bluuebunny/crossref_metadata_2025 huggingface dataset:
Aggregation in environmental systems – Part 1: Seasonal tracer cycles quantify young water fractions, but not mean transit times, in spatially heterogeneous catchments
Authors: Kirchner J. W.
Published: January 2016

Abstract. Environmental heterogeneity is ubiquitous, but environmental systems are often analyzed as if they were homogeneous instead, resulting in aggregation errors that are rarely explored and almost never quantified. Here I use simple benchmark tests to explore this general problem in one specific context: the use of seasonal cycles in chemical or isotopic tracers (such as Cl−, δ18O, or δ2H) to estimate timescales of storage in catchments. Timescales of catchment storage are typically quantified by the mean transit time, meaning the average time that elapses between parcels of water entering as precipitation and leaving again as streamflow. Longer mean transit times imply greater damping of seasonal tracer cycles. Thus, the amplitudes of tracer cycles in precipitation and streamflow are commonly used to calculate catchment mean transit times. Here I show that these calculations will typically be wrong by several hundred percent, when applied to catchments with realistic degrees of spatial heterogeneity. This aggregation bias arises from the strong nonlinearity in the relationship between tracer cycle amplitude and mean travel time. I propose an alternative storage metric, the young water fraction in streamflow, defined as the fraction of runoff with transit times of less than roughly 0.2 years. I show that this young water fraction (not to be confused with event-based "new water" in hydrograph separations) is accurately predicted by seasonal tracer cycles within a precision of a few percent, across the entire range of mean transit times from almost zero to almost infinity. Importantly, this relationship is also virtually free from aggregation error. That is, seasonal tracer cycles also accurately predict the young water fraction in runoff from highly heterogeneous mixtures of subcatchments with strongly contrasting transit-time distributions. Thus, although tracer cycle amplitudes yield biased and unreliable estimates of catchment mean travel times in heterogeneous catchments, they can be used to reliably estimate the fraction of young water in runoff.
Sensitivity of future water availability projections to Global Climate Model, evapotranspiration estimation method, and greenhouse gas emission scenario
Authors: Chang S. , Graham W. D. , Hwang S. , Muñoz-Carpena R.
Published: January 2016

Abstract. Projecting water availability under various possible future climate scenarios depends on the choice of Global Climate Model (GCM), evapotranspiration (ET) estimation method and Representative Concentration Pathway (RCP) trajectory. The relative contribution of each of these factors must be evaluated in order to choose an appropriate ensemble of future scenarios for water resources planning. In this study variance-based global sensitivity analysis and Monte Carlo filtering were used to evaluate the relative sensitivity of projected changes in precipitation (P), ET and water availability (defined here as P–ET) to choice of GCM, ET estimation method and RCP trajectory over the continental United States (US) for two distinct future periods: 2030–2060 (future period 1) and 2070–2100 (future period 2). A total of 9 GCMs, 10 ET methods and 3 RCP trajectories were used to quantify the range of future projections and estimate the relative sensitivity of future projections to each of these factors. In general, for all regions of the US, changes in future precipitation are most sensitive to the choice of GCM, while changes in future ET are most sensitive to the choice of ET estimation method. For changes in future water availability, the choice of GCM is the most influential factor in the cool season (December–March) and the choice of ET estimation method is most important in the warm season (May–October) for all regions except the South East US where GCM and ET have approximately equal influence throughout most of the year. Although the choice of RCP trajectory is generally less important than the choice of GCM or ET method, the impact of RCP trajectory increases in future period 2 over future period 1 for all factors. Monte Carlo filtering results indicate that particular GCMs and ET methods drive the projection of wetter or drier future conditions much more than RCP trajectory; however the set of GCMs and ET methods that produce wetter or drier projections varies substantially by region. Results of this study indicate that, in addition to using an ensemble of GCMs and several RCP trajectories, a range of regionally-relevant ET estimation methods should be used to develop a robust range of future conditions for water resource planning under climate change.
Assessment of land use impact on hydraulic threshold conditions for gully head cut initiation
Authors: Samani Aliakbar Nazari , Chen Qiuwen , Khalighi Shahram , Wasson Robert James
Published: January 2016

Abstract. Gully erosion is a geomorphic threshold phenomenon controlled by different environmental factors as well as human activities. In this research, we examined the effect of land use on hydraulic flow and the consequent head cut initiation for similar soil conditions using an experimental plot of 15m*0.4m. Results indicated that boundary shear stresses τcr for gully initiation in rangeland, dry farming and abandoned land are 192, 43 and 174, respectively, due to the differences in surface vegetation cover. Moreover, the dyne/cm2 turbulence of flow and soil response to an increase in water depth showed complicated behavior, which could be attributed to the effect of surface micro relief features and land use impacts. Compared to dry farming, the short vegetation cover in the rangeland decreased the effect of ground cover on flow regime. Even after seven years of abandonment, the response of agricultural land to increasing shear stress was similar to that of dry farming, which indicated the low resilience and high erosional susceptibility of soil in dry land was the environments. The main explanation for dramatic (3-4 fold) variations of τcr in dry vegetation cover and soil surface conditions. In fact, the remarkable decrease of τcr farming was related to the effect of tillage practice on soil susceptibility and aggregate used in some strength. The findings indicated that a critical shear stress of 35 dyne/cm2 physically based models for erosion prediction is not appropriate for estimating gully erosion. In addition, the duration of land abandonment has a crucial influence on soil erodibility that has been less considered in erosion models.
Remote-sensing algorithm for surface evapotranspiration considering landscape and statistical effects on mixed-pixels
Authors: Peng Z. Q. , Xin X. Z. , Jiao J. J. , Zhou T. , Liu Q. H.
Published: January 2016

