Influence of concurrence of extreme drought and heat events on carbon and energy fluxes in dominant ecosystems in the Pacific Northwest region

Abstract. The impacts of drought intensities and vapor pressure deficits (VPD) beyond historic norms in Pacific Northwest (PNW), USA, are critical in understanding the potential future function and resilience of ecosystems in the region. While ecosystems in this region are adapted to seasonal droughts, June 2015 temperatures were the highest recorded in the region and strongly coupled with relatively low soil moisture. June is usually the best month for growth in the PNW. Here, we examined the impact of the June 2015 climate extremes on carbon and energy fluxes at sagebrush in the high desert, young and mature ponderosa pine in the semi-arid Great Basin, and Douglas-fir in the mesic Coast Range ecoregion compared to an average climate year (2014). We assessed if the ecosystems recover from extreme climate stress within the growing season. The monthly anomalies in temperature and VPD were 3 standard deviations, and precipitation was 1 standard deviation, outside the 30-year mean at all sites. In sagebrush, the carry-over effect of precipitation (i.e., intensive precipitation prior to the drought and heat) mitigated the immediate impact of extreme climate stress, leading to 25–40 % increase in net ecosystem production (NEP) and gross primary production (GPP), with little change in ecosystem respiration (RE) and 65 % increase in latent heat flux, compared to the June 2014. The drought and heat lowered NEP by 35–65 % and GPP by 15–33 % in ponderosa pine and Douglas-fir. A greater increase in latent heat flux was observed in Douglas-fir (110 %) than in ponderosa pine (

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Land–Atmosphere Interaction in Tropical Africa

Oxford Research Encyclopedia of Climate Science ◽

10.1093/acrefore/9780190228620.013.779 ◽

2020 ◽

Author(s):

Cathy Hohenegger

Keyword(s):

Heat Flux ◽

Soil Moisture ◽

Latent Heat ◽

Latent Heat Flux ◽

Surface State ◽

Land Surface ◽

Large Scale ◽

Moisture Distribution ◽

Sahel Region ◽

The Impact

Even though many features of the vegetation and of the soil moisture distribution over Africa reflect its climatic zones, the land surface has the potential to feed back on the atmosphere and on the climate of Africa. The land surface and the atmosphere communicate via the surface energy budget. A particularly important control of the land surface, besides its control on albedo, is on the partitioning between sensible and latent heat flux. In a soil moisture-limited regime, for instance, an increase in soil moisture leads to an increase in latent heat flux at the expanse of the sensible heat flux. The result is a cooling and a moistening of the planetary boundary layer. On the one hand, this thermodynamically affects the atmosphere by altering the stability and the moisture content of the vertical column. Depending on the initial atmospheric profile, convection may be enhanced or suppressed. On the other hand, a confined perturbation of the surface state also has a dynamical imprint on the atmospheric flow by generating horizontal gradients in temperature and pressure. Such gradients spin up shallow circulations that affect the development of convection. Whereas the importance of such circulations for the triggering of convection over the Sahel region is well accepted and well understood, the effect of such circulations on precipitation amounts as well as on mature convective systems remains unclear. Likewise, the magnitude of the impact of large-scale perturbations of the land surface state on the large-scale circulation of the atmosphere, such as the West African monsoon, has long been debated. One key issue is that such interactions have been mainly investigated in general circulation models where the key involved processes have to rely on uncertain parameterizations, making a definite assessment difficult.

