Christiaan van der Tol studies the energy and water balance of Earth
‘My primary focus is water and energy. I’m mainly interested in assessing the energy balance of this planet,’ says Christiaan van der Tol, associate professor in 'Ecohydrology and Earth Observation' at the University of Twente. Within his field of expertise, the scientist uses remote sensing to study the relations between water, energy and other resources on Earth.
‘There are many things we can see from satellite data,’ says Van der Tol. One of these many uses of remote sensing, and one of the topics Van der Tol explores in his research, is monitoring vegetation. ‘Thanks to satellite data combined with field measurements, we can observe how plants respond to extreme weather, for example. We know that climate is changing, but we don’t know how it will impact vegetation. That is why we need a technique to observe vegetation behavior and changes on a large scale.’
The UT scientist is working on such techniques. ‘I’m exploring how we can use plants’ fluorescence to predict their behavior,’ he explains. ‘Plants’ leaves collect light, which they also re-emit. This light emission – fluorescence - is used as an indicator of photosynthetic energy conversion in plants and it can now be measured with satellites. I’m looking at what the use of this signal could be and how we can use it to predict changes in vegetation.’ Within this research line, Christiaan van der Tol is contributing to a satellite mission FLEX that is to be launched by the European Space Agency in three years. ‘The focus of the mission is to measure fluorescence from space and see what products can be generated from that data,’ he explains. ‘I contribute to the design of the mission and to what technology should be involved in it.’
Water, and more specifically water balance, is another important topic of Van der Tol’s work. ‘Understanding water balance is incredibly important,’ he says. ‘For example, we know that the rainfall in the Netherlands has increased, but we also know that the ground water levels have decreased. How is that possible? How much damage have droughts done? Answering such questions is very important for proper water management.’ And these answers can be (partially) provided by remote sensing. Through satellite images, Van der Tol aims to measure evaporation, for example. ‘Half of energy absorbed by earth is used for evaporation – which makes it very important for the climate,’ he stresses. ‘But there is no direct way to measure evaporation yet. We measure how much rain falls at weather stations, but we don’t know how much of it evaporates.’ The researcher is therefore exploring ways to observe changes in soil moisture and other means of monitoring evaporation from space.
‘We need to get the water balance right,’ highlights the associate professor. ‘And that can only be done locally, because soil and water are different everywhere. That is my focus. For me it’s about observing and understanding what is happening locally, so that we can make a difference there.’ The scientist has worked at various sites, including Kenya and Twente. ‘We use the Dinkel area as an experimental site. We have installed sensors at local farms, so that we can measure water in soil. That way we can help the local farmers to manage the water balance and contribute to building the right infrastructure.’
‘My main goal is to transfer my knowledge and research,’ says the associate professor. ‘I want my students to develop systematic scientific attitude and to provide independent information on the challenges we face. My task as a scientist is to provide reliable input to support decision making. I aim to quantify energy balance so that decision makers know what the consequences of their choices are – and I want to know that this will also be possible in the future. I can achieve that mostly through my students. My own research is only one brick. It’s important to lay it, but it is still only one part. Science is a collaborative effort.’
Christiaan van der Tol has supervised nearly 50 Msc research thesis projects and 15 PhD projects on topics of remote sensing of water fluxes and vegetation processes. He teaches fieldwork and data management skills in the MGEO master, and offers an elective in remote sensing of energy, water and vegetation growth.
Christiaan van der Tol is an associate professor in 'Ecohydrology and Earth Observation' at the Water Resources department of the Faculty of Geo-Information Science and Earth Observation (ITC), University of Twente. He obtained his MSc in Hydrology at Wageningen University (2001), and PhD in Earth Sciences at the Vrije Universiteit Amsterdam (2007), after which he started his career at ITC. In 2021 he was appointed as the head of his department.
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