Altered energy partitioning across terrestrial ecosystems in the European drought year 2018
Graf, Alexander ; Klosterhalfen, Anne ; Arriga, Nicola ; Bernhofer, Christian ; Bogena, Heye ; Bornet, Frédéric ; Brüggemann, Nicolas ; Brümmer, Christian ; Buchmann, Nina ; Chi, Jinshu ; Chipeaux, Christophe ; Cremonese, Edoardo ; Cuntz, Matthias ; Dušek, Jiří ; El-Madany, Tarek S. ; Fares, Silvano ; Fischer, Milan ; Foltýnová, Lenka ; Gharun, Mana ; Ghiasi, Shiva ; Gielen, Bert ; Gottschalk, Pia ; Grünwald, Thomas ; Heinemann, Günther ; Heinesch, Bernard ; Heliasz, Michal ; Holst, Jutta ; Hörtnagl, Lukas ; Ibrom, Andreas ; Ingwersen, Joachim ; Jurasinski, Gerald ; Klatt, Janina ; Knohl, Alexander ; Koebsch, Franziska ; Konopka, Jan ; Korkiakoski, Mika ; Kowalska, Natalia ; Kremer, Pascal ; Kruijt, Bart ; Lafont, Sebastien ; Léonard, Joël ; Ligne, Anne De; Longdoz, Bernard ; Loustau, Denis ; Magliulo, Vincenzo ; Mammarella, Ivan ; Manca, Giovanni ; Mauder, Matthias ; Migliavacca, Mirco ; Mölder, Meelis ; Neirynck, Johan ; Ney, Patrizia ; Nilsson, Mats ; Paul-Limoges, Eugénie ; Peichl, Matthias ; Pitacco, Andrea ; Poyda, Arne ; Rebmann, Corinna ; Roland, Marilyn ; Sachs, Torsten ; Schmidt, Marius ; Schrader, Frederik ; Siebicke, Lukas ; Šigut, Ladislav ; Tuittila, Eeva Stiina ; Varlagin, Andrej ; Vendrame, Nadia ; Vincke, Caroline ; Völksch, Ingo ; Weber, Stephan ; Wille, Christian ; Wizemann, Hans Dieter ; Zeeman, Matthias ; Vereecken, Harry - \ 2020
Philosophical Transactions of the Royal Society B. Biological sciences 375 (2020)1810. - ISSN 0962-8436 - 1 p.
eddy covariance - energy balance - evapotranspiration - heat flux - net carbon uptake - water-use efficiency
Drought and heat events, such as the 2018 European drought, interact with the exchange of energy between the land surface and the atmosphere, potentially affecting albedo, sensible and latent heat fluxes, as well as CO2 exchange. Each of these quantities may aggravate or mitigate the drought, heat, their side effects on productivity, water scarcity and global warming. We used measurements of 56 eddy covariance sites across Europe to examine the response of fluxes to extreme drought prevailing most of the year 2018 and how the response differed across various ecosystem types (forests, grasslands, croplands and peatlands). Each component of the surface radiation and energy balance observed in 2018 was compared to available data per site during a reference period 2004-2017. Based on anomalies in precipitation and reference evapotranspiration, we classified 46 sites as drought affected. These received on average 9% more solar radiation and released 32% more sensible heat to the atmosphere compared to the mean of the reference period. In general, drought decreased net CO2 uptake by 17.8%, but did not significantly change net evapotranspiration. The response of these fluxes differed characteristically between ecosystems; in particular, the general increase in the evaporative index was strongest in peatlands and weakest in croplands. This article is part of the theme issue 'Impacts of the 2018 severe drought and heatwave in Europe: from site to continental scale'.
