAL-0234: Climate, land-use and ecosystem services to aid achievement of a 1.5 degree warming threshold.

Anna Harper, Peter Cox, Tom Powell, Stephen Sitch, Jo House, Tim Lenton, Chris Huntingford

Scenarios that could limit global warming to 1.5°C or below 2C rely upon significant land-based mitigation to protect and enhance land carbon sinks (e.g. through reduced deforestation and forest management). Such mitigation extends to providing negative emissions technologies to remove CO2 from the atmosphere, such as afforestation and in particular BECCS. However, large-scale land-use change (LUC) could have unwelcome impacts on the provision of food and water, and on carbon storage in vegetation and soils – factors that could be further exacerbated by directly imposed climate change.
 
We use the land surface model JULES to investigate terrestrial carbon cycle impacts of LUC for climate mitigation. JULES is run with IMOGEN, a coupled climate-carbon cycle impacts model. We prescribe atmospheric CO2 concentrations based on a range of hypothetical future temperature scenarios that would result in climate change eventually stabilizing between 1.5 and 2.0°C above preindustrial. In tandem we include the range of climate model sensitivities reported in the AR5 to capture the related range of CO2 fertilization effects.
 
This presentation will provide an overview of the key results. First, we will evaluate impacts of land-use changes for mitigation contributing to 1.5°C and 2.0C climate targets, in terms of influence on the global carbon cycle. Then we can move to the key question: Do the negative impacts of land use change (on ecosystem services) outweigh the positive effects of avoiding some climate change? Second, we will explain how alternative levels of land-based mitigation will influence “allowable" anthropogenic CO2 emissions for the full ensemble of potential future climates.

A104 - ORAL-0345: Biophysical impacts of land use change critical for low emission scenarios

Benoit Guillod1, 2, Annette L. Hirsch1, Jonathan Doelman3, Lena Boysen4, Victor Brovkin4, Detlef Van Vuuren3, 5, Elke Stehfest3, Sonia Seneviratne1

1Institute for Atmospheric and Climate Science, Eidgenössische Technische Hochschule (ETH) Zürich, Zürich, Switzerland 2Institute for Environmental Decisions, ETH Zurich, Zurich, Switzerland 3PBL Netherlands Environmental Assessment Agency, Den Haag, The Netherlands 4The Land in the Earth System, Max Planck Institute for Meteorology, Hamburg, Germany 5Copernicus Institute for Sustainable Development, Utrecht University, Utrecht, The Netherlands

Radical greenhouse gas emission reductions are necessary to limit global warming to 1.5 or 2 degrees above pre-industrial climate, the objective stated in the Paris climate agreement. These could involve major land use change (LUC), such as afforestation, crop intensification and bioenergy production. The biophysical effects of LUC are not accounted for in the integrated assessment models that have created the scenarios to assess potential pathways to reach low global warming targets. Using state-of-the-art atmospheric global circulation models (GCMs) forced to 1.5 and 2 degrees climates (following the Half a degree Additional warming, Prognosis and Projected Impacts (HAPPI) experimental design), we assess the effects of three different LUC scenarios on local extremes: the RCP2.6 from CMIP5 and two newly developed scenarios that are consistent with RCP1.9 which represent different societal pathways for climate mitigation and adaptation.
 
Preliminary analyses with one GCM show that the biophysical impacts of LUC on hot extremes are of similar magnitude as the impacts of the difference in radiative forcing  between a 1.5 and a 2 degrees world, with crucial implications for the comparison between these two climate targets. This highlights the need to consider such effects in low emission scenarios and in the development of climate mitigation and adaptation pathways. Results from other GCMs, for which simulations are in progress, will also be included to evaluate the model sensitivity of these results.

