Simulated Energy Fluxes Research Articles

Systematic Evaluation of a High-Resolution CLM5 Simulation over Continental China for 1979–2018

Abstract The land surface model is extensively used to simulate turbulence fluxes and hydrological and momentum variables at the land–atmosphere interface. In this study, the Community Land Model, version 5 (CLM5), driven by the 0.1° × 0.1° Chinese Meteorological Forcing Dataset (CMFD) and the field-surveyed soil parameters, is used to simulate land surface processes during 1979–2018. Various high-quality land surface datasets are adopted to assess the model simulations. In general, the CLM5 well captures the monthly variations of 0–10-cm soil moisture in subregions, particularly in the Tibetan Plateau, with an anomaly correlation coefficient between 0.56 and 0.88. However, the simulated soil moisture shows overall wet biases in the whole country, resulting from several reasons. The model simulation is skillful in replicating both the magnitude and spatial pattern when they are compared with the MODIS snow cover dataset. Compared with in situ measured soil temperature in multiple soil layers within 320-cm soil depth from 1980 to 2018, the simulations accurately capture spatial patterns, vertical profiles, and long-term warming trends. For land surface energy components, the simulations have a highly temporal correlation with the observation of Chinese Flux Observation and Research Network (ChinaFLUX) cropland and grassland sites, except for four forest sites, where biases exist in both atmospheric forcing variables and surface vegetation phenology in the model default input dataset. In summary, this study reveals the overall capability of CLM5 in reproducing land surface energy fluxes and hydrological variables over conterminous China, and the validation results may also provide some references for future model improvement and application. Significance Statement The offline Community Land Model, version 5 (CLM5), driven by a 0.1° × 0.1° (∼10 km) horizontal resolution atmospheric forcing dataset and a set of field-surveyed soil parameters, are used to simulate the land surface hydrological and heat fluxes in continental China for 1980–2018. The simulated hydrological variables and energy fluxes are validated with various sources of high-quality observation-based datasets. From our systematic evaluations, the current CLM5 high–resolution simulation accurately captures the spatial patterns and temporal variations in most of the water and energy balance components, although biases exist in some simulated variables. Overall, this study reveals the capability of the offline CLM5 simulation in conterminous China and provides the reference for future model improvement and application.

Progress in gyrokinetic validation studies using NBI heated L-mode discharge in KSTAR

Progress in the first gyrokinetic validation study using KSTAR NBI heated L-mode discharge is reported in this paper. The energy flux levels simulated from gyrokinetic code, CGYRO[J. Candy et al., J. Comput. Phys. 324, 73–93 (2016)] were compared with experimental levels in this study for validation purposes. The linear stability analysis indicates that trapped electron modes (TEM) are the most unstable ion-scale modes at r/a = 0.5. The simulated energy flux was under-predicted compared to the experimental energy flux level within their uncertainties. We also observed that simulated energy flux levels were sensitive to the input parameters related to impurity density profile such as effective charge, Zeff, and inverse gradient scale length of impurity and main ion, a/Lnc and a/Lni, respectively. For the conclusive future validation studies, we identified the Zeff profile, which can give constraints on not only impurity but also main ion profiles, as necessary input.

Implementation and calibration of short-rotation eucalypt plantation module within the ECOSMOS land surface model

Eucalypt is one of the most-planted broadleaf genera around the globe, exhibiting high yield, plasticity and growing capacity on a broad range of environments. The main objective of this study is to present the integration of a specific module for eucalypt short-rotation plantations into ECOSMOS (Ecosystem Model Simulator). Different calibrations and validations, from intensively monitored sites, experimental networks, and plots in commercial stands were performed. We calibrated all ECOSMOS model biophysical and physiological parameters for the Eucalyptus module using three micrometeorological experiments. A generic genotype was calibrated and applied to evaluate the model performance in response to contrasting environments and genotypes, on a dataset from an experimental network with high Genotype x Environment interactions. The model was applied over commercial eucalypt plantations sites, where re-calibration was necessary for four parameters of the ECOSMOS-Eucalyptus module related to leaf carbon allocation and specific leaf area, because of significant differences in genotypes and management among datasets. Results showed the consistency of the biophysical and physiological processes solved by the model, simulated energy and carbon fluxes, soil water dynamics, and growth of different plant components when compared with observations; Nash-Sutcliffe efficiency (NSE) of 0.93, 0.43 and 0.27 for net radiation, net ecosystem exchange and evapotranspiration, respectively were obtained for the validation dataset. The generic genotype calibration varied greatly in simulating the eucalypt stem growth of the 26 locations. The generic calibration can be used as reference for eucalypt plantation’ areas in Brazil; however, a re-calibration is recommended for operational applications to adjust the ECOSMOS-Eucalyptus module to the management conditions, management practices and genotypes used by companies.

