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© 2018. The Authors. Thermal infrared sensing of evapotranspiration (E) through surface energy balance (SEB) models is challenging due to uncertainties in determining the aerodynamic conductance (gA) and due to inequalities between radiometric (TR) and aerodynamic temperatures (T0). We evaluated a novel analytical model, the Surface Temperature Initiated Closure (STIC1.2), that physically integrates TR observations into a combined Penman-Monteith Shuttleworth-Wallace (PM-SW) framework for directly estimating E, and overcoming the uncertainties associated with T0 and gA determination. An evaluation of STIC1.2 against high temporal frequency SEB flux measurements across an aridity gradient in Australia revealed a systematic error of 10–52% in E from mesic to arid ecosystem, and low systematic error in sensible heat fluxes (H) (12–25%) in all ecosystems. Uncertainty in TR versus moisture availability relationship, stationarity assumption in surface emissivity, and SEB closure corrections in E were predominantly responsible for systematic E errors in arid and semi-arid ecosystems. A discrete correlation (r) of the model errors with observed soil moisture variance (r = 0.33–0.43), evaporative index (r = 0.77–0.90), and climatological dryness (r = 0.60–0.77) explained a strong association between ecohydrological extremes and TR in determining the error structure of STIC1.2 predicted fluxes. Being independent of any leaf-scale biophysical parameterization, the model might be an important value addition in working group (WG2) of the Australian Energy and Water Exchange (OzEWEX) research initiative which focuses on observations to evaluate and compare biophysical models of energy and water cycle components.

Physical habitat is important in determining the carrying capacity of juvenile brown trout, and within freshwater management. Summer daytime physical habitat selection for the parr lifestage (7–20 cm) juvenile brown trout (Salmo trutta) was assessed in 6 small lowland streams. Habitat preference was determined for the four variables; water velocity, water depth, substrate and cover, and the preferences for physical habitat selection were expressed in terms of habitat suitability indices (HSI’s). The statistical confidence of HSI’s was evaluated using power analysis. It was found that a minimum of 22 fish observations was needed to have statistical confidence in the HSIs for water depth, and a minimum of 92 fish observations for water velocity during daytime summer conditions. Generally parr were utilising the deeper habitats, indicating preference for deeper water. Cover was also being selected for at all sites, but selection was inconsistent among sites for the variables substrate and velocity. The results indicate that during daytime summer conditions water depth is a significant variable for parr habitat selection in these small lowland streams, with cover also being important. Therefore, daytime refugia may be a critical limiting factor for parr in small lowland streams, and important for stream management actions under the Water Framework Directive.

The new Scientific Decade 2013-2022 of IAHS, entitled Panta RheiEverything Flows, is dedicated to research activities on change in hydrology and society. The purpose of Panta Rhei is to reach an improved interpretation of the processes governing the water cycle by focusing on their changing dynamics in connection with rapidly changing human systems. The practical aim is to improve our capability to make predictions of water resources dynamics to support sustainable societal development in a changing environment. The concept implies a focus on hydrological systems as a changing interface between environment and society, whose dynamics are essential to determine water security, human safety and development, and to set priorities for environmental management. The Scientific Decade 2013-2022 will devise innovative theoretical blueprints for the representation of processes including change and will focus on advanced monitoring and data analysis techniques. Interdisciplinarity will be sought by increased efforts to connect with the socio-economic sciences and geosciences in general. This paper presents a summary of the Science Plan of Panta Rhei, its targets, research questions and expected outcomes.

Leaf biochemistry and biophysical parameters are important for simulating soil‐vegetation‐atmosphere exchanges of energy, water, CO2 and ammonia. The accumulation of leaf nitrogen (N) in vegetation canopies is a major component of the ecosystem N balance, and leaf N concentration and leaf area index (LAI) are important determinants of the maximum CO2 uptake by plants and trees. In NEU, high spatial resolution remote sensing data from the SPOT satellite were acquired to prepare maps of leaf N and LAI for 5 European landscapes. Mapping was conducted using the REGFLEC model which is an automatic and image‐based methodology developed for regional chlorophyll (Cab) and LAI estimation (ie. Houborg and Andersen, JARS 3, 2009). REGFLEC combines models for atmospheric correction (6S), canopy reflectance (ACRM) and leaf optics (PROSPECT). Model performance previously proved promising in Denmark and in Maryland, USA. In this study, REGFLEC performance is evaluated and discussed using field measurements of leaf N, SPADmeter data and LAI in Denmark, Poland, Scotland, the Netherlands and Italy. The inverse model estimations of soil reflectance parameters and canopy parameters are discussed in relation to the prevailing soil types and vegetation characteristics of land cover classes across the 5 European landscapes.

