HYdropower and PREcipitation trends -Investigating historical and future precipitation trends in regions important for hydropower production

Impacts of climate change are becoming more evident, and the need for knowledge about future climate change is growing. An important aspect of anthropogenic climate change is changes in the global and local precipitation patterns and amounts, which have widespread consequences for society. There are considerable uncertainties connected to calculations of future regional precipitation changes. Growing scientific knowledge shows that future changes in precipitation extremes, such as those leading to floods or droughts, can be substantial. It is estimated that extreme precipitation on a global scale may increase by a factor of 2 to 3 more than the increase in mean precipitation. The purpose of the HYPRE project is to gain a more robust understanding of precipitation changes in selected regions. Activities in HYPRE focus on the Eastern Mediterranean region and South America, with a special focus on southern Brazil, Peru and central Chile. The project includes analysis of new and existing global and regional climate model simulations, and extensive evaluation against observations. Future projections using regional climate model simulations give clear indications of a precipitation reduction over central Chile throughout the 21st century. This is considered a robust result due to the strong agreement between many different climate models and between simulations with different levels of complexities. There are larger deviations in the results between models and complexity levels for precipitation projections over Peru and southern Brazil. A main finding is that climate modelling with very high resolution is required to adequately represent precipitation processes, and that basing precipitation projections on models with too coarse resolution can give misleading conclusions. In the long-term, increasing computational capacity will give more robust precipitation projections also for these regions. The Eastern Mediterranean region has already experienced a precipitation reduction and new climate model calculations indicate a widespread reduction in summer precipitation in the future climate, around 5-15% per 1 degree Celsius of global warming. Short-duration extreme precipitation reduces less than this, and in other regions of Europe the intensity of extreme precipitation events increases, and it increases more the shorter the duration (e.g., precipitation in 10 min. vs. 1 hour). There is also a tendency that the day of year with most precipitation occurs later in the year in a future climate in several regions in Europe. Globally, the frequency of extreme precipitation events is estimated to nearly double for every 1 degree Celsius of global warming. Aerosols, such as soot and sulphate particles, affect precipitation through complex processes and are a considerable source of uncertainty in climate models. Global climate model simulations show that increased concentrations of both soot particles and long-lived greenhouse gases (e.g., CO2) lead to reduced precipitation in the Mediterranean regions but with the strongest sensitivity to soot particles. Additional model simulations over a region south in Africa, where there are large emissions from biomass burning, show that soot particles are an important contributor to precipitation changes locally. Increased emissions of soot from biomass burning since pre-industrial time were a more important cause for the observed precipitation reduction during the dry season than increased emissions of the greenhouse gas CO2. Reducing local biomass burning aerosol emissions may therefore mitigate reduced precipitation in the region.

HYPRE har gitt ny informasjon om framtidige endringer i nedbør og ekstremnedbør i flere verdensregioner. Disse resultatene har vært viktige bidrag i å føre forskningsfeltet fremover, men er også viktige for de som tar avgjørelser om utslippsreduksjoner (f.eks. beslutningstakere) og/eller tilpasning til klimaendringer (f.eks. kraftbransjen). Brukerpartneren Statkraft hat fått muligheten til å benytte resultater fra klimamodellberegninger i deres hydrologiske verktøy, noe som potensielt kan gi viktig informasjon ved deres investeringsbeslutninger.

Over the last few decades, more and more parts of the society have experienced climate change impacts, and there is a growing concern for future climate change. A main focus has been given to temperature increases and changes to the hydrological cycle. While the range in future projected temperature changes is large, uncertainties in future regional changes in precipitation and its extremes are much larger. Growing scientific knowledge shows that extremes related to hydrological changes can be substantial. For Statkraft, a leading company in hydropower internationally, preparation for the future in terms of understanding changes to the hydrological cycle and its uncertainty is crucial. In the HYPRE project, the strong team of researchers will utilize a range of observational and global and regional model data to gain a more robust understanding of precipitation changes in selected regions. Through continuous interaction with the industry partner, main outcomes of the project will be useful for Statkraft in investment decisions, but also to prepare existing hydropower plants and their infrastructure for climate change. This project will build on already established collaboration. The Eastern Mediterranean and several parts of South America will be studied specifically in HYPRE. In South America, recent projections of future precipitation show strong regional patterns and relatively large inter-model differences. HYPRE seeks to increase knowledge on these differences for this region where precipitation is strongly affected by factors such as the Andes Mountains, El Niño Southern Oscillation, and possibly by aerosol emissions. In southern Europe, where precipitation has already declined and further decreases are projected for the future, a main focus will be changes in drought. For all regions, projections of changes in extreme precipitation, seasonality of precipitation, and duration of drought periods will be of high importance and a novel part of the project.