Energy, Resources and the Environment

Towards observation-based gridded runoff estimates for Europe

ERE Matters July 15, 2015

Words on Wednesday aims at promoting interesting/fun/exciting publications on topics related to Energy, Resources and the Environment. If you would like to be featured on WoW, please send us a link of the paper, or your own post, at ERE.Matters@gmail.com.

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Gudmundsson, L. and Seneviratne, S. I.: Towards observation-based gridded runoff estimates for Europe, Hydrol. Earth Syst. Sci., 19, 2859-2879, doi:10.5194/hess-19-2859-2015, 2015. http://www.hydrol-earth-syst-sci.net/19/2859/2015/hess-19-2859-2015.html

Abstract:

Terrestrial water variables are the key to understanding ecosystem processes, feed back on weather and climate, and are a prerequisite for human activities. To provide context for local investigations and to better understand phenomena that only emerge at large spatial scales, reliable information on continental-scale freshwater dynamics is necessary. To date streamflow is among the best-observed variables of terrestrial water systems. However, observation networks have a limited station density and often incomplete temporal coverage, limiting investigations to locations and times with observations. This paper presents a methodology to estimate continental-scale runoff on a 0.5° spatial grid with monthly resolution. The methodology is based on statistical upscaling of observed streamflow from small catchments in Europe and exploits readily available gridded atmospheric forcing data combined with the capability of machine learning techniques. The resulting runoff estimates are validated against (1) runoff from small catchments that were not used for model training, (2) river discharge from nine continental-scale river basins and (3) independent estimates of long-term mean evapotranspiration at the pan-European scale. In addition it is shown that the produced gridded runoff compares on average better to observations than a multi-model ensemble of comprehensive land surface models (LSMs), making it an ideal candidate for model evaluation and model development. In particular, the presented machine learning approach may help determining which factors are most relevant for an efficient modelling of runoff at regional scales. Finally, the resulting data product is used to derive a comprehensive runoff climatology for Europe and its potential for drought monitoring is illustrated.

Words on Wednesday: Remediation of degraded arable steppe soils in Moldova using vetch as green manure

ERE Matters July 8, 2015

Words on Wednesday aims at promoting interesting/fun/exciting publications on topics related to Energy, Resources and the Environment. If you would like to be featured on WoW, please send us a link of the paper, or your own post, at ERE.Matters@gmail.com.

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Wiesmeier, M., Lungu, M., Hübner, R., and Cerbari, V., 2015. Remediation of degraded arable steppe soils in Moldova using vetch as green manure, Solid Earth, 6, 609-620, doi:10.5194/se-6-609-2015, 2015.

Abstract:

In the Republic of Moldova, non-sustainable arable farming led to severe degradation and erosion of fertile steppe soils (Chernozems). As a result, the Chernozems lost about 40% of their initial amounts of soil organic carbon (SOC). The aim of this study was to remediate degraded arable soils and promote carbon sequestration by implementation of cover cropping and green manuring in Moldova. Thereby, the suitability of the legume hairy vetch (Vicia sativa) as cover crop under the dry continental climate of Moldova was examined. At two experimental sites, the effect of cover cropping on chemical and physical soil properties as well as on yields of subsequent main crops was determined. The results showed a significant increase of SOC after incorporation of hairy vetch mainly due to increases of aggregate-occluded and mineral-associated OC. This was related to a high above- and belowground biomass production of hairy vetch associated with a high input of carbon and nitrogen into arable soils. A calculation of SOC stocks based on equivalent soil masses revealed a sequestration of around 3 t C ha⁻¹yr⁻¹ as a result of hairy vetch cover cropping. The buildup of SOC was associated with an improvement of the soil structure as indicated by a distinct decrease of bulk density and a relative increase of macroaggregates at the expense of microaggregates and clods. As a result, yields of subsequent main crops increased by around 20%. Our results indicated that hairy vetch is a promising cover crop to remediate degraded steppe soils, control soil erosion and sequester substantial amounts of atmospheric C in arable soils of Moldova.

