Cumulative ozone effect on canopy stomatal resistance and the impact on boundary layer dynamics and CO2 assimilation at the diurnal scale: A case study for grassland in the Netherlands
Super, I. ; Vilà-Guerau De Arellano, J. ; Krol, M.C. - \ 2015
Journal of Geophysical Research: Biogeosciences 120 (2015). - ISSN 2169-8953 - p. 1348 - 1365.
climate-change - soil-moisture - vegetation - exposure - drought - yield - l. - conductance - sensitivity - atmosphere
Biological, chemical, and dynamical processes occurring at the surface strongly interact at diurnal scales. Therefore, this study examines the seasonal ozone impact on stomatal resistance, surface energy balance, boundary layer dynamics, and CO2 assimilation at this (sub)diurnal scale under changing conditions. We combine a seasonal canopy resistance module with a surface-boundary layer model that solves the diurnal evolution of dynamical and chemical variables in a well-mixed, convective boundary layer. The model is constrained with observations from Cabauw (Netherlands) for the dry year 2003, representing a well-mixed boundary layer at midlatitudes over water-stressed grassland. To quantify the ozone impact, the Cumulative Uptake of Ozone is calculated over a growing season, which gives an estimate of the reduction in stomatal aperture and photosynthesis. From a sensitivity analysis with mixed-layer temperature and soil moisture content we conclude that drought is the dominant factor that determines the surface energy partitioning and limits CO2 assimilation. Although drought causes stomatal closure, the results indicate that ozone damage, nevertheless, occurs. A second sensitivity analysis with CO2 and ozone shows that ozone damage causes an increase in stomatal resistance of up to 40% under high ozone levels and that CO2-induced stomatal closure limits ozone damage. The impact on boundary layer development through the effect of CO2 and ozone on the stomatal resistance is much smaller. At the diurnal scale soil moisture influences the surface energy partitioning, which affects the entrainment of ozone-rich air. Due to ozone damage, the CO2 assimilation flux is reduced by about 15%.
Two perspectives on the coupled carbon, water and energy exchange in the planetary boundary layer
Combe, M. ; Vilà-Guerau De Arellano, J. ; Ouwersloot, H.G. ; Jacobs, C.M.J. ; Peters, W. - \ 2015
Biogeosciences 12 (2015). - ISSN 1726-4170 - p. 103 - 123.
ensemble kalman filter - land-surface model - leaf-area index - soil-moisture - use efficiency - climate-change - crop model - stomatal conductance - data assimilation - plant geography
Understanding the interactions between the land surface and the atmosphere is key to modelling boundary-layer meteorology and cloud formation, as well as carbon cycling and crop yield. In this study we explore these interactions in the exchange of water, heat and CO2 in a cropland–atmosphere system at the diurnal and local scale. To that end, we couple an atmospheric mixed-layer model (MXL) to two land-surface schemes developed from two different perspectives: while one land-surface scheme (A-gs) simulates vegetation from an atmospheric point of view, the other (GECROS) simulates vegetation from a carbon-storage point of view. We calculate surface fluxes of heat, moisture and carbon, as well as the resulting atmospheric state and boundary-layer dynamics, over a maize field in the Netherlands, on a day for which we have a rich set of observations available. Particular emphasis is placed on understanding the role of upper-atmosphere conditions like subsidence in comparison to the role of surface forcings like soil moisture. We show that the atmospheric-oriented model (MXL-A-gs) outperforms the carbon storage-oriented model (MXL-GECROS) on this diurnal scale. We find this performance is partly due to the difference of scales at which the models were made to run. Most importantly, this performance strongly depends on the sensitivity of the modelled stomatal conductance to water stress, which is implemented differently in each model. This sensitivity also influences the magnitude of the surface fluxes of CO2, water and heat (surface control) and subsequently impacts the boundary-layer growth and entrainment fluxes (upper atmosphere control), which alter the atmospheric state. These findings suggest that observed CO2 mole fractions in the boundary layer can reflect strong influences of both the surface and upper-atmosphere conditions, and the interpretation of CO2 mole fraction variations depends on the assumed land-surface coupling. We illustrate this with a sensitivity analysis where high subsidence and soil moisture depletion, typical for periods of drought, have competing and opposite effects on the boundary-layer height h. The resulting net decrease in h induces a change of 12 ppm in the late-afternoon CO2 mole fraction. Also, the effect of such high subsidence and soil moisture depletion on the surface Bowen ratio are of the same magnitude. Thus, correctly including such two-way land-surface interactions on the diurnal scale can potentially improve our understanding and interpretation of observed variations in atmospheric CO2, as well as improve crop yield forecasts by better describing the water loss and carbon gain.