Critical Soil Moisture Derived From Satellite Observations Over Europe
Denissen, Jasper M.C. ; Teuling, Adriaan J. ; Reichstein, Markus ; Orth, René - \ 2020
Journal of Geophysical Research: Atmospheres 125 (2020)6. - ISSN 2169-897X
evapotranspiration - land-atmosphere interactions - remote sensing - soil moisture
Evapotranspiration (ET) is a crucial quantity through which land surface conditions can impact near-surface weather and vice versa. ET can be limited by energy or water availability. The transition between water- and energy-limited regimes is marked by the critical soil moisture (CSM), which is traditionally derived from small-sample laboratory analyses. Here, we aim to determine the CSM at a larger spatial scale relevant for climate modeling, using state-of-the-art gridded data sets. For this purpose, we introduce a new correlation-difference metric with which the CSM can be accurately inferred using multiple data streams. We perform such an analysis at the continental scale and determine a large-scale CSM as an emergent property. In addition, we determine small-scale CSMs at the grid cell scale and find substantial spatial variability. Consistently from both analyses we find that soil texture, climate conditions, and vegetation characteristics are influencing the CSM, with similar respective importance. In contrast, comparable CSMs are found when applying alternative large-scale energy and vegetation data sets, highlighting the robustness of our results. Based on our findings, the state of the vegetation and corresponding land-atmosphere coupling can be inferred, to first order, from easily accessible satellite observations of surface soil moisture.
Atmospheric Aridity and Apparent Soil Moisture Drought in European Forest During Heat Waves
Lansu, Eva M. ; Heerwaarden, C.C. van; Stegehuis, Annemiek I. ; Teuling, Adriaan J. - \ 2020
Geophysical Research Letters 47 (2020)6. - ISSN 0094-8276
apparent soil moisture drought - European forest - evapotranspiration - heat waves - land-atmosphere feedbacks - response to vapor pressure deficit
Land-atmosphere feedbacks, in particular the response of land evaporation to vapor pressure deficit (VPD) or the dryness of the air, remain poorly understood. Here we investigate the VPD response by analysis of a large database of eddy covariance flux observations and simulations using a conceptual model of the atmospheric boundary layer. Data analysis reveals that under high VPD and corresponding high temperatures, forest in particular reduces evaporation and emits more sensible heat. In contrast, grass increases evaporation and emits less sensible heat. Simulations show that this VPD feedback can induce significant temperature increases over forest of up to 2 K during heat wave conditions. It is inferred from the simulations that the effect of the VPD feedback corresponds to an apparent soil moisture depletion of more than 50%. This suggests that previous studies may have incorrectly attributed the effects of atmospheric aridity on temperature to soil dryness.
Praktijkproef onderwaterdrains Wormer- en Jisperveld
Akker, Jan van den; Diggelen, J.M.H. van; Houwelingen, Karel van; Kleef, Jan van; Pleijter, Matheijs ; Smolders, A.J.P. ; Turlings, L.G. ; Wielen, S. van der - \ 2016
Wageningen : Wageningen Environmental Research (Wageningen Environmental Research rapport 2765) - 67
drainage - grondwaterstand - bodemdaling - veengronden - emissie - evapotranspiratie - noord-holland - drainage - groundwater level - subsidence - peat soils - emission - evapotranspiration - noord-holland
Due to grassland evapotranspiration groundwater levels can be lowered decimeters below ditch water
level. Use of submerged drains reduces the lowering of groundwater levels and so peat oxidation and
subsidence and CO2 and N2O emissions. Submerged drains proved to increase the bearing capacity,
however, also the penetration resistance for a meadowbird beak increased. The capacity to capture
rain shower events increased. Groundwater and ditch water quality slightly improved. The infiltration
of ditch water increased considerably, however, was less than expected. Probably this is caused by a
hindered infiltration into the drain by sludge in the ditch. The use of a collector drain to regulate the
inlet is recommended.
Reducing ventilation requirements in semi-closed greenhouses increases water use efficiency
Katsoulas, N. ; Sapounas, A. ; Zwart, H.F. de; Dieleman, J.A. ; Stanghellini, C. - \ 2015
Agricultural Water Management 156 (2015). - ISSN 0378-3774 - p. 90 - 99.
closed greenhouses - climate conditions - plant-compounds - tomato yield - crop - evapotranspiration - irrigation - simulation - quality - leaf
We explore an under-appreciated side effect of semi-closed greenhouses: the ability to recover transpired water, thereby increasing water use efficiency. Semi-closed greenhouses are fit with cooling equipment, to limit natural ventilation requirements for temperature and humidity control. We assess the effect of cooling system capacity on ventilation needs of semi-closed greenhouses under different climate conditions and provide a general framework to evaluate potential water savings using the semi-closed greenhouse concept in different regions. We simulate greenhouse climate and crop yields for various cooling system capacities in Central Europe (The Netherlands) and Mediterranean (Greece and Algeria) by implementing a "cooling module" into an existing greenhouse model (KASPRO) and validating it using concurrent experimental data. Increasing the capacity of the cooling system has a double effect on water use efficiency (WUE): increase of fruit yield due to improved microclimate and lower water use, due to collection and reuse of vapour condensed in the heat exchanger and, to a lesser extent, lower crop transpiration. Thus WUE is strongly associated to the capacity of the cooling system. Finally, we show that there is a unique relationship between water use efficiency and the coupling of greenhouse environment to the outside air (an indicator of ventilation requirements), for all regions studied.
