Evapotranspiration of an Abandoned Grassland in the Italian Alps: Modeling the impact of shrub encroachment

Shrub encroachment of grasslands in the Alps is still a poorly studied phenomenon. Therefore, this study analyses the possible effect of shrub encroachment on actual evapotranspiration (ETa) at an abandoned grassland in the Northwestern Italian Alps, colonised by Elaeagnus Rhamnoides shrubs. This is done by means of micrometeorological and eddy covariance data collected during four growing seasons. Additionally, the Hydrus 1D hydrological model modified to account for a soil column with two vegetation types is used. This modified model is run with a variable percentage of shrubs on evapotranspiration, ranging from 0 to 80% and it is validated by using the measured eddy covariance-derived ETa. The Hydrus 1D model is also applied in its usual set-up, having only one vegetation type, to estimate the ETa from both grassland and shrubs separately. The performance of the modified model with two vegetation types is acceptable, although it is very variable between different growing seasons and in dry condition it could be further improved (R between 0.50 in 2016 and 0.73 in 2014 considering the probable actual percentage of ETa affected by shrubs. The percentage varies between 20% in 2016 and 60% in 2014). Besides, the model captures the inter-annual variability of ETa. The agreement of cumulative simulated and observed ETa is good, since the deviation between observed and modelled cumulative ETa is always lower, in the four analysed growing seasons, than 50 mm. The simulated ETa approximates the eddy covariance-derived ETa, however the modelled soil water content is very sensitive to precipitation events, more than the measured soil water content. Both models, with the modified and the usual setup, tend to overestimate the vegetation stress during dry periods. Nevertheless, the single vegetation model results allow us to conclude that the shrubs likely are responsible for an enhancement of ETa and an alteration of the hydrological cycle accordingly. Finally, we explore how some micro-meteorological drivers of ETa (vapour pressure deficit – VPD, net radiation, wind speed, air temperature and ground heat flux - G0) affect the difference between modelled and simulated ETa, and between simulated ETa from shrubs and from grass. Frequently, higher deviations from zero are found especially with high VPD and G0

Reducing wind erosion through agroforestry: a case study using large Eddy simulations

Wind erosion is seen as one of the main risks for modern agriculture in dry and sandy regions. Shelterbelts and agroforestry systems are known for their ability to reduce wind speed and, consequently, wind erosion. The current study considers temperate alley cropping agroforestry systems, where multiple tree strips (shelterbelts) are interleaved with either annual rotating crops or perennial grassland. The aim was to quantify the potential wind erosion reduction by alley cropping agroforestry systems and the effect of design decisions for a case study in Germany. By combining wind measurements and Large Eddy Simulations, the wind speed and potential wind erosion inside an agroforestry system were estimated. Our model simulations result in an average reduction in wind speed between 17% and 67%, and a reduction of average potential wind erosion between 24% and 97%. The most optimal reduction of the average potential wind erosion was larger than 92% for tree strips orientated perpendicular to the main wind direction, whereas for a diagonal orientation of the tree strips to the main wind direction we found an average reduction of 86%. Parallel orientated tree strips reduce wind erosion on average by less than 35%. Tree strips planted with ≤48 m distance provide a strong and constant reduction of wind erosion, even for tree strips of 2 m height the average reduction was 86%, when the tree strips were orientated optimal to the dominant wind direction. Our model simulations showed that alley cropping agroforestry systems in a temperate climate have a large potential to reduce wind erosion by more than 80% when the system is well-designed and managed

Evapotranspiration of an Abandoned Grassland in the Italian Alps: Influence of Local Topography, Intra- and Inter-Annual Variability and Environmental Drivers

Evapotranspiration is a key variable of the hydrological cycle but poorly studied in Alpine ecosystems. The current study aimed to characterise the impact of topography and temporal variability on actual evapotranspiration (ETa) and its environmental drivers at an Alpine abandoned grassland encroached by shrubs on a steep slope. Eddy covariance, meteorological, hydrological and soil data were analysed over four growing seasons, of which two had wet and two dry conditions. The topography caused a systematic morning inflexion of ETa in all growing seasons, reflecting the valley wind system. Inter-annual differences of ETa exceeded 100 mm, and ETa means and cumulative values were significantly different between wet and dry growing seasons in the four years. Besides, ETa had a larger temporal variability in wet growing seasons. A bimodality of ETa was found in all years, caused by the onset of plant activity in the morning hours. Energy- and water-limited ETa periods were identified by comparing ETa to potential evapotranspiration (ETo). Periods of fifteen days revealed the main intra- and inter-annual differences of the environmental variables (air temperature, vapour pressure deficit—VPD, precipitation and ETa). The fixed effects of a linear mixed model based on ETa drivers explained 56% of ETa variance. The most important ETa drivers were net radiation and VPD, followed by wind speed. In growing seasons characterised by dry conditions, air temperature and the ground heat flux at the surface (either both or one of them) influenced ETa as well. The current study contributed to the understanding of topographical and temporal effects on evapotranspiration and other micrometeorological variables in an Alpine ecosystem still rarely studied

