Conference Agenda

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Session Overview
115R: Water on land: The role of green water for social-ecological and Earth system resilience
Friday, 26/Apr/2019:
10:30am - 12:00pm

Session Chair: Lan Wang-Erlandsson
Session Chair: Patrick William Keys
Location: UniS-A -126
UniS building, room A-126, basement, 80 seats
Session Topics:
What are the visions for the planetary land system?

Session Abstract

Green water, i.e., soil moisture stocks and all evaporation flows from land, is fundamental for sustaining food production and terrestrial ecosystems, and for regulating the climate. By wettening the landscape, green water provides resilience, i.e., the capacity of a system to adapt and transform in the face of change, to social-ecological systems at the local scale as well as the Earth system at the planetary scale.

Land degradation, desertification, and deforestation are all human interventions in the land system that deplete social-ecological resilience through green water interference, and can locally manifest as drought, heatwave, and crop failure. Furthermore, green water interference through land system change can also have important non-local and regional-to-global scale implications, through influence on among others carbon sequestration, albedo of soil and vegetation, nutrient uptake, moisture recycling, monsoon onset, and partitioning between latent and sensible heat flux. Such biophysical resilience loss from human interference (e.g., deforestation of the Amazon) may trigger undesired self-amplifying feedbacks (e.g., slowdown of the water cycle) and cause regime shifts, i.e., drastic, persistent, and systemic changes (e.g., forest-savanna transition). The social consequences of biophysical resilience loss or regimes shifts can be severe and cause famine, political instability, and migration, especially in combination with climate change and weak social institutions.

On the positive side, knowledge of the role of green water have also created green water management solutions, such as vapor shift through rainwater harvesting, that increase harvest, serve local communities, and provide resilience a the larger scale. Great challenges, nevertheless, remain. What are the key processes through which green water matters for Earth system resilience at the planetary scale? How can synergies and trade-offs be built to manage green water resilience from the local to the global scale? And how can the full transformative potential of integrated land and water resources management be unleashed to deliver resilient and sustainable development?

This session welcomes both qualitative and quantitative research that explore the relationship between land management and green water, or that advance our understanding of the role of green water for resilience from a wide range of perspectives.

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Full talk
ID: 505 / 115R: 1
115R Water on land: The role of green water for social-ecological and Earth system resilience
Keywords: deforestation, climate risk, agriculture, Brazil, ecosystem services

Agricultural losses from biogeophysical climate change in Brazil: A business case for ecosystem protection?

Avery Cohn, Sally Thompson

Tufts University, United States of America

In the Amazon and Cerrado biomes of Brazil, slowing ecosystem conversion could help to protect valuable ecosystem services, but comes at the cost of foregone revenue from the expansion of agricultural activities. As part of a wider effort to estimate the likelihood that reducing ecosystem conversion will be net beneficial to key agricultural and government actors, we produced spatially explicit, near-term, probabilistic estimates of economic damage to the agricultural economy stemming from ecosystem services lost under ecosystem conversion. Underlying these estimates was an ecological forecasting framework. We assembled the framework using two sets of statistical models, selected for their predictive skill and drawing on remotely sensed and in situ evidence. The first model set predicted the response of agriculturally relevant rainfall and temperature parameters to regional land use and land cover change. The second set predicted the response of agricultural productivity to changes in the regional climate. Together with idealized land use and land cover scenarios, we linked these models and used them to forecast economic damage to the agricultural sector stemming from ecosystem conversion. The results of the forecast exhibited a high degree of uncertainty, but nevertheless revealed the costs of damage from a considerable area of ecosystem conversion to robustly exceed the opportunity cost of conservation. Partitioning the uncertainty demonstrated several priority areas for improved modeling and data in the agricultural, ecological, and climatological domains.

Full talk
ID: 338 / 115R: 2
115R Water on land: The role of green water for social-ecological and Earth system resilience
Keywords: Climate feedbacks, Soil Moisture Temperature Coupling (SMTC), Soil Moisture, Ethiopia, Tigray Region.