Available Energy of Trapped Electrons and Its Relation to Turbulent Transport.

Any collisionless plasma possesses some "available energy" (AE), defined as that part of the thermal energy that can be converted into instabilities and turbulence. Here, we present a calculation of the AE carried by magnetically trapped electrons in a flux tube of collisionless plasma. The AE is compared with nonlinear simulations of the energy flux resulting from collisionless turbulence driven by trapped-electron modes in various magnetic geometries. The numerical calculation of AE is rapid and shows a strong correlation with the simulated energy fluxes, which can be expressed as a power law and understood in terms of a simple model.

A remote sensing-based three-source energy balance model to improve global estimations of evapotranspiration in semi-arid tree-grass ecosystems.

It is well documented that energy balance and other remote sensing-based evapotranspiration (ET) models face greater uncertainty over water-limited tree-grass ecosystems (TGEs), representing nearly 1/6th of the global land surface. Their dual vegetation strata, the grass-dominated understory and tree-dominated overstory, make for distinct structural, physiological and phenological characteristics, which challenge models compared to more homogeneous and energy-limited ecosystems. Along with this, the contribution of grasses and trees to total transpiration (T), along with their different climatic drivers, is still largely unknown nor quantified in TGEs. This study proposes a thermal-based three-source energy balance (3SEB) model, accommodating an additional vegetation source within the well-known two-source energy balance (TSEB) model. The model was implemented at both tower and continental scales using eddy-covariance (EC) TGE sites, with variable tree canopy cover and rainfall (P) regimes and Meteosat Second Generation (MSG) images. 3SEB robustly simulated latent heat (LE) and related energy fluxes in all sites (Tower: LE RMSD ~60W/m2 ; MSG: LE RMSD ~90W/m2 ), improving over both TSEB and seasonally changing TSEB (TSEB-2S) models. In addition, 3SEB inherently partitions water fluxes between the tree, grass and soil sources. The modelled T correlated well with EC T estimates (r>.76), derived from a machine learning ET partitioning method. The T/ET was found positively related to both P and leaf area index, especially compared to the decomposed grass understory T/ET. However, trees and grasses had contrasting relations with respect to monthly P. These results demonstrate the importance in decomposing total ET into the different vegetation sources, as they have distinct climatic drivers, and hence, different relations to seasonal water availability. These promising results improved ET and energy flux estimations over complex TGEs, which may contribute to enhance global drought monitoring and understanding, and their responses to climate change feedbacks.

Evaluation of the Effect of Low Soil Temperature Stress on the Land Surface Energy Fluxes Simulation in the Site and Global Offline Experiments

AbstractThe root water uptake (RWU) rate of plants is influenced by various environmental factors. Low soil temperature stress can reduce RWU rate by inhibiting the growth of plant roots and increasing the hydraulic resistance of water transport among the soil‐plant‐atmosphere continuum. Given that low soil temperature stress is not accounted for in current land surface models (LSMs); in this study, we introduce three functions to represent low soil temperature stress, and modify the RWU scheme of the Common Land Model to quantify the role of low soil temperature stress on water and energy exchange between land and atmosphere. The simulated water and energy fluxes are evaluated using both in situ and global observational data sets. The results from in situ simulations show that ignoring effects of low soil temperature stress, latent, and sensible heat fluxes in spring are overestimated and underestimated, respectively, with the root mean square error up to 40 W/m2. By incorporating the low soil temperature stress functions into the RWU scheme, nearly 40% of the simulated errors are reduced. The global simulated results also highlight the importance of accounting for low soil temperature stress on increasing the accuracy of the modeled latent heat flux over high latitude areas. While uncertainties from related physical processes and parameters warrant further investigations, our results indicate that consideration of low soil temperature stress significantly affects water and energy transport from land to atmosphere by restricting RWU rate, emphasizing the need to integrate it in LSMs to increase the model reliability, especially over cold regions.