Abstract. Evapotranspiration (ET) plays an important role in surface-atmosphere interactions. Remote sensing has long been identified as a technology that is capable of monitoring ET. However, spatial problems greatly affect the accuracy of ET retrievals by satellite. The objective of this paper is to reduce the spatial-scale uncertainty produced by surface heterogeneity using Chinese HJ-1B data. Two upscaling schemes with area-weighting aggregation for different steps and variables were applied. One scheme is input parameter upscaling (IPUS), which refers to parameter aggregation, and the other is temperature sharpening and flux aggregation (TSFA). Footprint validation results show that TSFA is more accurate and less uncertain than IPUS, and additional analysis shows that TSFA can capture land surface heterogeneities and integrate the effect of overlooked land types in the mixed pixel.
Assessment of extreme flood events in changing climate for a long-term planning of socio-economic infrastructure in the Russian Arctic
Authors: Shevnina E. , Kurzeneva E. , Kovalenko V. , Vihma T.
Published: January 2016

Abstract. Climate warming has been and is expected to continue faster in the Arctic than at lower latitudes, which generates major challenges for adaptation. Among others, long-term planning of development of socio-economic infrastructure requires climate-based forecasts of the frequency and magnitude of extreme flood events. To estimate the cost of facilities and operational risks, a probabilistic form of long-term forecasting is preferable. A stochastic model allowing to simulate the probability density function (PDF) of hydrological variables based on a projected climatology, without modelling hydrological time series, is applied to estimate extreme flood events caused by spring snow melting in the Russian Arctic. The model is validated by cross-comparison of modelled and empirical PDFs using historical time series. The PDF parameters of spring flood runoff are assessed in a regional scale under the SRES and RCP climate scenarios for 2010–2039. For the Russian Arctic, an increase of 17–23 \\% in the mean values and a decrease of 5–16 \\% in the coefficients of variation of the spring flood runoff are expected. Territories are outlined where engineering calculations of the extreme maximum discharges should be corrected to account for the expected climate change. The extreme maximum discharge for a bridge construction over the Nadym River is calculated.
Travel time based thermal tracer tomography
Authors: Somogyvári M. , Bayer P. , Brauchler R.
Published: January 2016

Abstract. Active thermal tracer testing is a technique to get information about the flow and transport properties of an aquifer. In this paper we propose an innovative methodology, using active thermal tracers in a tomographical setup to reconstruct cross-well hydraulic conductivity profiles. This is facilitated by assuming that the propagation of the injected thermal tracer is mainly controlled by advection. To reduce the effects of density and viscosity changes and thermal diffusion, early time diagnostics are used and specific travel times of the tracer breakthrough curves are extracted. These travel times are inverted with an eikonal solver using the staggered grid method to reduce constraints from the pre-defined grid geometry and to improve the resolution. Finally, non-reliable pixels are removed from the derived hydraulic conductivity tomograms. The method is applied to successfully reconstruct cross-well profiles as well a 3-D block of a high resolution fluvio-aeolian aquifer analog dataset. Sensitivity analysis reveals a negligible role of the injection temperature, but more attention has to be drawn to other technical parameters such as the injection rate. This is investigated in more detail through model-based testing using diverse hydraulic and thermal conditions in order to delineate the feasible range of applications for the new tomographic approach.
Modeling glacial lake outburst flood process chain: the case of Lake Palcacocha and Huaraz, Peru
Authors: Somos-Valenzuela M. A. , Chisolm R. E. , Rivas D. S. , Portocarrero C. , McKinney D. C.
Published: January 2016