Land surface feedbacks on spring precipitation in the Netherlands
Daniels, E.E. ; Hutjes, R.W.A. ; Lenderink, G. ; Ronda, R.J. ; Holtslag, A.A.M. - \ 2015
Journal of Hydrometeorology 16 (2015). - ISSN 1525-755X - p. 232 - 243.
urban heat-island - soil-moisture - coastal precipitation - aerosol impacts - canopy model - climate - urbanization - europe - rainfall - wrf
In this paper the Weather Research and Forecasting (WRF) model is used to investigate the sensitivity of precipitation to soil moisture and urban areas in the Netherlands. We analyze the average output of a four day event from 10-13 May 1999 for which the individual days had similar synoptical forcing. Four simulations are conducted to test the impact of soil moisture changes on precipitation. We find a positive soil moisture-precipitation feedback, i.e. wet (dry) soils increase (decrease) the amount of precipitation. We execute two additional experiments in which urban areas in the Netherlands are expanded and one in which urban areas are completely removed. Expansion of urban areas results in an increase of the sensible heat flux and a deeper planetary boundary layer, similar to reducing soil moisture. Expanding urban areas reduces precipitation over the Netherlands as a whole, but the local response is not clear. Within existing urban areas, mean and maximum temperature increases of respectively 0.4 and 2 K are found under an urban coverage scenario for 2040. The ratio of evaporation to precipitation (a measure of the soil moisture-precipitation feedback) in the urbanization experiments is only about one third (23%) of that in the soil moisture experiments (67%). Triggering of precipitation, on the other hand, is relatively high in the urban expansion experiments. The effects of reduced moisture availability and enhanced triggering in the urban expansion experiments compensate each other, leading to the moderate reduction in precipitation.
The Wageningen Lowland Runoff Simulator (WALRUS): a lumped rainfall-runoff model for catchments with shallow groundwater
Brauer, C.C. ; Teuling, A.J. ; Torfs, P.J.J.F. ; Uijlenhoet, R. - \ 2014
Geoscientific Model Development 7 (2014)5. - ISSN 1991-959X - p. 2313 - 2332.
flow route contributions - surface water interactions - soil-moisture - process conceptualization - hydrological models - root-growth - tile drain - scale - calibration - discharge
We present the Wageningen Lowland Runoff Simulator (WALRUS), a novel rainfall-runoff model to fill the gap between complex, spatially distributed models which are often used in lowland catchments and simple, parametric (conceptual) models which have mostly been developed for sloping catchments. WALRUS explicitly accounts for processes that are important in lowland areas, notably (1) groundwater-unsaturated zone coupling, (2) wetness-dependent flow routes, (3) groundwater-surface water feedbacks and (4) seepage and surface water supply. WALRUS consists of a coupled groundwater-vadose zone reservoir, a quickflow reservoir and a surface water reservoir. WALRUS is suitable for operational use because it is computationally efficient and numerically stable (achieved with a flexible time step approach). In the open source model code default relations have been implemented, leaving only four parameters which require calibration. For research purposes, these defaults can easily be changed. Numerical experiments show that the implemented feedbacks have the desired effect on the system variables.
Effects of Irrigation in India on the Atmospheric Water Budget
Tuinenburg, O.A. ; Hutjes, R.W.A. ; Stacke, T. ; Wiltshire, A. ; Lucas-Picher, P. - \ 2014
Journal of Hydrometeorology 15 (2014)3. - ISSN 1525-755X - p. 1028 - 1050.
soil-moisture - part i - precipitation - climate - monsoon - scheme - models - cycle - parameterization - representation
The effect of large-scale irrigation in India on the moisture budget of the atmosphere was investigated using three regional climate models and one global climate model, all of which performed an irrigated run and a natural run without irrigation. Using a common irrigation map, year-round irrigation was represented by adding water to the soil moisture to keep it at 90% of the maximum soil moisture storage capacity, regardless of water availability. For two focus regions, the seasonal cycle of irrigation matched that of the reference dataset, but irrigation application varied between the models by up to 0.8 mm day(-1). Because of the irrigation, evaporation increased in all models, but precipitation decreased because of a strong decrease in atmospheric moisture convergence. A moisture tracking scheme was used to track individual evaporated moisture parcels through the atmosphere to determine where these lead to precipitation. Up to 35% of the evaporation moisture from the Ganges basin is recycling within the river basin. However, because of a decreased moisture convergence into the river basin, the total amount of precipitation in the Ganges basin decreases. Although a significant fraction of the evaporation moisture recycles within the river basin, the changes in large-scale wind patterns due to irrigation shift the precipitation from the eastern parts of India and Nepal to the northern and western parts of India and Pakistan. In these areas where precipitation increases, the relative precipitation increase is larger than the relative decrease in the areas where precipitation decreases. It is concluded 1) that the direct effects of irrigation on precipitation are small and are not uniform across the models; 2) that a fraction of up to 35% of any marginal evaporation increase (for example, due to irrigation) will recycle within the river basin; and 3) that when irrigation is applied on a large scale, the dominant effect will be a change in large-scale atmospheric flow that decreases precipitation in eastern India and increases it in western and northern India.
