Nordic Association for Hydrology
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Best oral and poster presentations by students at the Nordic Hydrology Conference 2026
At each Nordic Hydrology Conference, the board of the Nordic Association for Hydrology (NHF) together with the organisers, awards two students with prizes for best oral and poster presentations. The 2026 winners are Sadegh Kaboli and Pietari Pöykkö. Below, we interview the two PhD candidates to find out more about their work and the paths which led them to hydrology.
Photo: Pietari (left) and Sadegh (right) with their certificates at the closing ceremony of the Nordic Hydrology Conference 2026 in Åland. Photo credit: Jenny Turton, NVE.
Sadegh Kaboli is a PhD candidate at University of Turku in Finland. His poster titled ‘A six-decade assessment of interannual variability and long-term shifts in peak snowmelt flood timing in unregulated boreal catchments’ presents some of his latest findings. His work is to investigate the changes in snowmelt induced flooding in Finland and understanding how and why this has changed over time.
Pietari Pöykkö is a PhD candidate at University of Oulu in Finland. His research is focused on changes in characteristics and regimes of groundwater in Finland. His presentation titled ‘How has the annual groundwater cycle changes in Finland over the past 50 years?’ highlights the changes in groundwater levels over time, especially with the relationship to snowfall.
Sadegh has used 60 years of data and identified that the timing of peak snowmelt-induced flooding is now happening earlier in the spring. Pietari has used 50 years of data to show that groundwater regimes have changed over time with higher winter groundwater levels, lower and longer summer levels, and earlier spring recharge from snowmelt.
Whilst both works are independent, the two researchers have similar conclusions, highlighting the interconnectedness of hydrology and meteorology, as well as the role of climate change in altering all aspects of the system.
Despite focusing on different aspects of hydrology, your research is connected through snowfall. Can you briefly describe your work and the impact?
Sadegh: The key take away is that snowmelt induced floods are happening earlier in the season. Finland is snow dominated and flooding is highly sensitive to temperature. Snow accumulation and snowmelt processes are being influenced by global warming.
Pietari: My findings are connected to Sadegh’s study – similar results through a different lens. The key to recharging groundwater is in the snowmelt, which is now happening earlier in the year. The behaviour of the groundwater in the northern parts of Finland is now starting to represent the southern areas.
Sadegh: Similar spatial patterns are found in my work. There is a high latitudinal difference in the variables. Further north, the flooding peaks later in the year, as the snow melts later. We see gradual delays in the snowmelt peaks towards the north. But the peaks are now happening earlier in spring, even in the Arctic region.
Photo: Torill Engen Skaugen, leader of the board of the Nordic Association of Hydrology (NHF) presents Sadegh with his award. Photo credit: Jenny Turton, NVE.
Why is your research important to society?
Sadegh: Snowmelt is a source of water for both domestic and agriculture use, as well as for energy generation. In Finland, the snowmelt is important for all these aspects. Snowmelt processes are shifting in time and location. Renewable energy creation could be affected, and the companies need to know this information because they use the peak flow to make the most energy generation.
Pietari: Groundwater contributes to streamflow for hydropower and domestic use. We’re now observing a decline in groundwater levels earlier in the year. Groundwater levels in summer are now lower, and staying lower for longer, which is a problem for household wells and water supply. It is not yet a nationwide problem, currently problematic on individual scales, but it could continue.
Would your work have been possible without long datasets?
Sadegh: In Finland, we have a wide range of open datasets. Not just in hydrology but also water chemistry and quality. We can therefore be creative with the data because it is available. A good and solid approach to data collection over six decades means that we can find robust results.
Pietari: Without the reliable data, the studies wouldn’t be possible. Producing this type of long-term dataset requires strong institutions and collaboration. No single institute or commercial organisation or group could organize such national measurement programs on their own. Strong national institutions are essential for this.
Why did you decide to have a career in hydrology research?
Pietari: I was always interested in technical systems and the environment. I like practical applications. I did my master’s on quality control of groundwater data at Syke (the Finnish Environment Institute). I found that the data had not been extensively used or looked at, even though it is highly valuable and good quality. It’s a great effort to produce the data, which was done by earlier scientists. I wanted to see if I could find something interesting to consider from the data, and the Digital Waters program was just starting, which seemed like an interesting idea. I am now using this data in my research.