Reconciling spatial and temporal soi moisture effects on aftrnoon rainfall
Guillod, B.P. ; Orlowsky, B. ; Miralles, D.G. ; Teuling, A.J. ; Seneviratne, S.I. - \ 2015
Nature Communications 6 (2015). - ISSN 2041-1723
energy system ceres - stratiform precipitation - atmospheric controls - surface irradiances - land - evaporation - scale - feedback - evapotranspiration - variability
Soil moisture impacts on precipitation have been strongly debated. Recent observational evidence of afternoon rain falling preferentially over land parcels that are drier than the surrounding areas (negative spatial effect), contrasts with previous reports of a predominant positive temporal effect. However, whether spatial effects relating to soil moisture heterogeneity translate into similar temporal effects remains unknown. Here we show that afternoon precipitation events tend to occur during wet and heterogeneous soil moisture conditions, while being located over comparatively drier patches. Using remote-sensing data and a common analysis framework, spatial and temporal correlations with opposite signs are shown to coexist within the same region and data set. Positive temporal coupling might enhance precipitation persistence, while negative spatial coupling tends to regionally homogenize land surface conditions. Although the apparent positive temporal coupling does not necessarily imply a causal relationship, these results reconcile the notions of moisture recycling with local, spatially negative feedbacks.
Assessment of evaporative water loss from Dutch cities
Jacobs, C.M.J. ; Elbers, J.A. ; Brolsma, R. ; Hartogensis, O.K. ; Moors, E.J. ; Rodríguez-CarreteroMárquez, M.T. ; Hove, B. van - \ 2015
Building and Environment 83 (2015). - ISSN 0360-1323 - p. 27 - 38.
klimaatverandering - temperatuur - stedelijke gebieden - evaporatie - waterbudget - rotterdam - veluwe - climatic change - temperature - urban areas - evaporation - water budget - rotterdam - veluwe - urban heat-island - energy-balance - large-aperture - evapotranspiration - exchange - surface - scintillometers - requirements - environments - manchester
Reliable estimates of evaporative water loss are required to assess the urban water budget in support of division of water resources among various needs, including heat mitigation measures in cities relying on evaporative cooling. We report on urban evaporative water loss from Arnhem and Rotterdam in the Netherlands, using eddy covariance, scintillometer and sapflow observations. Evaporation is assessed at daily to seasonal and annual timescale. For the summer half-year (April–September), observations from Arnhem and Rotterdam are consistent regarding magnitude and variability of evaporation that typically varies between 0.5 and 1.0 mm of evaporation per day. The mean daily evaporative cooling rate was 20–25 Wm-2, 11–14% of the average incoming solar radiation. Evaporation by trees related to sapflow was found to be a small term on the water budget at the city or neighbourhood scale. However, locally the contribution may be significant, given observed maxima of daily sap flows up to 170 l per tree. In Arnhem, evaporation is strongly linked with precipitation, possibly owing to building style. During the summer season, 60% of the precipitation evaporated again. In Rotterdam, the link between evaporation and precipitation is much weaker. An analysis of meteorological observations shows that estimation of urban evaporation from routine weather data using the concept of reference evaporation would be a particularly challenging task. City-scale evaporation may not scale with reference evaporation and the urban fabric results in strong microweather variability. Observations like the ones presented here can be used to evaluate and improve methods for routine urban evaporation estimates.
