Jan Friesen

Helmholtz Centre for Environmental Research | UFZ · Systemic Environmental Biotechnology

Pysewer provides a framework to automatically generate cost-efficient sewer network layouts using minimal data requirements. It is build around an algorithm for generation of viable sewer-network layouts. The approximated sewer network is represented by sources (households/buildings), potential pathways, and one or multiple sinks. The algorithm ap...

Due to accelerating climate change and the need for new development to accommodate population growth, adaptation of urban drainage systems has become a pressing issue in cities. Questions arise whether decentralised urban drainage systems are a better alternative to centralised systems, and whether Nature Based Solutions' (NBS) multifunctionality a...

Rural and semi-urban areas in arid/semi-arid regions are facing severe water scarcity and a series of environmental challenges nowadays, specifically due to rapid urbanization and economic development, climate change, population growth, increasing water demand, influxes of refugees caused by war and regional political conflict, etc. To solve the em...

For decades, there has been ongoing discussion about whether centralized or decentralized wastewater management systems are better. Decision-makers need to define the best option but do not always have the necessary tools to develop, compare, and identify the most appropriate solution. To address this, studies have been conducted on a settlement le...

The potential for sudden tree dieback exists when there is significant variation in perturbation frequency and intensity, which can alter canopy-atmosphere interactions, like canopy rainfall partitioning. In the context of close-to-nature silviculture practices, dieback trees can endure for several decades in specific environments. Therefore, it is...

Urban trees provide vital ecosystem services, and assessing their health is crucial for managing urban infrastructure. Traditional methods of assessing crown density, an indicator of tree vitality, involve horizontal perspectives of unobstructed canopies. This study presents a novel method for estimating crown density in urban street trees that are...

Safe access to water and sanitation is a basic human right and is set as the United Nations Sustainable Development Goal 6. Yet, more than half of global wastewater is not treated, thus polluting the environment and posing a health risk to society. Cost is a significant barrier to water treatment in many emerging economies because of the building a...

Precipitation chemistry data provide important information for environmental studies on large-scale element cycling and anthropogenic impacts on our atmosphere, but also for hydrochemical models and groundwater recharge estimations via the Chloride Mass Balance method. Such recharge data play a crucial role in groundwater management, particularly i...

Urban blue-green infrastructures (BGIs) fulfill a variety of functions that enable cities to cope with climate change and additional urban anthropogenic pressures such as increasing population density, heat island effects, biodiversity loss, and progressive sealing of permeable surfaces. In the urban water cycle, BGIs can play an important role whe...

The amphibian skin microbiome is important in maintaining host health, but is vulnerable to perturbation from changes in biotic and abiotic conditions. Anthropogenic habitat disturbance and emerging infectious diseases are both potential disrupters of the skin microbiome, in addition to being major drivers of amphibian decline globally. We investig...

Mountains are an essential component of the global life-support system. They are characterized by a rugged, heterogenous landscape with rapidly changing environmental conditions providing myriad ecological niches over relatively small spatial scales. Although montane species are well adapted to life at extremes, they are highly vulnerable to human...

While net precipitation entering the soil is commonly measured in woody ecosystems, there is a lack of field measurements for herbaceous vegetation. Small canopy heights and fragile stem structures are the primary challenges for net precipitation sampling in grasslands under field conditions. We designed a new in situ device, “interception tubes”,...

The emergence of the chytridiomycete fungal pathogen Batrachochytrium dendrobatidis (Bd), causing the disease chytridiomycosis, has caused collapse of amphibian communities in numerous mountain systems. The health of amphibians and of mountain freshwater habitats they inhabit is also threatened by ongoing changes in environmental, and anthropogenic...

Safe access to sanitation is at the core of the United Nations Sustainable Development Goal (SDG) #6. Currently, it is estimated that this goal cannot be met by 2030. Despite all kinds of administrational hurdles, meeting SDG#6 depends on considerable investment. In order to get a chance at fulfilling SGD#6, the most cost-effective wastewater manag...