Abstract. One of the consequences of recent glacier recession in the Cordillera Blanca, Peru, is the risk of Glacial Lake Outburst Floods (GLOFs) from lakes that have formed at the base of retreating glaciers. GLOFs are often triggered by avalanches falling into glacial lakes, initiating a chain of processes that may culminate in significant inundation and destruction downstream. This paper presents simulations of all of the processes involved in a potential GLOF originating from Lake Palcacocha, the source of a previously catastrophic GLOF on 13 December 1941, killing 1800 people in the city of Huaraz, Peru. The chain of processes simulated here includes: (1) avalanches above the lake, (2) lake dynamics resulting from the avalanche impact, including wave generation, propagation, and run-up across lakes, (3) terminal moraine overtopping and dynamic moraine erosion simulations to determine the possibility of breaching, (4) flood propagation along downstream valleys; and (5) inundation of populated areas. The results of each process feed into simulations of subsequent processes in the chain, finally resulting in estimates of inundation in the city of Huaraz. The results of the inundation simulations were converted into flood intensity and hazard maps (based on an intensity-likelihood matrix) that may be useful for city planning and regulation. Three avalanche events with volumes ranging from 0.5–3 × 106 m3 were simulated, and two scenarios of 15 and 30 m lake lowering were simulated to assess the potential of mitigating the hazard level in Huaraz. For all three avalanche events, three-dimensional hydrodynamic models show large waves generated in the lake from the impact resulting in overtopping of the damming-moraine. Despite very high discharge rates (up to 63.4 × 103 m3 s−1), the erosion from the overtopping wave did not result in failure of the damming-moraine when simulated with a hydro-morphodynamic model using excessively conservative soil characteristics that provide very little erosion resistance. With the current lake level, all three avalanche events result in inundation in Huaraz due to wave overtopping, and the resulting hazard map shows a total affected area of 2.01 km2, most of which is in the high-hazard category. Lowering the lake has the potential to reduce the affected area by up to 35 % resulting in a smaller portion of the inundated area in the high-hazard category.
A review of current and possible future human-water interactions in Myanmar's river basins
Authors: Taft L. , Evers M.
Published: January 2016

Abstract. Rivers provide a large number of ecosystem services and riparian people depend directly and indirectly on water availability, quality and quantity of the river waters. The country's economy, the people's well-being and income particularly in agriculturally dominated countries is strongly determined by the availability of sufficient water. This is particularly true for the country of Myanmar in Southeast Asia, where more than 65 % of the population live in rural areas, working in the agricultural sector. Only few research exist on river basins in Myanmar at all and sound knowledge is very limited. Though detailed knowledge and understanding on human-water dynamics in the country is required because Myanmar's society, economy, ecosystems and water resources are facing major challenges due to political and economic reforms and massive and rapid investments from neighbouring countries. However, not only policy and economy modify the need for water. Climate variability and change is another essential driver within human-water systems. Myanmar's climate is influenced by the Indian Monsoon circulation which is subject to interannual and also regional variability. Particularly the central dry zone and the Ayeyarwady delta are prone to extreme events such as serious drought periods and extreme floods. On the one hand, the farmers depend on frequent river flood events for irrigation; on the other hand, they suffer from these water-related extreme events. It is expected that theses climatic extreme events will likely increase in frequency and magnitude in the future as a result of climate change. Different national and international interests in the abundant water resources may provide opportunities and risks at the same time for Myanmar. Several dam projects along the main courses of the rivers are currently in the planning phase. Dams will most likely modify the river flows, the sediment loads and also the still rich biodiversity in the river basins, in a still unknown dimension. Relevant aspects for future development of Myanmar's river basins combine environment-water-related factors, climate, economic and social development, water management and land use changes. Research on this interplays need to capture the spatial and temporal dynamics of this drivers. Yet, it is only possible to gain a full understanding of all these complex interrelationships, when multi-scale spatiotemporal information will be analysed in an inter- and transdisciplinary approach. This paper gives a structured overview on the current scientific knowledge available and reveals the relevance of this information with regard to human-water/human-environment interactions in Myanmar's river basins.
Geoscience on television: a review of science communication literature in the context of geosciences
Authors: Hut R. W. , Land-Zandstra A. M. , Smeets I. , Stoof C.
Published: January 2016

Abstract. Geoscience communication is becoming increasingly important as climate change increases the occurrence of natural hazards around the world. Few geoscientists are trained in effective science communication, and awareness of the formal science communication literature is also low. This can be challenging when interacting with journalists on a powerful medium like TV. To provide geoscience communicators with background knowledge on effective science communication on television, we reviewed relevant theory in the context of geosciences and discuss six major themes: scientist motivation, target audience, narratives and storytelling, jargon and information transfer, relationship between scientists and journalists, and stereotypes of scientists on TV. We illustrate each theme with a case study of geosciences on TV and discuss relevant science communication literature. We then highlight how this literature applies to the geosciences and identify knowledge gaps related to science communication in the geosciences. As TV offers a unique opportunity to reach many viewers, we hope this review can not only positively contribute to effective geoscience communication but also to the wider geoscience debate in society.
Can mussels be used as sentinel organisms for characterisation of pollution in urban water systems?
Authors: Reichwaldt Elke S. , Ghadouani Anas
Published: January 2016