Contribution of Dynamic Vegetation Phenology to Decadal Climate Predictability
Weiss, M. ; Miller, P.A. ; Hurk, B.J.J.M. van den; Noije, T. van; Stefanescu, S. ; Haarsma, R. ; Ulft, L.H. van; Hazeleger, W. ; Sager, P. Le; Smith, B. ; Schurgers, G. - \ 2014
Journal of Climate 27 (2014)22. - ISSN 0894-8755 - p. 8563 - 8577.
leaf-area index - ensemble forecasts - data assimilation - soil-moisture - model - prediction - system - impact - skill - oscillation
In this study, the impact of coupling and initializing the leaf area index from the dynamic vegetation model Lund-Potsdam-Jena General Ecosystem Simulator (LPJ-GUESS) is analyzed on skill of decadal predictions in the fully coupled atmosphere-land-ocean-sea ice model, the European Consortium Earth System Model (EC-Earth). Similar to the impact of initializing the model with the observed oceanic state, initializing the leaf area index (LAI) fields obtained from an offline LPJ-GUESS simulation forced by the observed atmospheric state leads to a systematic drift. A different treatment of the water and soil moisture budget in LPJ-GUESS is a likely cause of this drift. The coupled system reduces the cold bias of the reference model over land by reducing LAI (and the associated evaporative cooling), particularly outside the growing season. The coupling with the interactive vegetation module implies more degrees of freedom in the coupled model, which generates more noise that can mask a portion of the extra signal that is generated. The forecast reliability improves marginally, particularly early in the forecast. Ranked probability skill scores are also improved slightly in most areas analyzed, but the signal is not fully coherent over the forecast interval because of the relatively low number of ensemble members. Methods to remove the LAI drift and allow coupling of other variables probably need to be implemented before significant forecast skill can be expected.
Shallow cumulus rooted in photosynthesis
Vilà-Guerau De Arellano, J. ; Ouwersloot, H.G. ; Baldocchi, D. ; Jacobs, C.M.J. - \ 2014
Geophysical Research Letters 41 (2014)5. - ISSN 0094-8276 - p. 1796 - 1802.
heterogeneous land surfaces - boundary-layer - soil-moisture - gas-exchange - water - formulation - vegetation - clouds - fluxes - co2
We study the interactions between plant evapotranspiration, controlled by photosynthesis (C3 and C4 grasses), and moist thermals responsible for the formation of shallow cumulus clouds (SCu). Our findings are based on a series of systematic numerical experiments at fine spatial and temporal scales using large eddy simulations explicitly coupled to a plant-physiology model. The shading provided by SCu leads to strong spatial variability in photosynthesis and the surface energy balance. This in turn results in SCu characterized by less extreme and less skewed values of liquid water path. The larger water use efficiency of C4 grass leads to two opposite effects that influence boundary layer clouds: more vigorous and deeper thermals due to the larger buoyancy surface flux (positive effect) characterized by less moisture content (negative). We find that under these midlatitude and well-watered soil conditions, SCu are characterized by a larger cloud cover and liquid water path over C4 grass fields.
Subcloud-Layer Feedbacks Driven by the Mass Flux of Shallow Cumulus Convection over Land
Stratum, B.J.H. van; Vilà-Guerau De Arellano, J. ; Heerwaarden, C.C. van; Ouwersloot, H.G. - \ 2014
Journal of the Atmospheric Sciences 71 (2014)3. - ISSN 0022-4928 - p. 881 - 895.
large-eddy simulation - capped boundary-layer - topped mixed layers - relative-humidity - daytime evolution - soil-moisture - part i - cloud - model - equilibrium
The processes and feedbacks associated with the mass flux of shallow cumulus clouds over land are studied by analyzing the results from large-eddy simulations and a mixed-layer model. The primary focus is to study the development of the (well mixed) subcloud layer and understand the four primary feedbacks between the subcloud-layer dynamics and cumulus mass flux. Guided by numerical experiments in large-eddy simulations that show the transition from clear to cloudy boundary layers at midlatitudes over land, the feedbacks introduced by shallow cumuli are first conceptually described. To study the complex interplay between the subcloud and cloud layer, a mixed-layer model is proposed and validated with large-eddy simulations for the Atmospheric Radiation Measurement Southern Great Plains case. The mixed-layer model is shown to identify and reproduce the most relevant feedbacks in the transition from clear to cloudy boundary layers: a reduced mixed-layer growth and drying of the subcloud layer by enhanced entrainment and mass flux transport of moisture to the cloud layer. To complete the study, the strength of the different feedbacks is further quantified by an analysis of the individual contributions to the tendency of the relative humidity at the top of the mixed layer.