Sadegh: My research is also related to my master’s in civil engineering. During the master’s program, you select your direction and a professor told me about climate and the role of hydrology in impacting real lives, through agriculture and reservoirs. That’s when I became interested in hydrology and the environment and asked if I could work with this professor. I want to solve real life issues and do something big for society, so I will start with snow and temperature. I am originally from Iran, and my supervisor is too, but has been working in Finland for many years, so that personal connection was also important to my career. We have now developed the idea for my research together as master’s thesis and now it has continued for my PhD.
You both have around 1.5 to 2 years left of your PhD studies. What would you like to do next?
Pietari: I am still open to options. I enjoy research and investigating the natural world, but I also enjoy more concrete projects and investigating the consequences. Research can sometimes feel abstract or like you’re only making small changes over a long time. With more applied work, I’d like to see the difference I can make straight away. All options are open though.
Sadegh: I’d really like to stay in academia. When you work on your topic, you come up with a lot of new ideas and want to find answers to remaining questions. I want to improve ideas and to mature them. I want to make sure that my research is societally useful. That’s our job.
"It is important for the Nordic Association of Hydrology to recognize students and early career scientists in this way, to highlight the excellent research being done by the new generation of hydrologists. It was a tough job to decide on the winners. We had 26 eligible presentations and over 40 posters. Thank you to all the students and judges for their hard work in contributing to the NHC 2026.” Torill Engen Skaugen, Leader of the Board, Nordic Association of Hydrology (NHF).
The Nordic Hydrology Conferences are organized every second year and take place in different cities in the Nordic and Baltic countries. The conference is organized by the Nordic Association of Hydrology (NHF) and a local organizing team. The next Nordic Hydrology Conference will take place in August 2028 in Riga, Latvia. Let’s hope our two prize winners can present their final work there.
Photo: Torill Engen Skaugen, leader of the board of the Nordic Association of Hydrology (NHF), presents Pietari with his award.
Photo credit: Jenny Turton, NVE.
Read the abstracts from our student winners:
Sadegh Kaboli, University of Turku
Abstract: Changes in the timing of peak snowmelt floods have been observed in snow-dominated boreal catchments in recent decades. Snowmelt is a vital freshwater resource for human and energy needs, yet it is also a leading cause of flooding in high-latitude and high altitude cold environments. Despite its importance, the mechanisms governing changes in the timing of peak snowmelt flood and its substantial interannual variability remain poorly understood, particularly in relation to the effects of large-scale climate modes of variability. To address this knowledge gap, this study introduces new criteria for classifying catchments as snowmelt‑dominated by incorporating a thermally defined spring season. Building on this definition, a machine‑learning predictive framework based on a random forest model was developed using a wide range of dynamic and static predictors over the period 1961–2023 to predict peak snowmelt flood timing in several unregulated catchments across Finland. Application of this framework enabled the reconstruction of a continuous six‑decade record of peak snowmelt flood timing. Using this reconstructed record, long‑term trends in peak snowmelt flood timing were examined using the Mann–Kendall test and Sen’s slope estimator. The analysis further explored the role of large‑scale atmospheric circulation patterns in driving interannual variability in peak snowmelt flood timing, as well as the influence of global warming on long‑term changes in flood timing.
Pietari Pöykkö, University of Oulu
Abstract: Groundwater-level seasonality (“regime”) is shifting as the climate changes, affecting drought and flood hazards, water supply, agriculture, and ecosystems. Shallow aquifers are especially sensitive because they respond quickly to meteorological forcing. This is particularly important in boreal and subarctic environments, where winter freezing has historically modulated recharge and evapotranspiration, but the intensity and duration of the frost season are changing. We analyzed 50-year groundwater-level records from 53 monitoring stations across Finland to characterize subarctic groundwater regimes and their evolution. After methodological evaluation, regimes were classified using partitioning around medoids clustering with Pearson correlation distances, and principal component analysis of normalized monthly groundwater levels was used to summarize the seasonal variability. The clustering identified four regimes, organized primarily along a southwest–northeast gradient that corresponds to increasing frost-season intensity and associated temperature and snow conditions. Comparing 1975–1999 and 2000–2024 shows regimes shifting northeastward toward colder regions. Locally, the changes are seen as higher winter groundwater levels, lower and longer summer levels, and with spring recharge maximum advancement (on average by half a month). Regime expression also depended on aquifer size. Within the studied range (0.1–41 km²), larger aquifers displayed a delayed regime, consistent with longer flow paths and greater storage. Overall, the spatial patterns and the geographic migration of groundwater regimes were clear using the combined clustering–PCA approach. The results imply increasing seasonal hydrological risks, and differing regional impacts. This emphasizes long-term monitoring as essential for groundwater management and for regional risk preparedness.