A105 - ORAL-0406: Advancing our understanding of the impacts of historic and projected land use in the Earth System: The Land Use Model

Intercomparison Project (LUMIP)

David Lawrence1, George Hurtt2, Almut Arneth3, Victor Brovkin4, Katherine Calvin5, Chris Jones6, Julia Pongratz4, Sonia Seneviratne7, Elena Shevliakova8, Peter Lawrence1, Andrew Jones9

1Climate and Global Dynamics Laboratory, National Center for Atmospheric Research, Boulder, Colorado, The United States of America 2University of Maryland, College park, College Park, MD, The United States of America 3Karlsruhe Institute of Technology, Institute of Meteorology and Climate research, Atmospheric Environmental Research, Garmisch-Partenkirchen, Germany 4Biogeochemistry Department, Max Planck Institute for Chemistry, Mainz, Germany 5Pacific Northwest National Laboratory, Washington, D.C., The United States of America 6Met Office, Exeter, United Kingdom 7Institute for Atmospheric and Climate Science, Eidgenössische Technische Hochschule (ETH) Zürich, Zürich, Switzerland 8Princeton University, Princeton, NJ, The United States of America 9Lawrence Berkeley National Laboratory, Berkeley, The United States of America

Human land-use activities have resulted in large changes to the Earth surface, with resulting implications for climate. In the future, land-use activities are likely to intensify to meet growing demands for food, fiber, and energy. The Land Use Model Intercomparison Project (LUMIP) aims to further advance understanding of the broad question of impacts of land-use and land-cover change (LULCC) as well as more detailed science questions to get at process-level attribution, uncertainty, and data requirements in more depth and sophistication than possible in a multi-model context to date. There will be focus on separation and quantification of the effects on climate from LULCC relative to all forcings, separation of biogeochemical from biogeophysical effects of land use, the unique impacts of land-cover change versus land-management change, modulation of land-use impact on climate by land-atmosphere coupling strength, and the extent that impacts of enhanced CO2 concentrations on plant photosynthesis are modulated by land use. LUMIP involves three major sets of science activities: (1) development of an updated and expanded historical and future land-use dataset, (2) an experimental protocol for specific LUMIP experiments for CMIP6, and (3) definition of metrics and diagnostic protocols that quantify model performance with respect to LULCC.
 
Experiments include idealized coupled and land-only model simulations designed to advance process-level understanding of LULCC climate impacts, with a focus on the impact of land management. Additional experiments quantify the historic impact of land use and the potential for future land management decisions to aid in mitigation of climate change. We will present the experimental protocol, explain the rationale, outline plans for analysis, and describe the subgrid land-use tile data request for selected variables. Finally, we will present preliminary results from LUMIP experiments with CESM and CLM.

A106 -ORAL-0269: Livestock Grazing and Terrestrial Carbon Sequestration in Mongolia

Qinxue WANG1, Tomohiro OKADERA1, Eer DENI1, Masataka WATANABE2, Ochirbat BATKHISHIG3

1National Institute for Environmental Studies, Tsukuba, Japan 2Research and Development Initiative, Chuo University, Tokyo, Japan 3Institute of Geography and Geoecology, Mongolian Academy of Sciences, Ulaanbaatar, Mongolia

Grassland ecosystems play a critical role in regulating carbon (C) sequestration from atmosphere. In order to evaluate C sequestration by terrestrial ecosystems, we have developed an ecosystem-grazing model to evaluate the spatiotemporal distribution of C sequestration under the influence of both climate change and livestockgrazing. To validate the model, we have established a ground observation network to monitor CO2 fluxes by eddy covariance method in different grassland ecosystems Our results showed that the amount of C sequestration by forest steppe and meadow steppe in 2000-2015 was much larger than that by other types, which is near 2 times that absorbed by dry steppe, and more than 3 times that absorbed by semi-desert steppe. We also found that the surface water deficit index (WDI), equivalently soil moisture,is the most important driving factor for C sequestration in both dry steppe and semi-desert steppe, but the land surface temperature (LST) is the most important driving factor for C sequestration in forest steppe and meadow steppe. However, both WDI and LST make a great influence on C sequestration in typical steppe, which are vastly distributed in the central Mongolia.
 
