Elsevier

Journal of Hydrology

Volume 599, August 2021, 126360
Journal of Hydrology

Research papers
REAL-Fog part 2: A novel approach to calculate high resoluted spatio-temporal fog deposition: A daily fog deposition data set for entire Germany for 1949–2018

https://doi.org/10.1016/j.jhydrol.2021.126360Get rights and content

Highlights

  • Fog deposition rises with altitude.

  • Annual sum of fog deposition varies a lot between a stand and a catchment.

  • The fog deposition altitude relation is different for each mountain.

  • No temporal trend was found in the fog deposition over the last 70 years.

Abstract

Fog deposition depends strongly on location and orographic setting. Even if the absolute amount can be small at some locations, it could play a decisive role. This is also true for Germany. In the lowlands, the annual amount of fog precipitation is in the range of a few mm per year, in the higher altitudes of the low mountain ranges a few hundred mm per year. In this article, we estimated the fog deposition based on the REAL-Fog model for Germany at daily time steps and one kilometre spatial resolution for a 70-year period for the years 1949 to 2018. These results were compared with another fog deposition modelling approach, station measurements and water balance modelling for different catchments in our study region. Comparing the results gives quite an interesting insight and outlook to the challenges to face in the future. The gridded data of the daily sum of the fog deposition we made available via HydroShare repository.

Introduction

Fog deposition is a part of the total precipitation that occurs in many parts of the world (Gultepe et al., 2007, Klemm et al., 2012, Tiedemann, 2001). While it is a rare phenomenon in large parts of the world with a few millimetres per year, it is commonplace in other parts. The higher amounts occur mainly in mountains regions below the tree line and near the coast of the oceans. It can reach values around several hundred or even thousands of mm per year and exceed the measured rain and snowfall precipitation. For instance, in the table mountain in South Africa, fog deposition exceeded 3,000 mm per year and the annual precipitation was less than 2,000 mm (Nagel, 1956). Unlike falling precipitation, fog deposition is not recorded in the standard measurements of the meteorological services, thus its spatial occurrence is limited to indirectly quantification. As consequences the input and output of water in sites with a considerable amount of fog deposition is imbalanced, so that runoff and evaporation can be higher than the falling precipitation (Hutley et al., 1997, Cameron et al., 1997, Zimmermann and Zimmermann, 2002). Non-rainfall water sources studied in drylands and wetlands had an important contribution to the decay of plant litter by enabling microbial activity (Gliksman et al., 2017, Jacobson et al., 2015, Evans et al., 2020, Newell et al., 1985, Kuehn et al., 2004), and for the activity of biological crusts (Hill et al., 2015, Maestre et al., 2010). Non-rainfall water sources can reduce drought stress and can be harvested in areas where it is economically feasible and provide additional water source in drylands (Wang et al., 2017). In addition, in areas with poor water supplies and high occurrence of fog, it can be collected with fog nets to use the water as a source of drinking water (Schemenauer and Cereceda, 1994). In this article, we want to focus on the fog deposition at the vegetation in Germany to determine the additional water input into the water balance. However, the methods presented here are not specifically adapted to the study area and can be transferred to other areas.

Investigations of fog deposition in Germany began at the beginning of the 20th century, when Linke (1916) carried out precipitation measurements in and outside a spruce stand in the Taunus and found that 66% additional precipitation was recorded in the stand due to dripping fog than outside the stand. Dieckmann (1931) used a fine cylindrical wire mesh, which he fixed over a Hellmann rain gauge to determine the fog precipitation on the Mt. Brocken. Rubner (1932) carried out similar measurements in the Ore Mountains but used glass rods instead of wire mesh. The idea of a standard measuring instrument for fog precipitation was taken up by Grunow (1952). He further developed the wired mesh cylinder attachment and carried out comparative measurements throughout Germany (Grunow, 1953, Grunow, 1955, Grunow, 1958, Grunow, 1963, Grunow and Tollner, 1969). It turned out that good comparative measurements of different locations were possible. However, the actually collected quantity of precipitation at the vegetation could not be determined satisfactorily. Thus, the fog-catcher "Hohenpeißenberger Nebelfänger” (german for fog catcher that was invented at Mt. Hohenpeißenberg,) described in Grunow (1953) and developed for the previous mentioned studies was, contrary to the previous plans, not introduced across the country. Modern fog catchers have to deal with the same issue (Schemenauer and Cereceda, 1994, Fuzzi et al., 1997). Wrzesinsky, 2004, Klemm et al., 2005, Klemm and Wrzesinsky, 2007 determined fog precipitation using the direct eddy covariance method, and while it is possible to measure the fog precipitation in a stand; it is not suitable for spatial investigation.

