Assessing the effectiveness of Sustainable Land Management for large-scale climate change adaptation

JPC Eekhout and J de Vente

July 17-30, 2019

LANDSIM-Regional Hands-On Training, Wageningen, The Netherlands

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Abstract

Climate change will strongly affect essential ecosystem services, like the provision of freshwater, food production, soil erosion and flood control. Sustainable Land Management (SLM) practices are increasingly promoted to contribute to climate change mitigation and adaptation, but there is lack of evidence at scales most relevant for policymaking. We evaluated the effectiveness of SLM in a large Mediterranean catchment where climate change is projected to significantly reduce water security. We show that the on-site and off-site impacts of climate change are almost entirely reversed by the large-scale implementation of SLM under moderate climate change conditions, characterized by limited reductions in annual precipitation but significant increased precipitation intensity. Under more extreme reductions of annual precipitation, SLM implementation reduces the impacts on water security, but cannot prevent significant increased plant water stress and reduced water availability. Under these conditions, additional adaptation measures are required considering their interactions and trade-offs regarding water security.
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Slide 1 of Assessing the effectiveness of Sustainable Land Management for large-scale climate change adaptation
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In this presentation I will give a short introduction to SLM and how we implemented this into the model, then I will show results from an implementation in the Segura river catchment.
Slide 2 of Assessing the effectiveness of Sustainable Land Management for large-scale climate change adaptation
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Climate change projects increase extreme weather events, such as extreme precipitation and droughts.
Slide 3 of Assessing the effectiveness of Sustainable Land Management for large-scale climate change adaptation
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This will cause decreased water availability and food production, and increased soil erosion and flood frequency. SLM is suggested to be an effective climate change adaptation strategy to combat the impact of climate change on hydrology and soil erosion.
Slide 4 of Assessing the effectiveness of Sustainable Land Management for large-scale climate change adaptation
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SLM is defined as follows: SLM supports the prevention and reduction of land degradation, protects biodiversity, and includes established approaches such as conservation agriculture, cover crops, organic amendments, crop diversification, and integrated nutrient and water management.
Slide 5 of Assessing the effectiveness of Sustainable Land Management for large-scale climate change adaptation
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The WOCAT database includes several examples of soil water conservation measures, including agronomic and vegetative measures, some examples are shown in the next slide. Besides, there are structural measures, such as check dams and terraces, and management measures.
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In several field experiments we have evaluated the effectiveness of SLM on soil erosion, soil moisture and crop yield. Green manure is a SLM technique where a mixture of cereals and leguminous cover crops are seeded in autumn and later ploughed into the soil. The combination of reduced tillage and green manure was selected from stakeholder consultation process as most effective measures for our study area.
Slide 7 of Assessing the effectiveness of Sustainable Land Management for large-scale climate change adaptation
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In this model study, we implemented SLM in cereals (RT), tree crops (RT+GM) and vineyards (RT+GM).
Slide 8 of Assessing the effectiveness of Sustainable Land Management for large-scale climate change adaptation
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We changed the organic matter content and bulk density with values obtained from the field experiments and from the literature. These changes will affect the water holding capacity of the soil.
Slide 9 of Assessing the effectiveness of Sustainable Land Management for large-scale climate change adaptation
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We also changed vegetation properties. NDVI was changed in the period September-May with values taken from cereals as substitute for green manure.
Slide 10 of Assessing the effectiveness of Sustainable Land Management for large-scale climate change adaptation
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Here we show how NDVI was changed for tree crops with green manure.
Slide 11 of Assessing the effectiveness of Sustainable Land Management for large-scale climate change adaptation
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Several vegetation parameters related to the soil erosion module were changed, including plant height, stem density and stem diameter.
Slide 12 of Assessing the effectiveness of Sustainable Land Management for large-scale climate change adaptation
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The changes to these soil erosion parameters will affect several soil erosion processes, such as detachment by raindrop impact (F), detachment by runoff (H) and in-field deposition (D).
Slide 13 of Assessing the effectiveness of Sustainable Land Management for large-scale climate change adaptation
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The study area is located in southeast Spain. This slide shows the main characteristics of the study area.
Slide 14 of Assessing the effectiveness of Sustainable Land Management for large-scale climate change adaptation
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The study area can be mainly characterized by a semi-arid climate, with frequent extreme precipitation events reaching up to 100 mm per day.
Slide 15 of Assessing the effectiveness of Sustainable Land Management for large-scale climate change adaptation
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We applied 4 climate scenarios, divided over 2 RCPs and 2 periods. Data from an ensemble of 9 climate models was used. Here we show the results of the RCP8.5 scenario.
Slide 16 of Assessing the effectiveness of Sustainable Land Management for large-scale climate change adaptation
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SLM was implemented in 38% of the catchment. This map shows the percentage of the subcatchments covered with areas where SLM was implemented, with in some small subcatchments up to 70%.
Slide 17 of Assessing the effectiveness of Sustainable Land Management for large-scale climate change adaptation
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These maps show how the climate signal will change under climate change. Annual precipitation sum is projected to decrease, mainly in the headwaters. Extreme precipitation is projected to increase, mainly in the downstream part of the catchment.
Slide 18 of Assessing the effectiveness of Sustainable Land Management for large-scale climate change adaptation
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The catchment-average decrease of annual precipitation sum amounts to 3-18%. The catchment-average increase of extreme precipitation amounts to 20-24%.
Slide 19 of Assessing the effectiveness of Sustainable Land Management for large-scale climate change adaptation
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We have focused the results on several on-site and off-site water security indicators. Here we will show the results of plant water stress (PWS), hillslope erosion (SSY), reservoir inflow (Qres) and reservoir sediment yield (SY).
Slide 20 of Assessing the effectiveness of Sustainable Land Management for large-scale climate change adaptation
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Under climate change, an increase of plant water stress is projected, most obvious in the headwaters of the catchment, this is a very important change, because a large part of the catchment is already under a lot of stress, which is projected to increase under climate change.
Slide 21 of Assessing the effectiveness of Sustainable Land Management for large-scale climate change adaptation
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Under climate change and with implementation of SLM, there is still an increase of plant water stress in many parts of the catchment, but where SLM is implemented, plant water stress decreases to similar values under the reference scenario without SLM. However, under the far future scenario, plant water stress still increases significantly.
Slide 22 of Assessing the effectiveness of Sustainable Land Management for large-scale climate change adaptation
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Under climate change, soil erosion is projected to increase in almost all catchment, except some headwater subcatchments. With catchment average increases of 55% and 34% for the near future and far future scenarios.
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Under climate change and with SLM implemented, soil erosion also decreases, even with respect to the reference scenario without SLM, with catchment average decreases of 5 to 19%. The same pattern is visible for the reservoir sediment yield.
Slide 24 of Assessing the effectiveness of Sustainable Land Management for large-scale climate change adaptation
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A slight decrease of precipitation is projected under climate change, but because of an increase of extreme precipitation, we see an increase of surface runoff, which causes a decrease of infiltration and soil water content, ultimately leading to an increase of plant water stress. But also an increase of hillslope erosion.
Slide 25 of Assessing the effectiveness of Sustainable Land Management for large-scale climate change adaptation
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With SLM implemented, we see a lot of these processes reversed, such as an increase of infiltration and soil water content, leading to a smaller impact on plant water stress. We also see a decrease of surface runoff and hillslope erosion, which impacts reservoir inflow and flood discharge.
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We ultimately arrive to the following conclusion, that the on-site and off-site impacts of climate change are almost entirely reversed by large-scale implementation of sustainable land management.