Our result also showed that light grazing may actually enhance terrestrial C sequestration, but heavy grazing or overgrazing may cause a large decrease of C sequestration. We found that large areas of grasslands surrounding the capital city, Ulaanbaatar, have seriously degraded due to heavy grazing, although these areas originally have a high capacity of C sequestration. Overall, our results indicate that C sequestration in the most part of grassland are highly sensitive to grazing pressure and precipitation fluctuation. It was concluded that the recovery of degraded grasslands due to overgrazing could contribute to significant C sequestration by well-management of livestock numbers.

A107 - ORAL-0179: Restoration in a contested Delta: Multi-year greenhouse gas budgets of restored wetlands and drained peatlands across the Sacramento-San Joaquin Delta, California, USA.

Kyle Hemes1, Elke Eichelmann1, Samuel Chamberlain1, Sara Knox, Patricia Oikawa2, Dennis Baldocchi1

1University of California, Berkeley, Berkeley, The United States of America 2California State University, East Bay, Hayward, CA, The United States of America

Globally, delta ecosystems are critical for human livelihoods, but are at increasingly greater risk of degradation. The Sacramento-San Joaquin River Delta (‘Delta’)has been subsiding dramatically, losing close to 200 Tg of carbon since the mid 19th century due in large part to agriculture-induced oxidation of the peat soils through drainage and cultivation. Efforts to re-wet the peat soils through wetland restoration and flooded agricultural crops are attractive as climate mitigation activities and as part of market-based climate policies such as California’s Cap-and-Trade program. While flooded wetland systems have the potential to sequester significant amounts of carbon as photosynthesis outpaces aerobic respiration, the highly-reduced conditions can result in significant methane emissions. Due largely to variability in annual photosynthesis and methane emissions, there is high uncertainty in the net greenhouse gas (GHG) budget over the lifetime of a restored wetland.
 
Initial comparisons in the Delta have shown that conversion of drained peatlands to wetlands can, in some cases, yield a net GHG benefit. Other studies have reported net sources, and turnover times (from a source to a sink) of greater than 500 years. This study will utilize three years (2014-2016) of continuous, gap-filled, CO2 and CH4 flux data from a mesonetwork of seven eddy covariance towers in the Delta to compute GHG budgets for the restored wetlands and agricultural baseline sites measured.
 
Sustained global warming potentials will be used to model the source/sink nature of the ecosystem into the future. This work aims to describe the extent to which restored managed wetlands, compared to drained agricultural land uses, can provide a net GHG benefit and contribute to climate change mitigation in a nascent market-based system.

A108 -ORAL-0413: Ecosystem carbon sequestration through restoration of degraded lands in North Eastern India

Karabi Pathak1, Biplab Brahma1, Bandhana Kurmi1, Milon Das1, Panna Chandra Nath1, Arun Jyoti Nath1, Ashesh Kumar Das1

1Department of Ecology and Environmental Science, Assam University, Silchar, India

Land use conversion (LUC), especially through forest degradation and fire-based shifting cultivation on steep lands, is among principal anthropogenic atmospheric CO2 loading processes. This study evaluated the ecosystem carbon(C) stock for predominant land uses converted from forest in Northeastern India(NEI) to advance the scientific knowledge and minimize the anthropogenic emissions from LUC.
 
Field experiments were conducted over two years on six predominant land uses including:  (i) less disturbed forest (LDF), (ii) disturbed forest (DF), (iii) rubber (Hevea brasiliensis) plantation (RP), (iv) Areca (Areca catechu) plantation (ArP), (v) pan (Piper betle) jhum (slash and mulching) agroforestry (PB), and (vi) Imperata grassland (IG) for representative sites in NEI to assess changes in ecosystem C stock with progressive (e.g. DF to PB) and retrogressive(e.g. LDF to DF) LUC and management. The above ground biomass C, below ground biomass C and soil organic carbon (SOC) stocks were studied to evaluate ecosystem C stock for six land uses.
 