These are the introductory videos for an #AGU2020 virtual conference session "Precipitation Partitioning by Vegetation." The first interaction between precipitation and land surface is often with a plant canopy, which partitions precipitation into throughfall, stemflow or interception. Studying these processes answers important questions for many f...

Cyclone Mekunu hit the southern Arabian Peninsula in late May 2018 and brought rainfall amounts that accounted for up to six times the mean annual precipitation. Coming from the Arabian Sea, a quite underdocumented region with regard to cyclones, the storm eye crossed the Omani coast approx. 80 km east of the border to Yemen. Using automatic sample...

Forest cover dynamics are an important indicator for climate change as well as for land conversion studies. Based on an analysis of 30 years of Landsat data a forest cover time series was generated and analyzed for the Dhofar mountains in Oman. The Dhofar mountains in Southern Oman with its semi-arid cloud forest is an important asset for livestock...

The science comic 'Roots of the Past nourish present research' leads two students on a wild time travel to the first observations and observatories of plants and precipitation – the story of ecohydrology. Using past knowledge and new technologies they develop ideas for their own research.

Der Wissenschaftscomic 'Wurzeln der Vergangenheit ernähren Forschung der Gegenwart' führt zwei Studierende auf ein wilde Zeitreise zu den ersten Beobachtungen und Observatorien von Pflanzen und Niederschlag – der Geschichte der Ökohydrologie. Dabei entwickeln sie Ideen für Ihre eigene Forschung.

This chapter presents a history of the interdisciplinary field focused on improving our understanding of the first step in the terrestrial hydrologic cycle: precipitation partitioning by vegetation. We describe the origins of interest, rooted in observations from “The Father of Botany,” Theophrastus (350 BCE) and synthesize the early formal hydrolo...

Redistribution of precipitation water by plant canopies increases the spatial variation of net precipitation at the surface, affecting soil moisture patterns, localized preferential flow, and soil biogeochemical processes. This chapter reviews methods for assessing and the current state of knowledge on spatial patterns of the two net precipitation...

The interception of precipitation by vegetation has important consequences for climate and water resources. Although canopy interception has been studied for centuries, many fundamental unknowns remain. We present persistent questions that reflect challenges in measuring, representing, and understanding how terrestrial ecosystems intercept, partiti...

Net precipitation recharges soil- and groundwater beneath vegetation canopies and litter layers. Interactions between subsurface water and net precipitation fluxes differ, however, as there are multiple types of net precipitation: free throughfall (rain that passes through canopy gaps), throughfall, and stemflow (rain that drains down plant stems)....

This book presents research on precipitation partitioning processes in vegetated ecosystems, putting them into a global context. It describes the processes by which meteoric water comes into contact with the vegetation's canopy, typically the first surface contact of precipitation on land. It also discusses how precipitation partitioning by vegetat...

The first contact between precipitation and the land surface is often a plant canopy. The resulting precipitation partitioning by vegetation returns water back to the atmosphere (evaporation of intercepted precipitation) and redistributes water to the subcanopy surface as a "drip" flux (throughfall) and water that drains down plant stems (stemflow)...

Das Themenheft "Sumpfpflanzendächer" gibt einen Überblick über den Stand der Forschung und über praktische Erfahrungen mit dieser wenig bekannten Art der Dachbegrünung.

Automatic samplers represent a convenient way to gather rain samples for isotope (δ18O and δ2H) and water quality analyses. Yet, most commercial collectors are expensive and do not reduce post-sampling evaporation and the associated isotope fractionation sufficiently. Thus, we have developed a microcontroller-based automatic rain sampler for timer-...

Automatic samplers represent a convenient way to gather rain samples for isotope (δ18O and δ2H) and water quality analyses. Yet, most commercial collectors are expensive and do not reduce post-sampling evaporation and the associated isotope fractionation sufficiently. Thus, we have developed a microcontroller-based automatic rain sampler for timer-...

Advanced Tools for Integrated Water Resources Management, Volume Three, explores a wide breadth of emerging and state-of-the-art technologies used to study advanced tools for integrated water resources management. The book provides insights in chapters relating to How to involve the public - citizen science approaches for IWRM, Urban forestry as a...