Abstract. Urbanisation strongly impacts aquatic ecosystems by decreasing water quality and altering water cycles. Today, much effort is put towards the restoration and conservation of urban waterbodies to enhance ecosystem service provision leading to liveable and sustainable cities. To enable a sustainable management of waterbodies, the quantification of the temporal and spatial variability of pollution levels and biogeochemical processes is essential. Stable isotopes have widely been used to identify sources of pollution in ecosystems. For example, increased nitrogen levels in waterbodies are often accompanied with a higher nitrogen stable isotope signature (δ15N), which can then be detected in higher trophic levels such as mussels. The main aim of this study was to assess the suitability of nitrogen stable isotope as measured in mussels, as an indicator able to resolve spatial and temporal variability of nutrient pollution in an urban, tidally influenced estuary (Swan River estuary; Western Australia). Our results showed a trend by which sites with higher nitrates concentrations yielded higher nitrate δ15N values; however, nitrogen concentrations and nitrogen stable isotope signature of nitrate throughout the estuary were well within natural values, indicating groundwater inflow rather than pollution by human activity was responsible for differences between sites. The δ15N signature in mussels was very stable over time within each site which allowed for the detection of spatial difference and indicated that mussels can be used as time-integrated sentinel organism in urban systems. In addition, our study indicates that the nature of the relationship between δ15N in the mussels and the nitrate in the water can provide insights into site specific biogeochemical transformation of nutrients. We suggest that mussels and other sentinel organisms can become a robust tool for the detection and characterization of the dynamics of a number of emerging anthropogenic pollutants of concern in urban water systems.
A hybrid model to simulate the annual runoff of Kaidu River in northwest China
Authors: Xu J. , Chen Y. , Bai L. , Xu Y.
Published: January 2016

Abstract. The fluctuant and complicated hydrological process result in the uncertainty of runoff forecast. Thus, the multi-method integrated modeling approaches to simulate runoff are necessary. Integrating the ensemble empirical mode decomposition (EEMD), the back propagation artificial neural network (BPANN) and nonlinear regression equation, we put forward a hybrid model to simulate the annual runoff (AR) of the Kaidu River in northwest China. We also validated the simulated effect by using the coefficient of determination (CD) and Akaike information criterion (AIC) based on the observed data from 1960 to 2012 in Dashankou hydrological station. The average absolute and relative error show the high simulation accuracy of the the hybrid model. CD and AIC both illustrate that the simulated effect of the hybrid model is much better than that of a single BPANN. The hybrid model and integrated approach elicited by this study may be applied to simulate the annual runoff of the similar rivers in northwest China.
Flood risk reduction and flow buffering as ecosystem services: a flow persistence indicator for watershed health
Authors: van Noordwijk M. , Tanika L. , Lusiana B.
Published: January 2016

Abstract. Flood damage depends on location and adaptation of human presence and activity to inherent variability of river flow. Reduced predictability of river flow is a common sign of degrading watersheds associated with increased flooding risk and reduced dry-season flows. The dimensionless FlowPer parameter (Fp), representing predictability, is key to a parsimonious recursive model of river flow, Qt = FpQt−1 + (1−Fp)(Pt−Etx), with Q, P and E expressed in mm d−1. Fp varies between 0 and 1, and can be derived from a time-series of measured (or modeled) river flow data. The spatially averaged precipitation term Pt and preceding cumulative evapotranspiration since previous rain Etx are treated as constrained but unknown, stochastic variables. A decrease in Fp from 0.9 to 0.8 means peak flow doubling from 10 to 20% of peak rainfall (minus its accompanying Etx) and, in a numerical example, an increase in expected flood duration by 3 days. We compared Fp estimates from four meso-scale watersheds in Indonesia and Thailand, with varying climate, geology and land cover history, at a decadal time scale. Wet-season (3-monthly) Fp values are lower than dry-season values in climates with pronounced seasonality. A wet-season Fp value above 0.7 was achievable in forest-agroforestry mosaic case studies. Interannual variability in Fp is large relative to effects of land cover change; multiple years of paired-plot data are needed to reject no-change null-hypotheses. While empirical evidence at scale is understandably scarce, Fp trends over time serve as a holistic scale-dependent performance indicator of degrading/recovering watershed health.
Uncertainty assessment of a dominant-process catchment model of dissolved phosphorus transfer
Authors: Dupas R. , Salmon-Monviola J. , Beven K. , Durand P. , Haygarth P. M. , Hollaway M. J. , Gascuel-Odoux C.
Published: January 2016

