Intercomparison of regional-scale hydrological models and climate change impacts projected for 12 large river basins worldwide—a synthesis

An intercomparison of climate change impacts projected by nine regional-scale hydrological models for 12 large river basins on all continents was performed, and sources of uncertainty were quantified in the framework of the ISIMIP project. The models ECOMAG, HBV, HYMOD, HYPE, mHM, SWAT, SWIM, VIC and WaterGAP3 were applied in the following basins: Rhine and Tagus in Europe, Niger and Blue Nile in Africa, Ganges, Lena, Upper Yellow and Upper Yangtze in Asia, Upper Mississippi, MacKenzie and Upper Amazon in America, and Darling in Australia. The model calibration and validation was done using WATCH climate data for the period 1971–2000. The results, evaluated with 14 criteria, are mostly satisfactory, except for the low flow. Climate change impacts were analyzed using projections from five global climate models under four representative concentration pathways. Trends in the period 2070–2099 in relation to the reference period 1975–2004 were evaluated for three variables: the long-term mean annual flow and high and low flow percentiles Q10 and Q90, as well as for flows in three months high- and low-flow periods denoted as HF and LF. For three river basins: the Lena, MacKenzie and Tagus strong trends in all five variables were found (except for Q10 in the MacKenzie); trends with moderate certainty for three to five variables were confirmed for the Rhine, Ganges and Upper Mississippi; and increases in HF and LF were found for the Upper Amazon, Upper Yangtze and Upper Yellow. The analysis of projected streamflow seasonality demonstrated increasing streamflow volumes during the high-flow period in four basins influenced by monsoonal precipitation (Ganges, Upper Amazon, Upper Yangtze and Upper Yellow), an amplification of the snowmelt flood peaks in the Lena and MacKenzie, and a substantial decrease of discharge in the Tagus (all months). The overall average fractions of uncertainty for the annual mean flow projections in the multi-model ensemble applied for all basins were 57% for GCMs, 27% for RCPs, and 16% for hydrological models.Intercomparison of regional-scale hydrological models and climate change impacts projected for 12 large river basins worldwide—a synthesispublishedVersio

Assessing the impacts of 1.5 °C global warming – simulation protocol of the Inter-Sectoral Impact Model Intercomparison Project (ISIMIP2b)

In Paris, France, December 2015, the Conference of the Parties (COP) to the United Nations Framework Convention on Climate Change (UNFCCC) invited the Intergovernmental Panel on Climate Change (IPCC) to provide a "special report in 2018 on the impacts of global warming of 1.5°C above pre-industrial levels and related global greenhouse gas emission pathways". In Nairobi, Kenya, April 2016, the IPCC panel accepted the invitation. Here we describe the response devised within the Inter-Sectoral Impact Model Intercomparison Project (ISIMIP) to provide tailored, cross-sectorally consistent impact projections to broaden the scientific basis for the report. The simulation protocol is designed to allow for (1) separation of the impacts of historical warming starting from pre-industrial conditions from impacts of other drivers such as historical land-use changes (based on pre-industrial and historical impact model simulations); (2) quantification of the impacts of additional warming up to 1.5°C, including a potential overshoot and long-term impacts up to 2299, and comparison to higher levels of global mean temperature change (based on the low-emissions Representative Concentration Pathway RCP2.6 and a no-mitigation pathway RCP6.0) with socio-economic conditions fixed at 2005 levels; and (3) assessment of the climate effects based on the same climate scenarios while accounting for simultaneous changes in socio-economic conditions following the middle-of-the-road Shared Socioeconomic Pathway (SSP2, Fricko et al., 2016) and in particular differential bioenergy requirements associated with the transformation of the energy system to comply with RCP2.6 compared to RCP6.0. With the aim of providing the scientific basis for an aggregation of impacts across sectors and analysis of cross-sectoral interactions that may dampen or amplify sectoral impacts, the protocol is designed to facilitate consistent impact projections from a range of impact models across different sectors (global and regional hydrology, lakes, global crops, global vegetation, regional forests, global and regional marine ecosystems and fisheries, global and regional coastal infrastructure, energy supply and demand, temperature-related mortality, and global terrestrial biodiversity)