Mesoclimate regulation induced by landscape restoration and water harvesting in agroecosystems of the horn of Africa

Giulio Castelli1, Fabio Castelli2, Elena Bresci1

1Department of Agricultural, Food and Forestry Systems (GESAAF), Università degli Studi di Firenze, Italy; 2Department of Civil and Environmental Engineering (DICEA), Università degli Studi di Firenze, Italy

When changes are made in a landscape, these changes may impact on the local climate. In arid and semi-arid agroecosystems of the world, measures such as Landscape Restoration and Water Harvesting (LRWH) are implemented to revert land degradation and increase soil moisture, reducing runoff losses and increasing agricultural yields. The present work aims to analyse to what extent storing soil moisture, with adequate land and water management practices, can reduce temperatures in the hot months after the rainy season, because of Soil Moisture-Temperature Coupling (SMTC), in a semi-arid climate such as the one of northern Ethiopian highlands. Since it is reported that soil moisture deficit can enhance heatwaves in diverse regions of the world, it is hypothesized that increasing soil water availability, during the dry and hot periods, can mitigate hot temperatures. The analysis has been carried for Enabered catchment, in Tigray Region, Ethiopia, where the rainy season runs from June to September. Here, large scale LRWH implementation ended in 2008. An analysis based on remote sensing data has been carried out to evaluate (1) to what extent LRWH implementation can enhance soil moisture conservation at agroecosystem scale; (2) to what extent LRWH implementation can mitigate temperatures in the dry season at agroecosystem scale; and (3) if SMTC effect was evident. Results showed an increased capacity of the catchment to maintain soil moisture accumulated in the rainy season, and reduce temperatures. Increase of soil moisture was especially significant for September (P < 0.01), while temperature decrease was evident in October (P < 0.01) and November (P < 0.05), with decreases of Land Surface Temperatures up to 1.74 °C. A simple, parsimonious linear regression model demonstrated that SMTC is evident at catchment scale and that the implementation of LRWH measures provided a climate regulation effect in the watershed. The present work can reinforce the call for an increased adoption of water harvesting, land restoration and green water management, to increase the resilience of agricultural ecosystem located in arid and semi-arid areas, that represent a key element to achieve global food security.

Full talk
ID: 775 / 115R: 3
115R Water on land: The role of green water for social-ecological and Earth system resilience
Keywords: moisture recycling, tropical rainforest, resilience, drought

Dry periods amplify rainfall dependence on moisture recycling in the Amazon and Congo forests

Lan Wang-Erlandsson1,2, Ruud van der Ent3,4, Patrick Keys5, Ingo Fetzer1, Makoto Taniguchi2, Line Gordon1

1Stockholm Resilience Centre, Stockholm University, Sweden; 2Research Institute for Humanity and Nature, Japan; 3Department of Water Management, Delft University of Technology, the Netherlands; 4Department of Physical Geography, Utrecht University, the Netherlands; 5Colorado State University, USA

Forests in the Amazon and Congo are vulnerable to rainfall decrease, and particularly during dry seasons and dry years. We use 34 years of reanalysis, synthesis precipitation data, and the moisture tracking model WAM-2layers to analyze anomalies in Amazon and Congo moisture recycling during the dry seasons and dry years (i.e., years with high water deficit or low rainfall). We find that the relative importance of forests as moisture suppliers for rainfall increase considerably during dry seasons. Dry years further amplify the dry season forest moisture recycling by 10-15 % in parts of both the Amazon and Congo. If mean dry season precipitation would fall to dry year levels, the risk for a forest-savanna transition would be substantially elevated in both Amazon and Congo. Further, we find that evaporation anomaly is able to explain up to half of the seasonal precipitationshed anomalies, and at least a third of the dry year dry season anomalies. The dry period intensification of moisture recycling implies an increased dependence on the forest for its own moisture, which may amplify interactions between deforestation and droughts. Thus, we conclude that it will be important to understand how moisture recycling amplification will develop in the future, specifically in terms of its role in mediating deforestation, climate change, and forest resilience.