Integration of a Building Energy Model in an Urban Climate Model and its Application

We report the ability of an urban canopy model, coupled with a regional climate model, to simulate energy fluxes, the intra-urban variability of air temperature, urban-heat-island characteristics, indoor temperature variation, as well as anthropogenic heat emissions, in Berlin, Germany. A building energy model is implemented into the Double Canyon Effect Parametrization, which is coupled with the mesoscale climate model COSMO-CLM (COnsortium for Small-scale MOdelling in CLimate Mode) and takes into account heat generation within buildings and calculates the heat transfer between buildings and the urban atmosphere. The enhanced coupled urban model is applied in two simulations of 24-day duration for a winter and a summer period in 2018 in Berlin, using downscaled reanalysis data to a final grid spacing of 1 km. Model results are evaluated with observations of radiative and turbulent energy fluxes, 2-m air temperature, and indoor air temperature. The evaluation indicates that the improved model reproduces the diurnal characteristics of the observed turbulent heat fluxes, and considerably improves the simulated 2-m air temperature and urban heat island in winter, compared with the simulation without the building energy model. Our set-up also estimates the spatio–temporal variation of wintertime energy consumption due to heating with canyon geometry. The potential to save energy due to the urban heat island only becomes evident when comparing a suburban site with an urban site after applying the same grid-cell values for building and street widths. In summer, the model realistically reproduces the indoor air temperature and its temporal variation.

Seasonal Adaptation of the Thermal-Based Two-Source Energy Balance Model for Estimating Evapotranspiration in a Semiarid Tree-Grass Ecosystem

The thermal-based two-source energy balance (TSEB) model has accurately simulated energy fluxes in a wide range of landscapes with both remote and proximal sensing data. However, tree-grass ecosystems (TGE) have notably complex heterogeneous vegetation mixtures and dynamic phenological characteristics presenting clear challenges to earth observation and modeling methods. Particularly, the TSEB modeling structure assumes a single vegetation source, making it difficult to represent the multiple vegetation layers present in TGEs (i.e., trees and grasses) which have different phenological and structural characteristics. This study evaluates the implementation of TSEB in a TGE located in central Spain and proposes a new strategy to consider the spatial and temporal complexities observed. This was based on sensitivity analyses (SA) conducted on both primary remote sensing inputs (local SA) and model parameters (global SA). The model was subsequently modified considering phenological dynamics in semi-arid TGEs and assuming a dominant vegetation structure and cover (i.e., either grassland or broadleaved trees) for different seasons (TSEB-2S). The adaptation was compared against the default model and evaluated against eddy covariance (EC) flux measurements and lysimeters over the experimental site. TSEB-2S vastly improved over the default TSEB performance decreasing the mean bias and root-mean-square-deviation (RMSD) of latent heat (LE) from 40 and 82 W m−2 to −4 and 59 W m−2, respectively during 2015. TSEB-2S was further validated for two other EC towers and for different years (2015, 2016 and 2017) obtaining similar error statistics with RMSD of LE ranging between 57 and 63 W m−2. The results presented here demonstrate a relatively simple strategy to improve water and energy flux monitoring over a complex and vulnerable landscape, which are often poorly represented through remote sensing models.

Multi-year surface radiative properties and vegetation parameters for hydrologic modeling in regions of complex terrain—Methodology and evaluation over the Integrated Precipitation and Hydrology Experiment 2014 domain

