Papers by Ruud van der Ent
As our global fresh water resources are becoming more and more stressed it is important to know t... more As our global fresh water resources are becoming more and more stressed it is important to know the origin and fate of atmospheric moisture over continents. The patterns of moisture feedback between evaporation and precipitation over continents (moisture cycling) may shift due to climate change. This research investigates how moisture cycling changes in the IPCC A1B climate scenario. We perform an a posteriori analysis based on data from the ECHAM5 general circulation model. Hereby we compare the results of the control run and the A1B climate scenario. These results allow us to evaluate possible changes in water availability in the future. Moreover, because we are not only analyzing the state variables (e.g. precipitation), but also the shifts in moisture recycling patterns, we are able to show how different regions are connected through the atmosphere and rely on each other for their water resources. This knowledge can help us adapting our land and water management to contribute in a positive way to the allocation of our water resources.
ABSTRACT In some regions of the world, moisture recycling is to a considerable extent sustained b... more ABSTRACT In some regions of the world, moisture recycling is to a considerable extent sustained by terrestrial evaporation - a moisture flow that can be partly altered by humans through land-use change. With increasingly stressed fresh water resources as well as growing pressure on land, there is a need to advance our understanding of the entire impact chain of continental moisture recycling: from land-use to downwind precipitation. For the purpose of analyzing land-use change impacts on continental moisture recycling, we have developed a globally distributed land surface evaporation model (Eva) and coupled it to the moisture tracking scheme WAM. The Eva model estimates evaporative fluxes (incl. partitioning of interception and transpiration) based on predefined and satellite derived land use and soil properties. Land-use classes may easily be substituted for investigation of land-use change impacts. As our objective is specifically tuned to assess the effect of land-use change on evaporation and downwind precipitation, we have deliberately simplified the hydrological scheme of Eva (disregarding groundwater interaction and lateral flow). This is a balance act between the model's ability to represent all hydrological processes and its usability for isolated explorations of the land-moisture-precipitation nexus at the macro scale. The WAM-Eva coupling is a simple tool to apply in future studies on how different land-use scenarios may affect moisture recycling at a continental and global scale, and contributes to our understanding of how land management in one region may affect fresh water availability in another.
Hydrology and Earth System Sciences Discussions, 2014
ABSTRACT Moisture recycling, whereby evaporation from Earth's surface flows through the a... more ABSTRACT Moisture recycling, whereby evaporation from Earth's surface flows through the atmosphere and falls out as precipitation on land downwind, is increasingly being acknowledged as an important feature of the global Earth system. There is still substantial uncertainty of how the large-scale patterns of moisture recycling (moisture recycling regimes) vary with the background flow, and how the natural variability of the atmosphere can cause transitions between these regimes. Understanding the natural variability of moisture recycling in the absence of outside factors is critical for quantifying and determining the relative importance of external drivers such as land-use change or increasing greenhouse gases. This research explores this topic by quantifying the natural variability of moisture recycling for five regions globally, using the precipitationshed as the unit of analysis. We employ the Water Accounting Model (WAM 2.0), a numerical water transport model that vertically integrates atmospheric water vapour, to track how moisture flows through the atmosphere. Using reanalysis datasets, and multiple global indices of climatic variability (such as the El Nino Southern Oscillation and the North Atlantic Oscillation), natural variations in moisture recycling relationships are identified. The results suggest that some changes in the variability of moisture recycling relationships (and by extension, precipitationsheds) are related to global and regional climatic variability. Given that many large-scale features of climatic variability are expected to shift in varying ways with anthropogenic climate change, it may become possible to forecast how moisture recycling regimes may be expected to change. This has particular implications for ecosystem services that are dependent on the reliable delivery of precipitation, and the societies dependent on such services.