The total biomass C stock (Mg/ha) follow the sequence: LDF(167) > PB (151) > RP(134) > ArP(27) > DF(25) > IG(13). The SOC stock was the highest under LDF (133 Mg/ha)and the sequence was in the order: LDF>PB> RP> IG> ArP> DF. In comparison with DF as the control, the gain in ecosystem C was in the order: PB(125%)>RP(99%)>ArP(4%).
 
The LUC and management of DF through PB and RP showed the ecosystem C sequestration rate of 5 and 4 Mg/ha/yr, respectively. The ecosystem C sequestration rate was 0.5 and 4 Mg/ha/yr respectively, when IG was converted into ArP and RP. Therefore, restoration of degraded lands through RP and PB enhanced ecosystem C sequestration rate and reduced anthropogenic emissions from LUC. However, from the perspective of environment management and conservation, PB would be the better choice over RP for restoration of degraded lands because PB can provide diverse ecosystem services and other secondary benefits.

A109 -ORAL-0423: Comparing biogeochemical and biogeophysical cycles of different land covers under same climatic conditions in a semi-arid

region in Israel

Rafael Stern1, Madi Amer1, Eyal Rotenberg1, Dan Yakir1

1Weizmann Institute of Science, Rehovot, Israel

The carbon sink in the land Biosphere is considered as a major process with the potential to ameliorate climate change. However, assessment of the climatic effects of the land Biosphere requires a combined perspective of both the Biogechemical effects (such as the carbon sink), and also the Biogeophysical effects (such as the vegetation albedo and radiation balance), which can often have contrasting climatic effects. This work investigates the variations in the balance between these two effects among major vegetation types (pine forest, oak forest, wheat field and shrubland) under similar climatic conditions in southern Israel. This study relies on a state of the art field laboratory to carry out field measurements of radiative (incoming and outgoing short- and long-wave radiations) and non-radiative (sensible and latent heat) fluxes, together with fluxes of carbon (based on CO2 and a newly developed tracer - COS). The eddy covariance technique is also used. The study is being carried out along the seasonal cycle and across three years. There are already measurements from the autumn of 2016, and winter and spring of 2017.

A110 - ORAL-0100: The global spatial distribution of conservation agriculture and its implications for land-based climate change mitigation

and adaptation

Reinhard Prestele1, Annette L. Hirsch2, Edouard L. Davin2, Sonia Seneviratne2, Peter H. Verburg1, 3

1Environmental Geography Group, Department of Earth Sciences, Vrije Universiteit Amsterdam , Amsterdam, The Netherlands 2Institute for Atmospheric and Climate Science, Eidgenössische Technische Hochschule (ETH) Zürich, Zürich, Switzerland 3Swiss Federal Research Institute WSL, Birmensdorf, Switzerland

Conservation Agriculture (CA) uses a suite of soil and water conservation management techniques (no-till farming, crop residue management, and crop rotation) and has been proposed as a sustainable alternative to current conventional high-input agriculture.
Due to changes in surface and soil characteristics (e.g., albedo and soil organic carbon), CA management techniques have the potential to mitigate greenhouse gas emissions (accumulation of organic carbon in soils) and adapt agricultural systems towards warmer temperatures and increased water stress. Furthermore, changes in albedo and energy fluxes may contribute to alleviate temperature extremes on local to regional scale. Recent modeling studies to quantify the climate impacts of CA commonly apply these changes in surface and soil characteristics to all agricultural land and therefore may overestimate the climate benefits. To assess the mitigation and adaptation potentials of CA, we created a new global map of the extent of CA, which provides a more realistic implementation for climate models.
 
We compile a new global CA map by combining statistics with a downscaling procedure accounting for potentials and constraints of CA adoption and uncertainty due to data and process limitations. By our estimates, 122 to 215 Mha (9 to 15 %) of arable land are currently managed under a CA system globally. Based on the analysis of our present-day estimates and assumptions about changes in drivers and limitations of adoption, we create different scenarios how the area managed under CA may develop in future. We implement our CA maps in the Community Land Model (CLM) with additional amendments to the ground albedo and soil resistance to evaluate the potential biogeochemical and biophysical impacts associated with CA. Our CA data will be made available for implementation in additional ecosystem models.  