How Does Tree Density Affect Water Loss of Peatlands? A Mesocosm Experiment
Limpens, J. ; Holmgren, M. ; Jacobs, C.M.J. ; Zee, S.E.A.T.M. van der; Karofeld, E. ; Berendse, F. - \ 2014
PLoS ONE 9 (2014)3. - ISSN 1932-6203 - 11 p.
sphagnum mosses - vascular plants - carbon-dioxide - climate-change - boreal mire - scots pine - vegetation - bogs - evapotranspiration - table
Raised bogs have accumulated more atmospheric carbon than any other terrestrial ecosystem on Earth. Climate-induced expansion of trees and shrubs may turn these ecosystems from net carbon sinks into sources when associated with reduced water tables. Increasing water loss through tree evapotranspiration could potentially deepen water tables, thus stimulating peat decomposition and carbon release. Bridging the gap between modelling and field studies, we conducted a three-year mesocosm experiment subjecting natural bog vegetation to three birch tree densities, and studied the changes in subsurface temperature, water balance components, leaf area index and vegetation composition. We found the deepest water table in mesocosms with low tree density. Mesocosms with high tree density remained wettest (i.e. highest water tables) whereas the control treatment without trees had intermediate water tables. These differences are attributed mostly to differences in evapotranspiration. Although our mesocosm results cannot be directly scaled up to ecosystem level, the systematic effect of tree density suggests that as bogs become colonized by trees, the effect of trees on ecosystem water loss changes with time, with tree transpiration effects of drying becoming increasingly offset by shading effects during the later phases of tree encroachment. These density-dependent effects of trees on water loss have important implications for the structure and functioning of peatbogs.
Hoe klimaatrobuust is de gewasfactormethode van het Nationaal Hydrologisch Instrumentarium?
Walsum, P.E.V. van; Bolt, F.J.E. van der; Veldhuizen, A.A. - \ 2013
Stromingen : vakblad voor hydrologen 19 (2013)3/4. - ISSN 1382-6069 - p. 127 - 133.
grondwaterstand - evapotranspiratie - waterbehoefte - gewassen - modellen - groundwater level - evapotranspiration - water requirements - crops - models
Artikel naar aanleiding van het artikel “Metingen en proceskennis vereist voor nauwkeurige verdampingsberekening in grondwatermodellen”, van Bartholomeus e.a. in Stromingen, vol 19, #2 (2013). De SWAP-methode wordt in bovengenoemd artikel gebruikt als substituut voor werkelijke metingen om illustratieve berekeningen uit te voeren. Dat de getoetste ‘enkelvoudige’ gewasfactormethoden in dat opzicht tekort te schieten komt doordat er 1) in die methoden geen expliciet onderscheid wordt gemaakt tussen de verschillende verdampingstermen, en 2) de gewasfactor een versimpelde voorstelling vormt van (onder andere) de aerodynamische ruwheid; die kan de effecten van variaties in windsnelheid daarom niet volgen.
Comparing projections of future changes in runoff from hydrological and biome models in ISI-MIP
Davie, J.C.S. ; Falloon, P.D. ; Kahana, R. ; Dankers, R. ; Betts, R. ; Portmann, F.T. ; Wisser, D. ; Clark, D.B. ; Ito, A. ; Masaki, Y. ; Nishina, K. ; Fekete, B. ; Tessler, Z. ; Wada, Y. ; Liu, X. ; Tang, Q. ; Hagemann, S. ; Stacke, T. ; Pavlick, R. ; Schaphoff, S. ; Gosling, S.N. ; Franssen, W.H.P. ; Arnell, N. - \ 2013
Earth System dynamics 4 (2013)2. - ISSN 2190-4979 - p. 359 - 374.
climate-change - carbon-dioxide - integrated model - hadgem2 family - surface-water - river flow - vegetation - impact - co2 - evapotranspiration
Future changes in runoff can have important implications for water resources and flooding. In this study, runoff projections from ISI-MIP (Inter-sectoral Impact Model Inter-comparison Project) simulations forced with HadGEM2-ES bias-corrected climate data under the Representative Concentration Pathway 8.5 have been analysed for differences between impact models. Projections of change from a baseline period (1981-2010) to the future (2070-2099) from 12 impacts models which contributed to the hydrological and biomes sectors of ISI-MIP were studied. The biome models differed from the hydrological models by the inclusion of CO2 impacts and most also included a dynamic vegetation distribution. The biome and hydrological models agreed on the sign of runoff change for most regions of the world. However, in West Africa, the hydrological models projected drying, and the biome models a moistening. The biome models tended to produce larger increases and smaller decreases in regionally averaged runoff than the hydrological models, although there is large inter-model spread. The timing of runoff change was similar, but there were differences in magnitude, particularly at peak runoff. The impact of vegetation distribution change was much smaller than the projected change over time, while elevated CO2 had an effect as large as the magnitude of change over time projected by some models in some regions. The effect of CO2 on runoff was not consistent across the models, with two models showing increases and two decreases. There was also more spread in projections from the runs with elevated CO2 than with constant CO2. The biome models which gave increased runoff from elevated CO2 were also those which differed most from the hydrological models. Spatially, regions with most difference between model types tended to be projected to have most effect from elevated CO2, and seasonal differences were also similar, so elevated CO2 can partly explain the differences between hydrological and biome model runoff change projections. Therefore, this shows that a range of impact models should be considered to give the full range of uncertainty in impacts studies.