In South America, the exchange of moisture between the land and the atmosphere plays a crucial ro... more In South America, the exchange of moisture between the land and the atmosphere plays a crucial role. The tropical trees from the Amazonian forests pump a large amount of water from the ground and release it to the atmosphere. This atmospheric moisture contributes to rainfall over the Amazon basin, but is also transported by winds east of the Andes up to the subtropical La Plata basin. In this study, we use an atmospheric moisture tracking model to diagnose the amount and direction of moisture traveling for its origin (evaporation and transpiration by trees) to its destination (precipitation) in South America. We build a moisture recycling network and we explore its architecture using analysis methods developed in complex network theory. We show that atmospheric moisture runs through re-evaporation cycles (re-evaporation of precipitating water) on the way from the Amazon basin to the La Plata basin. We reveal the southeastern part of the Amazon Basin as a key intermediary region for ...
Atmospheric Chemistry and Physics, 2014
Continental moisture recycling is a crucial process of the South American climate system. In part... more Continental moisture recycling is a crucial process of the South American climate system. In particular, evapotranspiration from the Amazon basin contributes substantially to precipitation regionally as well as over other remote regions such as the La Plata basin. Here we present an indepth analysis of South American moisture recycling mechanisms. In particular, we quantify the importance of cascading moisture recycling (CMR), which describes moisture transport between two locations on the continent that involves reevaporation cycles along the way. Using an Eulerian atmospheric moisture tracking model forced by a combination of several historical climate data sets, we were able to construct a complex network of moisture recycling for South America. Our results show that CMR contributes about 9-10 % to the total precipitation over South America and 17-18 % over the La Plata basin. CMR increases the fraction of total precipitation over the La Plata basin that originates from the Amazon basin from 18-23 to 24-29 % during the wet season. We also show that the south-western part of the Amazon basin is not only a direct source of rainfall over the La Plata basin, but also a key intermediary region that distributes moisture originating from the entire Amazon basin towards the La Plata basin during the wet season. Our results suggest that land use change in this region might have a stronger impact on downwind rainfall than previously thought. Using complex network analysis techniques, we find the eastern side of the sub-tropical Andes to be a key region where CMR pathways are channeled. This study offers a better understanding of the interactions between the vegetation and the atmosphere on the water cycle, which is needed in a context of land use and climate change in South America.
ABSTRACT In some regions of the world, moisture recycling is to a considerable extent sustained b... more ABSTRACT In some regions of the world, moisture recycling is to a considerable extent sustained by terrestrial evaporation - a moisture flow that can be partly altered by humans through land-use change. With increasingly stressed fresh water resources as well as growing pressure on land, there is a need to advance our understanding of the entire impact chain of continental moisture recycling: from land-use to downwind precipitation. For the purpose of analyzing land-use change impacts on continental moisture recycling, we have developed a globally distributed land surface evaporation model (Eva) and coupled it to the moisture tracking scheme WAM. The Eva model estimates evaporative fluxes (incl. partitioning of interception and transpiration) based on predefined and satellite derived land use and soil properties. Land-use classes may easily be substituted for investigation of land-use change impacts. As our objective is specifically tuned to assess the effect of land-use change on evaporation and downwind precipitation, we have deliberately simplified the hydrological scheme of Eva (disregarding groundwater interaction and lateral flow). This is a balance act between the model's ability to represent all hydrological processes and its usability for isolated explorations of the land-moisture-precipitation nexus at the macro scale. The WAM-Eva coupling is a simple tool to apply in future studies on how different land-use scenarios may affect moisture recycling at a continental and global scale, and contributes to our understanding of how land management in one region may affect fresh water availability in another.
