Papers by Lan Wang Erlandsson
Beyond deforestation: water use in global agricultural commodity supply chains
Interest is increasing within the European Union (EU) policy space to understand the link between... more Interest is increasing within the European Union (EU) policy space to understand the link between tropical deforestation and imports of agricultural commodities. In 2017, the EU27’sa consumption of agricultural commodities was associated with close to 20% of global tropical deforestation (or 240,000 hectares), according to the newly released Commodity Footprints data (Croft et al., 2021) (see Box 1). Total tropical deforestation associated with the consumption of agricultural commodities in the EU and UK were only second to China, and ahead of India, the US and Japan in 2017 (Pendrill et al., 2020). Addressing this issue at the EU level can encourage other countries to follow, accelerating reductions in greenhouse gas emissions and preventing further loss of biodiversity and ecosystem services. Since 2018, several initiatives have been proposed acknowledging deforestation in supply chains (European Commission, Directorate General for the Environment., 2018; GRI Taskforce, 2020; MTES...
A planetary boundary for green water
Nature Reviews Earth & Environment, Apr 26, 2022
Green water — terrestrial precipitation, evaporation and soil moisture — is fundamental to Earth ... more Green water — terrestrial precipitation, evaporation and soil moisture — is fundamental to Earth system dynamics and is now extensively perturbed by human pressures at continental to planetary scales. However, green water lacks explicit consideration in the existing planetary boundaries framework that demarcates a global safe operating space for humanity. In this Perspective, we propose a green water planetary boundary and estimate its current status. The green water planetary boundary can be represented by the percentage of ice-free land area on which root-zone soil moisture deviates from Holocene variability for any month of the year. Provisional estimates of departures from Holocene-like conditions, alongside evidence of widespread deterioration in Earth system functioning, indicate that the green water planetary boundary is already transgressed. Moving forward, research needs to address and account for the role of root-zone soil moisture for Earth system resilience in view of ecohydrological, hydroclimatic and sociohydrological interactions. The planetary boundaries framework outlines a safe operating space for humanity according to key Earth system dynamics. This Perspective proposes the addition of a green water planetary boundary based on root-zone soil moisture and demonstrates that widespread green water modifications now present increasing risks to Earth system resilience.
Most River Basins will Follow their Budyko Curves under Global Warming
<p>The Budyko framework consists of a curvilinear relationship between the ... more <p>The Budyko framework consists of a curvilinear relationship between the evaporative ratio (i.e., actual evaporation over precipitation) and the aridity index (potential evaporation over precipitation) and defines evaporation’s water and energy limits. A basin’s movement within the Budyko space illustrates its hydroclimatic change and can help identify the main drivers of change. Basins are expected to move along their Budyko curves when only long-term changes in the aridity index drive changes in the evaporative ratio. We hypothesize that the increasing effects of global warming on the hydrological cycle will cause basins to move along their Budyko curves. To test our hypothesis, we quantify the movement in Budyko space of 353 river basins from 1901 to 2100 based on the outputs of nine models from the Coupled Model Intercomparison Project - Phase 5 (CMIP5). We find that significant increases in potential evaporation due to global warming will lead to basins moving primarily horizontally in Budyko space accompanied by minor changes in the evaporative ratio. However, 37% of the basins will still deviate from their Budyko curve trajectories, with less evaporation than expected by the framework. We elaborate on how land-use change, vegetation changes, or shifts in precipitation or snow to rain ratios can explain these deviations.</p>
Trees and forests multiply the oceanic supply of freshwater through moisture recycling, pointing ... more Trees and forests multiply the oceanic supply of freshwater through moisture recycling, pointing to an urgent need to halt deforestation and offering a way to increase the water-related benefits of forest restoration. E fficient and effective forest and water-related nature-based solutions to challenges in human development require a holistic understanding of the role of forest-water interactions in hydrologic flows and water supply in local, regional and continental landscapes. Forest and water resource management, however, tends to focus on river flows and to take rainfall for granted as an unruly, unmanageable input to the system (Ellison, Futter and Bishop, 2012). Thus, the potential impact of increased tree and forest cover on downwind rainfall and potential water supply is both underestimated and underappreciated.