Study regionSoutheast US (SE US). Study focusThis study probes the propagation of errors in standard remote-sensing vegetation products caused by cloud contamination and the impact of time-variant radiative properties for correctly describing land-surface properties in hydrologic models. Spatiotemporally-varying quality-controlled vegetation attributes (i.e., leaf area index and fractional vegetation coverage) and surface radiative properties (i.e., longwave broadband emissivity and shortwave broadband albedo) were derived from MODIS (Moderate Resolution Imaging Spectroradiometer) products over the SE US at 1 km × 1 km and hourly resolutions from 2007 to 2013. The data sets are publicly available. The impact of uncorrected standard vegetation products and static treatments of radiative properties was assessed systematically clearly illustrating improvements in simulated water and energy fluxes using the developed landscape attributes with a fully-distributed uncalibrated hydrologic model. New hydrological insights for the regionThrough simulations in the Southern Appalachian Mountains, we found that the spatiotemporal variability of radiative properties significantly influences the diurnal cycle of the surface energy budget with marked differences in sensible heat fluxes (up to 10–20%). Better performance of streamflow simulations achieved by using the improved vegetation attributes is tied to changes in rainfall interception and evapotranspiration, reflecting the importance of SE forests in the regional water cycle. The largest improvements in streamflow simulations result from larger corrections to MODIS products in the inner mountain region where cloudiness is persistent.

Optimization of laser-driven cylindrical implosions on the OMEGA laser

Laser-driven cylindrical implosions were conducted on the OMEGA laser as part of the laser-driven mini-MagLIF (Magnetized Liner Inertial Fusion) Campaign. Gated x-ray images were analyzed to infer shell trajectories and study the energy coupling in these implosions. Two-dimensional and three-dimensional HYDRA simulations were performed and post-processed to produce synthetic x-ray self-emission images for comparison. An analysis technique, which could be applied to both experimental and simulated x-ray images, was developed to characterize the shape and uniformity of the implosion. The analysis leads to a measurement of the average implosion velocity and axial implosion length, which can then be used to optimize the beam pointing and energy balance for future experiments. Discrepancies between simulation results and experiments allude to important physical processes that are not accounted for in the simulations. In 2-D simulations, the laser beam's azimuthal angle of incidence is not included because the ϕ-direction is not simulated, and thus, energy absorption is over-predicted. The 3-D simulation results are more consistent with the experiments, but the simulations do not include the calculation of cross-beam energy transfer or non-local thermal transport, which affects the energy coupled to the implosion. By appropriately adjusting the simulated energy balance and flux limit, the simulations can accurately model the experiments, which have achieved uniform implosions over a 700-μm-long region at velocities of approximately 200 km/s.

Biases in Model-Simulated Surface Energy Fluxes During the Indian Monsoon Onset Period

We use eddy-covariance measurements over a semi-natural grassland in the central Indo-Gangetic Basin to investigate biases in energy fluxes simulated by the Noah land-surface model for two monsoon onset periods: one with rain (2016) and one completely dry (2017). In the preliminary run with default parameters, the offline Noah LSM overestimates the midday (1000–1400 local time) sensible heat flux (H) by 279% (in 2016) and 108% (in 2017) and underestimates the midday latent heat flux (LE) by 56% (in 2016) and 67% (in 2017). These discrepancies in simulated energy fluxes propagate to and are amplified in coupled Weather Research and Forecasting model simulations, as seen from the High Asia Reanalysis dataset. One-dimensional Noah simulations with modified site-specific vegetation parameters not only improve the partitioning of the energy fluxes (Bowen ratio of 0.9 in modified run versus 3.1 in the default run), but also reduce the overestimation of the model-simulated soil and skin temperature. Thus, use of ambient site parameters in future studies is warranted to reduce uncertainties in short-term and long-term simulations over this region. Finally, we examine how biases in the model simulations can be attributed to lack of closure in the measured surface energy budget. The bias is smallest when the sensible heat flux post-closure method is used (5.2 $$\hbox {W } \hbox {m}^{-2}$$ for H and 16 $$\hbox {W } \hbox {m}^{-2}$$ for LE in 2016; 0.17 $$\hbox {W } \hbox {m}^{-2}$$ for H and 2.8 $$\hbox {W } \hbox {m}^{-2}$$ for LE in 2017), showing the importance of taking into account the surface energy imbalance at eddy-covariance sites when evaluating land-surface models.

