Jan Friesen - Academia.edu (original) (raw)

Papers by Jan Friesen

The cloud forests of the Dhofar mountains in Oman are one of few water limited seasonal cloud for... more 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 only green

Soil moisture is the key variable in the hydrological cycle. In the Volta Basin, West Africa, whe... more Soil moisture is the key variable in the hydrological cycle. In the Volta Basin, West Africa, where rainfed agriculture forms the main source of income for the majority of the population; productivity relies on available soil moisture or "green water". Progress will depend on good management of green water, and will be strongly based on monitoring results. Data scarcity in

Hydrological Processes, 2014

ABSTRACT Precipitation intercepted by forests plays a major role in >1/4 of the global lan... more ABSTRACT 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 precipitation interception beyond classical budgeting, then recommend future directions for improving water storage estimation. Comparison of techniques shows that methods submerging tree components produce the largest water storage capacity values. Whole tree lysimeters have been used with great success at quantifying water storage for the integrated system, yet are unable to separate trunk vs. canopy storage. Remote sensing, particularly signal attenuation, may permit this separation. Mechanical displacement methods show great promise and variety of techniques: pulley/spring system, branch strain sensors, trunk compression sensors, photography. Relating wind-sway to water storage also shows great promise with negligible environmental disruption, yet is currently at proof-of-concept stage. Suggested future directions focus on development of common features regarding all discussed methods: (i) measurement uncertainties or processes beyond interception influencing the observed signal, (ii) scaling approaches to move from single tree components to the single tree and forest scale, and (iii) temporal scaling to estimate the relevance of single interception components over longer time scales. Through addressing these research needs, we hope the scientific community can develop an “integrated” monitoring plan incorporating multiple measurement techniques to characterize forest-scale water storage dynamics while simultaneously investigating underlying (smaller-scale) components driving those dynamics across the spectrum of precipitation and forest conditions. This article is protected by copyright. All rights reserved.

ABSTRACT According to the latest IPCC projections, the Circum-Mediterranean region will be partic... more ABSTRACT 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 region are predicted to decrease by up to 50 % within the next 100 years. However, a profound basis for estimating and predicting the long-term effects of Global and Climate Change on the development of the quantity and quality of water resources and on ecosystems is still lacking. The main reason for this is that environmental monitoring, in particular in the Mediterranean region, is strongly disciplinarily oriented, and financing is usually limited to short-term periods. The TERENO-MED (Terrestrial Environmental Observatories in the Mediterranean) initiative aims to fill the described gap. Together with partners in the region, TERENO-MED will establish a Circum-Mediterranean network of Global Change observatories, and will investigate the effects of anthropogenic impacts and of climate change on Mediterranean water resources and ecosystems. Within a set of representative catchments around the Circum-Mediterranean region (Southern Europe, Northern Africa, Near East), observatory sites will be installed with state-of-the-art and innovative monitoring equipment, in order to measure hydrological states and fluxes on a long-term basis (minimum 15 years). Monitoring equipment will cover all scales, from the point to the regional scale using ground-based and remote sensing technologies. Based on the acquired information, TERENO-MED, together with partners across the Mediterranean region will develop model scenarios that may serve as a basis for sustainable political and economical decisions. In order to gain a deep understanding of the most relevant processes and feedbacks, and to deliver reliable future scenarios for the Mediterranean region, the two initiating Helmholtz Centres, UFZ (Helmholtz Centre for Environmental Research) and Forschungszentrum Juelich, are seeking interested German and international partners to conduct joint research within the planned monitoring network.