Water stress and their implications on the ecohydrology of rainforests
<p><span>Rainforests have been a major controller of local and global climate by main... more <p><span>Rainforests have been a major controller of local and global climate by maintaining carbon stocks and regulating global water cycle. However, the water cycle is increasingly impacted by climate change and ongoing deforestation, which forces rainforest ecosystems to adapt differently to increasing water-stress. To understand future rainforest dynamics towards changing hydroclimate, their resilience capacity to future changes and estimating potential tipping points, it is detrimental that we quantify moisture available to vegetation. However, due to the physical limitations in quantifying subsurface moisture availability of terrestrial ecosystems at continental scales, only rainfall is considered a primary control variable to represent the forest's ecohydrological status. In the present study, using remote-sensing derived rootzone storage capacity (<em>S</em><sub>r</sub>), we analyze the water-stress and drought coping strategies along rainforest-savanna transects in South America and Africa at different tree cover densities. We further classified the ecosystem's adaptability to water-stress into four classes:&#160;</span><em>lowly</em>,&#160;<em>moderately</em>,&#160;<em>highly&#160;</em>water-stressed forest, and&#160;<em>savanna-grassland</em>&#160;<span>regime using empirical and statistical analysis. Based on these analyses, we can show that forests subsequently invest in their rooting strategy and modify their above-ground forest cover in response to the water-stress experienced by it. We observed that remote sensing-based rootzone storage capacity reveals important subsoil forest dynamics and can act as an important hydroclimatic stress indicator for vegetation. Monitoring of rootzone storage capacity helps open new paths to understanding the eco-hydrological state, ecosystem resilience, and adaptation dynamics in a rapidly changing climate.</span></p><p>&#160;</p><p><img src="data:image/png;base64,…
Towards a green water planetary boundary
<p>Green water - soil moisture, evaporation, and precipitation over land - is fundamental t... more <p>Green water - soil moisture, evaporation, and precipitation over land - is fundamental to safeguard Earth system functioning. Nonlinear green-water driven changes in climate, ecosystems, biogeochemistry, and hydrology are becoming increasingly evident and widespread. Yet, considerations of continental to planetary scale green-water dynamics are yet to be assessed and incorporated in management and governance. Here, we propose a green water planetary boundary (PB) - as part of the planetary boundary framework that demarcates a global &#8220;safe-operating space&#8221; for humanity - for assessing green-water related changes that can affect the capacity of the Earth system to remain in Holocene-like conditions. We consider green-water related processes associated with all scales: spatially distributed units, regions or biomes, and the Earth system as a whole. The proposed green water PB variable is selected through expert elicitation based on a set of transparent evaluation criteria that consider both scientific and governability aspects. Finally, we clarify the appropriate use of a green water PB, outline remaining challenges, and propose a research agenda for future navigation and quantitative assessments of the biophysical Earth system scale boundaries of green water changes.</p>
On tracking moisture during heatwaves - a case of Europe
When does deforestation affect rainfall? Synergistic hydroclimatic resilience risks in the greater Amazon and Congo regions
Poor correlation between large-scale environmental flow violations and freshwater biodiversity: implications for water resource management and water planetary boundary
The freshwater ecosystems around the world are degrading, such that maintaining environmental flo... more The freshwater ecosystems around the world are degrading, such that maintaining environmental flow (EF) in river networks is critical to their preservation. The relationship between streamflow alte...
Terrestrial tropical ecosystems’ resilience is determined predominantly based on space-for-time s... more Terrestrial tropical ecosystems’ resilience is determined predominantly based on space-for-time substitution, which assumes that the current ‘static’ frequency distribution of ecosystems’ tree cover structure across space also holds across time. However, dynamic and temporal aspects are increasingly important to explicitly account for under ongoing rapid climate change. Here, we empirically study ecosystem stability and instability using remote sensing-derived tree cover change (ΔTC) over the last two decades. We find that considerable ΔTC predominantly takes place in intermediate tree cover ecosystems (i.e., areas with 30-60% tree cover), whereas high (>75%) and low (<10%) tree cover ecosystems only experience limited ΔTC. Our results further suggest that root zone storage capacity, which defines the adaptive capacity of the ecosystem to absorb water stress perturbations, does mediate the relationship between ecosystems’ stability and ΔTC by instigating investment in ecosyste...