Vegetation Growth Models Improve Surface Layer Flux Simulations of a Temperate Grassland

Core Ideas Detailed description of plant growth dynamics improves heat flux simulations. Harvest cannot be neglected to adequately simulate boundary layer energy fluxes. Complex plant growth models improve flux exchanges under drought conditions. Grassland models represent interactions of plant growth with soil and agricultural management based on underlying processes in different degrees of detail. To better understand the impact of these differences on the simulation of energy and matter exchange at the land‐surface layer, we compared the ability of five land‐surface models with different degrees of complexity to simulate energy fluxes in an intensively managed grassland in Switzerland. The aim was to evaluate the impacts of biomass growth, biomass harvest, soil profile characterization, and rooting depth on the dynamics of simulated near‐surface soil moisture contents and energy fluxes. The case study included a comparison of model results with continuous observations of latent heat, sensible heat, and net radiation for a site‐year. Energy fluxes were simulated more accurately by including a biomass growth model, encompassing the abrupt decline in leaf area caused by harvest. Site‐specific soil parametrization in combination with the absence of restrictions on rooting depth also improved the simulation results. The simulated energy fluxes of the five models differed significantly in the hot, dry month of July 2010 but were negligible under moist conditions in May. We conclude that the application of dynamic vegetation growth models improves energy flux simulations at the field scale in intensively managed grasslands during summer if biomass harvest dates and site‐specific soil profile descriptions are considered. Our results imply that regional‐scale simulations of grasslands will benefit significantly from high‐resolution input information on soil properties, land use, and management.

Evaluating common land model energy fluxes using FLUXNET data

Given the crucial role of land surface processes in global and regional climates, there is a pressing need to test and verify the performance of land surface models via comparisons to observations. In this study, the eddy covariance measurements from 20 FLUXNET sites spanning more than 100 site-years were utilized to evaluate the performance of the Common Land Model (CoLM) over different vegetation types in various climate zones. A decomposition method was employed to separate both the observed and simulated energy fluxes, i.e., the sensible heat flux, latent heat flux, net radiation, and ground heat flux, at three timescales ranging from stepwise (30 min) to monthly. A comparison between the simulations and observations indicated that CoLM produced satisfactory simulations of all four energy fluxes, although the different indexes did not exhibit consistent results among the different fluxes. A strong agreement between the simulations and observations was found for the seasonal cycles at the 20 sites, whereas CoLM underestimated the latent heat flux at the sites with distinct dry and wet seasons, which might be associated with its weakness in simulating soil water during the dry season. CoLM cannot explicitly simulate the midday depression of leaf gas exchange, which may explain why CoLM also has a maximum diurnal bias at noon in the summer. Of the eight selected vegetation types analyzed, CoLM performs best for evergreen broadleaf forests and worst for croplands and wetlands.

Massive outflows driven by magnetic effects in star-forming clouds with high mass accretion rates

The relation between the mass accretion rate onto the circumstellar disc and the rate of mass ejection by magnetically driven winds is investigated using three-dimensional magnetohydrodynamics simulations. Using a spherical cloud core with a varying ratio of thermal to gravitational energy, which determines the mass accretion rate onto the disc, to define the initial conditions, the outflow propagation for approximately 10^4 yr after protostar formation is then calculated for several cloud cores. The mass ejection rate and accretion rate are comparable only when the magnetic energy of the initial cloud core is comparable to the gravitational energy. Consequently, in strongly magnetised clouds a higher mass accretion rate naturally produces both massive protostars and massive outflows. The simulated outflow mass, momentum, kinetic energy and momentum flux agree well with observations, indicating that massive stars form through the same mechanism as low-mass stars but require a significantly strong magnetic field to launch massive outflows.

Integrating peatlands into the coupled Canadian Land Surface Scheme (CLASS) v3.6 and the Canadian Terrestrial Ecosystem Model (CTEM) v2.0