How evaluation of hydrological models influences results of climate impact assessment—an editorial

This paper introduces the Special Issue (SI) “How evaluation of hydrological models influences results of climate impact assessment.” The main objectives were as follows: (a) to test a comprehensive model calibration/validation procedure, consisting of five steps, for regional-scale hydrological models; (b) to evaluate performance of global-scale hydrological models; and (c) to reveal whether the calibration/validation methods and the model evaluation results influence climate impacts in terms of the magnitude of the change signal and the uncertainty range. Here, we shortly describe the river basins and large regions used as case studies; the hydrological models, data, and climate scenarios used in the studies; and the applied approaches for model evaluation and for analysis of projections for the future. After that, we summarize the main findings. The following general conclusions could be drawn. After successful comprehensive calibration and validation, the regional-scale models are more robust and their projections for the future differ from those of the model versions after the conventional calibration and validation. Therefore, climate impacts based on the former models are more trustworthy than those simulated by the latter models. Regarding the global-scale models, using only models with satisfactory or good performance on historical data and weighting them based on model evaluation results is a more reliable approach for impact assessment compared to the ensemble mean approach that is commonly used. The former method provides impact results with higher credibility and reduced spreads in comparison to the latter approach. The studies for this SI were performed in the framework of the Inter-Sectoral Impact Model Intercomparison Project (ISIMIP).Potsdam-Institut für Klimafolgenforschung (PIK) e.V. (3500

Impacts of Climate Change on Riverine Ecosystems: Alterations of Ecologically Relevant Flow Dynamics in the Danube River and Its Major Tributaries

River flow dynamics play an important role for aquatic and riparian ecosystems. Climate change is projected to significantly alter river flow regimes in Europe and worldwide. In this study, we evaluate future river flow alterations in the entire Danube River basin by means of ecologically relevant river flow indicators under different climate warming scenarios (Representative Concentration Pathway (RCP) 2.6, RCP 4.5, and RCP 8.5). The process-based watershed model SWIM was applied for 1124 sub-catchments to simulate daily time series of river discharge for the Danube River and its tributaries under future scenario conditions. The derived hydrological data series were then statistically analyzed using eight eco-hydrological indicators to distinguish intra-year variations in the streamflow regime. The results are used to: (a) analyze the possible impacts of climate change on the ecologically relevant flow regime components; and (b) identify regions at the highest risk of climate change-driven flow alterations. Our results indicate that climate change will distinctively alter the recent ecological flow regime of the Danube River and, in particular, the tributaries of the Middle and Lower Danube basin. While for the RCP 2.6 scenario the projected flow alterations might still be considered moderate for many rivers, the impacts might strongly accelerate if global mean temperatures rise more than 2 °C compared to pre-industrial times. Under RCP 4.5 and RCP 8.5 warming scenarios, the recent ecological flow regime might be highly altered, posing a serious threat to river and floodplain ecosystems

Impacts of Climate Change on the Hydrological Regime of the Danube River and Its Tributaries Using an Ensemble of Climate Scenarios

Information about the potential impacts of climate change on river runoff is needed to prepare efficient adaptation strategies. This study presents scenario projections for the future hydrological runoff regime in the Danube River Basin. The eco-hydrological watershed model Soil and Water Integrated Model (SWIM) was applied for the entire Danube River catchment, considering 1224 subbasins. After calibration and validation of the model, a set of high-resolution climate projections (bias-corrected and non-bias-corrected) served as meteorological drivers with which future daily river discharge under different climate warming scenario conditions was simulated. Despite existing uncertainties, robust trends could be identified. In the next 30 years, the seasonal stream-flow regime of the Danube and its tributaries is projected to change considerably. Our results show a general trend towards a decrease in summer runoff for the whole Danube basin and, additionally, in autumn runoff for the Middle and Lower Danube basin, aggravating the existing low flow periods. For the winter and early spring seasons, mainly January–March, an increase in river runoff is projected. Greater uncertainties show up in particular for winter runoff in the Dinaric Alps and the Lower Danube basin. The existing trends become very distinct until the end of the 21st century, especially for snow-influenced river regimes