Environmental Research Letters, 2020
Climate change and deforestation have increased the risk of drought-induced forest-to-savanna tra... more Climate change and deforestation have increased the risk of drought-induced forest-to-savanna transitions across the tropics and subtropics. However, the present understanding of forest-savanna transitions is generally focused on the influence of rainfall and fire regime changes, but does not take into account the adaptability of vegetation to droughts by utilizing subsoil moisture in a quantifiable metric. Using rootzone storage capacity (S r), which is a novel metric to represent the vegetation's ability to utilize subsoil moisture storage and tree cover (TC), we analyze and quantify the occurrence of these forest-savanna transitions along transects in South America and Africa. We found forest-savanna transition thresholds to occur around a S r of 550-750 mm for South America and 400-600 mm for Africa in the range of 30%-40% TC. Analysis of empirical and statistical patterns allowed us to classify the ecosystem's adaptability to droughts into four classes of drought coping strategies: lowly water-stressed forest (shallow roots, high TC), moderately water-stressed forest (investing in S r , high TC), highly water-stressed forest (trade-off between investments in S r and TC) and savanna-grassland regime (competitive rooting strategy, low TC). The insights from this study are useful for improved understanding of tropical eco-hydrological adaptation, drought coping strategies, and forest ecosystem regime shifts under future climate change.
Climate Dynamics, 2021
Heatwaves are extreme weather events that have become more frequent and intense in Europe over th... more Heatwaves are extreme weather events that have become more frequent and intense in Europe over the past decades. Heatwaves are often coupled to droughts. The combination of them lead to severe ecological and socio-economic impacts. Heatwaves can self-amplify through internal climatic feedback that reduces local precipitation. Understanding the terrestrial sources of local precipitation during heatwaves might help identify mitigation strategies on land management and change that alleviate impacts. Moisture recycling of local water sources through evaporation allows a region to maintain precipitation in the same region or, by being transported by winds, in adjacent regions. To understand the role of terrestrial moisture sources for sustaining precipitation during heatwaves, we backtrack and analyse the precipitation sources of Northern, Western, and Southern sub-regions across Europe during 20 heatwave periods between 1979 and 2018 using the moisture tracking model Water Accounting Mo...
The role of forests in securing water for agriculture globally
&amp;amp;amp;amp;lt;p&amp;amp;amp;amp;gt;Forests worldwide supply moisture to downwind pr... more &amp;amp;amp;amp;lt;p&amp;amp;amp;amp;gt;Forests worldwide supply moisture to downwind precipitation through moisture recycling. Agricultural areas located downwind of forests are, hence, susceptible to changes in precipitation caused by upwind forest changes. In fact, human activities have driven extensive forest cover changes in different parts of the world, in different directions, and at different rates. Nevertheless, the forest-agriculture relationship has yet to be systematically quantified and mapped globally. Previous regional studies in South America show that upwind deforestation of the Amazon forest can reduce downwind precipitation and thus decrease agricultural production. A global coverage analysis of forest-agriculture relationship is therefore necessary to identify other hotspot regions where downwind agriculture relies heavily on upwind forests. In this study, we establish the global source-to-sink relationship between forests and their downwind agriculture by analysing 10 years of high resolution (0.25&amp;amp;amp;amp;amp;#176;x0.25&amp;amp;amp;amp;amp;#176;) ERA5-based moisture flows processed by the UTrack moisture tracking model. We assess the seasonality of the reliance on forests considering the growing season of crops cultivated in the downwind regions. Our study provides a global overview of the cross-sectoral and remote dependence of agriculture on forests globally through moisture recycling.&amp;amp;amp;amp;lt;/p&amp;amp;amp;amp;gt;
The spatio-temporal evolution of groundwater dependent precipitation