Potassium applied under drought improves physiological and nutrient uptake performances of wheat (Triticum Aestivun L.)
Raza, M.A.S. ; Saleem, M.F. ; Shah, G.M. ; Jamil, M. ; Khan, I.H. - \ 2013
Journal of Soil Science and Plant Nutrition 13 (2013)1. - ISSN 0718-9516 - p. 175 - 185.
abiotic stresses - soil-moisture - crop yield - tolerance - plants - glycinebetaine - efficiency - system - zone
The physiological and nutrient uptake performance of two wheat (Triticum aestivum L.) cultivars (Lasani-2008 and Auqab-2000) to foliar application of 1% potassium (K) at three different growth stages (tillering, flower initiation and grain filling) was investigated under water limited environment in a wire house experiment at the Nuclear Institute for Agriculture and Biology, Faisalabad. The aim was to find out the best K application stage for improvement in drought tolerance potential. Drought stress was created by withholding irrigation at the three growth stages and then K was sprayed with carboxymethyl cellulose as a sticking agent, whereas Tween-20 was used as a surfactant for foliar spray. At maturity, aboveground nitrogen, phosphorus, K, sodium and calcium uptakes by the crop were measured. Besides, water potential, osmotic potential and turgor potential of crop were also estimated. The results indicated that the drought stress at all three critical growth stages of wheat adversely affected plant's nutrient uptake, water potential, osmotic potential and turgor potential of wheat plants. The exogenous application of K under drought stress at all three critical growth stages enhanced tolerance of wheat by reducing toxic nutrient's uptake and improving the physiological efficiency. In this regards, both varieties showed uniform behavior. Maximum improvement in all the recorded nutrients uptake and physiological parameters was achieved when K was applied at grain filling stage of both cultivars.
Land atmosphere feedbacks and their role in the water resources of the Ganges basin
Harding, R.J. ; Blyth, E.M. ; Tuinenburg, O.A. ; Wiltshire, A. - \ 2013
Science of the Total Environment 468-469 (2013). - ISSN 0048-9697 - p. S85 - S92.
asian summer monsoon - mixed-layer model - soil-moisture - climate-change - variability - evaporation - irrigation - precipitation - regions - scheme
The northern Indian subcontinent has frequently been identified as a hotspot for land atmosphere interactions. It is also a region with the highest concentration of irrigated land and highest (and increasing) population density in the world. The available water in the region with which to grow food depends on the Asian monsoon, groundwater and melt from Himalayan snows. Any changes or disruptions to these sources of water could threaten the food supply. It is therefore essential to understand how the land surface, and in particular irrigated land, interacts with the atmosphere. It is anticipated that the interactions will occur on many scales. To an extent the magnitude and form of these will depend on the depth of the atmosphere which is affected. Thus at the local, or micro, scale it is the surface layer (some 10s m deep) which is cooled and moistened by the evaporation of irrigated water, at the meso-scale the Planetary boundary layer (up to 1 or 2 km) will be modified with possible atmospheric moistening, increased cloud and rain formation and at very large scales the whole dynamics of the south Asian Monsoon will be affected. This illustrates a strong interaction between the Asian monsoon and the regional topography. Of considerable significance is the finding in this paper that up to 60% of the evaporation from irrigated areas in the summer months is ultimately recycled to Himalayan rainfall and so feedbacks to river flows in the Ganges. Crown Copyright (C) 2013 Published by Elsevier B.V. All rights reserved.
