Evapotranspiration and crop coefficients for coffee production systems in colombia using eddy covariance method

Abstract. Nitrogen dioxide (NO2) plays an important role in atmospheric pollution, in particular for tropospheric ozone production. However, the removal processes involved in NO2 deposition to terrestrial ecosystems are still the subject of ongoing discussion. This study reports NO2 flux measurements made over a meadow using the eddy covariance method. The measured NO2 deposition fluxes during daytime were about a factor of two lower than a priori calculated fluxes using the Surfatm model without taking into account an internal (also called mesophyllic or sub-stomatal) resistance. Neither an underestimation of the measured NO2 deposition flux due to chemical divergence or an in-canopy NO2 source nor an underestimation of the resistances used to model the NO2 deposition explained the large difference between measured and modelled NO2 fluxes. Thus, only the existence of the internal resistance could account for this large discrepancy between model and measurements. The median internal resistance was estimated to be 300 s m−1 during daytime, but exhibited a large variability (100–800 s m−1). In comparison, the stomatal resistance was only around 100 s m−1 during daytime. Hence, the internal resistance accounted for 50–90% of the total leaf resistance to NO2. This study presents the first clear evidence and quantification of the internal resistance using the eddy covariance method; i.e. plant functioning was not affected by changes of microclimatological (turbulent) conditions that typically occur when using enclosure methods.

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LOS ESPACIOS DE PRODUCCIÓN DE CAFÉ SUSTENTABLE EN MÉXICO EN LOS INICIOS DEL SIGLO XXI

Revista Pueblos y fronteras digital ◽

10.22201/cimsur.18704115e.2009.7.186 ◽

2009 ◽

Vol 4 (7) ◽

pp. 116

Author(s):

Pablo Pérez Akaki

Keyword(s):

Production Systems ◽

Coffee Production ◽

Alternative Systems ◽

The World

Este documento analiza los diferentes sistemas de producción cafetaleros que han cobrado importancia en el ámbito internacional a los que usualmente se les llama alternativos y sustentables, sin cuestionarse suficiente sobre el concepto mismo de sustentabilidad. Al revisar la evolución de estos sistemas a escala mundial, es claro que en ellos se presentan numerosas contradicciones que generan varias interrogantes sobre las bondades que anuncian. Además se analiza cómo estos han cobrado importancia en México y se realiza un esfuerzo de cuantificación de su importancia. Se presenta finalmente un caso que muestra que los sistemas alternativos son importantes, pero limitados para conseguir al menos la suficiencia económica que demandan los productores. ABSTRACT This document analyzes the different coffee production systems that have gained importance in the international sphere which are commonly referred to as alternative and sustainable, without sufficient questioning of the concept itself of sustainability. Upon reviewing the evolution of these systems at the world scale, it is clear that numerous contradictions are presented in them that generate various questions on the virtues they extol. The document also analyzes how they have acquired importance in Mexico and an effort is made to quantify the same. Finally, a case is presented that demonstrates that the alternative systems are significant but limited in their procurement of at least the economic sufficiency demanded by producers.

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Options to correct local turbulent flux measurements for large-scale fluxes using a LES-based approach

10.5194/amt-2021-126 ◽

2021 ◽

Author(s):

Matthias Mauder ◽

Andreas Ibrom ◽

Luise Wanner ◽

Frederik De Roo ◽

Peter Brugger ◽

...

Keyword(s):

Eddy Covariance ◽

Large Scale ◽

Heat Fluxes ◽

Eddy Covariance Method ◽

Boundary Layer Height ◽

Secondary Circulations ◽

Low Pass ◽

Measurement Height ◽

Flux Measurements ◽

Dispersive Fluxes

Abstract. The eddy-covariance method provides the most direct estimates for fluxes between ecosystems and the atmosphere. However, dispersive fluxes can occur in the presence of secondary circulations, which can inherently not be captured by such single-tower measurements. In this study, we present options to correct local flux measurements for such large-scale transport based on a non-local parametric model that has been developed from a set of idealized LES runs for three real-world sites. The test sites DK-Sor, DE-Fen, and DE-Gwg, represent typical conditions in the mid-latitudes with different measurement height, different terrain complexity and different landscape-scale heterogeneity. Different ways to determine the boundary-layer height, which is a necessary input variable for modelling the dispersive fluxes, are applied, either from operational radio-soundings and local in-situ measurements for the flat site or from backscatter-intensity profile obtained from collocated ceilometers for the two sites in complex terrain. The adjusted total fluxes are evaluated by assessing the improvement in energy balance closure and by comparing the resulting latent heat fluxes with evapotranspiration rates from nearby lysimeters. The results show that not only the accuracy of the flux estimates is improved but also the precision, which is indicated by RMSE values that are reduced by approximately 50 %. Nevertheless, it needs to be clear that this method is intended to correct for a bias in eddy-covariance measurements due to the presence of large-scale dispersive fluxes. Other reasons potentially causing a systematic under- or overestimation, such as low-pass filtering effects and missing storage terms, still need to be considered and minimized as much as possible. Moreover, additional transport induced by surface heterogeneities is not considered.

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