ABSTRACT The Mediterranean region is one of the most imperilled regions in the world concerning p... more ABSTRACT 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 increases in food, water and energy demand. Hence, natural resources, such as water and soils, as well as ecosystems are put under pressure and water availability and quality will be severely affected in the future. At the same time, climate and extreme event projections from climate models for the Mediterranean are, unlike for most regions worldwide, consistent in their trends based on various scenarios. This consistency in the model predictions shows that the Mediterranean will face some of the most severe increases in dryness worldwide (based on consecutive dry days and soil moisture), and indicate a decrease of up to 50 % in available water resources within the next 50-100 years. These developments are accentuated by the fact that in many of the Mediterranean countries, natural renewable water resources are fully exploited or over-exploited already today, mainly due to agricultural irrigation, but also touristic activities. At the same time, the Mediterranean region is a global hot spot of freshwater biodiversity, with a high proportion of endemic and endangered species. While trend projections for water availability and climate change derived from global studies are consistent, regional patterns and heterogeneities, as well as local adaptation measures will largely determine the functioning of societies and the health of ecosystems. However, a lack of environmental data prohibits the development of sustainable adaptation measures to water scarcity on a scientific basis. Building on the experiences gained in the national TERENO network, a Mediterranean observatory network will be set-up, coordinated by two Helmholtz Centres and jointly operated with local partners across the Mediterranean region. In a number of Mediterranean mesoscale hydrological catchments TERENO-MED will investigate the long-term effects of global change on the quality and the dynamics of water resources in human-influenced environments under water scarcity. The Helmholtz Centres UFZ (overall coordinator) and FZJ have therefore initiated the set-up of a network of global change observatories in 5-10 Mediterranean river catchments. The TERENO-MED observatories will: - investigate societally relevant water problems in the context of 'typical' Mediterranean environments, - provide long-term and quality-controlled data available to the scientific community, - be operated and maintained through local research institutes and universities, - establish common monitoring platforms and foster synergies between research organizations, - provide solutions to pressing local and regional water problems by building partnerships between scientific partners and regional authorities.

ABSTRACT Partitioning of rainwater in interception, throughfall and stemflow plays a crucial role... more ABSTRACT 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 hotspots leading to fast transport of water to the deep soil, where it is safe from evaporation. In this paper we investigate, whether climate factors or species properties are more conducive to dividing net precipitation into stemflow and throughfall. For this, we use measurements of stemflow and throughfall from two growing seasons in an semiarid cloud forest in Oman, where both wind-driven rain and cloud deposition occur together. Using multivariate statistics, we compare the drivers of stemflow, throughfall partitioning between periods with different wind and rain conditions to understand, weather periods of extremely inclined rain promote stemflow, or alternatively weather stemflow depends solely on the specific position, tree species and tree morphology (height, crown diameter). Our results indicate that in particular position and species shape stemflow rates, while variation between singular events are influenced by climate variables. Our results show the importance of tall vegetation in semiarid regions for shaping patterns of soil infiltration and potential for groundwater recharge.

The deduction by conventional means of qualitative and quantitative information about groundwater... more 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.

Accurate information on the distribution of sensible and latent heat fluxes as well as soil moist... more Accurate information on the distribution of sensible and latent heat fluxes as well as soil moisture is critical for evaluation of background characteristics. Since these fluxes are subject to rapid changes in time and space, it is nearly impossible to determine their spatial and temporal distributions over large areas from ground measurements alone. Therefore, prediction from remote sensing images is

Physics and Chemistry of The Earth, 2008

Maps of regional distributions of evaporation provide critical information on the interactions be... more 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 evaluate the performance of irrigation systems; and

Detection and Remediation Technologies for Mines and Minelike Targets X, 2005

In this paper we present the results of a study of some soil magnetic properties in Ghana. The so... more In this paper we present the results of a study of some soil magnetic properties in Ghana. The soils sampled formed in different parent materials: Granites, Birimian rocks, and Voltaian sandstones. We discuss the role of environmental controls such as parent material, soil drainage, and precipitation on the magnetic properties. The main conclusion of this reconnaissance study is that the eight different soil types sampled have their own unique magnetic signature. Future research will have to confirm whether this conclusion holds for other soils in Ghana. If it does, the measurement of magnetic soil properties may become a viable complement for the investigation of soil erosion, land degeneration, and pedogenesis. The magnetic soil properties measured would probably not pose any limitations for the use of electromagnetic sensors for the detection of land mines and UXO. * hendrick@nmt.edu; phone (+1) 505 835-5892; fax (+1) 505 835-6436;