As an alternative and supplement to the direct measurement of fog deposition, models have been developed to determine the same. Katata (2014) provides a comprehensive overview of the development of fog modelling. The deposition models, which work with resistance analogy, should be mentioned here. Lovett (1984) developed a model that could determine the fog deposition on numerous vegetation layers and the associated resistances as a function of wind speed, droplet size distribution and liquid water content. The model is a one dimensional over a homogeneous canopy, which does not include the edge effect due to heterogenous environment. This model was used and further developed by numerous authors, such as Miller et al., 1993, Pahl, 1996, Burkard et al., 2003. One variant was parameterized by Katata et al., 2008 with high agreement to the Lovett-model (R2 = 0.928), so that the fog deposition calculated by his model only depends on the wind speed, the stand height and the leaf area index (LAI) as well as the liquid water content (lwc) which makes it easier to use due to the reduced amount of parameters.

In this article, we combine the REAL-Fog method from Körner et al., 2020, which is refered here to as REAL-Fog Part 1, for the determination of the lwc of the atmosphere at ground level with the determination of the deposition velocity from Katata et al., 2008, to determine the fog deposition for Germany with a temporal resolution of one day. As a consequence, we use only station data for the meteorological input variables in our modelling and are completely independent of the extremely time-consuming calculations of, on the one hand, numerical weather models and the resistance analogy model according to Lovett (1984), on the other hand. The calculations are made for the years 1949 to 2018 on hourly basis and were aggregated to daily resolution. Validation data are rare and, unfortunately, most of the records of the time series of Grunow are lost (Plaß-Dülmer, DWD, personal communication). However, we use the few remaining data and, additionally, calculations for several mountains done by Pahl (1996) and direct measured fog deposition by Wrzesinsky (2004). Furthermore, we run the water balance model BROOK90 (Federer et al., 2003) with and without the fog deposition calculated by the REAL-Fog-model for several low mountain range catchments. Some of which had major problems in closing the water balance due to fog deposition in the past.

Our hypothesis is therefore the following: From the hourly station data of wind speed, temperature and humidity as well as the LAI and the vegetation height and a digital elevation model, the spatial fog deposition can be derived by means of the proposed model. From this, a data set for fog deposition in Germany for the years 1949–2018 can be created. Such a data set is novel in terms of spatial and temporal resolution and coverage as well as for the small amount of variables required.

Section snippets

Site description

We conducted our study for the entire area of current Germany, which includes the former German Democratic Republic (1949-1990) before the German Reunification. . Germany lies in the cool temperate climate zone, extending from the Baltic and North Sea coasts over the North German lowlands, the low mountain range threshold to the Upper Rhine Rift Valley, the Alpine foothills and finally to the Alps. Previous studies of fog deposition in Germany were conducted for the Erzgebirge (Zimmermann and

Data

We use meteorological station data of the German Meteorological Service (DWD), which are freely available via ftp (DWD 2020). Temperature and humidity data are processed as described in Körner et al., 2020 and interpolated with thin plate splines (Nychka et al., 2017). Wind speed data are calculated according to the logarithmic wind profile (Eq. (2)) from the measuring height, which differes from station to station, to 10 m uniform height (Table 1). Gaps in meteorological data were filled

Results and discussion

In this section, we summarize and discuss the results of our modelling. The evaluation is initially carried out in a spatially or temporally aggregated manner throughout Germany. In the second part, we focus on the quality and compare our results with site measurements and site modelling, as well as water balance modelling on a catchment area basis.

Summary and conclusions

We determined fog deposition on vegetation using the method of Katata et al. (2008) combined with the method of Körner et al. (2020) for determining liquid water content. The uniqueness of the method and the dataset generated in a fine temporal resolution (hourly and daily, for calculation steps and aggregation, respectivly) and a decent spatial resolution (1 km2) for 70 years between 1949 and 2018 data, which we make freely available. The comparison with the unfortunately very few available

CRediT authorship contribution statement

Philipp Körner: Conceptualization, Methodology, Software, Validation, Formal analysis, Investigation, Writing - original draft. Rico Kronenberg: Validation, Data curation, Writing - original draft, Software. Daniel Gliksman: Writing - review & editing. Christian Bernhofer: Writing - review & editing, Supervision.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

The authors gratefully acknowledge the anonymous reviewers in advance. We further thank the German Meteorological Service (DWD) for the public data access. I further thank Johannes Franke who aroused my interest in the subject of fog deposition. This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

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