Abstract. We developed a parsimonious topography-based hydrologic model coupled with a soil biogeochemistry sub-model in order to improve understanding and prediction of Soluble Reactive Phosphorus (SRP) transfer in agricultural headwater catchments. The model structure aims to capture the dominant hydrological and biogeochemical processes identified from multiscale observations in a research catchment (Kervidy-Naizin, 5 km2). Groundwater fluctuations, responsible for the connection of soil SRP production zones to the stream, were simulated with a fully-distributed hydrologic model at 20 m resolution. The spatial variability of the soil phosphorus status and the temporal variability of soil moisture and temperature, which had previously been identified as key controlling factor of SRP solubilisation in soils, were included as part of an empirical soil biogeochemistry sub-model. The modelling approach included an analysis of the information contained in the calibration data and propagation of uncertainty in model predictions using a GLUE "limits of acceptability" framework. Overall, the model appeared to perform well given the uncertainty in the observational data, with a Nash–Sutcliffe efficiency on daily SRP loads between 0.1 and 0.8 for acceptable models. The role of hydrological connectivity via groundwater fluctuation, and the role of increased SRP solubilisation following dry/hot periods were captured well. We conclude that in the absence of near continuous monitoring, the amount of information contained in the data is limited hence parsimonious models are more relevant than highly parameterised models. An analysis of uncertainty in the data is recommended for model calibration in order to provide reliable predictions.
Insights on the water mean transit time in a high-elevation tropical ecosystem
Authors: Mosquera G. M. , Segura C. , Vaché K. B. , Windhorst D. , Breuer L. , Crespo P.
Published: January 2016

Abstract. This study focuses on the investigation of the yet unknown mean transit time (MTT) of stream waters and its spatial variability in tropical alpine ecosystems (wet Andean páramo). The study site is the Zhurucay River Ecohydrological Observatory (7.53 km2) located in south Ecuador. A lumped parameter model considering five transit time distribution (TTD) functions was used to estimate MTTs. We used a unique data set of δ18O and δ2H isotopic composition of rainfall and streamflow water samples collected for three years (May 2011-May 2014) in a nested monitoring system of streams. Linear regression between MTT and landscape (soil and vegetation cover, geology, and topography) and hydrometric (runoff coefficient and specific discharge rates) variables was used to determine controls on MTT variability, as well as mean electrical conductivity (MEC) as a possible proxy for MTT. Results revealed that the exponential TTD function best describes the hydrology of the site, indicating a relatively simple transition from rainfall water to the streams through the organic horizon of the wet páramo soils. MTT of the streams is relatively short (0.15-0.73 yr, 53-264 days). Regression analysis revealed negative correlation between the catchment’s average slope and MTT (R2 = 0.78, p < 0.05). MTT showed no significant correlation with hydrometric variables whereas MEC increases with MTT (R2 = 0.89 p < 0.001). Overall, we conclude that: 1) MTT of streams confirms that the hydrology of the ecosystem is dominated by shallow subsurface flow; 2) the interplay between the high storage capacity of the wet páramo soils and the slope of the catchments provides the ecosystem with high regulation capacity; and 3) MEC is an efficient predictor of MTT variability in this system of catchments with relatively homogeneous geology.
Shallow groundwater in sub-Saharan Africa: neglected opportunity for sustainable intensification of small-scale agriculture?
Authors: Gowing John , Parkin Geoff , Forsythe Nathan , Walker David , Haile Alemseged Tamiru , Alamirew Demis
Published: January 2016

Abstract. There is a need for an evidence-based approach to identify how best to support development of groundwater for small scale irrigation in sub-Saharan Africa (SSA). We argue that it is important to focus this effort on shallow groundwater resources which are most likely to be used by poor rural communities in SSA. However, it is important to consider constraints, since shallow groundwater resources are likely to be vulnerable to over-exploitation and climatic variability. We examine here the opportunities and constraints and draw upon evidence from Ethiopia. We present a methodology for assessing and interpreting available shallow groundwater resources and argue that participatory monitoring of local water resources is desirable and feasible. We consider possib le models for developing distributed small-scale irrigation and assess its technical feasibility. Because of power limits on water lifting and also because of available technology for well construction, groundwater at depths of 50 m or 60 m cannot be regarded as easily accessible for small-scale irrigation. We therefore adopt a working definition of shallow groundwater as < 20 m depth. This detailed case study in the Dangila woreda in Ethiopia explores the feasibility of exploiting shallow groundwater for small-scale irrigation over a range of rainfall conditions. Variability of rainfall over the study period (9 % to 96 % probability of non-exceedance) does not translate into equivalent variability in groundwater levels and river baseflow. Groundwater levels, monitored by local communities, persist into the dry season to at least the end of December in most shallow wells, indicating that groundwater is available for irrigation use after the cessation of the wet season. Arguments historically put forward against the promotion of groundwater use for agriculture in SSA on the basis that aquifers are unproductive and irrigation will have unacceptable impacts on wetlands and other groundwater-dependent ecosystems appear exaggerated. It would be unwise to generalise from this case study to the whole of SSA, but useful insights into the wider issues are revealed by the case study approach. We believe there is a case for arguing that shallow groundwater in sub-Saharan Africa represents a neglected opportunity for sustainable intensification of small-scale agriculture.
A post-wildfire response in cave dripwater chemistry
Authors: Nagra Gurinder , Treble Pauline C. , Andersen Martin S. , Fairchild Ian J. , Coleborn Katie , Baker Andy
Published: January 2016