Estimating crop-specific evapotranspiration using remote-sensing imagery at various spatial resolutions for improving crop growth modelling
Sepulcre-Canto, G. ; Gellens-Meulenberghs, F. ; Arboleda, A. ; Duveiller, G. ; Wit, A.J.W. de; Eerens, H. ; Djaby, B. ; Defourny, P. - \ 2013
International Journal of Remote Sensing 34 (2013)9-10. - ISSN 0143-1161 - p. 3274 - 3288.
soil-moisture - index - china
By governing water transfer between vegetation and atmosphere, evapotranspiration (ET) can have a strong influence on crop yields. An estimation of ET from remote sensing is proposed by the EUMETSAT ‘Satellite Application Facility’ (SAF) on Land Surface Analysis (LSA). This ET product is obtained operationally every 30 min using a simplified SVAT scheme that uses, as input, a combination of remotely sensed data and atmospheric model outputs. The standard operational mode uses other LSA-SAF products coming from SEVIRI imagery (the albedo, the downwelling surface shortwave flux, and the downwelling surface longwave flux), meteorological data, and the ECOCLIMAP database to identify and characterize the land cover. With the overall objective of adapting this ET product to crop growth monitoring necessities, this study focused first on improving the ET product by integrating crop-specific information from high and medium spatial resolution remote-sensing data. A Landsat (30 m)-based crop type classification is used to identify areas where the target crop, winter wheat, is located and where crop-specific Moderate Resolution Imaging Spectroradiometer (MODIS) (250 m) time series of green area index (GAI) can be extracted. The SVAT model was run for 1 year (2007) over a study area covering Belgium and part of France using this supplementary information. Results were compared to those obtained using the standard operational mode. ET results were also compared with ground truth data measured in an eddy covariance station. Furthermore, transpiration and potential transpiration maps were retrieved and compared with those produced using the Crop Growth Monitoring System (CGMS), which is run operationally by the European Commission's Joint Research Centre to produce in-season forecast of major European crops. The potential of using ET obtained from remote sensing to improve crop growth modelling in such a framework is studied and discussed. Finally, the use of the ET product is also explored by integrating it in a simpler modelling approach based on light-use efficiency. The Carnegie–Ames–Stanford Approach (CASA) agroecosystem model was therefore applied to obtain net primary production, dry matter productivity, and crop yield using only LSA-SAF products. The values of yield were compared with those obtained using CGMS, and the dry matter productivity values with those produced at the Flemish Institute for Technological Research (VITO). Results showed the potential of using this simplified remote-sensing method for crop monitoring
Benchmark products for land evapotranspiration: LandFlux-EVAL multi-data set synthesis
Mueller, B. ; Hirschi, M. ; Jimenez, C. ; Ciais, P. ; Dirmeyer, P.A. ; Dolman, A.J. ; Fisher, J.B. ; Jung, M. ; Ludwig, F. ; Maignan, F. - \ 2013
Hydrology and Earth System Sciences 17 (2013). - ISSN 1027-5606 - p. 3707 - 3720.
reanalysis data - soil-moisture - global-scale - surface - climate - trends - model - 20th-century - variability - evaporation
Land evapotranspiration (ET) estimates are available from several global datasets. Here, monthly global land ET synthesis products, merged from these individual datasets over the time periods 1989–1995 (7 yr) and 1989–2005 (17 yr), are presented. The 5 merged synthesis products over the shorter period are based on a total of 40 distinct datasets while those over the longer period are based on a total of 14 datasets. In the individual datasets, ET is derived from satellite and/or in-situ observations (diagnostic datasets) or calculated via land-surface models (LSMs) driven with observationsbased forcing and atmospheric reanalyses. Statistics for four merged synthesis prod10 ucts are provided, one including all datasets and three including only datasets from one category each (diagnostic, LSMs, and reanalyses). The multi-annual variations of ET in the merged synthesis products display realistic responses. They are also consistent with previous findings of a global increase in ET between 1989 and 1997 (1.15mmyr-2 in our merged product) followed by a decrease in this trend (-1.40mmyr-2), although 15 these trends are relatively small compared to the uncertainty of absolute ET values. The global mean ET from the merged synthesis products (based on all datasets) is 1.35mm per day for both the 1989–1995 and 1989–2005 products, which is relatively low compared to previously published estimates. We estimate global runoff (precipitation minus ET) to 34 406 km3 per year for a total land area of 130 922 km2. Precipitation, 20 being an important driving factor and input to most simulated ET datasets, presents uncertainties between single datasets as large as those in the ET estimates. In order to reduce uncertainties in current ET products, improving the accuracy of the input variables, especially precipitation, as well as the parameterizations of ET are crucial.