Mapping was conducted using the REGFLEC model which is an automatic and image-based methodology developed for regional chlorophyll (Cab) and LAI estimation (i.e., Houborg et al., 2007; Houborg and Boegh, 2008; Houborg and Andersen, JARS 3, 2009). REGFLEC combines models for atmospheric correction (6S), canopy reflectance (ACRM) and leaf optics (PROSPECT). The REGFLEC tool corrects for impacts of atmospheric scattering and absorption, soil background reflectance and species specific vegetation characteristics (ie. leaf angle distribution). In this study, the REGFLEC model tool is applied to high spatial (10-20 m) resolution SPOT satellite data for mapping LAI and leaf N of agricultural landscapes located in Denmark, Poland, Scotland, the Netherlands and Italy (Table 1). Non-destructive field measurements of LAI (LAI-2000, LiCor, USA), Cab and leaf N contents were made within 1-2 weeks of the date for satellite image acquisition and used to evaluate remote sensing predictions. A number of additional GPS registrations were made to support the image (land use) classification required by the REGFLEC methodology. Cab and leaf N contents were measured using a SPAD meter (SPAD 502-DL, Minolta, USA) which was calibrated for different leaf types to assess Cab (r2 = 0.73-0.93) and leaf N (r2 = 0.62-0.89) of the monitored crop types. In addition, the Cab and leaf N contents of leaf samples were analyzed in laboratory to establish empirical relationships for converting Cab predictions to leaf N contents.

Surface water–groundwater interactions at the stream interface influences, and at times controls the stream temperature, a critical water property driving biogeochemical processes. This study investigates the effects of these interactions on temperature of Stream Elverdamsåen in Denmark using the Distributed Temperature Sensing (DTS) system and instream temperature modelling. Locations of surface water–groundwater interactions were identified from the temperature data collected over a 2-km stream reach using a DTS system with 1-m spatial and 5-min temporal resolution. The stream under consideration exhibits three distinct thermal regimes within a 2 km reach length due to two major interactions. An energy balance model is used to simulate the instream temperature and to quantify the effect of these interactions on the stream temperature. This research demonstrates the effect of reach level small scale surface water–groundwater interactions on heterogeneous behaviour of stream temperature.

This paper discusses preliminary remote sensing (MODIS) based hydrological modelling results for the Danish island Sjælland (7330 km2) in relation to project objectives and methodologies of a new research project “Implementing Earth observation and advanced satellite based atmospheric sounders for effective land surface representation in water resource modeling” (2009- 2012). The purpose of the new research project is to develop remote sensing based model tools capable of quantifying the relative effects of site-specific land use change and climate variability at different spatial scales. For this purpose, a) internal catchment processes will be studied using a Distributed Temperature Sensing (DTS) system, b) Earth observations will be used to upscale from field to regional scales, and c) at the largest scale, satellite based atmospheric sounders and meso-scale climate modelling will be used to study and verify the modelling of land surface hydrology processes.

Canopy fluxes of water vapour and CO2 from a sparse millet crop are simulated on the basis of a leaf scale model designed to predict stomatal conductance, leaf temperature, transpiration rate and photosynthetic rate for millet on a diurnal basis. The modelled leaf fluxes are extrapolated using two different big-leaf approaches. In the traditional big-leaf approach, all leaves are exposed to the same microenvironment which is different from the environmental conditions above the canopy, whereas in the modified big-leaf approach the canopy is regarded as a partly shaded big-leaf. In the sun/shade big-leaf model, soil reflection, diffuse radiation and separate evaluations of the radiation load on sunlit and shaded leaf surfaces are taken into account. Due to the low fraction of shaded leaves in the sparse canopy, the two types of big-leaf models predict both canopy fluxes equally well. The sensitivity of the modelled fluxes to the various input parameters was ranked for the identification of the most important parameters controlling photosynthesis and transpiration. This information is used for identification of more simple scaling models aimed at predicting daily canopy fluxes. The influx of sensible heat to the leaf was found to be an important energy source for transpiration. It was confirmed that daily transpiration can be parameterized by the air humidity gradient using only the leaf area index (LAI) for the evaluation of seasonal changes in bulk stomatal conductance. The photosynthetic rate was found to be most sensitive to radiation and leaf temperature. It is shown that the daily canopy photosynthesis can he estimated on the basis of LAI and midday values (1200 h) of incoming radiation density and leaf temperature.