Abstract. Cave environments are sensitive because surface environmental changes can affect both the isotopic composition and solute concentration of infiltrating cave dripwaters. These changes subsequently affect the speleothem geochemical record. One such agent of change is wildfire, however its effect on karst processes remains poorly understood. Using dripwater data from a shallow cave, at a forested site in southwest Australia, we provide a unique analysis of the post-wildfire effects on dripwater δ18O and solute concentrations. We analyse how wildfires affect on local controls, i.e. vegetation cover, evapotranspiration and carbonate water-rock interactions, effects cave dripwater hydrology and geochemistry. We compare our post-wildfire data with modelled drip water δ18O, regional groundwater chemistry, and a second cave dripwater dataset, to determine the extent to which wildfire affects cave dripwater composition. We find in our forested, shallow cave site, by effecting surface evaporation and transpiration rates wildfire can have a multi-year impact on subsurface hydrology and dripwater chemistry. Here we open a new avenue for speleothem science in fire-prone regions, focusing on the geochemical records of speleothems as potential paleo-fire archives.
Combined measurement and modeling of the hydrological impact of hydraulic redistribution using CLM4.5 at eight AmeriFlux sites
Authors: Fu C. , Wang G. , Goulden M. L. , Scott R. L. , Bible K. , Cardon Z. G.
Published: January 2016

Abstract. Effects of hydraulic redistribution (HR) on hydrological, biogeochemical, and ecological processes have been demonstrated in the field, but the current generation of standard earth system models does not include a representation of HR. Though recent studies have examined the effect of incorporating HR into land surface models, few (if any) has tackled the magnitude of the HR flux itself or the soil moisture dynamics from which HR magnitude can be directly inferred. Here we incorporated Ryel et al.'s (2002) empirical equation describing HR into the NCAR Community Land Model Version 4.5 (CLM4.5), and examined the ability of the resulting hybrid model to capture the magnitude of HR flux and/or soil moisture dynamics from which HR can be directly inferred, to assess the impact of HR on surface water and energy budgets, and to explore how it may depend on climate regimes and vegetation conditions. Eight AmeriFlux sites characterized by contrasting climate regimes and multiple vegetation types were studied, including the US-Wrc Wind River Crane site in Washington State, the US-SRM Santa Rita Mesquite Savanna site in southern Arizona, and six sites along the Southern California Climate Gradient (US-SCs, g, f, w, c, and d). HR flux, evapotranspiration, and soil moisture were properly simulated in the present study, even in the face of various uncertainties. Our cross-ecosystem comparison showed that the timing, magnitude, and direction (upward or downward) of HR vary across ecosystems, and incorporation of HR into CLM4.5 improved the model-measurement match particularly during dry seasons. Our results also reveal that HR has important hydrological impact (on evapotranspiration, Bowen ratio, and soil moisture) in ecosystems that have a pronounced dry season but are not overall so dry that sparse vegetation and very low soil moisture limit HR.
Eco-hydrological effects of stream-aquifer water interaction: A case study of the Heihe River Basin, northwestern China
Authors: Zeng Yujin , Xie Zhenghui , Yu Yan , Liu Shuang , Wang Linying , Jia Binghao , Qin Peihua , Chen Yaning
Published: January 2016

Abstract. A scheme describing the process of stream-aquifer interaction was incorporated into the land model CLM4.5 to investigate the effects of stream water conveyance over riparian banks on ecological and hydrological processes. Two groups of simulations for five typical river cross-sections in the middle reaches of the arid zone Heihe River Basin were conducted. The simulated riparian ground water table at a propagation distance of less than 1 km followed the intra-annual flu ctuation of the river water level, and the correlation was excellent (R2 = 0.9) between the river water level and the groundwater table at the distance 60 m from the river. The correlation rapidly decreased as distance increased. In response to the variability of the water table, soil moisture at deep layers also followed the variation of river water level all year, while soil moisture at the surface layer was more sensitive to the river water level in the drought season than in the wet season. With increased soil moisture, the average gross primary productivity and respiration of riparian vegetation within 300 m from the river at a typical section of the river increased by approximately 0.03 mg C m−2 s−1 and 0.02 mg C m −2 s−1, respectively, in the growing season. Consequently, the net ecosystem exchange increased by approximately 0.01 mg C m−2 s−1, and the evapotranspiration increased by approximately 3 mm d−1. Furthermore, the length of the growing season of riparian vegetation also increased by 2–3 months due to the sustaining water recharge from the river.
Qualification concept for optical multi-scale multi-sensor systems
Authors: Loderer A. , Hausotte T.
Published: January 2016