This is the story of Precipita, the waterwitch of Leipzig Germany, and the critical roles that urban forests play in protecting the city from her hydrological whims! As we made this comic with the City of Leipzig in Germany we also translated it into German. The science comic is based on a book chapter "Urban Forestry: An Underutilized Tool in Wa...

Scientists are trained to tell stories, scientific stories. Training is also needed to comprehend and contextualize these highly nuanced and technical stories because they are designed to explicitly convey scientific results, delineate their limitations, and describe a reproducible “plot” so that any thorough reenactment can achieve a similar concl...

Since the beginning of human settlement, people have observed water in its many forms, recording the ways that water supports and subverts life... like a cunning and capricious witch. This is the story of Precipita, the waterwitch of Leipzig Germany, and the critical roles that urban forests play in protecting the city from her hydrological whims!...

Study region: The Dhofar mountains are located on the Arabian Peninsula in Southern Oman. Unlike other regions of Oman, the Dhofar mountains have an annual monsoon season that results in a semi-arid cloud forest. The region highly depends on groundwater resources and the Dhofar mountain range is the major recharge area for the Salalah coastal plain...

The temporal dynamics of forest canopy rainfall partitioning are important to forest ecology and management as it influences all subsequent hydrological processes along the rainfall-to-discharge flow path. Despite a growing body of literature on the importance of coupled hydrological–ecological interactions during periodic forest life cycle events,...

This comic by authors Jan Friesen and Skander Elleuche together with illustrator Tyasseta and colorist Siloy explains the use of halophytes for bioenergy and is based on the review article: A. Debez*, I. Belghith*, J. Friesen*, C. Montzka*, S. Elleuche* (2017) Facing the challenge of sustainable bioenergy production: Could halophytes be part of the...

Urban forestry widely affects urban environments, impacting a city's microclimate, recreational value, and water resources. With regard to water resources, urban trees and forests can, for example, dampen the effects of extreme precipitation or help evaporate precipitation to reduce stormwater runoff. Yet, urban planners rarely consider urban fores...

Evaporation from wet-canopy (\(E_\mathrm{C}\)) and stem (\(E_\mathrm{S}\)) surfaces during rainfall represents a significant portion of municipal-to-global scale hydrologic cycles. For urban ecosystems, \(E_\mathrm{C}\) and \(E_\mathrm{S}\) dynamics play valuable roles in stormwater management. Despite this, canopy-interception loss studies typical...

Freezing temperatures can influence the material properties of trees. Understanding how forest biometeorological interactions respond to freezing temperatures is important for forest science and management, as its effects can cascade through coupled hydrological and ecological processes including limitations on tree growth, changes to canopy interc...

Due to steadily growing population and economic transitions in the more populous countries, renewable sources of energy are needed more than ever. Plant biomass as a raw source of bioenergy and biofuel products may meet the demand for sustainable energy; however, such plants typically compete with food crops, which should not be wasted for producin...

Many mechanisms aid invasive plants' competitive interactions. Yet, the extent to which invasive plants alter canopy hydrometeorological mechanisms determining the quantity and distribution of rainwater resources to soils have never been assessed. We examine these mechanisms for a global invader, Ailanthus altissima, across an invasion chronosequen...

Global gridded precipitation is an essential driving input for hydrologic models to simulate runoff dynamics in large river basins. However, the data often fail to adequately represent precipitation variability in mountainous regions due to orographic effects and sparse and highly uncertain gauge data. Water balance simulations in tropical montane...

Graphic novella by artist Bagus Seta (Tyasseta) based on the scientific story told in Sadeghi et al. (2017), Agricultural and Forest Meteorology, 240, 10.

This article provides an overview about the Bode River catchment that was selected as the hydrological observatory and main region for hydro-ecological research within the TERrestrial ENvironmental Observatories Harz/Central German Lowland Observatory. It first provides information about the general characteristics of the catchment including climat...