Summer temperatures in Europe and land heat fluxes in observation-based data and regional climate simulations
Stegehuis, A.I. ; Vautard, R. ; Ciais, Ph. ; Teuling, A.J. ; Jung, P. - \ 2013
Climate Dynamics 41 (2013)2. - ISSN 0930-7575 - p. 455 - 477.
weather regimes - soil-moisture - variability - ensemble - precipitation - performance - heatwaves - surface - projections - reanalysis
The occurrence and intensity of heatwaves is expected to increase with climate change. Early warnings of hot summers have therefore a great socio-economical value. Previous studies have shown that hot summers are preceded by a Southern European rainfall deficit during winter, and higher spring temperatures. Changes in the surface energy budget are believed to drive this evolution, in particular changes in the latent and sensible heat fluxes. However these have rarely been investigated due to the lack of long-term reliable observation data. In this study, we analyzed several data-derived gridded products of latent and sensible heat fluxes, based on flux tower observations, together with re-analyses and regional climate model simulations over Europe. We find that warm summers are preceded by an increase in latent heat flux in early spring. During warm summers, an increase in available energy results in an excess of both latent and sensible heat fluxes over most of Europe, but a latent heat flux decrease over the Iberian Peninsula. This indicates that, on average, a summertime soil-moisture limited evapotranspiration regime only prevails in the Iberian Peninsula. In general, the models that we analyzed overestimate latent heat and underestimate sensible heat as compared to the flux tower derived data-product. Most models show considerable drying during warm seasons, leading to the establishment of a soil-moisture limited regime across Europe in summer. This over-estimation by the current generation of models of latent heat and hence of soil moisture deficit over Europe in summer has potential consequences for future summertime climate projections and the projected frequency of heat waves. We also show that a northward propagation of drought during warm summers is found in model results, a phenomenon which is also seen in the flux tower data-product. Our results lead to a better understanding of the role of latent and sensible heat flux in summer heatwaves, and provide a framework for benchmark of modeling studies.
Surface and atmospheric controls on the onset of moist convection over land
Gentine, P. ; Holtslag, A.A.M. ; Andrea, F. D'; Ek, M. - \ 2013
Journal of Hydrometeorology 14 (2013). - ISSN 1525-755X - p. 1443 - 1462.
large-eddy simulation - fraction diurnal behavior - probabilistic bulk model - coupled mixed-layer - boundary-layer - soil-moisture - evaporative fraction - relative-humidity - hydrologic perspective - spatial variability
The onset of moist convection over land is investigated using a conceptual approach with a slab boundary layer model. We here determine the essential factors for the onset of boundary layer clouds over land, and study their relative importance. They are: 1) the ratio of the temperature to the moisture lapse rates of the free troposphere, i.e. the inversion Bowen ratio, 2) the mean-daily surface temperature, 3) the relative humidity of the free troposphere and 4) the surface evaporative fraction. A clear transition is observed between two regimes of moistening of the boundary layer as assessed by the relative humidity at the boundary layer top. In the first so-called wet soil advantage regime, the moistening results from the increase of the mixed-layer specific humidity, which linearly depends on the surface evaporative fraction and inversion Bowen ratio through a dynamic boundary layer factor. In the second so-called dry soil advantage regime, the relative humidity tendency at the boundary layer top is controlled by the thermodynamics and changes in the moist adiabatic induced by the decreased temperature at the boundary layer top and consequent reduction in saturation water vapor pressure. This regime pertains for very deep boundary layers under weakly stratified free troposphere over hot surface conditions. In the context of the conceptual model, a rise in free-tropospheric temperature (global warming) increases the occurrence of deep convection and reduces the cloud cover over moist surfaces. This study provides new intuition and predictive capacity on the mechanism controlling the occurrence of moist convection over land
Diagnosing evaporative fraction over land from boundary-layer clouds
Gentine, P. ; Ferguson, C.R. ; Holtslag, A.A.M. - \ 2013
Journal of Geophysical Research: Atmospheres 118 (2013)15. - ISSN 2169-897X - p. 8185 - 8196.
large-aperture scintillometer - large-eddy simulation - relative-humidity - mixed-layer - cumulus convection - diurnal behavior - soil-moisture - atmosphere interaction - surface-temperature - spatial variability
The potential use of continental fair-weather shallow cumuli as a way to retrieve the daily surface evaporative fraction over land is evaluated in convective conditions. The proposed method utilizes the fact that both the timing of cloud occurrence and the cloud base height at the time of occurrence provide strong constraints on the surface energy balance and evaporative fraction. The retrieval is especially reliable in the presence of relatively stable and humid free troposphere profiles. The advantage of the method is that it provides a more direct estimate of the surface evaporative fraction than indirect estimation based on inversion of a highly parameterized land surface model. In addition, the evaporative fraction is obtained at a scale of a few kilometers, which is more pertinent for weather and climate studies. The retrieval strategy is tested and validated for three contrasting climates: the U.S. southern Great Plains, West Africa, and the Netherlands. We suggest that the use of satellite observations of shallow cumuli can help constrain the retrieval of the surface evaporative fraction within a data assimilation scheme/reanalysis
Stable atmospheric boundary layers and diurnal Cycles-Challenges for Weather and Climate Models
Holtslag, A.A.M. ; Svensson, G. ; Baas, P. ; Basu, S. ; Beare, B. ; Beljaars, A.C.M. ; Bosveld, F.C. ; Cuxart, J. ; Lindvall, J. ; Steeneveld, G.J. ; Tjernstrom, M. ; Wiel, B.J.H. van de - \ 2013
Bulletin of the American Meteorological Society 94 (2013). - ISSN 0003-0007 - p. 1691 - 1706.
