Next Article in Journal
A Web Based Interface for Distributed Short-Term Soil Moisture Forecasts
Previous Article in Journal
Establishment of an Inventory for the Life Cycle Cost (LCC) Analysis of a Water Supply System
Article Menu
Issue 8 (August) cover image

Export Article

Open AccessArticle
Water 2017, 9(8), 607; https://doi.org/10.3390/w9080607

Agreement of Four Equations for Computing Dewfall in Northern Germany

1
College of Soil and Water Conservation, Beijing Forestry University, 35 Qinghua East Road, Beijing 100083, China
2
Helmholtz Center for Environmental Research–UFZ, Department Soil System Science, Lysimeter Station, Falkenberg 55, D-39615 Altmaerkische Wische, Germany
3
Faculty of Natural Sciences III, Martin-Luther-University Halle-Wittenberg, Julius-Kühn-Straße 23, D-06112 Halle (Saale), Germany
*
Author to whom correspondence should be addressed.
Received: 3 June 2017 / Revised: 2 August 2017 / Accepted: 8 August 2017 / Published: 15 August 2017
Full-Text   |   PDF [2832 KB, uploaded 23 August 2017]   |  

Abstract

The energy balance (EB), turbulent vapour transport (TVT), Penman-Monteith (PM) and Bowen ratio energy balance (BREB) equation were used to estimate dewfall based on meteorological data. Initially there were big disagreements between the estimates from these four equations. However, after multiplying the heat and vapour conductance terms by 0.33 the agreement was much better. This implies that the disagreements derived from improper conductance values. Initially we did not consider the effect of atmospheric stability on the conductances. With stability correction the conductances were on average 0.5 times the values without stability correction. To arrive at the aforementioned 0.33, the conductances with stability correction still need to be lower by a factor of 0.66. The value of the von Karman constant and the relationships for the zero plane displacement and the roughness length we used in our conductance computations are widely used, but not the only possible ones. With different values and relationships also suggested in the literature one can reach this factor. However, it is also possible that our wind speed data contributed to the fact that the conductances we computed were too high. Their computation for a given canopy—atmosphere system requires wind speeds from a wind profile in equilibrium with the vegetation. This in turn requires an adequate fetch around the investigated surface. The highly varied vegetation in and around the site where the study was conducted makes adequate fetch rather doubtful. To obtain valid conductance values the atmospheric stability conditions must be considered, the appropriate values for the von Karman constant, the zero plane displacement and roughness length must be used, and there must be adequate fetch. The BREB equation does not contain a conductance term and therefore does not suffer from the problems just stated. The other three equations do. However, the BREB, like the EB and TVT equations, need the surface temperature which is not routinely measured. This then leaves the PM equation from which this temperature has been eliminated as the only option. Hence, in a future study dewfall estimates from the PM equation should be compared with direct measurements with a high precision weighing lysimeter. View Full-Text
Keywords: dewfall; energy balance; turbulent vapour transport; Penman-Monteith equation; Bowen ratio; vapour conductance dewfall; energy balance; turbulent vapour transport; Penman-Monteith equation; Bowen ratio; vapour conductance
Figures

Figure 1

This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).
SciFeed

Share & Cite This Article

MDPI and ACS Style

Xiao, H.; Meissner, R.; Borg, H.; Wang, R.; Cao, Q. Agreement of Four Equations for Computing Dewfall in Northern Germany. Water 2017, 9, 607.

Show more citation formats Show less citations formats

Note that from the first issue of 2016, MDPI journals use article numbers instead of page numbers. See further details here.

Related Articles

Article Metrics

Article Access Statistics

1

Comments

[Return to top]
Water EISSN 2073-4441 Published by MDPI AG, Basel, Switzerland RSS E-Mail Table of Contents Alert
Back to Top