Semi-arid regions are facing the challenge of managing water resources under conditions of increasing scarcity and drought. These are recently pressured by the impact of climate change favoring the shifting from using surface water to groundwater without taking sustainability issues into account. Likewise, water scarcity raises the competition for...

Many mechanisms aid invasive plants’ competitive interactions. Yet, the extent to which invasive plants alter canopy hydrometeorological mechanisms determining the quantity and distribution of rainwater resources to soils has never been assessed. We examine these mechanisms for a global invader, Ailanthus altissima, across an invasion chronosequenc...

In arid regions like the Arabian Peninsula, available water resources are essentially restricted to groundwater, requiring a detailed understanding of the local and regional hydrogeological conditions and water budgets. In the framework of the IWAS initiative, the 1.8 × 106 km2 large sedimentary Upper Mega Aquifer of the Arabian Peninsula was chose...

Trees concentrate rainfall to near-stem soils via stemflow. When canopy structures are organized appropriately, stemflow can even induce preferential flow through soils, transporting nutrients to biogeochemically active areas. Bark structure significantly affects stemflow, yet bark-stemflow studies are primarily qualitative. We used a LaserBark to...

Precipitation intercepted by forests plays a major role in >1/4 of the global land area's hydrologic cycle. Direct in situ measurement of intercepted precipitation is challenging and, thus, it's typically indirectly estimated through comparing precipitation under forest cover and in the open. We discuss/compare measurement methods for forest precip...

Due to the ability of stable water isotopes to characterize the origin of water and connected processes of groundwater recharge, we used the isotope variations of hydrogen and oxygen in different water sources for assessing the recharge process in the Dhofar region. δ(18)O and δ(2)H of precipitation, spring water, and groundwater cover a range from...

The deduction by conventional means of qualitative and quantitative information about groundwater discharge into lakes is complicated. Nevertheless, at least for semi-arid regions with limited surface water availability, this information is crucial to ensure future water availability for drinking and irrigation purposes. Overcoming this lack of dis...

The deduction by conventional means of qualitative and quantitative information about groundwater discharge into lakes is complicated. Nevertheless, at least for semi-arid regions with limited surface water availability, this information is crucial to ensure future water availability for drinking and irrigation purposes. Overcoming this lack of di...

Measurement uncertainty through splash losses is a known issue in rainfall measurements. In the case of rain gauges this has resulted in standard funnel designs. In forest hydrology and specifically for throughfall measurements few standard trough designs or evaluation reports exist. We present a laboratory experiment in which the splash loss for d...

Partitioning of rainwater in interception, throughfall and stemflow plays a crucial role for potential soil water fluxes, especially in semiarid regions. On the one hand, reducing interception and enhancing net precipitation is crucial for maximizing rain yield. On the other hand, a large proportion of stemflow is likely to induce infiltration hots...

The Mediterranean region is one of the most imperilled regions in the world concerning present and future water scarcity. The region is delicately positioned at the crossroads between East and West, interlinking Europe, Asia and Africa. Societal and economic changes causing population growth, industrialisation and urbanisation lead to significant i...

Key Points Evaluated method may allow removal of multidirectional bending strains Canopy water loading signal may be isolated using the evaluated method Sample storms show water loading response to rainfall until storage capacity

Information on groundwater discharge over large spatial scales are essential for groundwater management particularly in (semi-) arid regions. If discharge areas are known, direct measurements over larger spatial scales are complicated to obtain by conventional means, why thermal remote sensing is increasingly applied to localize and quantify ground...

A difference has been detected between the C-band wind scatterometer measurements from the morning (descending) and evening (ascending) passes of the European Remote Sensing (ERS) 1/2 satellite. In the West African savanna, for example, these differences correspond to the onset of vegetation water stress. A literature review of the current state of...

Soil moisture estimates from the European Remote Sensing Satellite (ERS)-1, ERS-2, and Metop scatterometer instruments are available as time series starting in 1991. To better understand the satellite signal backscatter data and the corresponding soil moisture estimates, differences between different overpass times are analyzed. An analysis of more...