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Energy balance in a renewal sugarcane area with fallow period and soybean cultivation

Ciência e Natura ◽

10.5902/2179460x53222 ◽

2020 ◽

Vol 42 ◽

pp. e39

Author(s):

Rubmara Ketzer Oliveira ◽

Luciano Sobral Fraga Junior ◽

Larissa Brêtas Moura ◽

Debora Regina Roberti ◽

Felipe Gustavo Pilau

Keyword(s):

Heat Flux ◽

Energy Balance ◽

Latent Heat ◽

Latent Heat Flux ◽

Sensible Heat Flux ◽

Heat Fluxes ◽

Rainfall Regime ◽

Sensible Heat ◽

Energy Fluxes ◽

Fallow Period

Brazil is the main sugarcane producer in the world, which is intended for various purposes, from food to power generation. Soybean cultivation in areas of sugarcane under renewal has been growing progressively in Brazil. Quantifying energy fluxes at different stages of this process is essential for better management. The work was carried out in Piracicaba city, with the objective of analyzing the behavior of energy fluxes and the closing of the energy balance in a sugarcane renewal area with a fallow period followed by soybean cultivation. The latent and sensitive heat fluxes were obtained with the “Eddy covariance” method. The closing of the energy balance in the fallow period with straw-covered uncovered and soybean-cultivated soil presented a correlation coefficient of 0.88, 0.78 and 0.71, respectively. In the period without cultivation, the sensible heat flux was predominant in relation to the latent heat flux, varying according to the rainfall regime. The presence of straw under the soil in the fallow period affected the latent heat flux. With soybean cultivation, the latent heat flux surpassed the sensible heat flux.

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Improving the representation of cropland sites in the Community Land Model (CLM) version 5.0

10.5194/gmd-2020-241 ◽

2020 ◽

Author(s):

Theresa Boas ◽

Heye Bogena ◽

Thomas Grünwald ◽

Bernard Heinesch ◽

Dongryeol Ryu ◽

...

Keyword(s):

Land Use ◽

Heat Flux ◽

Winter Wheat ◽

Latent Heat ◽

Latent Heat Flux ◽

Field Data ◽

Energy Fluxes ◽

Cash Crop ◽

Cover Cropping ◽

Community Land Model

Abstract. The incorporation of a comprehensive crop module in land surface models offers the possibility to study the effect of agricultural land use and land management changes on the terrestrial water, energy and biogeochemical cycles. It may help to improve the simulation of biogeophysical and biogeochemical processes on regional and global scales in the framework of climate and land use change. In this study, the performance of the crop module of the Community Land Model version 5 (CLM5) was evaluated at point scale with site specific field data focussing on the simulation of seasonal and inter-annual variations in crop growth, planting and harvesting cycles, and crop yields as well as water, energy and carbon fluxes. In order to better represent agricultural sites, the model was modified by (1) implementing the winter wheat subroutines after Lu et al. (2017) in CLM5; (2) implementing plant specific parameters for sugar beet, potatoes and winter wheat, thereby adding these crop functional types (CFT) to the list of actively managed crops in CLM5; (3) introducing a cover cropping subroutine that allows multiple crop types on the same column within one year. The latter modification allows the simulation of cropping during winter months before usual cash crop planting begins in spring, which is a common agricultural management technique in humid and sub-humid regions. We compared simulation results with field data and found that both the parameterization of the CFTs, as well as the winter wheat subroutines, led to a significant simulation improvement in terms of energy fluxes, leaf area index (LAI), net ecosystem exchange (RMSE reduction for latent and sensible heat by up to 57 % and 59 % respectively) and crop yield (up to 87 % improvement in winter wheat yield prediction) compared with default model results. The cover cropping subroutine yielded a substantial improvement in representation of field conditions after harvest of the main cash crop (winter season) in terms of LAI curve and latent heat flux (reduction of winter time RMSE for latent heat flux by 42 %). We anticipate that our model modifications offer opportunities to improve yield predictions, to study the effects of large-scale cover cropping on energy fluxes, soil carbon and nitrogen pools, and soil water storage in future studies with CLM5.

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Greenhouse gas and energy fluxes in a boreal peatland forest after clear-cutting

Biogeosciences ◽

10.5194/bg-16-3703-2019 ◽

2019 ◽

Vol 16 (19) ◽

pp. 3703-3723 ◽

Cited By ~ 7

Author(s):

Mika Korkiakoski ◽

Juha-Pekka Tuovinen ◽

Timo Penttilä ◽

Sakari Sarkkola ◽

Paavo Ojanen ◽

...

