Evaluating model performance: towards a non-parametric variant of the Kling-Gupta efficiency

ABSTRACT

Goodness-of-fit measures are important for an objective evaluation of runoff model performance. The Kling-Gupta efficiency (R_KG), which has been introduced as an improvement of the widely used Nash-Sutcliffe efficiency, considers different types of model errors, namely the error in the mean, the variability, and the dynamics. The calculation of R_KG is implicitly based on the assumptions of data linearity, data normality, and the absence of outliers. In this study, we propose a modification of R_KG as an efficiency measure comprising non-parametric components, i.e. the Spearman rank correlation and the normalized flow–duration curve. The performances of model simulations for 100 catchments using the new measure were compared to those obtained using R_KG based on a number of statistical metrics and hydrological signatures. The new measure resulted overall in better or comparable model performances, and thus it was concluded that efficiency measures with non-parametric components provide a suitable alternative to commonly used measures.     

Experimental impact features in Stardust aerogel: How track morphology reflects particle structure,composition, and density

Abstract– The Stardust collector shows diverse aerogel track shapes created by impacts of cometary dust. Tracks have been classified into three broad types (A, B, and C), based on relative dimensions of the elongate “stylus” (in Type A “carrots”) and broad “bulb” regions (Types B and C), with occurrence of smaller “styli” in Type B. From our experiments, using a diverse suite of projectile particles shot under Stardust cometary encounter conditions onto similar aerogel targets, we describe differences in impactor behavior and aerogel response resulting in the observed range of Stardust track shapes. We compare tracks made by mineral grains, natural and artificial aggregates of differing subgrain sizes, and diverse organic materials. Impacts of glasses and robust mineral grains generate elongate, narrow Type A tracks (as expected), but with differing levels of abrasion and lateral branch creation. Aggregate particles, both natural and artificial, of a wide range of compositions and volatile contents produce diverse Type B or C shapes. Creation of bulbous tracks is dependent upon impactor internal structure, grain size distribution, and strength, rather than overall grain density or content of volatile components. Nevertheless, pure organic particles do create Type C, or squat Type A* tracks, with length to width ratios dependent upon both specific organic composition and impactor grain size. From comparison with the published shape data for Stardust aerogel tracks, we conclude that the abundant larger Type B tracks on the Stardust collector represent impacts by particles similar to our carbonaceous chondrite meteorite powders.     

H<Subscript>2</Subscript>O storage capacity of olivine and low-Ca pyroxene from 10 to 13 GPa: consequences for dehydration melting above the transition zone

The onset of hydrous partial melting in the mantle above the transition zone is dictated by the H₂O storage capacity of peridotite, which is defined as the maximum concentration that the solid assemblage can store at P and T without stabilizing a hydrous fluid or melt. H₂O storage capacities of minerals in simple systems do not adequately constrain the peridotite water storage capacity because simpler systems do not account for enhanced hydrous melt stability and reduced H₂O activity facilitated by the additional components of multiply saturated peridotite. In this study, we determine peridotite-saturated olivine and pyroxene water storage capacities at 10–13 GPa and 1,350–1,450°C by employing layered experiments, in which the bottom ~2/3 of the capsule consists of hydrated KLB-1 oxide analog peridotite and the top ~1/3 of the capsule is a nearly monomineralic layer of hydrated Mg# 89.6 olivine. This method facilitates the growth of ~200-μm olivine crystals, as well as accessory low-Ca pyroxenes up to ~50 μm in diameter. The presence of small amounts of hydrous melt ensures that crystalline phases have maximal H₂O contents possible, while in equilibrium with the full peridotite assemblage (melt + ol + pyx + gt). At 12 GPa, olivine and pyroxene water storage capacities decrease from ~1,000 to 650 ppm, and ~1,400 to 1,100 ppm, respectively, as temperature increases from 1,350 to 1,450°C. Combining our results with those from a companion study at 5–8 GPa (Ardia et al., in prep.) at 1,450°C, the olivine water storage capacity increases linearly with increasing pressure and is defined by the relation C_{\textH2 \textO}^\textolivine ( \textppm ) = 57.6( ±16 ) ×P( \textGPa ) - 169( ±18 ). C_{{{\text{H}}_{2} {\text{O}}}}^{\text{olivine}} \left( {\text{ppm}} \right) = 57.6\left( { \pm 16} \right) \times P\left( {\text{GPa}} \right) - 169\left( { \pm 18} \right). Adjustment of this trend for small increases in temperature along the mantle geotherm, combined with experimental determinations of D_{\textH2 \textO}^{\textpyx/olivine} D_{{{\text{H}}_{2} {\text{O}}}}^{\text{pyx/olivine}} from this study and estimates of D_{\textH2 \textO}^{\textgt/\textolivine} D_{{{\text{H}}_{2} {\text{O}}}}^{{{\text{gt}}/{\text{olivine}}}} , allows for estimation of peridotite H₂O storage capacity, which is 440 ± 200 ppm at 400 km. This suggests that MORB source upper mantle, which contains 50–200 ppm bulk H₂O, is not wet enough to incite a global melt layer above the 410-km discontinuity. However, OIB source mantle and residues of subducted slabs, which contain 300–1,000 ppm bulk H₂O, can exceed the peridotite H₂O storage capacity and incite localized hydrous partial melting in the deep upper mantle. Experimentally determined values of D_{\textH2 \textO}^{\textpyx/\textolivine} D_{{{\text{H}}_{2} {\text{O}}}}^{{{\text{pyx}}/{\text{olivine}}}} at 10–13 GPa have a narrow range of 1.35 ± 0.13, meaning that olivine is probably the most important host of H₂O in the deep upper mantle. The increase in hydration of olivine with depth in the upper mantle may have significant influence on viscosity and other transport properties.     