low-level jets - land-surface - contrasting nights - soil-moisture - ecmwf model - sea-ice - turbulence - cases-99 - parameterization - fluxes
The representation of the atmospheric boundary layer is an important part of weather and climate models and impacts many applications such as air quality and wind energy. Over the years, the performance in modeling 2 m temperature and 10 m wind speed has improved but errors are still significant. This is in particular the case under clear skies and low wind-speed conditions at night as well as during winter in stably stratified conditions over land and ice. In this paper, we review these issues and provide an overview of the current understanding and model performance. Results from weather forecast and climate models are used to illustrate the state of the art, as well as findings and recommendations from three inter-comparison studies held within the “Global Energy and Water Exchanges (GEWEX)” Atmospheric Boundary Layer Study (GABLS). Within GABLS, the focus has been on the examination of the representation of the stable boundary layer and the diurnal cycle over land in clear sky conditions. For this purpose, single-column versions of weather and climate models have been compared with observations, research models and Large Eddy Simulations. The intercomparison cases are based on observations taken in the Arctic, Kansas and at Cabauw in the Netherlands. From these studies, we find that even for the non-cloudy boundary layer important parameterization challenges remain.
Exploring the Impact of Land Cover and Topography on Rainfall Maxima in the Netherlands
Maat, H.W. ter; Moors, E.J. ; Hutjes, R.W.A. ; Holtslag, A.A.M. ; Dolman, A.J. - \ 2013
Journal of Hydrometeorology 14 (2013)2. - ISSN 1525-755X - p. 524 - 542.
landgebruik - bossen - neerslag - bodemwater - simulatie - modellen - veluwe - land use - forests - precipitation - soil water - simulation - models - veluwe - climate-change - convective boundary - soil-moisture - surface - model - evaporation - prediction - diffusion - exchange
The relative contribution of topography and land use on precipitation is analyzed in this paper for a forested area in the Netherlands. This area has an average yearly precipitation sum that can be 75–100 mm higher than the rest of the country. To analyze this contribution, different configurations of land use and topography are fed into a mesoscale model. The authors use the Regional Atmospheric Modeling System (RAMS) coupled with a land surface scheme simulating water vapor, heat, and momentum fluxes [Soil–Water–Atmosphere Plant System–Carbon (SWAPS-C)]. The model simulations are executed for two periods that cover varying large-scale synoptic conditions of summer and winter periods. The output of the experiments leads to the conclusion that the precipitation maximum at the Veluwe is forced by topography and land use. The effect of the forested area on the processes that influence precipitation is smaller in summertime conditions when the precipitation has a convective character. In frontal conditions, the forest has a more pronounced effect on local precipitation through the convergence of moisture. The effect of topography on monthly domain-averaged precipitation around the Veluwe is a 17% increase in the winter and a 10% increase in the summer, which is quite remarkable for topography with a maximum elevation of just above 100 m and moderate steepness. From this study, it appears that the version of RAMS using Mellor–Yamada turbulence parameterization simulates precipitation better in wintertime, but the configuration with the medium-range forecast (MRF) turbulence parameterization improves the simulation of precipitation in convective circumstances.
Simultaneous assimilation of satellite and eddy covariance data for improving terrestrial water and carbon simulations at a semi-arid woodland site in Botswana
Kato, T. ; Knorr, W. ; Scholtze, M. ; Veenendaal, E.M. ; Kaminski, T. ; Kattge, J. ; Gobron, N. - \ 2013
Biogeosciences 10 (2013). - ISSN 1726-4170 - p. 789 - 802.