Keyword(s):

Heat Flux ◽

Greenhouse Gas ◽

Co2 Emissions ◽

Latent Heat ◽

Latent Heat Flux ◽

Ground Vegetation ◽

Energy Fluxes ◽

Clear Cutting ◽

Logging Residues ◽

The Mean

Abstract. The most common forest management method in Fennoscandia is rotation forestry, including clear-cutting and forest regeneration. In clear-cutting, stem wood is removed and the logging residues are either removed or left on site. Clear-cutting changes the microclimate and vegetation structure at the site, both of which affect the site's carbon balance. Peat soils with poor aeration and high carbon densities are especially prone to such changes, and significant changes in greenhouse gas exchange can be expected. We measured carbon dioxide (CO2) and energy fluxes with the eddy covariance method for 2 years (April 2016–March 2018) after clear-cutting a drained peatland forest. We observed a significant rise (23 cm) in the water table level and a large CO2 source (first year: 3086±148 g CO2 m−2 yr−1; second year: 2072±124 g CO2 m−2 yr−1). These large CO2 emissions resulted from the very low gross primary production (GPP) following the removal of photosynthesizing trees and the decline of ground vegetation, unable to compensate for the decomposition of logging residues and peat. During the second summer (June–August) after the clear-cutting, GPP had already increased by 96 % and total ecosystem respiration decreased by 14 % from the previous summer. The mean daytime ratio of sensible to latent heat flux decreased after harvesting from 2.6 in May 2016 to 1.0 in August 2016, and in 2017 it varied mostly within 0.6–1.0. In April–September, the mean daytime sensible heat flux was 33 % lower and latent heat flux 40 % higher in 2017, probably due to the recovery of ground vegetation that increased evapotranspiration and albedo of the site. In addition to CO2 and energy fluxes, we measured methane (CH4) and nitrous oxide (N2O) fluxes with manual chambers. After the clear-cutting, the site turned from a small CH4 sink into a small source and from N2O neutral to a significant N2O source. Compared to the large CO2 emissions, the 100-year global warming potential (GWP100) of the CH4 emissions was negligible. Also, the GWP100 due to increased N2O emissions was less than 10 % of that of the CO2 emission change.

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Land-atmosphere coupling during compound extreme heat and drought events in the LUCAS experiment: a new coupling metric for climate extremes

10.5194/egusphere-egu21-15797 ◽

2021 ◽

Author(s):

Rita M. Cardoso ◽

Daniela D. C. A. Lima ◽

Pedro M. M. Soares ◽

Diana Rechid ◽

Marcus Breil ◽

...

Keyword(s):