The suitability of annual tree growth rings as environmental archives: Evidence from Sr,Nd, Pb and Ca isotopes in spruce growth rings from the Strengbach watershed

The combination of the Sr, Nd and Pb isotope systems, recognized as tracers of sources, with the Ca isotope system, known to reveal biology-related fractionations, allowed us to test the reliability of spruce (Picea abies) growth rings as environmental archives through time (from 1916 to 1983) in a forest ecosystem affected by acid atmospheric deposition. Sr and Pb isotopes have already been applied in former tree-ring studies, whereas the suitability of Nd and Ca isotope systems is checked in the present article. Our Sr and Nd isotope data indicate an evolution in the cation origin with a geogenic origin for the oldest rings and an atmospheric origin for the youngest rings. Ca isotopes show, for their part, an isotopic homogeneity which could be linked to the very low weathering flux of Ca. Since this flux is weak the spruces’ root systems have pumped the Ca mainly from the organic matter-rich top-soil over the past century. In contrast, the annual growth rings studied are not reliable and suitable archives of past Pb pollution.     

Why do people not learn from flood disasters? Evidence from Vietnam’s northwestern mountains

This article explores how the causes and impacts of a flood event as perceived by local people shape immediate responses and future mitigation efforts in mountainous northwest Vietnam. Local flood perception is contrasted with scientific perspectives to determine whether a singular flood event will trigger adjustments in mitigation strategies in an otherwise rarely flood-affected area. We present findings from interdisciplinary research drawing on both socioeconomic and biophysical data. Evidence suggests that individual farmers?? willingness to engage in flood mitigation is curbed by the common perception that flooding is caused by the interplay of a bundle of external factors, with climatic factors and water management failures being the most prominent ones. Most farmers did not link the severity of flooding to existing land use systems, thus underlining the lack of a sense of personal responsibility among farmers for flood mitigation measures. We conclude that local governments cannot depend on there being a sufficient degree of intrinsic motivation among farmers to make them implement soil conservation techniques to mitigate future flooding. Policy makers will need to design measures to raise farmers?? awareness of the complex interplay between land use and hydrology and to enhance collective action in soil conservation by providing appropriate incentives and implementing coherent long-term strategies.     

Application of the fluorescence quenching titration method to the complexation of copper (II) in the Gironde Estuary (France)

Quenching of fluorescence emission by the Cu²⁺ ion is measured in five samples from the Gironde Estuary (France). Non-linear regression analysis allows us to calculate from experimental data the values of C_L (complexing capacities or total ligand concentrations), K (conditional stability constants) and I_ML (residual fluorescence at the end of the titration). The results obtained on the Gironde estuarine samples indicate that C_L values are very low (<0.1 micromolar) and K values decrease from upstream to downstream. The relatively high values of I_ML are an indication that much of the organic fluorescing matter does not bind to Cu²⁺.     