A111- ORAL-0365: Mapping a changing energy landscape in Tunisia with relation to climate change and national environmental policy.

Faten Attig Bahar1, 2, Melik Sahraoui3, Mohamed Sadok Guellouz4, Slim Kaddeche2

1 University of Carthage, Polytechnic School of Tunisia, Tunis, Tunisia 2University of Carthage, National Institute of Applied Sciences and Technology, Laboratory of Materials, Measurements and Applications., Tunis, Tunisia 3University of Carthage, Polytechnic School of Tunisia, Laboratory of Systems and Applied Mechanics., Tunis, Tunisia 4University of Carthage, National Engineering School of Bizerte, Bizerte, Tunisia

Climate change has received great attention during the last decade for its impact on the earth ecosystem, activities and on the world economy. The world summit on sustainable development WSSD/ONG, Earth Summit 2002 in Johannesburg, held 10 years after Earth Summit in Rio 1992, discussed the sustainable development by the United Nations and pointed out the disastrous and harmful impact of use on non-clean energy use as a cause of pollution and overexploitation of resources on human health and the environment. Therefore, the necessity of developing policies and regulatory frameworks aiming to protect the environment, reduce air pollution and attenuate the CO2 gas emission to the atmosphere has become crucial.
 
Due to the fact that energy and climate change are intrinsically linked and that the way in which we consume energy determines society environmental impact, and in order to avoid risks of global warming and climate change these issues were the main topics in the  Kyoto protocol, COP 21, COP22. Along with improving system efficiency,the use of renewable energy could be that alternative which has become exceedingly important with its improved and more commercial affordability and figured in many countries development plan.
 
From the World Energy Outlook (iea 2016), it is presented in current European plans to significantly reduce the usage of fossil fuel by providing 20% of electric energy and 30% of thermal energy sources by the year of 2020. Tunisia is a part of the EU Research and Innovation programme Horizon 2020 and aims to provide 12% of electricity by 2020 and 30% of electricity by 2030 produced from renewable sources.
 
In this paper we present the sustainable energy programmes in Tunisia from 1986 to 2030 and we discuss their short and long term impact on CO2 emission, the human activities and the sustainable development of the country.

A112 - ORAL-0363: Climate Change Adaptation in Northern Nigeria

Saadatu Baba1

1Kaduna State University, Kaduna, Nigeria

Northern Nigeria is among the so called 'hot spots' of climate change in the world. This research assesses climate change vulnerability and adaptation strategies in smallholder farming households in northern Nigeria. These subsistence farmers whose livelihoods depend on climate variability are among the most vulnerable people to the impacts of climate change in the world - in food security, health and water. These impacts are already being felt, and there is an urgent need to strengthen adaptation measures and incorporate them into local and national planning. The research identifies what resources are vulnerable to climate change, those most important for adaptation and the measures required to build upon existing adaptation strategies. The study uses mostly participatory methods, and focuses on biophysical factors as well as social vulnerability (including gender) in 20 farming households in rural northern Nigeria. Local authorities do not have specific planned adaptation measures, therefore the objective of the research is to inform community and local government action on climate change adaptation.

A113 - ORAL-0204: Welfare effect of climate adaptation technologies among farmers in Delta State, Nigeria

Felix Achoja1

1Delta State University, Asaba Campus, Nigeria., ASABA, Nigeria

Adaptation technologies are practices carried out by crop farmers to cope with the adverse consequences of climate extremes on household welfare such as income shocks, poverty and hunger. This study thus investigated the capacity of adaptation technologies adoption to improve the welfare of adapting crop farmers in Delta state, Nigeria. Primary data elicited from randomly selected 122 crop farmers with structured questionnaire, were analyzed with parametric and non- parametric statistical tools. The result shows that average farm income increased from N21,639 to N34,050. That is N12,411 (57.4%) increase in net farm income was attributed to the practice of relevant adaptation technologies. The increase in adaptation-based income of the surveyed farmers was significantly influenced by soil conservation (0.624), irrigation (0.415) and crop diversification (0.359). When farmers substituted crop diversification for new varieties technology their income increased by 6% (N2043). The 57.4% increase in adaptation-based farm income has implications for poverty alleviation and improved food security among vulnerable farm families. We recommended that crop farmers should concentrate adaptation efforts and resources on the relevant adaptation technologies such as soil conservation, irrigation and crop diversification technologies. Extension workers should convey this information to potential adapters in order to improve their welfare.