Hoe met remote sensing via de vegetatie bodem en water kunnen worden gekarteerd
Roelofsen, H.D. ; Amerongen, J. van; Kooistra, L. ; Runhaar, J. ; Witte, J.P. - \ 2013
Stromingen : vakblad voor hydrologen 19 (2013)2. - ISSN 1382-6069 - p. 107 - 120.
remote sensing - ecohydrologie - vegetatietypen - evapotranspiratie - grondwaterstand - monitoring - remote sensing - ecohydrology - vegetation types - evapotranspiration - groundwater level - monitoring
Remote sensing is de verzamelterm voor diverse vormen van aardobservatie. Zoals observaties van het aardoppervlak door satellieten (spaceborne remote sensing). Observaties vanuit vliegtuigen (airborne remote sensing) zijn eveneens mogelijk. De vraag wat remote sensing kan betekenen voor hydrologische toepassingen stond centraal tijdens de NHV voorjaarsbijeenkomst, in mei 2012. Daar betoogden wij dat diverse hydrologische grootheden afgeleid kunnen worden van remote sensing beelden. Dit artikel is een verdere uitwerking van dit betoog. We willen met deze bijdrage aantonen dat de natuurlijke vegetatie een nuttige vertaalsleutel kan vormen tussen remote sensing observaties enerzijds en eigenschappen van de ondergrond anderzijds.
Market outlook for satellite-based RE index insurance in agribusiness
Asseldonk, M.A.P.M. van - \ 2013
The Hague : LEI, part of Wageningen UR (LEI memorandum 13-085) - 34
evapotranspiratie - meteorologie - remote sensing - satellieten - afrika - evapotranspiration - meteorology - remote sensing - satellites - africa
In the current report a market outlook for satellite-based RE index insurance is elaborated on. Special thanks for the contributions of Andries Rosema of EARS Earth Environment Monitoring BV and Erik Klaassens of ECORYS Nederland BV. Also the views of experts who were consulted are acknowledged (see for the list of experts Appendix I).
Quantitative simulation tools to analyze up- and downstream interactions of soil and water conservation measures: Supporting policy making in the Green Water Credits program of Kenya
Hunink, J.E. ; Droogers, P. ; Kauffman, J.H. ; Mwaniki, B.M. ; Bouma, J. - \ 2012
Journal of Environmental Management 111 (2012). - ISSN 0301-4797 - p. 187 - 194.
land-use change - management-practices - sediment yield - model - swat - runoff - evapotranspiration - catchment - payments - services
Upstream soil and water conservation measures in catchments can have positive impact both upstream in terms of less erosion and higher crop yields, but also downstream by less sediment flow into reservoirs and increased groundwater recharge. Green Water Credits (GWC) schemes are being developed to encourage upstream farmers to invest in soil and water conservation practices which will positively effect upstream and downstream water availability. Quantitative information on water and sediment fluxes is crucial as a basis for such financial schemes. A pilot design project in the large and strategically important Upper-Tana Basin in Kenya has the objective to develop a methodological framework for this purpose. The essence of the methodology is the integration and use of a collection of public domain tools and datasets: the so-called Green water and Blue water Assessment Toolkit (GBAT). This toolkit was applied in order to study different options to implement GWC in agricultural rainfed land for the pilot study. Impact of vegetative contour strips, mulching, and tied ridges were determined for: (i) three upstream key indicators: soil loss, crop transpiration and soil evaporation, and (ii) two downstream indicators: sediment inflow in reservoirs and groundwater recharge. All effects were compared with a baseline scenario of average conditions. Thus, not only actual land management was considered but also potential benefits of changed land use practices. Results of the simulations indicate that especially applying contour strips or tied ridges significantly reduces soil losses and increases groundwater recharge in the catchment. The model was used to build spatial expressions of the proposed management practices in order to assess their effectiveness. The developed procedure allows exploring the effects of soil conservation measures in a catchment to support the implementation of GWC.