First assessment of the Caulerpa racemosa (Caulerpales, Chlorophyta) invasion along the French Mediterranean coast

The introduced green alga Caulerpa racemosa var. cylindracea has been rapidly spreading in the Mediterranean Sea since 1990. It was first observed in France in 1997 (Marseilles). In early 2004, the stretch of the French Mediterranean coastline and the surface area affected by the invasion were estimated at about 83 km and 4014 ha, respectively. The depth range of colonized areas was usually 10-35 m depth. Shallow (0-10 m) and deep (down to 40 m) dense meadows were rarely observed. In contrast to the dead matte of Posidonia oceanica, which constituted the most widely colonized substratum, dense P. oceanica meadows and fine sand with large ripple-marks were not invaded. Few rocky areas were colonized and coarse sand bottoms were usually colonized below 20 m depth. All the colonized areas were exposed to human activities and more than 40% were fishing areas. Mild climate, suitable substrata, presence of vectors of dispersal and absence of efficient biological control make the French Mediterranean coast particularly vulnerable to the further spread of the alga.     

The effect of bulk composition on the solidus of carbonated eclogite from partial melting experiments at 3 GPa

To explore the effect of bulk composition on the solidus of carbonated eclogite, we determined near-solidus phase relations at 3 GPa for four different nominally anhydrous, carbonated eclogites. Starting materials (SLEC1, SLEC2, SLEC3, and SLEC4) were prepared by adding variable proportions and compositions of carbonate to a natural eclogite xenolith (66039B) from Salt Lake crater, Hawaii. Near-solidus partial melts for all bulk compositions are Fe–Na calcio-dolomitic and coexist with garnet + clinopyroxene + ilmenite ± calcio-dolomitic solid solution. The solidus for SLEC1 (Ca#=100 × molar Ca/(Ca + Mg + Fe_T)=32, 1.63 wt% Na₂O, and 5 wt% CO₂) is bracketed between 1,050°C and 1,075°C (Dasgupta et al. in Earth Planet Sci Lett 227:73–85, 2004), whereas initial melting for SLEC3 (Ca# 41, 1.4 wt% Na₂O, and 4.4 wt% CO₂) is between 1,175°C and 1,200°C. The solidus for SLEC2 (Ca# 33, 1.75 wt% Na₂O, and 15 wt% CO₂) is estimated to be near 1,100°C and the solidus for SLEC3 (Ca# 37, 1.47 wt% Na₂O, and 2.2 wt% CO₂) is between 1,100°C and 1,125°C. Solidus temperatures increase with increasing Ca# of the bulk, owing to the strong influence of the calcite–magnesite binary solidus-minimum on the solidus of carbonate bearing eclogite. Bulk compositions that produce near-solidus crystalline carbonate closer in composition to the minimum along the CaCO₃-MgCO₃ join have lower solidus temperatures. Variations in total CO₂ have significant effect on the solidus if CO₂ is added as CaCO₃, but not if CO₂ is added as a complex mixture that maintains the cationic ratios of the bulk-rock. Thus, as partial melting experiments necessarily have more CO₂ than that likely to be found in natural carbonated eclogites, care must be taken to assure that the compositional shifts associated with excess CO₂ do not unduly influence melting behavior. Near-solidus dolomite and calcite solid solutions have higher Ca/(Ca + Mg) than bulk eclogite compositions, owing to Ca–Mg exchange equilibrium between carbonates and silicates. Carbonates in natural mantle eclogite, which have low bulk CO₂ concentration, will have Ca/Mg buffered by reactions with silicates. Consequently, experiments with high bulk CO₂ may not mimic natural carbonated eclogite phase equilibria unless care is taken to ensure that CO₂ enrichment does not result in inappropriate equilibrium carbonate compositions. Compositions of eclogite-derived carbonate melt span the range of natural carbonatites from oceanic and continental settings. Ca#s of carbonatitic partial melts of eclogite vary significantly and overlap those of partial melts of carbonated lherzolite, however, for a constant Ca-content, Mg# of carbonatites derived from eclogitic sources are likely to be lower than the Mg# of those generated from peridotite.     

Connexion porphyre cuprifère–épithermaux de type low-sulfidation : analyse structurale et représentation 3D du secteur de Bolcana,monts Apuseni,Roumanie

The AuPbZn low-sulfidation epithermal ore deposits of Troita, Trestia, and Magura (Apuseni Mountains, Romania) are spatially related to the Bolcana Cu-porphyry. In an attempt to demonstrate the connection between these mineralizations, a geometric study was made based on structural measurements and GOCAD^© geomodeller 3D representation of deposits. This study indicates that a specific spatial distribution of the different Au and PbZn veins of the epithermal deposits occurs around the Cu-porphyry, which cannot result from telescoped systems. To cite this article: O. Cardon et al., C. R. Geoscience 337 (2005).