Wind speed measurements using distributed fiber optics: a wind tunnel study

Near-surface wind speed is typically only measured by point observations. The so-called Actively Heated Fiber-Optic (AHFO) technique, however, has the potential to provide high-resolution distributed observations, allowing for better understanding of different processes. However, before it can be widely used, its performance needs to be tested in a range of settings. Therefore, in this work, experimental results on this novel observational wind-probing technique are presented. We utilized a controlled wind-tunnel setup to assess both the accuracy and the precision of AHFO as well as its potential for outdoor atmospheric operation. The technique allows for wind speed characterization with a spatial resolution of 0.3 m on a 1 s time scale. The flow in the wind tunnel is varied in a controlled manner, such that the mean wind, ranges between 1 and 17 m/s. Comparison of the AHFO measurements with observations from a sonic anemometer shows a high overall correlation, ranging from 0.94-0.99. Also, both precision and accuracy are greater than 95 %. As such, it is concluded that the AHFO has potential to be employed as an outdoor observational technique in addition to existing techniques. In particular, it allows for characterization of spatial varying fields of mean wind in complex terrain, such as in canopy flows or in sloping terrain. In the future the technique could be combined with regular Distributed Temperature Sensing (DTS) for turbulent heat flux estimation in micrometeorological/hydrological applications

Genetic Programming in Hydrology: Using genetic programming in conceptual modelling

This report introduces the use of Genetic Programming (GP) into hydrology by describing the results of GP using conceptual hydrological models as physical representation. First the possibilities of GP are tested on synthetic data, which results in a shortlist of good working objective functions and insight in the most important GP settings. The test on real data in the Belgium Ardennes showed that GP using the objective functions KG10, MM and Shafii performed better. Nevertheless all three models performed not well on simulating the low flows and high peaks. Furthermore GP using KG10 and MM both results in simple serial models which perform well overall, but bad on quick response runoff. Shafii resulted in parallel models which show quick response flow, however GP it is not able to capture the fast responses correctly (yet). GP has the potential to improve the understanding in the behaviour of catchments, however it still needs the human mind to observe, compare and analyse the modelling results. The main consideration with GP is to look for a balance between: model search space, objective function, randomness and (computational) time. The challenge is how to lead GP in an efficient way without removing the possibility of finding unknown patterns.Additional thesisWater Managemen

Groundwater recharge in Myanmar - Estimations in the Chindwin catchment by base flow separation and SWAT

First estimations for the groundwater recharge in the Chindwin basin in Myanmar are presented in this report. This estimations are based on base flow separation and a SWAT model. Multiple base flow separation methods are applied and these are compared with the base flow produced by the SWAT model. This first estimations show a range of 248-670 mm average groundwater recharge per year, which is roughly 11-30% of the average annual rain in the catchment. The upper limit, produced by SWAT, seems to be too high, as the total flow is overestimated due to a rate of evaporation which is too low compared with remote sensing based evaporation. In the Chindwin it appeared that it is rather difficult to separate the base flow due to the highly sensitive alpha parameter, which determines the response behaviour of the base flow, also there seem to be multiple groundwater components. This makes it hard to perform base flow separation, but also increases the difficulty of calibrating the SWAT model, especially the base flow component. However the SWAT model shows a clear spatial groundwater recharge pattern even though it needs further optimization. Optimizing a (hydraulic) model can be cumbersome and especially in a developing environment as Myanmar it is also interesting to look at other possibilities/models, like Water Accounting +, which are more flexible to adapt to changes as new dams or increase in groundwater irrigation.InternshipWater Managemen

Reducing Wind Erosion through Agroforestry: A Case Study Using Large Eddy Simulations

Wind erosion is seen as one of the main risks for modern agriculture in dry and sandy regions. Shelterbelts and agroforestry systems are known for their ability to reduce wind speed and, consequently, wind erosion. The current study considers temperate alley cropping agroforestry systems, where multiple tree strips (shelterbelts) are interleaved with either annual rotating crops or perennial grassland. The aim was to quantify the potential wind erosion reduction by alley cropping agroforestry systems and the effect of design decisions for a case study in Germany. By combining wind measurements and Large Eddy Simulations, the wind speed and potential wind erosion inside an agroforestry system were estimated. Our model simulations result in an average reduction in wind speed between 17% and 67%, and a reduction of average potential wind erosion between 24% and 97%. The most optimal reduction of the average potential wind erosion was larger than 92% for tree strips orientated perpendicular to the main wind direction, whereas for a diagonal orientation of the tree strips to the main wind direction we found an average reduction of 86%. Parallel orientated tree strips reduce wind erosion on average by less than 35%. Tree strips planted with ≤48 m distance provide a strong and constant reduction of wind erosion, even for tree strips of 2 m height the average reduction was 86%, when the tree strips were orientated optimal to the dominant wind direction. Our model simulations showed that alley cropping agroforestry systems in a temperate climate have a large potential to reduce wind erosion by more than 80% when the system is well-designed and managed