Swiss prealpine Rietholzbach research catchment and lysimeter: 32 year time series and 2003 drought event
Seneviratne, S.I. ; Lehner, I. ; Gurtz, J. ; Teuling, A.J. ; Lang, H. ; Moser, U. ; Grebner, D. ; Menzel, L. ; Schroff, K. ; Vitvar, T. ; Zappa, M. - \ 2012
Water Resources Research 48 (2012)6. - ISSN 0043-1397 - 20 p.
soil-moisture memory - european summer - united-states - heat-wave - groundwater recharge - spatial variability - carbon-dioxide - climate-change - water-vapor - evapotranspiration
The prealpine Rietholzbach research catchment provides long-term continuous hydroclimatological measurements in northeastern Switzerland, including lysimeter evapotranspiration measurements since 1976, and soil moisture measurements since 1994. We analyze here the monthly data record over 32 years (1976–2007), with a focus on the extreme 2003 European drought. In particular, we assess whether the well-established hypothesis that the 2003 event was due to spring precipitation deficits is valid at the site. The Rietholzbach measurements are found to be internally consistent and representative for a larger region in Switzerland. Despite the scale discrepancy (3.14 m2 versus 3.31 km2), the lysimeter seepage and catchment-wide streamflow show similar monthly dynamics. High correlations are further found with other streamflow measurements within the Thur river basin (1750 km2) and—for interannual anomalies—also in most of northern Switzerland. Analyses for 2003 confirm the occurrence of extreme heat and drought conditions at Rietholzbach. However, unlike findings from regional-scale modeling studies, they reveal a late onset of the soil moisture deficit (from June onward), despite large precipitation deficits from mid-February to mid-April. These early spring deficits were mostly compensated for by decreased runoff during this period and excess precipitation in the preceding weeks to months (including in the 2002 fall). Our results show that evapotranspiration excess in June 2003 was the main driver initiating the 2003 summer drought conditions in Rietholzbach, contributing 60% of the June 2003 water storage deficit. Finally, long-lasting drought effects on the lysimeter water storage due to rewetting inhibition were recorded until spring 2004.
Ontwikkeling emissiemanagementsysteem grondgebonden teelt; de lysimeter en drainmeter
Voogt, W. ; Zwinkels, F. ; Balendonck, J. ; Dorland, H. van; Winkel, A. van; Heinen, M. - \ 2012
Bleiswijk : Wageningen UR Glastuinbouw (Rapporten GTB 1190) - 52
cultuurmethoden - glastuinbouw - lysimeters - instrumenten (meters) - waterstroming - emissie - drainage - evapotranspiratie - drainagesystemen - cultural methods - greenhouse horticulture - lysimeters - instruments - water flow - emission - drainage - evapotranspiration - drainage systems
Het hoofddoel van het project ‘Glastuinbouw Waterproof, grondgebonden’ was het ontwikkelen van een aantal middelen voor telers van grondgebonden teelten, waarmee zij emissiedoelstellingen kunnen halen. De leidende gedachte hierbij is dat een gesloten waterkringloop zoals toegepast bij substraatteelten onhaalbaar is. Emissiereductie zal vooral via het waterspoor behaald moeten worden en daarom is een brongerichte aanpak, de irrigatie afgestemd op de evapotranspiratie, het meest effectief. Het project omvatte in de eerste plaats het ontwikkelen en combineren van een aantal technische hulpmiddelen en in de tweede plaats het installeren en testen in de praktijk. In dit rapport worden de lysimeter en de bijbehorende drainmeter besproken.
Analyzing transient closed chamber effects on canopy gas exchange for optimizing flux calculation timing
Langensiepen, M. ; Kupisch, M. ; Wijk, M.T. van; Ewert, F. - \ 2012
Agricultural and Forest Meteorology 164 (2012). - ISSN 0168-1923 - p. 61 - 70.