Abstract. This article describes a new qualification concept for dimensional measurements on optical measuring systems. Using the example of a prototypical multi-scale multi-sensor fringe projection system for production-related inspections of sheet-bulk metal-formed parts, current measuring procedures of the optical system are introduced. Out of the shown procedures' deficiencies, a new concept is developed for determining the orientations and positions of the sensors' measuring ranges in a common coordinate system. The principle element of the concept is a newly developed flexible reference artefact, adapted to the measuring task of the fringe projection system. Due to its dull surface, the artefact is optimized for optical measuring systems, like the used fringe projection sensors. By measuring the reference artefact with each fringe projection sensor and aligning the resulting data sets on a digital reference model of the artefact, sensor-specific transformation matrices can be calculated which allow transformation of the sensors' data sets into a common coordinate system, without the need for any overlapping areas. This approach is concluded in an automated measuring procedure, using alignment algorithms from commercial available software where necessary. With the automated measuring procedure, geometrical relations between individual measured features can be determined and dimensional measuring beyond the measuring range of a sensor became possible. Due to a series of experiments, the advantages of the new qualification concept in comparison with the current measuring procedures are finally revealed.
Calibration and validation of FLFArs -- a new flood loss function for Australian residential structures
Authors: Hasanzadeh Nafari R. , Ngo T. , Lehman W.
Published: January 2016

Abstract. Rapid urbanisation, climate change and unsustainable developments are increasing the risk of floods. Flood is a frequent natural hazard that has significant financial consequences for Australia. The emergency response system in Australia is very successful and has saved many lives over the years. However, the preparedness for natural disaster impacts in terms of loss reduction and damage mitigation has been less successful. In this paper, a newly derived flood loss function for Australian residential structures (FLFArs) has been presented and calibrated by using historic data collected from an extreme event in Queensland, Australia, that occurred in 2013. Afterwards, the performance of the method developed in this work (contrasted to one Australian model and one model from USA) has been compared with the observed damage data collected from a 2012 flood event in Maranoa, Queensland. Based on this analysis, validation of the selected methodologies has been performed in terms of Australian geographical conditions. Results obtained from the new empirically based function (FLFArs) and the other models indicate that it is apparent that the precision of flood damage models is strongly dependent on selected stage damage curves, and flood damage estimation without model calibration might result in inaccurate predictions of losses. Therefore, it is very important to be aware of the associated uncertainties in flood risk assessment, especially if models have not been calibrated with real damage data.
Can an early-warning system help minimize the impacts of coastal storms? A case study of the 2012 Halloween storm, northern Italy
Authors: Harley M. D. , Valentini A. , Armaroli C. , Perini L. , Calabrese L. , Ciavola P.
Published: January 2016

Abstract. The Emilia-Romagna early-warning system (ER-EWS) is a state-of-the-art coastal forecasting system that comprises a series of numerical models (COSMO, ROMS, SWAN and XBeach) to obtain a daily 3-day forecast of coastal storm hazard at eight key sites along the Emilia-Romagna coastline (northern Italy). On the night of 31 October 2012, a major storm event occurred that resulted in elevated water levels (equivalent to a 1-in-20- to 1-in-50-year event) and widespread erosion and flooding. Since this storm happened just 1 month prior to the roll-out of the ER-EWS, the forecast performance related to this event is unknown. The aim of this study was to therefore reanalyse the ER-EWS as if it had been operating a day before the event and determine to what extent the forecasts may have helped reduce storm impacts. Three different reanalysis modes were undertaken: (1) a default forecast (DF) mode based on 3-day wave and water-level forecasts and default XBeach parameters; (2) a measured offshore (MO) forecast mode using wave and water-level measurements and default XBeach parameters; and (3) a calibrated XBeach (CX) mode using measured boundary conditions and an optimized parameter set obtained through an extensive calibration process. The results indicate that, while a "code-red" alert would have been issued for the DF mode, an underprediction of the extreme water levels of this event limited high-hazard forecasts to only two of the eight ER-EWS sites. Forecasts based on measured offshore conditions (the MO mode) more-accurately indicate high-hazard conditions for all eight sites. Further considerable improvements are observed using an optimized XBeach parameter set (the CX mode) compared to default parameters. A series of what-if scenarios at one of the sites show that artificial dunes, which are a common management strategy along this coastline, could have hypothetically been constructed as an emergency procedure to potentially reduce storm impacts.
Global Distribution of Winter Lightning: a threat to wind turbines and aircraft
Authors: Montanyà J. , Fabró F. , van der Velde O. , March V. , Williams E. R. , Pineda N. , Romero D. , Solà G. , Freijo M.
Published: January 2016

Abstract. Lightning is one of the major threats to multi-megawatt wind turbines and a concern for new generation of aircraft. That is because the use of lightweight of some composite materials. Both wind turbines and aircraft can initiate lightning and very favourable conditions for lightning initiation occur in winter thunderstorms. Moreover, winter thunderstorms are characterized for producing very energetic lightning. The paper reviews the different type of lightning interactions and summarizes the well-known winter thunderstorm areas. However, up to now comprehensive maps of global distribution of winter lightning prevalence to be used for risk assessment have been unavailable. In this paper we present the global winter lightning activity for a period of 5 years. Using lightning location data and meteorological re-analysis data, three maps are created: annual winter lightning stroke density, seasonal variation of the winter lightning and the annual number of winter thunderstorm days. In the northern hemisphere, the maps confirmed Japan to be one of the most active regions but other areas such as the Mediterranean and the US are active as well. In the southern hemisphere, Argentina and New Zealand experience the highest activity. The maps provided here can be used for providing risk assessment.
The influence of expertise on rockfall failure probability assessment – an original experimentation
Authors: Delonca A. , Verdel T. , Gunzburger Y.
Published: January 2016