The sewer system of urban Maputo

During three months information about the sewer system of Maputo was gathered, mostly at DNA, DAS, CRA, AdeM, AIAS and at the Municipality of Maputo. The information, consisting of reports, papers, maps, presentations and websites, was used to estimate the potential amount of wastewater in the sewer system of Urban Maputo. This wastewater could be available for reuse in Maputo, at the WWTP, being this the main purpose of the project “Sustainable freshwater supply in urbanizing Maputo, Mozambique” led by TU Delft, UNESCO-IHE and the Mozambican University UEM.The sewer network consists of system one and system two. System one was built by the Portuguese in the 40s as a drainage system, but nowadays it functions as a combined sewer and it discharges directly into the bay. System two, built by DHV, a Dutch consultancy firm, in the 80s consists of sewer lines, a WWTP and two pumping stations. These pumping stations are also supposed to pump a part of the water of system one to the WWTP. However, because of sand in the pipes the pumping stations are not being operated.The billed amount of drinking water was used to calculate the flow in systems one and two. These data were obtained per neighbourhood and multiplied by 0.8, a guideline in Maputo for the amount of drinking water ending up in the sewers. For the water flowing in the sewer network, three cases are estimated, the actual status, system two completely working and the total volume of system one and two. The actual flow into the WWTP is 3957 m3/day with 20,665 m3/day being directly discharged into the bay. If the pumping stations of system two were operating, 10,266 m3/day would flow to the WWTP and 14,357 m3/day would be directed into the bay (Figure 1). By measuring the amount of influent at the WWTP, using the existing Venturi meter, the calculations were validated. The measurements show a flow arriving to the WWTP in the order of the magnitude of the calculations .This influent is generated by approximately 38,000 users that are connected to the sewer system.The sewer network of Maputo has a few critical parts which should be repaired as soon as possible, and better maintained in the future. First of all the pumping station of system two should be turned on. Before this is possible the sand in the sewers in front pumping station two must be removed and the pipes should stay clean. Sand and plastic bags ends up in the sewer system through drains or open manholes. To overcome clogging, drains and manholes have to be better maintained.Another recommendation is to collect the wastewater being discharged by system one and convey it to the existing WWTP or to a new one. The municipality has plans for this but lacks financing.All the water which is collected by system two is conveyed to the WWTP, but the WWTP is not functioning well. There is white slime in the effluent and colourful tarnish, which is a sign of bacteria being present in the effluent. The effluent is either directly used for irrigation of crops, which poses a risk for human health, or directed to the estuary.At the moment there are detailed plans to introduce a sanitation fee, which is necessary to improve, operate and maintain the system. CRA has been working on introducing the fee for several years already and they expect to introduce it within the coming years.At least these thesis's citated our document: - http://resolver.tudelft.nl/uuid:a6a87995-d31c-4d34-a909-d84364a6165a - http://resolver.tudelft.nl/uuid:d07583ed-acd8-43ea-8575-550ac693c1b7Sustainable freshwater supply in urbanizing Maputo, Mozambiqu

Revisiting wind speed measurements using actively heated fiber optics: A wind tunnel study

Near-surface wind speed is typically only measured by point observations. The actively heated fiber-optic (AHFO) technique, however, has the potential to provide high-resolution distributed observations of wind speeds, allowing for better spatial characterization of fine-scale processes. Before AHFO can be widely used, its performance needs to be tested in a range of settings. In this work, experimental results on this novel observational wind-probing technique are presented. We utilized a controlled wind tunnel setup to assess both the accuracy and the precision of AHFO under a range of operational conditions (wind speed, angles of attack and temperature difference). The technique allows for wind speed characterization with a spatial resolution of 0.3 m on a 1 s timescale. The flow in the wind tunnel was varied in a controlled manner such that the mean wind ranged between 1 and 17 m s-1. The AHFO measurements are compared to sonic anemometer measurements and show a high coefficient of determination (0.92–0.96) for all individual angles, after correcting the AHFO measurements for the angle of attack. Both the precision and accuracy of the AHFO measurements were also greater than 95 % for all conditions. We conclude that AHFO has the potential to measure wind speed, and we present a method to help choose the heating settings of AHFO. AHFO allows for the characterization of spatially varying fields of mean wind. In the future, the technique could potentially be combined with conventional distributed temperature sensing (DTS) for sensible heat flux estimation in micrometeorological and hydrological applications.Water ResourcesAtmospheric Remote Sensin