portable chamber - h2o fluxes - sap flow - co2 - evapotranspiration - transpiration - trees - crop - temperature - forest
Transient type canopy chambers are still the only currently available practical solution for rapid screening of gas-exchange in agricultural fields. The technique has been criticized for its effect on canopy microclimate during measurement which affects the transport regime and regulation of plant gas-exchange. Field studies in which the technique has been compared against independent methods are still fragmentary. The aims of this study were to quantify the changes of the physical environment during chamber placement, to determine optimum flux measuring windows, to compare three flux-calculation procedures, and to test the performance of the method against independent measurements of sap-flow. Two wheat experiments were conducted for these purposes under German temperate climate conditions. Leaf transpiration and sap-flow remained relatively constant during the first 120 s after chamber deployment, but changed considerably afterwards. Canopy H2O fluxes could thus be inferred from concentration measurement series during this interval. A saturation function, previously not mentioned in the literature, was compared against the commonly used constant and quadratic regression methods and identified as the most suitable method for calculating vapor fluxes. The study reconfirmed that small proportional changes of CO2 concentrations during the calculation interval facilitate the application of the frequently applied quadratic regression method for calculating CO2 fluxes. Sap-flow, leaf and canopy gas-exchange were severely perturbed after chamber removal. Revisiting times of same sample locations need to be planned accordingly. The study confirms that the transient chamber technique can be applied for determining canopy gas-exchange, provided that characteristic time intervals within concentration measuring series are determined and their non-linearity tested to establish appropriate flux calculation procedures.
Assessment of strip tillage systems for maize production in semi-arid Ethiopia: effects on grain yield, water balance and water productivity
Temesgen, M. ; Savenije, H.H.G. ; Rockström, J. ; Hoogmoed, W.B. - \ 2012
Physics and Chemistry of the Earth 47-48 (2012). - ISSN 1474-7065 - p. 156 - 165.
hydraulic-properties - soil - evapotranspiration - generation - drought - area
The Maresha, the traditional Ethiopian plow, requires repeated cross-plowing which causes increased surface runoff, less infiltration and hence lower water availability to crops. The main reasons for increased surface runoff and reduced infiltration are plowing along the slope and the formation of a plow pan at shallow depths. Conservation tillage is seen as a way to alleviate these problems. The widely advocated zero-tillage, however, is not feasible for smallholder farmers in semi-arid regions of Ethiopia because of difficulties in maintaining adequate soil cover, the practice of communal grazing, and high costs of herbicides. Strip tillage systems, on the other hand, may offer a solution. This study was initiated to test strip tillage systems and to evaluate the impacts of new tillage systems on the water balance and grain yields of maize. Experiments have been conducted in a semi-arid area called Melkawoba in the central Rift Valley of Ethiopia during 2003-2005. Strip tillage systems involved cultivation along planting lines at a spacing of 0.75 m using the Maresha plow followed by subsoiling along the same lines (STS) or without subsoiling (ST). Results have been compared with traditional tillage involving 3 to 4 overpasses with the Maresha plow (CONV). Soil moisture has been monitored to a depth of 1.8 m using a Time Domain Reflectometer (TDR) while surface runoff has been measured using a specially designed rectangular trough installed at the bottom of each plot. STS resulted in the least surface runoff (Qs=18 mm-season-1) and the highest grain yields (Y=2130 kg-ha-1) followed by ST (Qs=26 mm-season-1, Y=1840 kg-ha-1) and CONV (Qs=43 mm-season-1, Y=1720 kg-ha-1) provided sowing was carried out within a week after subsoiling. Thus, STS resulted in the highest water productivity, WP=0.60 kg-m-3, followed by ST (WP=0.52 kg-m-3) and CONV (WP=0.48 kg-m-3). The main conclusion of the paper is that even in dry areas reasonable yields can be obtained provided moisture conservation in the root zone is guaranteed. In this regard subsoiling is essential. Moreover, it is concluded that the time between subsoiling and planting is a key factor and should not exceed one week
Reference evapotranspiration with radiation-based and temperature-based method - impact on hydrological drought using WATCH Forcing Data
Melsen, L.A. ; Wanders, N. ; Huijgevoort, M.H.J. van; Weedon, G.P. - \ 2011
Brussel : European Commission (Technical report / WATCH no. 39) - 67
evapotranspiratie - hydrologie - hydrologische gegevens - droogte - evapotranspiration - hydrology - hydrological data - drought
Seasonal evaluation of the land surface sheme HTESSEL against remote sensing derived energy fluxes of the Transdanubian regions in Hungary
Wipfler, E.L. ; Metselaar, K. ; Dam, J.C. van; Feddes, R.A. ; Meijgaard, E. van; Ulft, L.H. van; Hurk, B. van den; Zwart, S.J. ; Bastiaanssen, W.G.M. - \ 2011
Hydrology and Earth System Sciences 15 (2011)4. - ISSN 1027-5606 - p. 1257 - 1271.
