The Influence Of Climate Change On Hydrological Extremes: Floods & Droughts

Climate change impact on hydrological extremes was studied by the project under the same name, acronym CHIHE, over the years 2014-2016. The research from this study was performed at the Institute of Geophysics, Polish Academy of Sciences and was financed by the Norway Grants. It involved a group of scientists from Poland, Norway and also one Polish and two PhD students from Ethiopia, The overall aim of the project was to investigate the effect of climate change on extreme flows (floods and droughts) in selected twinned catchments in Poland and Norway.

The project followed the simulation-based approach. It included the research on bias corrections of climate model simulations, the procedures for development of hydrological projections using an ensemble approach, uncertainty assessment, nonstationary flood frequency analysis, statistical analysis of trends, flood risk assessment and adaptation issues. The know-how developed during the CHIHE project forms the foundations of cutting-edge research on the subject of the influence of climate change on the environment and society. The knowledge gained is useful in numerous applications related to water management in both countries and also at international level.

Establishing A Benchmark For Flooding In Poland

The assessment of likely changes in drought indices under a future climate in Poland and Norway can be used to inform discussions on climate change adaptation in relevant sectors (e.g. agriculture, water supply, hydropower). The establishment of a benchmark database of nearly natural catchments for the long-term climate change impact studies, following the Norwegian experience, is an important step for the development of a climate change adaptation strategy for the whole of Poland. Here we show that the relative changes of high flow projections, which are based on 30-year periods, are not consistent with the trends estimated using a 130 year-long time horizon. One such reason might be the result of interdecadal variability seen to affect 30-year records.

The project’s scientific outcomes have the form of eight Technical Reports, several peer-reviewed published papers in international journals from the JRC list, two published peer-reviewed book chapters and a topical issue “The impacts of changes in climate and land use on hydrological processes”, published in Acta Geophysica, including papers from the project and two other international projects on similar subjects, FLORIST and CHASE-PL.

It might be interesting for the reader to know that we use the word “projections” rather than “predictions”. That means that the results of the research may give some information on the possible direction of changes of hydrological extremes but not about the timing of those changes (particular years of droughts or floods). From the above it follows that we do not have very specific knowledge on future flow regimes; the results obtained are highly uncertain and climate processes are random.

The most interesting discovery of the project is the confirmed variability of global warming. Namely, the farther north a faster increase of temperatures is projected. In 2100 a much larger increase of temperature is expected in the northern parts of Norway in comparison with Poland. In addition, in catchments with a snow-driven flood regime, the maximum annual flows can decrease even when the mean flow increases. Also, seasonal changes occur, and the flood regime may change from snow-driven to rainfall-driven. Most important is the assumption of continuous changes of climate; the changes might, in fact, be abrupt, leading to an unpredicted character of the catchment response to meteorological events.

This article is a compilation of research published by Renata Romanowicz, among others, and highlighted below:

• Romanowicz RJ, Bogdanowicz E, Debele SE, Doroszkiewicz J, Hisdal H, Lawrence D, Meresa HK, Napiórkowski JJ, Osuch M, Strupczewski WG, Wilson D, Wong WK (2016) Climate Change Impact on Hydrological Extremes: Preliminary Results from the Polish-Norwegian Project. Acta Geophys. 64 (2): 477-509. doi: 10.1515/acgeo-2016-0009.
• Meresa HK, Osuch M, Romanowicz R (2016) Hydro-meteorological drought projections into the 21-st century for selected Polish catchments. Water, 8, 206; doi:10.3390/w8050206
• Osuch M, Lawrence D, Meresa HK, Napiórkowski JJ, Romanowicz RJ, 2016, Projected changes in flood indices in selected catchments in Poland in the 21st century. Stochastic Environmental Research and Risk Assessment; DOI:10.1007/s00477-016-1296-5
• Romanowicz, R.J. Acta Geophys. (2017) 65: 785. https://doi.org/10.1007/s11600-017-0079-9