Land Use ◽

Heat Flux ◽

Soil Moisture ◽

Land Cover ◽

Latent Heat ◽

Latent Heat Flux ◽

Heat Waves ◽

Extreme Heat ◽

Positive Temperature ◽

The Impact

Land-atmosphere energy and water exchanges are fundamentally linked to soil-moisture. The distribution of the planets&#8217; biomes hinges on the surface-atmosphere coupling since soil moisture and temperature feedbacks have a strong influence on plant transpiration and photosynthesis. Land use/land cover changes (LUC) modify locally land surface properties that control the land-atmosphere mass, energy, and momentum exchanges. The impact of these changes depends on the scale and nature of land cover modifications and is very difficult to quantify. However, large inconsistencies in the LUC impacts are observed between models, highlighting the need for common LUC across a large ensemble of models. The Flagship Pilot Study LUCAS (Land Use & Climate Across Scales) provides a coordinated effort to study LUC using an ensemble of regional climate models (RCMs). In the first phase of the project 3 experiments were performed for continental Europe: EVAL (current climate); GRASS (trees replaced by grassland) and FOREST (grasses and shrubs replaced by trees). &#160;An analysis of the energy and moisture balance for the three experiments is performed, focusing on the relationship between the fluxes partitioning, heat waves and droughts. To better asses the link between extreme temperatures and soil moisture or evapotranspiration, a new coupling metric for short time scales is proposed, the Latent Heat Flux-Temperature Coupling Magnitude (LETCM). This new metric is computed for a specific period, considering the positive temperature extremes and the negative latent heat flux extremes. Areas with positive magnitude values imply higher temperature anomaly, due to a negative latent heat flux anomaly. This new metric only considers periods of strong coupling, with positive signals in areas of high temperatures and evaporative stress, allowing for the detection of events that are extreme for energy and water cycle. Concurrently, a new decile based normalised drought index is used to examine the concurrent heat extremes and droughts. The analysis focuses on the three experiments revealing that the number, amplitude and spatial distribution of compound extreme heat and drought is highly model dependant. The impact of afforestation or deforestation is not consistent across models.Acknowledgements&#160;The authors wish to acknowledge project LEADING (PTDC/CTA-MET/28914/2017) and FCT - project UIDB/50019/2020 - Instituto Dom Luiz.

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Distinguishing between early- and late-covering crops in the land surface model Noah-MP: impact on simulated surface energy fluxes and temperature

Biogeosciences ◽

10.5194/bg-17-2791-2020 ◽

2020 ◽

Vol 17 (10) ◽

pp. 2791-2805

Author(s):

Kristina Bohm ◽

Joachim Ingwersen ◽

Josipa Milovac ◽

Thilo Streck

Keyword(s):

Land Use ◽

Heat Flux ◽

Surface Energy ◽

Latent Heat ◽

Latent Heat Flux ◽

Land Surface ◽

Land Surface Model ◽

Surface Model ◽

Energy Fluxes ◽

Surface Energy Fluxes

Abstract. Land surface models are essential parts of climate and weather models. The widely used Noah-MP land surface model requires information on the leaf area index (LAI) and green vegetation fraction (GVF) as key inputs of its evapotranspiration scheme. The model aggregates all agricultural areas into a land use class termed “cropland and pasture”. In a previous study we showed that, on a regional scale, the GVF has a bimodal distribution formed by two crop groups differing in phenology and growth dynamics: early-covering crops (ECC; e.g., winter wheat, winter rapeseed, winter barley) and late-covering crops (LCC; e.g., corn, silage maize, sugar beet). That result can be generalized for central Europe. The present study quantifies the effect of splitting the land use class cropland and pasture of Noah-MP into ECC and LCC on surface energy fluxes and temperature. We further studied the influence of increasing the LCC share, which in the study area (the Kraichgau region, southwest Germany) is mainly the result of heavily subsidized biomass production, on energy partitioning at the land surface. We used the GVF dynamics derived from high-resolution (5 m × 5 m) RapidEye satellite data and measured LAI data for the simulations. Our results confirm that the GVF and LAI strongly influence the partitioning of surface energy fluxes, resulting in pronounced differences between simulations of ECC and LCC. Splitting up the generic crop into ECC and LCC had the strongest effect on land surface exchange processes in July–August. During this period, ECC are at the senescence growth stage or already harvested, while LCC have a well-developed ground-covering canopy. The generic crop resulted in humid bias, i.e., an increase in evapotranspiration by +0.5 mm d−1 (latent heat flux is 1.3 MJ m−2 d−1), decrease in sensible heat flux (H) by 1.2 MJ m−2 d−1 and decrease in surface temperature by −1 ∘C. The bias increased as the shares of ECC and LCC became similar. The observed differences will impact the simulations of processes in the planetary boundary layer. Increasing the LCC share from 28 % to 38 % in the Kraichgau region led to a decrease in latent heat flux (LE) and a heating up of the land surface in the early growing season. Over the second part of the season, LE increased and the land surface cooled down by up to 1 ∘C.