ABSTRACT The contribution of land evaporation to local and remote precipitation (i.e., moisture r... more ABSTRACT The contribution of land evaporation to local and remote precipitation (i.e., moisture recycling) is of significant importance to sustain water resources and ecosystems. But how important are different evaporation components in sustaining precipitation? This is the first paper to present moisture recycling metrics for partitioned evaporation. In the companion paper, Part 1, evaporation was partitioned into vegetation interception, floor interception, soil moisture evaporation and open water evaporation (constituting the direct, purely physical fluxes, largely dominated by interception), and transpiration (delayed, biophysical flux). Here, we track these components forward as well as backward in time. We also include age tracers to study the atmospheric residence times of these evaporation components. As the main result we present a new image of the global hydrological cycle that includes quantification of partitioned evaporation and moisture recycling as well as the atmospheric residence times of all fluxes. We demonstrate that evaporated interception is more likely to return as precipitation on land than transpired water. On average, direct evaporation (essentially interception) is found to have an atmospheric residence time of eight days, while transpiration typically resides nine days in the atmosphere. Interception recycling has a much shorter local length scale than transpiration recycling, thus interception generally precipitates closer to its evaporative source than transpiration, which is particularly pronounced outside the tropics. We conclude that interception mainly works as an intensifier of the local hydrological cycle during wet spells. On the other hand, transpiration remains active during dry spells and is transported over much larger distances downwind where it can act as a significant source of moisture. Thus, as various land-use types can differ considerably in their partitioning between interception and transpiration, our results stress that land-use changes (e.g., forest to cropland conversion) do not only affect the magnitude of moisture recycling, but could also influence the moisture recycling patterns and lead to a redistribution of water resources. As such, this research highlights that land-use changes can have complex effects on the atmospheric branch of the hydrological cycle.
Nature, 2014
arising from S. Jasechko et al. Nature 496, 347-350 (2013)10.1038/nature11983How best to assess t... more arising from S. Jasechko et al. Nature 496, 347-350 (2013)10.1038/nature11983How best to assess the respective importance of plant transpiration over evaporation from open waters, soils and short-term storage such as tree canopies and understories (interception) has long been debated. On the basis of data from lake catchments, Jasechko et al. conclude that transpiration accounts for 80-90% of total land evaporation globally (Fig. 1a). However, another choice of input data, together with more conservative accounting of the related uncertainties, reduces and widens the transpiration ratio estimation to 35-80%. Hence, climate models do not necessarily conflict with observations, but more measurements on the catchment scale are needed to reduce the uncertainty range. There is a Reply to this Brief Communications Arising by Jasechko, S. et al. Nature 506, http://dx.doi.org/10.1038/nature12926 (2014).
Hydrology and Earth System Sciences, 2012
Soil-atmosphere feedback is a key for understanding the hydrological cycle and the direction of p... more Soil-atmosphere feedback is a key for understanding the hydrological cycle and the direction of potential system changes. This paper presents an analytical framework to study the interplay between soil and atmospheric moisture, using as input only the boundary conditions at the upstream end of an atmospheric moisture stream line. The 5 underlying Eulerian-Langrangean approach assumes advective moisture transport with average wind speed along the stream line and vertical moisture exchange with the soil compartment of uniform vertical properties. Precipitation, evaporation from interception and runoff are assumed to depend through simple functional relationships on the soil moisture or the atmospheric moisture. Evaporation from soil moisture (including tran-10 spiration) depends on both state variables, which introduces a nonlinear relationship between the two compartments. This nonlinear relationship can explain some apparently paradoxical phenomena such as a local decrease of precipitation accompanied by a runoff increase.
Environmental Science & Technology, 2014
Aiming to enhance the analysis of water consumption and resulting consequences along the supply c... more Aiming to enhance the analysis of water consumption and resulting consequences along the supply chain of products, the water accounting and vulnerability evaluation (WAVE) model is introduced. On the accounting level, atmospheric evaporation recycling within drainage basins is considered for the first time, which can reduce water consumption volumes by up to 32%. Rather than predicting impacts, WAVE analyzes the vulnerability of basins to freshwater depletion. Based on local blue water scarcity, the water depletion index (WDI) denotes the risk that water consumption can lead to depletion of freshwater resources. Water scarcity is determined by relating annual water consumption to availability in more than 11,000 basins. Additionally, WDI accounts for the presence of lakes and aquifers which have been neglected in water scarcity assessments so far. By setting WDI to the highest value in (semi)arid basins, absolute freshwater shortage is taken into account in addition to relative scarcity. This avoids mathematical artifacts of previous indicators which turn zero in deserts if consumption is zero. As illustrated in a case study of biofuels, WAVE can help to interpret volumetric water footprint figures and, thus, promotes a sustainable use of global freshwater resources.