Abstract. Peatlands, which contain large carbon stocks that must be accounted for in the global carbon budget, are poorly represented in many earth system models. We integrated peatlands into the coupled Canadian Land Surface Scheme (CLASS) and the Canadian Terrestrial Ecosystem Model (CTEM), which together simulate the fluxes of water, energy, and CO2 at the land surface–atmosphere boundary in the family of Canadian Earth system models (CanESMs). New components and algorithms were added to represent the unique features of peatlands, such as their characteristic ground floor vegetation (mosses), the slow decomposition of carbon in the water-logged soils and the interaction between the water, energy, and carbon cycles. This paper presents the modifications introduced into the CLASS–CTEM modelling framework together with site-level evaluations of the model performance for simulated water, energy and carbon fluxes at eight different peatland sites. The simulated daily gross primary production (GPP) and ecosystem respiration are well correlated with observations, with values of the Pearson correlation coefficient higher than 0.8 and 0.75 respectively. The simulated mean annual net ecosystem production at the eight test sites is 87 g C m−2 yr−1, which is 22 g C m−2 yr−1 higher than the observed annual mean. The general peatland model compares well with other site-level and regional-level models for peatlands, and is able to represent bogs and fens under a range of climatic and geographical conditions.

Validation studies of gyrokinetic ITG and TEM turbulence simulations in a JT-60U tokamak using multiple flux matching

Quantitative validation studies of flux-tube gyrokinetic Vlasov simulations on ion and electron heat transport are carried out for the JT-60U tokamak experiment. The ion temperature gradient (ITG) and/or trapped electron modes (TEM) driven turbulent transport and zonal flow generations are investigated for an L-mode plasma in the local turbulence limit with a sufficiently small normalized ion thermal gyroradius and weak mean radial electric fields. Nonlinear turbulence simulations by the GKV code successfully reproduce radial profiles of the ion and electron energy fluxes in the core region. The numerical results show that the TEM-driven zonal flow generation in the outer region is more significant than that in the core region with ITG- and ITG–TEM-dominated turbulence, leading to moderate transport shortfall of the ion energy flux. Error levels in the prediction of the ion and electron temperature gradient profiles in the core region are estimated as less than , based on a multiple flux matching technique, where the simulated ion and electron energy fluxes are simultaneously matched to the experimental values.

Lake–river and lake–atmosphere interactions in a changing climate over Northeast Canada

Lakes influence the regional climate and hydrology in a number of ways and therefore they should be represented in climate models in a realistic manner. Lack of representation of lakes in models can lead to errors in simulated energy and water fluxes, for lake-rich regions. This study focuses on the assessment of the impact of climate change on lakes and hydrology as well as on the influence of lakes on projected changes to regional climate and surface hydrology, particularly streamflows, for Northeast Canada. To this end, transient climate change simulations spanning the 1950–2100 period are performed, with and without lakes, with the fifth generation of the Canadian Regional Climate Model (CRCM5), driven by the Canadian Earth System Model (CanESM2) at the lateral boundaries for Representative Concentration Pathway 8.5. An additional CRCM5 simulation, driven by European Centre for Medium-Range Weather Forecasts Re-Analysis Interim (ERA-Interim) for the 1980–2010 period, is performed in order to assess performance and boundary forcing errors. Performance errors are assessed by comparing the ERA-Interim-driven simulation with available observation datasets, for the 1980–2010 period, for selected variables: 2-m air temperature, total precipitation, snow water equivalent and streamflow. The validation results indicate reasonable model performance over the study region. Boundary forcing errors are studied by comparing ERA-Interim-driven simulation with the one driven by CanESM2 for the current 1980–2010 period, to identify regions and seasons for which projected changes should be interpreted with extra caution. Comparison of projected changes from the CRCM5 simulations with and without lakes suggest that the presence of lakes results in a dampening of projected increases to 2-m air temperature for all seasons almost everywhere in the study domain, with maximum dampening of the order of 2 °C occurring during winter, mostly in the vicinity of the lakes. As for streamflows, projected increases to spring streamflows, based on the simulation with lakes, are found to be smaller than that without lakes and this is due to the storage effect of lakes. Similarly, lower decreases in summer streamflows in future climate are noted in the simulation with lakes due to the gradual release of snowmelt water stored in lakes. An additional CRCM5 transient climate change simulation with lakes and interflow, i.e. lateral flow in the soil layers, is compared with the simulation with lakes, but without interflow, to assess the impact of interflow on projected changes to regional climate and hydrology. Maximum interflow is projected to shift earlier in spring and the maximum interflow rate is expected to decrease by around 25 % in future. Results suggest that the impact of interflow on projected changes to precipitation, soil moisture and humidity are modest, even though the interflow intensity is changing noticeably in future climate. The impact of the interflow on projected changes to streamflows is in the range of ±50 m3/s. This study thus for the first time demonstrates the impact of lakes and interflow on projected changes to the regional climate and hydrology for the study region using a single regional modelling system.