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Impact of the Anomalous Latent Heat Flux Over the Kuroshio Extension on Western North American Rainfall in Spring: Interannual Variation and Mechanism

Frontiers in Earth Science ◽

10.3389/feart.2020.609619 ◽

2021 ◽

Vol 8 ◽

Author(s):

Jingchao Long ◽

Chunlei Liu ◽

Zifeng Liu ◽

Jianjun Xu

Keyword(s):

Heat Flux ◽

North America ◽

Latent Heat ◽

Latent Heat Flux ◽

Cyclonic Circulation ◽

Western Canada ◽

Jet Stream ◽

The Impact ◽

The Kuroshio ◽

Anomalous Cyclonic Circulation

The Kuroshio and its extension (KE) significantly influences regional climate through meridional heat transport from the tropical ocean. In this study, the observational and reanalysis datasets are used to investigate the impact of the latent heat flux (LHF) over the KE region on downstream rainfall and the underlying mechanism. The result shows a “seesaw” structure in rainfall anomaly, dominating the Western Canada and the southwestern North America with a correlation coefficient of 0.77 between the two modes. In strong LHF years, strengthened LHF favors to enhance precipitation in the Western Canada and reduce that in the southwestern North America. This is primarily associated with an anomalous cyclonic circulation over the KE region, which enhances southwesterly precipitation and latent heating in the middle troposphere. The heating excites an anomalous cyclonic circulation to its west and an anticyclonic circulation to its east, helping to reinforce the existing anomalous cyclonic circulation in turn and form a positive feedback. The conditions associated with La Niña events favor to above processes. To the upper troposphere, the deepened anomalous cyclonic circulation due to enhanced eddy activities and atmospheric baroclinic instability over the KE strengthens subtropical westerly jet stream and thereby extends eastward on the 200 hPa level. Correspondingly, an elongated zonally lower level cyclonic circulation anomaly across the North Pacific leads to a moisture convergence in the Western Canada, which is mainly resulted from the anomalous positive vorticity advection over the left side of the exit region of the jet stream. The opposite circumstance occurs in weak LHF years, presenting an opposed anomalous circulation and rainfall pattern.

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Horizontal heat impacts of a bare facade on air temperature in an adjacent green plot within pedestrian heights in Beijing

Indoor and Built Environment ◽

10.1177/1420326x19892673 ◽

2019 ◽

pp. 1420326X1989267

Author(s):

Hongxuan Zhou ◽

Guan Wang ◽

Dan Hu ◽

Jing Sun

Keyword(s):

Heat Flux ◽

Latent Heat ◽

Latent Heat Flux ◽

Air Temperature ◽

Sensible Heat Flux ◽

Atmospheric Environment ◽

Dominant Factor ◽

Sensible Heat ◽

Significance Level ◽

The Impact

This study focuses on the horizontal heat impact of facades on the surrounding atmospheric environment at pedestrian heights. The results show that (1) the horizontal heat impact of a facade on the surrounding atmosphere was relatively uniform due to the homogeneous energy flux near the facade; (2) the significance of horizontal heat impacts gradually weakened with height, and the average significance was 48.74% in the spring and 47.81% in the summer; (3) energy factors, such as net radiation, soil heat flux, sensible heat flux, latent heat flux, and ground radiation, influenced the significance of the air temperature difference between the two observation sites where the investigation was conducted; one site was near the facade (distance = 0.30 m), the other one was far from the wall (distance = 10 m), and no dominant factor was found; and (4) the sensible heat flux was higher at the site near the facade than at the site far from the facade at the 0.05 significance level in the summer, which could be attributed to the strong horizontal heat impact from the facade. In contrast, the impact of the facade on the latent heat flux was not significant at the 0.05 significance level in the summer.