aardoppervlak - evapotranspiratie - remote sensing - klimaatverandering - modellen - hongarije - land surface - evapotranspiration - remote sensing - climatic change - models - hungary - terrestrial water storage - era-40 reanalysis - balance closure - climate models - field - atmosphere - hydrology - impact - basin
The skill of the land surface model HTESSEL is assessed to reproduce evaporation in response to land surface characteristics and atmospheric forcing, both being spatially variable. Evaporation estimates for the 2005 growing season are inferred from satellite observations of the Western part of Hungary and compared to model outcomes. Atmospheric forcings are obtained from a hindcast run with the Regional Climate Model RACMO2. Although HTESSEL slightly underpredicts the seasonal evaporative fraction as compared to satellite estimates, the mean, 10th and 90th percentile of this variable are of the same magnitude as the satellite observations. The initial water as stored in the soil and snow layer does not have a significant effect on the statistical properties of the evaporative fraction. However, the spatial distribution of the initial soil and snow water significantly affects the spatial distribution of the calculated evaporative fraction and the models ability to reproduce evaporation correctly in low precipitation areas in the considered region. HTESSEL performs weaker in dryer areas. In Western Hungary these areas are situated in the Danube valley, which is partly covered by irrigated cropland and which also may be affected by shallow groundwater. Incorporating (lateral) groundwater flow and irrigation, processes that are not included now, may improve HTESSELs ability to predict evaporation correctly. Evaluation of the model skills using other test areas and larger evaluation periods is needed to confirm the results.
Crop coefficient, yield response to water stress and water productivity of teff (Eragrostis tef (Zucc.)
Araya, A. ; Stroosnijder, L. ; Girmay, G. ; Keesstra, S.D. - \ 2011
Agricultural Water Management 98 (2011)5. - ISSN 0378-3774 - p. 775 - 783.
use efficiency - winter-wheat - supplemental irrigation - evapotranspiration - maize - agriculture - evaporation - trotter
In the semi-arid region of Tigray, Northen Ethiopia a two season experiment was conducted to measure evapotranspiration, estimate yield response to water stress and derive the crop coefficient of teff using the single crop coefficient approach with simple, locally made lysimeters and field plots. During the experiment we also estimated the water productivity of teff taking into account long-term rainfall probability scenarios and different levels of farmers’ skills. During the experimental seasons (2008 and 2009), the average potential evapotranspiration of teff ranged from 260 to 317 mm. The total seasonal water requirement of teff was found to lower in contrast to the assumptions of regional agronomists that teff water requirement is comparable to that of wheat and barley (375 mm). The average single crop coefficient values (kc) for the initial, mid and late season stages of teff were 0.8–1, 0.95–1.1 and 0.4–0.5, respectively. The seasonal yield response to water stress was 1.04, which indicates that teff exhibits a moderately sensitive and linear response to water stress. The results suggest that teff is likely to give significantly higher grain yield when a nearly optimal water supply is provided. The study showed that, in locations where standard equipment is not affordably available, indicative (rough) crop evapotranspiration values can be obtained by using field plots and employing locally made lysimeters. The difference in economic water productivity (EWP) and the crop water productivity (CWP) for teff were assessed under very wet, wet, normal, dry and very dry scenarios. In addition two groups of farmers were evaluated, a moderately (I) and a highly skilled (II) group. The results showed that higher EWP and CWP were obtained under very wet scenario than very dry scenario. There was also a 22% increase in EWP and CWP under group II compared to group I farmers. The increase was due to a 22% reduction in unwanted water losses achieved through use of improved technology and better irrigation skills. Both EWP and CWP can be used to evaluate the pond irrigation water productivity (IWP) for a given climate, crop and soil type, and skill and technology level of the farmer. For special crops like teff extra criteria may be needed in order to properly evaluate the pond irrigation water productivity. During the experimental seasons, a high IWP for teff was attained when about 90% of the optimal water need of the crop was met. IWP can be used as an indicator as how much supplementary irrigation has to be applied in relation to the rainfall and other sources of water supply in order to assure greatest yield from a total area. However, the supplemental irrigation requirement of the crops may vary with season due to seasonal rainfall variability