The relationship between reference canopy conductance and simplified hydraulic architecture

Terrestrial ecosystems are dominated by vascular plants that form a mosaic of hydraulic conduits to water movement from the soil to the atmosphere. Together with canopy leaf area, canopy stomatal conductance regulates plant water use and thereby photosynthesis and growth. Although stomatal conductance is coordinated with plant hydraulic conductance, governing relationships across species has not yet been formulated at a practical level that can be employed in large-scale models. Here, combinations of published conductance measurements obtained with several methodologies across boreal to tropical climates were used to explore relationships between canopy conductance rates and hydraulic constraints. A parsimonious hydraulic model requiring sapwood-to-leaf area ratio and canopy height generated acceptable agreement with measurements across a range of biomes (r²=0.75)$(r^2=0.75)$. The results suggest that, at long time scales, the functional convergence among ecosystems in the relationship between water-use and hydraulic architecture eclipses inter-specific variation in physiology and anatomy of the transport system. Prognostic applicability of this model requires independent knowledge of sapwood-to-leaf area. In this study, we did not find a strong relationship between sapwood-to-leaf area and physical or climatic variables that are readily determinable at coarse scales, though the results suggest that climate may have a mediating influence on the relationship between sapwood-to-leaf area and height. Within temperate forests, canopy height alone explained a large amount of the variance in reference canopy conductance (r²=0.68)$(r^2=0.68)$ and this relationship may be more immediately applicable in the terrestrial ecosystem models.     

Bias correction method of high-resolution satellite-based precipitation product for Peninsular Malaysia

Theoretical and Applied Climatology - Satellite-based precipitation (SBP) is emerging as a reliable source for high-resolution rainfall estimates over the globe. However, uncertainty in SBP is...     

Transboundary aquifers: conceptual models for development of international law

More than one-half of the world's population is dependent on ground water for everyday uses such as drinking, cooking, and hygiene. In fact, it is the most extracted natural resource in the world. As a result of growing populations and expanding economies, many aquifers today are being depleted while others are being contaminated. Notwithstanding the world's considerable reliance on this resource, ground water resources have long received only secondary attention as compared to surface water, especially among legislatures and policymakers. Today, while there are hundreds of treaties governing transboundary rivers and lakes, there is only one international agreement that directly addresses a transboundary aquifer. Given that many of the aquifers on which humanity so heavily relies cross international borders, there is a considerable gap in the sound management, allocation, and protection of such resources. In order to prevent future disputes over transboundary aquifers and to maximize the beneficial use of this resource, international law must be clarified as it applies to transboundary ground water resources. Moreover, it must be defined with a firm basis in sound scientific understanding. In this paper we offer six conceptual models is which ground water resources can have transboudary consequences. The models are intended to help in assessing the applicability and scientific soundness of existing and proposed rules governing transboundary ground water resources. In addition, we consider the development of international law as it applies to ground water resources and make recommendations based on the models and principles of hydrogeology. The objective is the development of clear, logical, and science-based norms of state conducts as they relate to aquifers that traverse political boundaries.     

Exponential time integrators for stochastic partial differential equations in 3D reservoir simulation

The transport of chemically reactive solutes (e.g. surfactants, CO₂ or dissolved minerals) is of fundamental importance to a wide range of applications in oil and gas reservoirs such as enhanced oil recovery and mineral scale formation. In this work, we investigate exponential time integrators, in conjunction with an upwind weighted finite volume discretisation in space, for the efficient and accurate simulation of advection–dispersion processes including non-linear chemical reactions in highly heterogeneous 3D oil reservoirs. We model sub-grid fluctuations in transport velocities and uncertainty in the reaction term by writing the advection–dispersion–reaction equation as a stochastic partial differential equation with multiplicative noise. The exponential integrators are based on the variation of constants solution and solve the linear system exactly. While this is at the expense of computing the exponential of the stiff matrix representing the finite volume discretisation, the use of real Léja point or the Krylov subspace technique to approximate the exponential makes these methods competitive compared to standard finite difference-based time integrators. For the deterministic system, we investigate two exponential time integrators, the second-order accurate exponential Euler midpoint (EEM) scheme and exponential time differencing of order one (ETD1). All our numerical examples demonstrate that our methods can compete in terms of efficiency and accuracy compared with standard first-order semi-implicit time integrators when solving (stochastic) partial differential equations that model mixing and chemical reactions in 3D heterogeneous porous media. Our results suggest that exponential time integrators such as the ETD1 and EEM schemes could be applied to typical 3D reservoir models comprising tens to hundreds of thousands unknowns.     