Hochwasserrisiken und Klimawandel in Europa

Hochwasserrisiken und Klimawandel in Europa: Die Folgen des Klimawandels für hydrologische Extreme gehören zu den in der Öffentlichkeit am meisten diskutierten Klimarisiken in Deutschland. Tatsächlich ist es aber schwierig, in beobachteten Zeitreihen schon robuste Trends zu entdecken, da extreme Hochwasser seltene Ereignisse und für eine robuste Abschätzung die Zeitreihen oft zu kurz sind. Mit fortschreitendem Anstieg der Temperatur projizieren modellgestützte Hochwasseranalysen aber einen Anstieg der Hochwasserschäden in Deutschland. Hydrologische Modelle können dabei genutzt werden, um die reinen Auswirkungen des Klimatrends auf die Hochwasserentstehung von anderen Einflussfaktoren, wie z.B. von Änderungen in der Landnutzung oder in der Wasserbewirtschaftung, zu trennen. So sind die höchsten beobachteten winterlichen Abflüsse in Deutschland im Zeitraum 1951-2002 in einigen großen Flüssen um ca. ein Drittel gestiegen, wobei eine Modellanalyse zeigt, dass dieser Trend größtenteils durch Klimatrends hervorgerufen wurde. Flood risks and climate change in Europe: The consequences of climate change for hydrological extremes are among the most widely discussed climate risks in Germany. In fact, it is difficult to discover robust trends in observed time series, since extreme floods are rare events and for a robust estimation the time series are often too short. Model-based flood analyses, however, show that flood related losses increase in Germany with advancing rise in temperature. Hydrological models can be used to separate the pure effects of climate trends on flood generation from other influencing factors, such as changes in land use or water management. For example, the highest observed winter discharges in the period 1951-2002 in Germany have risen by approximately one-third in some large rivers, and a model analysis shows that this trend was largely caused by climate trends

How evaluation of hydrological models influences results of climate impact assessment—an editorial

This paper introduces the Special Issue (SI) “How evaluation of hydrological models influences results of climate impact assessment.” The main objectives were as follows: (a) to test a comprehensive model calibration/validation procedure, consisting of five steps, for regional-scale hydrological models; (b) to evaluate performance of global-scale hydrological models; and (c) to reveal whether the calibration/validation methods and the model evaluation results influence climate impacts in terms of the magnitude of the change signal and the uncertainty range. Here, we shortly describe the river basins and large regions used as case studies; the hydrological models, data, and climate scenarios used in the studies; and the applied approaches for model evaluation and for analysis of projections for the future. After that, we summarize the main findings. The following general conclusions could be drawn. After successful comprehensive calibration and validation, the regional-scale models are more robust and their projections for the future differ from those of the model versions after the conventional calibration and validation. Therefore, climate impacts based on the former models are more trustworthy than those simulated by the latter models. Regarding the global-scale models, using only models with satisfactory or good performance on historical data and weighting them based on model evaluation results is a more reliable approach for impact assessment compared to the ensemble mean approach that is commonly used. The former method provides impact results with higher credibility and reduced spreads in comparison to the latter approach. The studies for this SI were performed in the framework of the Inter-Sectoral Impact Model Intercomparison Project (ISIMIP). © 2020, The Author(s)

The impact of climate change and variability on the generation of electrical power

Climate variability and change affect electricity generation in several ways. Electricity generation is directly dependent on climate/weather parameters like wind (wind power generation) or air temperature and resulting water temperature (thermal power plants). River discharge as a result of precipitation and temperature, the latter being one main factor influencing evapotranspiration, is important for hydro power generation and cooling of thermal power plants. In this study possible effects of climate variability and change on electricity generation in Germany are analyzed. Considered is electricity generation by thermal power plants, wind power plants and hydro power plants. While hydro power plants and thermal power plants are affected negatively due to declining river discharge or higher water temperatures, for wind power generation no clear tendency was found. The reduction for hydro power generation could be leveled out by a slight increase in installed capacity and modernization of turbines and generators. By a replacement of old once-through cooling systems by closed-circuit cooling systems for new thermal power plants the negative impacts on electricity generation can be reduced significantly. The planned increase of installed capacity for wind power generation clearly surpasses the changes arising from climate change