Water Resources Research, 2013

ABSTRACT [1] To improve the water budgeting of forested catchments and inform relevant hydrologic... more ABSTRACT [1] To improve the water budgeting of forested catchments and inform relevant hydrologic theory regarding water cycling within forests, the scientific community has been seeking simple, inexpensive, direct methods for determining rain water storage on in situ tree canopies. This paper evaluates an installation arrangement and routine for one such method: mechanical displacement sensors placed on a tree's trunk to directly monitor compression under canopy water loading from rainfall. The evaluated installation routine aligns mechanical displacement sensors along orthogonal axes passing through the mechanical center of the trunk to reduce wind-induced noise. The experimental attainment of neutral bending axes for a subject hardwood and softwood tree suggests the routine is precise and approximates the trunk's mechanical center well regardless of differences in cellular axial stiffness between heart and sapwood. When installed in this precise sensor arrangement, bending tests of different loading directions produced a consistent signal ratio between sensor pairs of approximately −1 (1 unit compression/1 unit elongation), allowing the identification and removal of bending strains from the raw strain signals to isolate the compression component attributable to canopy water storage loads. The same experiments performed on sensors just 5 cm off the trunk's computed mechanical center were unable to produce neutral bending axes or consistent signal ratios during bending from variable loading directions. Results from the method evaluation were translated into a data processing technique that is then applied to strain data collected through two sample rain events (one each for the hardwood and softwood trees). The processed strain data showed a clear synchronicity between rainfall and canopy loading, as well as periods of maximized canopy water loading (canopy storage capacity). Our results indicate that the evaluated arrangement and installation procedure for mechanical displacement sensors may be able to provide scientists with simple, direct canopy water storage estimates at high temporal resolution and sensitivity.

Water Resources Research, 2008

1] A method for measuring whole-tree interception of precipitation is presented which employs mec... more 1] 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. This direct and nondestructive method is demonstrated to be sensitive to less than 5 kg of interception field tests in Netherlands and Ghana.

Water Resources Management, 2012

Assessing and managing water resources in developing and dryland regions is still fraught with di... more 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 inform decision-making. However, several of these steps often turn out to be problematic when faced with development issues and severe strains on water resources.

The cloud forests of the Dhofar mountains in Oman are one of few water limited seasonal cloud for... more 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 only green

Soil moisture is the key variable in the hydrological cycle. In the Volta Basin, West Africa, whe... more Soil moisture is the key variable in the hydrological cycle. In the Volta Basin, West Africa, where rainfed agriculture forms the main source of income for the majority of the population; productivity relies on available soil moisture or "green water". Progress will depend on good management of green water, and will be strongly based on monitoring results. Data scarcity in

Hydrological Processes, 2014

ABSTRACT Precipitation intercepted by forests plays a major role in >1/4 of the global lan... more ABSTRACT 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 precipitation interception beyond classical budgeting, then recommend future directions for improving water storage estimation. Comparison of techniques shows that methods submerging tree components produce the largest water storage capacity values. Whole tree lysimeters have been used with great success at quantifying water storage for the integrated system, yet are unable to separate trunk vs. canopy storage. Remote sensing, particularly signal attenuation, may permit this separation. Mechanical displacement methods show great promise and variety of techniques: pulley/spring system, branch strain sensors, trunk compression sensors, photography. Relating wind-sway to water storage also shows great promise with negligible environmental disruption, yet is currently at proof-of-concept stage. Suggested future directions focus on development of common features regarding all discussed methods: (i) measurement uncertainties or processes beyond interception influencing the observed signal, (ii) scaling approaches to move from single tree components to the single tree and forest scale, and (iii) temporal scaling to estimate the relevance of single interception components over longer time scales. Through addressing these research needs, we hope the scientific community can develop an “integrated” monitoring plan incorporating multiple measurement techniques to characterize forest-scale water storage dynamics while simultaneously investigating underlying (smaller-scale) components driving those dynamics across the spectrum of precipitation and forest conditions. This article is protected by copyright. All rights reserved.