&amp;amp;amp;amp;amp;lt;div&amp;amp;amp;amp;amp;gt;&amp;amp;amp;amp;amp;lt;span&a... more &amp;amp;amp;amp;amp;lt;div&amp;amp;amp;amp;amp;gt;&amp;amp;amp;amp;amp;lt;span&amp;amp;amp;amp;amp;gt;A&amp;amp;amp;amp;amp;lt;strong&amp;amp;amp;amp;amp;gt; &amp;amp;amp;amp;amp;lt;/strong&amp;amp;amp;amp;amp;gt;substantial portion of groundwater abstracted from aquifers is used for irrigation and evaporated to the atmosphere, potentially contributing towards downwind precipitation. While the fate of evaporation fluxes from land have been analysed, the atmospheric pathways of evaporation originating from groundwater have not yet been globally quantified. This study analysed the geographical distribution, the seasonality and the magnitude of groundwater-dependent precipitation (Pgw)&amp;amp;amp;amp;amp;amp;#160;&amp;amp;amp;amp;amp;lt;/span&amp;amp;amp;amp;amp;gt;&amp;amp;amp;amp;amp;lt;span&amp;amp;amp;amp;amp;gt;at a global scale and for a selection of countries and river basins. The Eulerian moisture tracking WAM-2layers model was used to process meteorological and groundwater abstraction input data from 1980 to 2010. &amp;amp;amp;amp;amp;amp;#160;Results show considerable contributions of groundwater to precipitation downwind of the most heavily irrigated areas, leading to net groundwater losses over these areas. Globally, 40% of the Pgw&amp;amp;amp;amp;amp;amp;#160;&amp;amp;amp;amp;amp;lt;/span&amp;amp;amp;amp;amp;gt;&amp;amp;amp;amp;amp;lt;span&amp;amp;amp;amp;amp;gt;precipitates directly in the oceans, and do not contribute to biomass production in terrestrial ecosystems. Some of the countries with the highest rates of groundwater abstraction (India, the USA, Pakistan and Iran), receive low volumes of Pgw&amp;amp;amp;amp;amp;amp;#160;&amp;amp;amp;amp;amp;lt;/span&amp;amp;amp;amp;amp;gt;&amp;amp;amp;amp;amp;lt;span&amp;amp;amp;amp;amp;gt;and are net losers of groundwater resources. The countries with the highest net gain of groundwater are China, Canada and Russia. At river basin scale, the Indus, Ganges and Mississippi basins are net losers of groundwater to downwind Pgw&amp;amp;amp;amp;amp;lt;/span&amp;amp;amp;amp;amp;gt;&amp;amp;amp;amp;amp;lt;span&amp;amp;amp;amp;amp;gt;, while the Yangtze, Tarim and Brahmaputra basins receive more Pgw&amp;amp;amp;amp;amp;amp;#160;&amp;amp;amp;amp;amp;lt;/span&amp;amp;amp;amp;amp;gt;&amp;amp;amp;amp;amp;lt;span&amp;amp;amp;amp;amp;gt;than their groundwater withdrawals. The share of precipitation that originates from groundwater varies considerably with seasons, and can be especially high when low local precipitation levels occur in combination with high upwind groundwater abstraction. Furthermore, precipitation dependence on&amp;amp;amp;amp;amp;amp;#160;&amp;amp;amp;amp;amp;lt;/span&amp;amp;amp;amp;amp;gt;&amp;amp;amp;amp;amp;lt;span&amp;amp;amp;amp;amp;gt;groundwater (&amp;amp;amp;amp;amp;amp;#961;gw)&amp;amp;amp;amp;amp;lt;/span&amp;amp;amp;amp;amp;gt;&amp;amp;amp;amp;amp;lt;span&amp;amp;amp;amp;amp;gt;, has steadily increased between 1980 to 2010 in all studied areas and globally. Our study suggests that the countries and basins with a high and increasing dependency on &amp;amp;amp;amp;amp;amp;#961;gw&amp;amp;amp;amp;amp;amp;#160;&amp;amp;amp;amp;amp;lt;/span&amp;amp;amp;amp;amp;gt;&amp;amp;amp;amp;amp;lt;span&amp;amp;amp;amp;amp;gt;to support their precipitation can be vulnerable to groundwater availability upwind.&amp;amp;amp;amp;amp;lt;/span&amp;amp;amp;amp;amp;gt;&amp;amp;amp;amp;amp;lt;/div&amp;amp;amp;amp;amp;gt;
Tropical forests modify the conditions they depend on through feedbacks at different spatial scal... more Tropical forests modify the conditions they depend on through feedbacks at different spatial scales. These feedbacks shape the hysteresis (history-dependence) of tropical forests, thus controlling their resilience to deforestation and response to climate change. Here, we determine the emergent hysteresis from local-scale tipping points and regional-scale forestrainfall feedbacks across the tropics under the recent climate and a severe climate-change scenario. By integrating remote sensing, a global hydrological model, and detailed atmospheric moisture tracking simulations, we find that forest-rainfall feedback expands the geographic range of possible forest distributions, especially in the Amazon. The Amazon forest could partially recover from complete deforestation, but may lose that resilience later this century. The Congo forest currently lacks resilience, but is predicted to gain it under climate change, whereas forests in Australasia are resilient under both current and future climates. Our results show how tropical forests shape their own distributions and create the climatic conditions that enable them.