Bulk densities (BD) and soil organic carbon (SOC) contents
of topsoil horizons of control and experimental sites in Orhei
and Cahul after incorporation of HVW and harvest of the main crop. Error bars represent standard deviation (n = 10).

Words on Wednesday: Poroelastic responses of confined aquifers to subsurface strain changes and their use for volcano monitoring

ERE Matters July 1, 2015

Words on Wednesday aims at promoting interesting/fun/exciting publications on topics related to Energy, Resources and the Environment. If you would like to be featured on WoW, please send us a link of the paper, or your own post, at ERE.Matters@gmail.com.

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Strehlow, K., Gottsmann, J. H., and Rust, A. C., 2015. Poroelastic responses of confined aquifers to subsurface strain changes and their use for volcano monitoring, Solid Earth Discuss., 7, 1673-1729, doi:10.5194/sed-7-1673-2015.

Abstract:

Well water level changes associated with magmatic unrest can be interpreted as a result of pore pressure changes in the aquifer due to crustal deformation, and so could provide constraints on the subsurface processes causing this strain. We use Finite Element Analysis to demonstrate the response of aquifers to volumetric strain induced by pressurised magma reservoirs. Two different aquifers are invoked – an unconsolidated pyroclastic deposit and a vesicular lava flow – and embedded in an impermeable crust, overlying a magma chamber. The time-dependent, fully coupled models simulate crustal deformation accompanying chamber pressurisation and the resulting hydraulic head changes as well as porous flow in the aquifer. The simulated deformational strain leads to centimetres (pyroclastic aquifer) to meters (lava flow aquifer) of hydraulic head changes; both strain and hydraulic head change with time due to substantial porous flow in the hydrological system. Well level changes are particularly sensitive to chamber volume and shape, followed by chamber depth and the phase of the pore fluid. The Young’s Modulus and permeability of the aquifer, as well as the strength of pressurisation also have significant influence on the hydraulic head signal. While source characteristics, the distance between chamber and aquifer and the elastic stratigraphy determine the strain field and its partitioning, flow and coupling parameters define how the aquifer responds to this strain and how signals change with time. We investigated a period of pre-eruptive head changes recorded at Usu volcano, Japan, where well data were interpreted using an analytical deformation model. We find that generic analytical models can fail to capture the complex pre-eruptive subsurface mechanics leading to well level changes, due to aquifer pressure changes being sensitive to chamber shape and lithological heterogeneities. In addition, the presence of a pore fluid and its flow have a significant influence on the strain signal in the aquifer and are commonly neglected in analytical models. These findings highlight the need for numerical models for the interpretation of observed well level signals. However, simulated water table changes do mirror volumetric strain and wells can therefore serve as comparatively cheap strain meters that could provide important insights into pre-eruptive dynamics.

2-D axisymmetric model setup: a boundary load dP is applied on a cavity at depth, with the radius r for the spherical case or vertical semi-axis b for the ellipsoidal case, respectively. This changes the strain conditions in the surrounding linear elastic host rock (granitic crust), the poroelastic aquifer and the overlying linear elastic cap rock (clay). The watersaturated aquifer is modelled as either a vesicular lava flow or unconsolidated pyroclasts. An aquifer not covering the chamber but starting at some lateral distance L is realised by setting the darker grey region impermeable. The bottom boundary is fixed, the upper boundary is treated as a free surface, the lateral boundaries have a roller condition. There is no flow outside the aquifer, stress and displacement at the internal boundaries are continuous. An extract of the finite element mesh is shown only for illustration. The mesh density is finer around the cavity, at aquifer boundaries and the free surface.

Whodunit?: It was Mankind With the Greenhouse Gases in the Atmosphere

ERE Matters June 29, 2015

Last week I came across this beautifully illustrated account of what is causing the planet’s rising temperature, based on findings obtained by NASA’s Goddard Institute of Space Studies. The graphic is designed by Erik Roston and Blacki Migliozzi, in collaboration with Kate Marvel and Gavin Schmidt of NASA-GISS.

Check out the full article What’s really warming the world? on Bloomberg Business

The Late Holocene Fever by Christian Massari (Winner in the EGU Photo Contest 2015; taken from ImagGeo)