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The Impact of Vertical Measurement Depth on the Information Content of Soil Moisture for Latent Heat Flux Estimation

Journal of Hydrometeorology ◽

10.1175/jhm-d-16-0044.1 ◽

2016 ◽

Vol 17 (9) ◽

pp. 2419-2430 ◽

Cited By ~ 17

Author(s):

Jianxiu Qiu ◽

Wade T. Crow ◽

Grey S. Nearing

Keyword(s):

Heat Flux ◽

Time Series ◽

Soil Moisture ◽

Information Content ◽

Latent Heat ◽

Latent Heat Flux ◽

Heat Flux Estimation ◽

Vertical Support ◽

Flux Estimation ◽

The Impact

Abstract This study aims to identify the impact of vertical support on the information content of soil moisture (SM) for latent heat flux estimation. This objective is achieved via calculation of the mutual information (MI) content between multiple soil moisture variables (with different vertical supports) and current/future evaporative fraction (EF) using ground-based soil moisture and latent/sensible heat flux observations acquired from the AmeriFlux network within the contiguous United States. Through the intercomparison of MI results from different SM–EF pairs, the general value (for latent heat flux estimation) of superficial soil moisture observations , vertically integrated soil moisture observations , and vertically extrapolated soil moisture time series [soil wetness index (SWI) from a simple low-pass transformation of ] are examined. Results suggest that, contrary to expectations, 2-day averages of and have comparable mutual information with regards to EF. That is, there is no clear evidence that the information content for flux estimation is enhanced via deepening the vertical support of superficial soil moisture observations. In addition, the utility of SWI in monitoring and forecasting EF is partially dependent on the adopted parameterization of time-scale parameter T in the exponential filter. Similar results are obtained when analyses are conducted at the monthly time scale, only with larger error bars. The contrast between the results of this paper and past work focusing on utilizing soil moisture to predict vegetation condition demonstrates that the particular application should be considered when characterizing the information content of soil moisture time series measurements.

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Impact of Deforestation on Land–Atmosphere Coupling Strength and Climate in Southeast Asia

Sustainability ◽

10.3390/su12156140 ◽

2020 ◽

Vol 12 (15) ◽

pp. 6140

Author(s):

Merja H. Tölle

Keyword(s):

Heat Flux ◽

Land Cover ◽

Southeast Asia ◽

Latent Heat ◽

Latent Heat Flux ◽

Coupling Strength ◽

El Niño ◽

El Nino ◽

La Nina ◽

The Impact

Southeast Asia (SEA) is a deforestation hotspot. A thorough understanding of the accompanying biogeophysical consequences is crucial for sustainable future development of the region’s ecosystem functions and society. In this study, data from ERA-Interim driven simulations conducted with the state-of-the-art regional climate model COSMO-CLM (CCLM; version 4.8.17) at 14 km horizontal resolution are analyzed over SEA for the period from 1990 to 2004, and during El Niño–Southern Oscillation (ENSO) events for November to March. A simulation with large-scale deforested land cover is compared to a simulation with no land cover change. In order to attribute the differences due to deforestation to feedback mechanisms, the coupling strength concept is applied based on Pearson correlation coefficients. The correlations were calculated based on 10-day means between the latent heat flux and maximum temperature, the latent and sensible heat flux, and the latent heat flux and planetary boundary layer height. The results show that the coupling strength between land and atmosphere increased for all correlations due to deforestation. This implies a strong impact of the land on the atmosphere after deforestation. Differences in environmental conditions due to deforestation are most effective during La Niña years. The strength of La Nina events on the region is reduced as the impact of deforestation on the atmosphere with drier and warmer conditions superimpose this effect. The correlation strength also intensified and shifted towards stronger coupling during El Niño events for both Control and Grass simulations. However, El Niño years have the potential to become even warmer and drier than during usual conditions without deforestation. This could favor an increase in the formation of tropical cyclones. Whether deforestation will lead to a permanent transition to agricultural production increases in this region cannot be concluded. Rather, the impact of deforestation will be an additional threat besides global warming in the next decades due to the increase in the occurrence of multiple extreme events. This may change the type and severity of upcoming impacts and the vulnerability and sustainability of our society.

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