land-surface model - isba-a-gs - atmospheric co2 - soil-moisture - exchange - photosynthesis - transpiration - uncertainties - variability - biosphere
Terrestrial productivity in semi-arid woodlands is strongly susceptible to changes in precipitation, and semi-arid woodlands constitute an important element of the global water and carbon cycles. Here, we use the Carbon Cycle Data Assimilation System (CCDAS) to investigate the key parameters controlling ecological and hydrological activities for a semi-arid savanna woodland site in Maun, Botswana. Twenty-four eco-hydrological process parameters of a terrestrial ecosystem model are optimized against two data streams separately and simultaneously: daily averaged latent heat flux (LHF) derived from eddy covariance measurements, and decadal fraction of absorbed photosynthetically active radiation (FAPAR) derived from the Sea-viewing Wide Field-of-view Sensor (SeaWiFS). Assimilation of both data streams LHF and FAPAR for the years 2000 and 2001 leads to improved agreement between measured and simulated quantities not only for LHF and FAPAR, but also for photosynthetic CO2 uptake. The mean uncertainty reduction (relative to the prior) over all parameters is 14.9% for the simultaneous assimilation of LHF and FAPAR, 8.5% for assimilating LHF only, and 6.1% for assimilating FAPAR only. The set of parameters with the highest uncertainty reduction is similar between assimilating only FAPAR or only LHF. The highest uncertainty reduction for all three cases is found for a parameter quantifying maximum plant-available soil moisture. This indicates that not only LHF but also satellite-derived FAPAR data can be used to constrain and indirectly observe hydrological quantities.
Attributing the impacts of land-cover changes in temperate regions on surface temperature and heat fluxes to specific causes: Results from the first LUCID set of simulations
Boisier, J.P. ; Noblet-Ducoudré, N. de; Pitman, A.J. ; Cruz, F.T. ; Delire, C. ; Hurk, B.J.J.M. van den; Molen, M.K. van der; Müller, C. ; Voldoire, A. - \ 2012
Journal of Geophysical Research: Atmospheres 117 (2012)D12. - ISSN 2169-897X
climate system model - soil-moisture - sensitivity - feedbacks - forcings - exchange - forest - energy - biomes - albedo
Surface cooling in temperate regions is a common biogeophysical response to historical Land-Use induced Land Cover Change (LULCC). The climate models involved in LUCID show, however, significant differences in the magnitude and the seasonal partitioning of the temperature change. The LULCC-induced cooling is directed by decreases in absorbed solar radiation, but its amplitude is 30 to 50% smaller than the one that would be expected from the sole radiative changes. This results from direct impacts on the total turbulent energy flux (related to changes in land-cover properties other than albedo, such as evapotranspiration efficiency or surface roughness) that decreases at all seasons, and thereby induces a relative warming in all models. The magnitude of those processes varies significantly from model to model, resulting on different climate responses to LULCC. To address this uncertainty, we analyzed the LULCC impacts on surface albedo, latent heat and total turbulent energy flux, using a multivariate statistical analysis to mimic the models' responses. The differences are explained by two major ‘features’ varying from one model to another: the land-cover distribution and the simulated sensitivity to LULCC. The latter explains more than half of the inter-model spread and resides in how the land-surface functioning is parameterized, in particular regarding the evapotranspiration partitioning within the different land-cover types, as well as the role of leaf area index in the flux calculations. This uncertainty has to be narrowed through a more rigorous evaluation of our land-surface models.
A generic method for hydrological drought identification across different climate regions
Huijgevoort, M.H.J. van; Hazenberg, P. ; Lanen, H.A.J. van; Uijlenhoet, R. - \ 2012
Hydrology and Earth System Sciences 16 (2012). - ISSN 1027-5606 - p. 2437 - 2451.
environment simulator jules - conterminous united-states - soil-moisture - model description - multimodel ensemble - land-surface - 20th-century - precipitation - temperature - definition
The identification of hydrological drought at global scale has received considerable attention during the last decade. However, climate-induced variation in runoff across the world makes such analyses rather complicated. This especially holds for the drier regions of the world (both cold and warm), where, for a considerable period of time, zero runoff can be observed. In the current paper, we present a method that enables to identify drought at global scale across climate regimes in a consistent manner. The method combines the characteristics of the classical variable threshold level method that is best applicable in regions with non-zero runoff most of the time, and the consecutive dry days (period) method that is better suited for areas where zero runoff occurs. The newly presented method allows a drought in periods with runoff to continue in the following period without runoff. The method is demonstrated by identifying droughts from discharge observations of four rivers situated within different climate regimes, as well as from simulated runoff data at global scale obtained from an ensemble of five different land surface models. The identified drought events obtained by the new approach are compared to those resulting from application of the variable threshold level method or the consecutive dry period method separately. Results show that, in general, for drier regions, the threshold level method overestimates drought duration, because zero runoff periods are included in a drought, according to the definition used within this method. The consecutive dry period method underestimates drought occurrence, since it cannot identify droughts for periods with runoff. The developed method especially shows its relevance in transitional areas, because, in wetter regions, results are identical to the classical threshold level method. By combining both methods, the new method is able to identify single drought events that occur during positive and zero runoff periods, leading to a more realistic global drought characterization, especially within drier environments.