Biogeosciences, 2012
It is well known that rivers connect upstream and downstream ecosystems within watersheds. Here w... more It is well known that rivers connect upstream and downstream ecosystems within watersheds. Here we describe the concept of precipitationsheds to show how upwind terrestrial evaporation source areas contribute moisture for precipitation to downwind sink regions. We illustrate the importance of upwind land cover in precipitationsheds to sustain precipitation in critically water stressed downwind areas, specifically dryland agricultural areas. We first identify seven regions where rainfed agriculture is particularly vulnerable to reductions in precipitation, and then map their precipitationsheds. We then develop a framework for qualitatively assessing the vulnerability of precipitation for these seven agricultural regions. We illustrate that the sink regions have varying degrees of vulnerability to changes in upwind evaporation rates depending on the extent of the precipitationshed, source region land use intensity and expected land cover changes in the source region.
Atmospheric Chemistry and Physics, 2011
It is difficult to quantify the degree to which terrestrial evaporation supports the occurrence o... more It is difficult to quantify the degree to which terrestrial evaporation supports the occurrence of precipitation within a certain study region (i.e. regional moisture recycling) due to the scale-and shape-dependence of regional moisture recycling ratios. In this paper we present a novel approach to quantify the spatial and temporal scale of moisture 5
The importance of moisture feedback between continental precipitation and evaporation, referred t... more The importance of moisture feedback between continental precipitation and evaporation, referred to as moisture recycling, is still under debate. Most of the research in the past focused on the contribution of recycling to precipitation within a certain region only. This paper clearly distinguishes between different definitions of moisture recycling. This allows us to study the complete process of continental moisture recycling. In addition to identifying how much of the precipitation originates from continental sources, a new definition is used to identify regions which are major moisture suppliers for continental precipitation. An accounting procedure based on ERA-40 reanalysis data is used to calculate moisture recycling ratios. As such, this paper derives new information from existing data. It is estimated that on average 38 % of the continental precipitation has continental origin and that 52 % of the continental evaporation returns as precipitation over continents. This paper demonstrates the important role of topography in the Andes and the Tibetan Plateau where regional moisture recycling is a key process. The Amazon and the Congo are identified as very important regions for sustaining continental precipitation. It is also demonstrated that moisture recycling from the Eurasian continent is the major supplier of the fresh water resources of China.
As our global fresh water resources are becoming more and more stressed it is important to know t... more As our global fresh water resources are becoming more and more stressed it is important to know the origin and fate of atmospheric moisture over continents. The patterns of moisture feedback between evaporation and precipitation over continents (moisture cycling) may shift due to ...
ABSTRACT In the classical representation of the hydrological cycle, water evaporates from the oce... more ABSTRACT In the classical representation of the hydrological cycle, water evaporates from the ocean, from where it is advected to the continents, where it precipitates as rain or snow, turns into runoff, which eventually flows back to the ocean completing the cycle. However, this picture is much too simple as we showed that about 40% of the land precipitation has its origin in land evaporation (i.e. recycled water) rather than oceanic evaporation (van der Ent et al., 2010. WRR). The potential effect on precipitation from human-induced changes will thus not only act through an increased evaporation flux over the ocean, which is expected to change with global warming, but also through the evaporation flux over land, which is affected by land use changes as well as global warming. In this research we follow the water through the atmosphere and present the concept of the precipitationshed: the probabilistic source area of precipitation for a specific region. We also present the concept of the evaporationshed: the probabilistic sink area of evaporation from a specific region. Knowing where the water comes from is valuable information on the susceptibility of a region to changes in its precipitationshed. Such changes can for example include higher sea surface temperatures or deforestation. On the other hand, being able to predict where the water goes helps us to assess the effects of these human-induced changes. Furthermore, this research consist of several case-studies illustrating the applicability of the precipitation- and evaporationshed concepts.
Global Change Biology, 2012
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Papers by Ruud van der Ent