Water Resources Research, 2020
Fresh water-the bloodstream of the biosphere-is at the center of the planetary drama of the Anthr... more Fresh water-the bloodstream of the biosphere-is at the center of the planetary drama of the Anthropocene. Water fluxes and stores regulate the Earth's climate and are essential for thriving aquatic and terrestrial ecosystems, as well as water, food, and energy security. But the water cycle is also being modified by humans at an unprecedented scale and rate. A holistic understanding of freshwater's role for Earth system resilience and the detection and monitoring of anthropogenic water cycle modifications across scales is urgent, yet existing methods and frameworks are not well suited for this. In this paper we highlight four core Earth system functions of water (hydroclimatic regulation, hydroecological regulation, storage, and transport) and key related processes. Building on systems and resilience theory, we review the evidence of regional-scale regime shifts and disruptions of the Earth system functions of water. We then propose a framework for detecting, monitoring, and establishing safe limits to water cycle modifications and identify four possible spatially explicit methods for their quantification. In sum, this paper presents an ambitious scientific and policy grand challenge that could substantially improve our understanding of the role of water in the Earth system and cross-scale management of water cycle modifications that would be a complementary approach to existing water management tools. Plain language summary Freshwater is crucially important for all life on Earth. There is abundant research and evidence on how different processes within the water cycle regulate climate and support ecosystems, and by extension, human societies. Humans are also a major force disturbing those processes and modifying the water cycle. These modifications include, for instance, surface water withdrawals, groundwater pumping, deforestation and other land cover change, and ice melt due to warming climate. As most previous research on human-water interactions focuses on understanding systems at smaller scales, such as a watershed or a nation, comprehensive understanding of what human modifications of the water cycle mean for the stability of the planet is still lacking. In this paper we propose a new framework for analysing and establishing limits to a variety of human modifications of the water cycle, ©2020. American Geophysical Union. All Rights Reserved.
Water, 2019
The authors wish to make the following correction to this paper: The author name “Zahra Kalantary... more The authors wish to make the following correction to this paper: The author name “Zahra Kalantary” should be “Zahra Kalantari” [...]
The planetary boundaries framework defines the ‘safe operating space for humanity’ in terms of ni... more The planetary boundaries framework defines the ‘safe operating space for humanity’ in terms of nine important global processes influenced by humans which can destabilize the Earth System if perturbed. The planetary boundary for freshwater use attempts to provide a global limit to anthropogenic water cycle modifications, but it has been challenging to translate and apply it to the regional and local scales at which societally relevant water problems and management typically occur. We develop an integrative cross-scale approach considering how the water planetary boundary could help guide sustainable water management and governance at different sub-global contexts defined by physical features (e.g. watershed or aquifer), political borders (e.g. city, nation, or group of nations), or commercial entities (e.g. a corporation, industry or trade group, financial institution). The integration of the water planetary boundary at these sub-global contexts occurs via two approaches: (i) calcula...
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Papers by Lan Wang Erlandsson