Effects of root water uptake formulation on simulated water and energy budgets at local and basin scales

Roots connect water stored beneath the Earth’s surface to water in the atmosphere. The fully integrated hydrologic model ParFlow coupled to the Common Land Model is used to investigate the influence of the root uptake formulation on simulated water and energy fluxes and budgets at local and watershed scales. The effects of four functional representations of vegetation water stress and plant wilting behavior are evaluated in the semi-arid Little Washita watershed of the Southern Great Plains, USA. Monthly mean latent and sensible heat fluxes differ by more than 25 W m−2 over much of the study area during hot, dry summer conditions. This difference indicates that the root uptake formulation has a substantial impact on simulated land energy fluxes and land–atmosphere interactions. Differences in annual evapotranspiration and stream discharge over the watershed exceed 14.5 and 55.5 % between simulations, respectively, demonstrating significant impacts on simulated water budgets. Notably, the analysis reveals that spatial variability in the sensitivity of local-scale water and energy fluxes to root uptake formulation is primarily driven by feedbacks between water table dynamics, soil moisture, and land energy fluxes. These results have important implications for model development, calibration, and validation.

Impact of future urbanization on a hot summer: a case study of Israel

Israel’s population is projected to increase significantly through the middle of the current century, requiring further expansion of the built environment to accommodate additional inhabitants and accompanying urban infrastructure. This study examines the climatic impacts of future urban expansion through simulated near-surface temperature and energy flux components associated with built environment growth. The Weather Research and Forecasting model was used to simulate present day extreme summertime conditions, at 1-km resolution, utilizing contemporary urban representation. To determine impacts associated with the physical growth of the urban environment, sensitivity simulations, also at 1-km resolution, incorporating projected changes in urban areas for Israel-based national development plans, were performed. Spatially and diurnally averaged at the national scale, projected urbanization is shown to increase summertime temperatures 0.4–0.8 °C, with greater temperature rise in northern compared to southern parts of the country. Across the diurnal cycle, urban impacts on near-surface warming are minimal during daytime hours, but exceed 3 °C across many urban locales during nighttime hours. The results presented here demonstrate the spatio-temporal impact of future urban expansion in Israel on temperature. The magnitude of these changes highlight the need for strategically designed regional and national planning to alleviate potentially deleterious climatic impacts associated with the physical growth of the built environment.

Evaluating the dual‐boundary forcing concept in subsurface–land surface interactions of the hydrological cycle

AbstractSubsurface and land surface processes (e.g. groundwater flow, evapotranspiration) of the hydrological cycle are connected via complex feedback mechanisms, which are difficult to analyze and quantify. In this study, the dual‐boundary forcing concept that reveals space–time coherence between groundwater dynamics and land surface processes is evaluated. The underlying hypothesis is that a simplified representation of groundwater dynamics may alter the variability of land surface processes, which may eventually affect the prognostic capability of a numerical model. A coupled subsurface–land surface model ParFlow.CLM is applied over the Rur catchment, Germany, and the mass and energy fluxes of the coupled water and energy cycles are simulated over three consecutive years considering three different lower boundary conditions (dynamic, constant, and free‐drainage) based on groundwater dynamics to substantiate the aforementioned hypothesis. Continuous wavelet transform technique is applied to analyze scale‐dependent variability of the simulated mass and energy fluxes. The results show clear differences in temporal variability of latent heat flux simulated by the model configurations with different lower boundary conditions at monthly to multi‐month time scales (~32–91 days) especially under soil moisture limited conditions. The results also suggest that temporal variability of latent heat flux is affected at even smaller time scales (~1–3 days) if a simple gravity drainage lower boundary condition is considered in the coupled model. This study demonstrates the importance of a physically consistent representation of groundwater dynamics in a numerical model, which may be important to consider in local weather prediction models and water resources assessments, e.g. drought prediction. Copyright © 2015 John Wiley & Sons, Ltd.