According to the latest IPCC projections, the Circum-Mediterranean region will be particularly affected by Global and Climate Change. These changes include population growth, increases in food, water and energy demands, changes in land use patterns and urbanization/industrialization, while at the same time, the renewable water resources in the regi...

We investigate the heterogeneity of below canopy fluxes and particularly the sources of enhanced canopy drainage fluxes (stemflow versus throughfall dripping points) in a semiarid cloud forests in Oman. Our results are probably applicable to other ecosystems. We used measurements of stemflow from two wet seasons and small-scale measurements of thro...

Assessing and managing water resources in developing and dryland regions is still fraught with difficulties. The typical tool chain of water resources management starts with the collection of data, subsequently processes and analyses the collected information within the natural and socio-economic setting, and finally generates end products that inf...

In forests rainfall partitioning provides highly organized rainfall patterns caused by rainfall funneling through vegetation structure. The patterns of rainfall partitioning have already been studied in great detail at a cloud forest enclosure in Dhofar, Oman. How those organized rainfall patterns on the surface advance into the root zone and deepe...

There is a growing interest in the understanding of the dynamics of sap flow and the transpiration process in plants. In this study, Xylem sap flux was monitored in a 4-year-old cashew (Anacardium occidentale) orchard for eight months (2–4 weeks per month), covering both wet and dry seasons of 2002 at Ejura in Ghana. Sap flux (Fd) was related diurn...

This technical note presents an instrumental method for the precise and timely installation of mechanical displacement sensors to investigate stem compression and relaxation associated with whole-tree rainwater loading and evaporation, respectively. We developed this procedure in response to the conclusions of Friesen et al. (20086. Friesen , J. 2...

This technical note presents an instrumental method for the precise and timely installation of mechanical displacement sensors to investigate stem compression and relaxation associated with whole-tree rainwater loading and evaporation, respectively. We developed this procedure in response to the conclusions of Friesen et al. (2008), which called fo...

Recently, large differences in backscatter between the ascending (evening) and descending (morning) tracks of the wind scatterometer onboard the ERS-1 and ERS-2 satellites have been identified in times and locations of vegetation water stress. This suggests that vegetation might be considered as a source of information rather than a barrier to soil...

Acoustic disdrometers are widely used as rainfall gauges, as the components are low cost and low maintenance as no moving parts are involved. We tested whether acoustic disdrometers could be used in combination with throughfall pipes in a semiarid cloud forest in Oman. Especially under forest canopy tipping buckets require high maintenance in terms...

The cloud forests of the Dhofar mountains in Oman are one of few water limited seasonal cloud forests in the world. Because of the dry conditions (annual rainfall is only 114-252 mm depending on the location), cloud water interception by tree canopies (horizontal precipitation) is believed to play a major role for survival of the forest. Being the...

Securing water resources for drinking water and food production is a matter of high societal importance for the countries on the Arabian Peninsula. The available water resources are largely restricted to groundwater. Therefore, developing appropriate methodologies for the estimation of groundwater recharge is crucial for the development of sustaina...

A method for measuring whole-tree interception of precipitation is presented which employs mechanical displacement sensors to measure trunk compression caused by the water captured by the tree canopy. Next to measuring changes in canopy water storage the presented technique offers a wide range of observations linked to mass change of the tree canop...

Soil moisture estimates from the ERS-1, -2, and MetOp scatterometer instruments are available as a long time series since 1991. Especially in semi arid regions, such as West Africa, the soil moisture estimates provided by the TU Vienna show good soil moisture signals. To better understand the satellite backscatter data and the corresponding soil mo...

Current global satellite scatterometer-based soil moisture retrieval algorithms do not take soil characteristics into account. In this paper, the characteristic time length of the soil water index has been calibrated for ten sampling frequencies and for different soil conductivity associated with 12 soil texture classes. The calibration experiment...

Maps of regional distributions of evaporation provide critical information on the interactions between land surface and the atmosphere since they allow (i) to follow where, when, and how much water has moved into the atmosphere by evaporation; (ii) to monitor crop performance and the effects of droughts for famine prediction; (iii) to better evalua...