A numerical Round Robin on tunnels under seismic actions

Although the seismic behaviour of shallow circular tunnels in soft ground is generally safer than aboveground structures, some tunnels were recently damaged during earthquakes. In some cases, damage was associated with strong ground shaking and site amplification, which increased the stress level in the tunnel lining. Pseudo-static and simplified dynamic analyses enable to assess transient changes in internal forces during shaking. Nevertheless, experimental evidences of permanent changes in internal loads in the tunnel lining would suggest that a full dynamic analysis including plastic soil behaviour should be performed when modelling the dynamic interaction between the tunnel and the ground. While sophisticated numerical methods can be used to predict seismic internal forces on tunnel structures during earthquakes, the accuracy of their predictions should be validated against field measurements, but the latter are seldom available. A series of centrifuge tests were therefore carried out at the University of Cambridge (UK) on tunnel models in sand, in the framework of a research project funded by the Italian Civil Protection Department. A numerical Round Robin on Tunnel Tests was later promoted among some research groups to predict the observed behaviour by means of numerical modelling. In this paper, the main results of five selected numerical predictions are summarized and compared with the experimental results.     

Scaling Properties of Biologically Active Scalar Concentration Fluctuations in the Atmospheric Surface Layer over a Managed Peatland

The higher-order scalar concentration fluctuation properties are examined in the context of Monin–Obukhov similarity theory for a variety of greenhouse gases that have distinct and separate source/sink locations along an otherwise ideal micrometeorological field site. Air temperature and concentrations of water vapour, carbon dioxide and methane were measured at high frequency (10 Hz) above a flat and extensive peat-land soil in the San Joaquin–Sacramento Delta (California, USA) area, subjected to year-round grazing by beef cattle. Because of the heterogeneous distribution of the sources and sinks of CO₂ and especially CH₄ emitted by cattle, the scaling behaviour of the higher-order statistical properties diverged from predictions based on a balance between their production and dissipation rate terms, which can obtained for temperature and H₂O during stationary conditions. We identify and label these departures as ‘exogenous’ because they depend on heterogeneities and non-stationarities induced by boundary conditions on the flow. Spectral analysis revealed that the exogenous effects show their signatures in regions with frequencies lower than those associated with scalar vertical transport by turbulence, though the two regions may partially overlap in some cases. Cospectra of vertical fluxes appear less influenced by these exogenous effects because of the modulating role of the vertical velocity at low frequencies. Finally, under certain conditions, the presence of such exogenous factors in higher-order scalar fluctuation statistics may be ‘fingerprinted’ by a large storage term in the mean scalar budget.     

铊矿床成矿规律

对全球主要铊矿床的成矿地质背景、成矿时代、控矿构造、赋矿围岩和成矿物理化学条件进行了综合对比分析,得出了全球铊矿床的分布特征与成矿规律:铊矿床主要产出于沉积岩发育的中-低温成矿域中,且成矿时代较新;铊矿床的赋矿围岩通常为铊背景值高的沉积岩;大多数铊矿床具有典型的低温成矿特征.     

Temporal features in thunder days in the United States

1901–80 data for the contiguous U.S. show that secular variability of thunder days was very much less than that of precipitation or of frequency of extra tropical cyclones. Overall, there may have been a slight decline, but more evident was an increase to the thirties followed by a falling off, broken only by a peak in the seventies. These up-and-down movements were evident in most months of the year and regions of the U.S. The general decrease, however, was clear only in the South East and replaced by an increase in the Upper Great Lakes region. Secular variation in thunder day frequency was slightly correlated positively with that of extra tropical cyclone frequency and negatively with sea level pressure. The analysis also confirmed well known seasonal and regional patterns of thunder activity.