Abstract. To date, many rockfall failure probability assessment still consider qualitative observations into their analysis. Based on this statement, knowledge and expertise are supposed to be major parameters in the determination of the rockfall assessment. To test this hypothesis, an experiment has been carried out in order to evaluate the influence of the subjective assessment. Three populations have been selected, having different levels of expertise: (1) students in geosciences, (2) researchers in geosciences and (3) confirmed experts. These three populations have evaluated the rockfall failure probability level considering two different methods: the Laboratoire des Ponts et Chaussées (LPC) method and a method partly based on the Slope Mass Rating (SMR) method. To complement the analysis, an "a-priori" assessment of the rockfall failure probability has been requested of each population, without using any method. The LPC method has been used knowing that it is the most widely used method in France for official hazard mapping. It combines two main indicators: the susceptibility to instability and the expected magnitude. Reversely, the SMR method has been used as an ad hoc quantitative method to investigate the effect of the level of quantification within the method. These procedure has been applied on a test site divided into three different sectors. A statistical treatment of the results (descriptive statistical analysis, chi-square independent test and ANOVA) shows that there is a significant influence of the method used on the rockfall probability assessment, whatever the sector. Furthermore, there is a non-significant influence of the level of expertise of the population for two of the three sectors. On sector 1, there is a significant influence of the level of expertise, explained by the importance of the temporal probability assessment in the rockfall hazard assessment process. The SMR-based method seems highly sensitive to the "site activity" indicator and exhibits an important dispersion in its results. On the other hand, the results are more similar to the LPC qualitative method, even in the case of sector 1.
A modified tank model including snowmelt and infiltration time lags for deep-seated landslides in Alpine Environments (Aggenalm, Germany)
Authors: Nie W. , Krautblatter M. , Leith K. , Thuro K. , Festl J.
Published: January 2016

Abstract. Deep-seated landslides are an important and widespread natural hazard within alpine regions, and can have a massive impact on infrastructure. Pore water pressure plays an important role in determining the stability of hydro-triggered deep-seated landslides. We improve current methods of groundwater level prediction by introducing a means to account for time lags associated with groundwater supply caused by snow accumulation, snowmelt, and infiltration in deep-seated landslides. In this study, we demonstrate a simple method to improve the estimation of these time lags using a modified tank model to calculate groundwater levels. In a deep-seated landslide in Bavaria, Germany, our results predict daily changes in pore water pressure ranging from -1 to 1.6 kPa depending on daily rainfall and snowmelt. The inclusion of time lags improves the results of standard tank models by ~36% (linear correlation with measurement) after heavy rainfall and, respectively, by ~82% following snowmelt in a 1-2 day period. For the modified tank model, we introduced a representation of snow accumulation and snowmelt, based on a temperature index and an equivalent infiltration method, i.e. the melted snow water equivalent. This compares well to the in situ measurement for the same time interval which reflect changes of pore water pressure with 0-8% relative error in rainfall season (standard tank model: 2-16% relative error) and with 0-7% relative error in snowmelt season (standard tank model: 2-45% relative error). Here we demonstrate a modified tank model for deep-seated landslides that includes snow and infiltration effects and can effectively predict changes in pore water pressure in alpine environments.
Extended Application of the CNOP-P method in the Inner Mongolia using the Common Land Model
Authors: Wang Bo , Huo Zhenhua , Yuan Yujing , Wu Shang
Published: January 2016

Abstract. An extension method of the conditional nonlinear optimal perturbation about parameter (CNOP-P) is adopted to study the soil parameter optimization for the Hulunbeier Steppe within the common land model (CoLM) with the differential evolution (DE) method. Using National Center for Environmental Prediction/Department of Energy (NCEP/DOE) Atmospheric Model Intercomparison Project-II (AMIP-II) 6-hourly Reanalysis Gaussian Grid data and National Meteorological Center (NMC) Reanalysis 6-hourly surface fluxes data, three experiments (I and II) were designed to study the impact of the percentages of sand and clay of the shallow soil in CoLM on simulating the shallow soil moisture. To study the shallow soil moisture and the latent heat flux simultaneously, experiment (III) is designed. The optimal parameters obtained by the extended CNOP-P method are used to predict the shallow soil moisture in the following month. In all the three experiments, after optimization stage, the optimal soil parameters could significantly improve the simulation ability of CoLM in the Inner Mongolia to the shallow soil moisture at the stage of prediction; the optimal parameters attained by the double-parameter optimal experiment could make CoLM simulate the shallow soil moisture better than the single-parameter optimal experiment in the optimization slot. Moreover, the results of experiments (I and II) justify the conclusion that the more accurate the atmospheric forcing data and observation data are, the more effective the results of optimization will be.