First, we would like to introduce our reason for writing this article. We are PhD students from Delft University of Technology and Kyoto University and were invited to write about our scientific adventure during the IAHS conference held in Gothenburg, as newcomers to IAHS. Here we share some of our experience and IAHS adventure with you.

The conference registration and ice-breaking session on Sunday was a perfect opportunity for conference participants to get to know each other, and prepare their mind for one week of fruitful conversations, presentations and discussions. The conference materials provided were very useful in guiding the participants through the entire assembly. We were amazed by the wide scope of the sessions and presentations. It was very easy to pick a session which was related to our topic, but it was unfortunate to have to miss other sessions which looked interesting but were held at the same time. The sections below describe our individual impressions of the main sessions that we attended during the conference. Photo, from the left: Shervan, Cai, Jaqueline and Tomohiro

Gothenburg, Sweden: for all of us it was our first visit Gothenburg and Sweden. Although as PhD students we are supposed to work hard during conferences, we still managed to visit the city and beautiful islands of the Southern Archipelago (Swedish: Göteborgs skärgård). From Amsterdam, it was a one-hour direct flight to Gothenburg, but from Kyoto the flight was much longer, about twelve hours, with a stop in Frankfurt. The summer weather in Gothenburg was comfortable, especially for Asian participants like Japanese, and we were happy to attend this conference under pleasant climate. 

Jacqueline: I did a poster presentation for the Assembly because I was too late to submit a paper for oral presentation. Generally, most of the sessions were not really connected to my field of research (morphology and tidal dynamics in estuaries), but some of the techniques and ideas presented might be applicable to my work. The presentations in the symposium I was attending Deltas: Landforms, ecosystems and human activities, focused mostly on the sediment transport in a delta. Variation in the amount of sediment flowing downstream due to human intervention such as building dams, deforestation, and flow diversion for irrigation, strongly influence the morphological changes of a delta. For example, recent studies show that the Mississippi Delta is drowning because of the substantial decrease in the fluvial sediment transport resulting from dam construction upstream. These studies are important because deltas are the most densely populated areas in the world. As a result, it is important to protect and maintain the sustainability of deltaic environments.

My work, however, is mainly related to prediction in ungauged estuaries. The objective of my study is to link the river to the tidal region (delta area) utilizing hydraulic geometry theory, which later can be used to predict the bankfull discharge from estuary shape. Research on hydraulic geometry theory in river regimes has been carried out for decades, but few studies have concentrated on the tidal region. Thus, it is interesting to investigate whether the hydraulic geometry theory for a river can also be applied to the tidal region.

Cai: My area of interest mainly focuses on the study of estuaries, the transition zone between river and sea. So, I attended the symposium on Deltas: Landforms, ecosystems and human activities, which was jointly organised by IAHS (River) and IAPSO (Sea). I was so excited because it was a great honour to present my PhD research to both hydrologists and oceanographers. However, I felt a bit nervous since I was the speaker immediately after the three keynote speakers in this session. I had a feeling that the audience's expectation would be rather high after the keynote presentations. I presented a paper on a consistent analytical framework for understanding the influences of external changes (e.g. human interventions or sea-level rise) on tidal hydrodynamics in estuaries.

Because knowledge of computational hydraulics is becoming popular, the quest for analytical solutions seems to become a curiosity rather than necessity. In the engineering community world-wide most of the impact studies of human interventions on tidal hydrodynamics in estuaries have been done by making use of numerical models. However, for an enhanced understanding of human influences on estuarine processes, nothing surmounts analytical models, especially when it comes to giving insight to the dynamics of flow and providing a rapid technique for assessing human impacts e.g. dam construction, flow withdrawal and dredging, on tidal wave propagation.

Shervan: Most sessions dealing with rainfall/runoff modelling were focused on applicability of models under changing conditions as well as transferability of models to unknown catchments. I participitated in the workshop on Testing simulation and forecasting models in non-stationary conditions. Different research groups selected a basin from a set of basins provided by the workshop conveners to compare models for their non-stationarity of hydrological response within the selected catchments. The challenge for prediction under non-stationary conditions is the dependency of models on calibration. The parameters selected for a model are usually set as optimal parameter sets within the calibration period. However, any change in the hydrological regime of the system in future may not be reproducible by the optimal parameter sets.

I presented my work on simulating runoff without any need for calibration based on constraining a semi-distributed conceptual model. The method is based on hydrological response units derived from the HAND map. HAND is an abbreviation for Height Above Nearest Drainage, which can be easily extracted from a DEM (digital elevation model). I still have to investigate this new framework and its capabilities for different catchments. I appreciated the whole idea of the workshop for comparing models on different catchments. From my point of view, it gave us an insight to how models work on different catchments, which eventually helps us to understand our models and our catchments better.

Tanaka: My research field is rainfall/runoff modelling. Hence, I attended the Testing simulation and forecasting models in non-stationary conditions workshop, for which I conducted simulations for two basins, the Flinders River and the Garonne River catchments. I did a poster presentation to show preliminary results from my simulations and received much important advice from other participants. I had constructed a numerical model to deepen understanding as to what extent components have impacts on reproducibility. Many existing models have several components and they are usually complicated, but I think the impact of each component on simulation should be evaluated in order to provide more insights to unknown catchments.

I also gave an oral presentation in HW06, the Anthropogenic radionuclide contamination of water and sediment: short-term and long-term consequences workshop, to discuss radioactive substances released into the environment by nuclear accidents. In particular, a rainfall–sediment runoff model was used to simulate the runoff of Cs-137, released from the Fukushima Nuclear Power Plant, from a river catchment. It was quite beneficial to share my research from the modelling side and to learn of important findings or perspectives from the measurement side. Meanwhile, what impressed me was that not only the Japanese participants, but also participants from other countries are quite familiar with this topic. I recognized that this topic is a worldwide one and we have to conduct further research to contribute to the solutions.

IAHS assemblies are not entirely about scientific sessions. The plenary session of IAHS was one of the most interesting events during the conference; it was held on the Wednesday evening and chaired by Gordon Young. The most exciting moment of the meeting was the Tison Award ceremony. The award was made to Federico Lombardo and Elena Volpi (both from Italy) for their work on “Rainfall downscaling in time: theoretical and empirical comparison between multifractal and Hurst-Kolmogorov discrete random cascades”. Additionally, the IAHS International Hydrology Prize was given to Prof. Günter Blöschl (Austria) for his outstanding contribution to rainfall/runoff modelling as well his leadership within IAHS. At the end of this meeting, the presidency of IAHS for the next four years was handed to Prof. Hubert Savenije from Delft University of Technology.

The IAHS Early Career Hydrological Scientist meeting has given us great inspiration and confidence in choosing hydrology as our career path. The discussion and sharing sessions with the invited scientists and key speaker, Prof. Thorsten Wagener, provided a significant insight into the future in being a hydrologist.

More generally, and apart from the detailed scientific discussions, the IAHS conference in Gothenburg increased our knowledge of the hydrological scientists’ community and their interaction. This is of course both important and interesting for young scientists like us. We had plenty of fun as we presented our own research as well as our philosophies and triggered cooperation with other researchers, which in turn has led to further development of our studies. Furthermore, this medium scale conference also serves as a good platform for us young scientists to be recognized by the community, and subsequently increases the opportunity of making our research known.

Jacqueline Isabella Gisen (TU Delft), Huayang Cai (TU Delft), Shervan Gharari (TU Delft), Tomohiro Tanaka (Kyoto University)