ABSTRACT According to the latest IPCC projections, the Circum-Mediterranean region will be partic... more ABSTRACT 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 region are predicted to decrease by up to 50 % within the next 100 years. However, a profound basis for estimating and predicting the long-term effects of Global and Climate Change on the development of the quantity and quality of water resources and on ecosystems is still lacking. The main reason for this is that environmental monitoring, in particular in the Mediterranean region, is strongly disciplinarily oriented, and financing is usually limited to short-term periods. The TERENO-MED (Terrestrial Environmental Observatories in the Mediterranean) initiative aims to fill the described gap. Together with partners in the region, TERENO-MED will establish a Circum-Mediterranean network of Global Change observatories, and will investigate the effects of anthropogenic impacts and of climate change on Mediterranean water resources and ecosystems. Within a set of representative catchments around the Circum-Mediterranean region (Southern Europe, Northern Africa, Near East), observatory sites will be installed with state-of-the-art and innovative monitoring equipment, in order to measure hydrological states and fluxes on a long-term basis (minimum 15 years). Monitoring equipment will cover all scales, from the point to the regional scale using ground-based and remote sensing technologies. Based on the acquired information, TERENO-MED, together with partners across the Mediterranean region will develop model scenarios that may serve as a basis for sustainable political and economical decisions. In order to gain a deep understanding of the most relevant processes and feedbacks, and to deliver reliable future scenarios for the Mediterranean region, the two initiating Helmholtz Centres, UFZ (Helmholtz Centre for Environmental Research) and Forschungszentrum Juelich, are seeking interested German and international partners to conduct joint research within the planned monitoring network.

ABSTRACT The Mediterranean region is one of the most imperilled regions in the world concerning p... more ABSTRACT 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 increases in food, water and energy demand. Hence, natural resources, such as water and soils, as well as ecosystems are put under pressure and water availability and quality will be severely affected in the future. At the same time, climate and extreme event projections from climate models for the Mediterranean are, unlike for most regions worldwide, consistent in their trends based on various scenarios. This consistency in the model predictions shows that the Mediterranean will face some of the most severe increases in dryness worldwide (based on consecutive dry days and soil moisture), and indicate a decrease of up to 50 % in available water resources within the next 50-100 years. These developments are accentuated by the fact that in many of the Mediterranean countries, natural renewable water resources are fully exploited or over-exploited already today, mainly due to agricultural irrigation, but also touristic activities. At the same time, the Mediterranean region is a global hot spot of freshwater biodiversity, with a high proportion of endemic and endangered species. While trend projections for water availability and climate change derived from global studies are consistent, regional patterns and heterogeneities, as well as local adaptation measures will largely determine the functioning of societies and the health of ecosystems. However, a lack of environmental data prohibits the development of sustainable adaptation measures to water scarcity on a scientific basis. Building on the experiences gained in the national TERENO network, a Mediterranean observatory network will be set-up, coordinated by two Helmholtz Centres and jointly operated with local partners across the Mediterranean region. In a number of Mediterranean mesoscale hydrological catchments TERENO-MED will investigate the long-term effects of global change on the quality and the dynamics of water resources in human-influenced environments under water scarcity. The Helmholtz Centres UFZ (overall coordinator) and FZJ have therefore initiated the set-up of a network of global change observatories in 5-10 Mediterranean river catchments. The TERENO-MED observatories will: - investigate societally relevant water problems in the context of 'typical' Mediterranean environments, - provide long-term and quality-controlled data available to the scientific community, - be operated and maintained through local research institutes and universities, - establish common monitoring platforms and foster synergies between research organizations, - provide solutions to pressing local and regional water problems by building partnerships between scientific partners and regional authorities.

ABSTRACT Partitioning of rainwater in interception, throughfall and stemflow plays a crucial role... more ABSTRACT 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 hotspots leading to fast transport of water to the deep soil, where it is safe from evaporation. In this paper we investigate, whether climate factors or species properties are more conducive to dividing net precipitation into stemflow and throughfall. For this, we use measurements of stemflow and throughfall from two growing seasons in an semiarid cloud forest in Oman, where both wind-driven rain and cloud deposition occur together. Using multivariate statistics, we compare the drivers of stemflow, throughfall partitioning between periods with different wind and rain conditions to understand, weather periods of extremely inclined rain promote stemflow, or alternatively weather stemflow depends solely on the specific position, tree species and tree morphology (height, crown diameter). Our results indicate that in particular position and species shape stemflow rates, while variation between singular events are influenced by climate variables. Our results show the importance of tall vegetation in semiarid regions for shaping patterns of soil infiltration and potential for groundwater recharge.