Full talk
ID: 780 / 115R: 4
115R Water on land: The role of green water for social-ecological and Earth system resilience
Keywords: climate, soil moisture, green water, cropland, yield

The importance of green water for understanding climate change impacts on crops

Nathan Mueller1, Angela Rigden2, Paul Levine1, Ethan Butler3, Peter Huybers2, James Randerson1

1University of California, Irvine, United States of America; 2Harvard University, United States of America; 3University of Minnesota, United States of America

Agricultural climate impact projections routinely rely upon temperature-based statistical models to characterize historical variability and project future crop yields, and exposure to extremely hot temperatures is associated with severe crop losses. However, high temperatures over land are often associated with soil moisture deficits, meaning reductions in yield due to reduced green water flows may be conflated with crop stress from high temperatures. Relying on temperature as an explanatory variable in yield projections therefore makes the implicit assumption that the historical association between soil moisture deficits and high temperatures will stay constant in a changing climate. Here we examine the historical association between soil moisture and summer temperatures, focusing on the US Great Plains. We then utilize climate model output to assess possible future trajectories of this association, finding that the historical pattern shifts substantially in a changing climate. Although there are interesting wetting and drying patterns, most warming occurs without the corresponding change in soil moisture that would have been inferred from the historical pattern. Therefore, temperature-based statistical crop yield models may be biased towards implicitly overestimating future reductions in green water flows and yields. The magnitude of this bias is assessed using a series of statistical models for rainfed and irrigated maize and soybean.

Full talk
ID: 751 / 115R: 5
115R Water on land: The role of green water for social-ecological and Earth system resilience
Keywords: Green water, agricultural intensification, land use change, sustainable development

The interaction between the expansion and intensification of brazilian soybean production systems, and their effects on green water flows

Rafaela Flach

Hamburg University, Germany

Over the last couple of decades, cropland expansion has significantly re-allocated green water from terrestrial ecosystems towards agriculture. This type of land use change results in additional availability of land and water resources, but also connected to impacts to biodiversity and changes in the water cycle. Alongside this expansion, agricultural intensification practices such as double cropping result in greater output per unit of land and water, as well as more productive use of the available water throughout the annual cycle. Double-cropping systems have been shown to have much higher water-recycling potential than single cropping systems, being more similar to the natural vegetation in certain areas. We investigate the influence of these two processes – horizontal cropland expansion and agricultural intensification – in agricultural water use and green water flows in Brazil, with the objective to understand the trade-offs and synergies for land and water productivity. We applied the biophysical model EPIC to estimate yields and consumptive water use for single and double cropping of soybeans, maize and cotton in Brazil for 1990-2015. The results show a prevalence of cropland expansion, mostly in the Amazon and Cerrado regions, as the main cause of changes in total green water use. The yield increase in this period, related to technological improvements and management options, contributed to a more productive use of land and water resources throughout the country. However, when comparing single and double cropping systems, an even higher improvement of resource use per hectare is observed. Exploiting the potential for double cropping could be a sustainable option to increase agricultural production without further land conversion, while taking better advantage of the available water throughout the year. Finally, although our model results support the evidence for increase in the water-recycling potential that double-cropping, there are limitations to its similarity to natural vegetation levels.

Full talk
ID: 747 / 115R: 6
115R Water on land: The role of green water for social-ecological and Earth system resilience
Keywords: Green water, Migration, Resilience, Karamoja, Remote sensing, Soil moisture

Green water and livestock mobility in karamoja understanding the karimojong phrase “we follow our water”

Shuaib Lwasa, Benon Nabaasa

Makerere University, Uganda

The Karimojong of North Eastern Uganda are a nomadic pastoralist group largely dependent on livestock for a livelihood and have over time evolved a robust livestock system. Though pastoralism has proven to be a resilient system, the past few decades in the history of the planet have witnessed alterations in the earth’s systems. These shifts have in turn triggered responsive adaptation interventions among the pastoralists chief of which is frequent and longer livestock migrations in search of water and pasture. Pastoralism in Karamoja is heavily weather dependent and the dynamics of water and pasture are not only significant influences on the Karimojong socio-economic sphere but such dynamics also are key shapers of the Karimojong landscape. Although blue water is crucial for pastoralists and their livestock, Karimojong seasonal migrations and way of life are more often determined by green water in form of forage biomass spatial and temporal fluctuations which in turn depend on soil moisture. The Karimojong graze in a pattern that trails the receding soil moisture hence the local adage “We follow our water”. By tracking both herder movements and the spatial and temporal variation of soil moisture, this study makes quantitative conclusions in line with the Karimojong phrase “we follow our water”. Preliminary results reveal that soil moisture variations are a precursor to pastoralist movements, which migrations in turn set in a cascade of slow onset landscape changes. The study underpins the significance of green water in influencing the Karimojong way of life and in shaping the landscape onto which they subsist.

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