A114 - ORAL-0110: The neglected nonlocal effects of deforestation

Johannes Winckler1, 2, Christian Reick1, Julia Pongratz1

1Max Planck Institute for Meteorology, Hamburg, Germany 2International Max Planck Research School on Earth System Modelling, Hamburg, Germany

Deforestation changes surface temperature locally via biogeophysical effects by changing the water, energy and momentum balance. In addition to these locally induced changes (local effects), deforestation at a given location can cause changes in temperature elsewhere via advection and changes in circulation (nonlocal effects). Most previous studies considered only the total (local plus nonlocal) effects, for which global deforestation was simulated to cause a global mean cooling. Recent modelling and observational studies focused on the isolated local effects. Observational studies suggest that the local effects of deforestation cause a warming when averaged globally. This contrast between local warming and total cooling indicates that nonlocal effects of deforestation counteract the local effects by a global cooling signal. However this hypothesis could not be tested in previous studies because the nonlocal effects could not be isolated. It was further unclear how the nonlocal effects depend on the areal extent and spatial distribution of deforestation. To investigate this, we use a fully coupled climate model and separate local and nonlocal effects of deforestation in separate simulations with varying areal extent and spatial distribution of deforestation.
 
We find that, when globally averaged, local effects are counteracted by the nonlocal effects (up to 0.1K local warming versus -0.3K nonlocal cooling). The nonlocal cooling scales linearly with the number of deforested grid boxes, so this 1:-3 relationship is valid also for smaller-scale deforestation. Furthermore, the nonlocal cooling is apparent also for a more realistic spatial distribution of deforestation, and even for tropical deforestation.  We conclude that the local effects of deforestation alone --and thus also observations-- yield a highly incomplete picture of the total biobeophysical climate effects. The nonlocal effects should not be neglected if the biogeophysical effects of deforestation are considered for an implementation in climate policies that aim at global mitigation.

A115 -ORAL-0501: Irrigation mitigates against heat extremes

Wim Thiery1,2, Erich Fischer1, Auke Visser1, Annette Hirsch1, Edouard Davin1, Dave Lawrence3, Mathias Hauser1 and Sonia Seneviratne1

1Institute for Atmospheric and Climate Science, ETH Zurich, Switzerland  Department of Hydrology and Hydraulic Engineering, Vrije Universiteit Brussel, Belgium 3National Center for Atmospheric Research (NCAR), USA

Irrigation is an essential practice for sustaining global food production and many regional economies. Emerging scientific evidence indicates that irrigation substantially affects mean climate conditions in different regions of the world. Yet how this practice influences temperature extremes is currently unknown. Here we use gridded observations and ensemble simulations with the Community Earth System Model to assess the impacts of irrigation on hot extremes. While the influence of irrigation on annual mean temperatures is limited, we find a large impact on temperature extremes, with a particularly strong cooling during the hottest day of the year (-0.78 K averaged over irrigated land). The strong influence on hot extremes stems from the timing of irrigation and its influence on land-atmosphere coupling strength. Together these effects result in asymmetric temperature responses, with a more pronounced cooling during hot and/or dry periods. The influence of irrigation is even more pronounced when considering subgrid-scale model output, suggesting that local effects of land management are far more important than previously thought. Finally we find that present-day irrigation is partly masking GHG-induced warming of extreme temperatures, with particularly strong effects in South Asia. Our results overall underline that irrigation substantially reduces our exposure to hot temperature extremes and highlight the need to account for irrigation in future climate projections.