The deduction by conventional means of qualitative and quantitative information about groundwater... more 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.

Accurate information on the distribution of sensible and latent heat fluxes as well as soil moist... more Accurate information on the distribution of sensible and latent heat fluxes as well as soil moisture is critical for evaluation of background characteristics. Since these fluxes are subject to rapid changes in time and space, it is nearly impossible to determine their spatial and temporal distributions over large areas from ground measurements alone. Therefore, prediction from remote sensing images is

Physics and Chemistry of The Earth, 2008

Maps of regional distributions of evaporation provide critical information on the interactions be... more 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 evaluate the performance of irrigation systems; and

Detection and Remediation Technologies for Mines and Minelike Targets X, 2005

In this paper we present the results of a study of some soil magnetic properties in Ghana. The so... more In this paper we present the results of a study of some soil magnetic properties in Ghana. The soils sampled formed in different parent materials: Granites, Birimian rocks, and Voltaian sandstones. We discuss the role of environmental controls such as parent material, soil drainage, and precipitation on the magnetic properties. The main conclusion of this reconnaissance study is that the eight different soil types sampled have their own unique magnetic signature. Future research will have to confirm whether this conclusion holds for other soils in Ghana. If it does, the measurement of magnetic soil properties may become a viable complement for the investigation of soil erosion, land degeneration, and pedogenesis. The magnetic soil properties measured would probably not pose any limitations for the use of electromagnetic sensors for the detection of land mines and UXO. * hendrick@nmt.edu; phone (+1) 505 835-5892; fax (+1) 505 835-6436;

Water Resources Research, 2013

ABSTRACT [1] To improve the water budgeting of forested catchments and inform relevant hydrologic... more ABSTRACT [1] To improve the water budgeting of forested catchments and inform relevant hydrologic theory regarding water cycling within forests, the scientific community has been seeking simple, inexpensive, direct methods for determining rain water storage on in situ tree canopies. This paper evaluates an installation arrangement and routine for one such method: mechanical displacement sensors placed on a tree's trunk to directly monitor compression under canopy water loading from rainfall. The evaluated installation routine aligns mechanical displacement sensors along orthogonal axes passing through the mechanical center of the trunk to reduce wind-induced noise. The experimental attainment of neutral bending axes for a subject hardwood and softwood tree suggests the routine is precise and approximates the trunk's mechanical center well regardless of differences in cellular axial stiffness between heart and sapwood. When installed in this precise sensor arrangement, bending tests of different loading directions produced a consistent signal ratio between sensor pairs of approximately −1 (1 unit compression/1 unit elongation), allowing the identification and removal of bending strains from the raw strain signals to isolate the compression component attributable to canopy water storage loads. The same experiments performed on sensors just 5 cm off the trunk's computed mechanical center were unable to produce neutral bending axes or consistent signal ratios during bending from variable loading directions. Results from the method evaluation were translated into a data processing technique that is then applied to strain data collected through two sample rain events (one each for the hardwood and softwood trees). The processed strain data showed a clear synchronicity between rainfall and canopy loading, as well as periods of maximized canopy water loading (canopy storage capacity). Our results indicate that the evaluated arrangement and installation procedure for mechanical displacement sensors may be able to provide scientists with simple, direct canopy water storage estimates at high temporal resolution and sensitivity.

Water Resources Research, 2008

1] A method for measuring whole-tree interception of precipitation is presented which employs mec... more 1] 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. This direct and nondestructive method is demonstrated to be sensitive to less than 5 kg of interception field tests in Netherlands and Ghana.

Water Resources Management, 2012

Assessing and managing water resources in developing and dryland regions is still fraught with di... more 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 inform decision-making. However, several of these steps often turn out to be problematic when faced with development issues and severe strains on water resources.