Hagen Koch

Evaluation of sources of uncertainty in projected hydrological changes under climate change in 12 large-scale river basins

This paper aims to evaluate sources of uncertainty in projected hydrological changes under climate change in twelve large-scale river basins worldwide, considering the mean flow and the two runoff quantiles Q10 (high flow), and Q90 (low flow). First, changes in annual low flow, annual high flow and mean annual runoff were evaluated using simulation results from a multi-hydrological-model (nine hydrological models, HMs) and a multi-scenario approach (four Representative Concentration Pathways, RCPs, five CMIP5 General Circulation Models, GCMs). Then, three major sources of uncertainty (from GCMs, RCPs and HMs) were analyzed using the ANOVA method, which allows for decomposing variances and indicating the main sources of uncertainty along the GCM-RCP-HM model chain. Robust changes in at least one runoff quantile or the mean flow, meaning a high or moderate agreement of GCMs and HMs, were found for five river basins: the Lena, Tagus, Rhine, Ganges, and Mackenzie. The analysis of uncertainties showed that in general the largest share of uncertainty is related to GCMs, followed by RCPs, and the smallest to HMs. The hydrological models are the lowest contributors of uncertainty for Q10 and mean flow, but their share is more significant for Q90.

Modelling climate and land-use change impacts with SWIM: lessons learnt from multiple applications

Abstract The Soil and Water Integrated Model (SWIM) is a continuous-time semi-distributed ecohydrological model, integrating hydrological processes, vegetation, nutrients and erosion. It was developed for impact assessment at the river basin scale. SWIM is coupled to GIS and has modest data requirements. During the last decade SWIM was extensively tested in mesoscale and large catchments for hydrological processes (discharge, groundwater), nutrients, extreme events (floods and low flows), crop yield and erosion. Several modules were developed further (wetlands and snow dynamics) or introduced (glaciers, reservoirs). After validation, SWIM can be applied for impact assessment. Four exemplary studies are presented here, and several questions important to the impact modelling community are discussed. For which processes and areas can the model be used? Where are the limits in model application? How to apply the model in data-poor situations or in ungauged basins? How to use the model in basins subject to strong anthropogenic pressure? Editor D. Koutsoyiannis; Associate editor C. Perrin

Trends in water demand and water availability for power plants—scenario analyses for the German capital Berlin

The availability of electric power is an important prerequisite for the development or maintenance of high living standards. Global change, including socio-economic change and climate change, is a challenge for those who have to deal with the long-term management of thermoelectric power plants. Power plants have lifetimes of several decades. Their water demand changes with climate parameters in the short and medium term. In the long term, the water demand will change as old units are retired and new generating units are built. The present paper analyses the effects of global change and options for adapting to water shortages for power plants in the German capital Berlin in the short and long term. The interconnection between power plants, i.e. water demand, and water resources management, i.e. water availability, is described. Using different models, scenarios of socio-economic and climate change are analysed. One finding is that by changing the cooling system of power plants from a once-through system to a closed-circuit cooling system the vulnerability of power plants can be reduced considerably. Such modified cooling systems also are much more robust with respect to the effects of climate change and declining streamflows due to human activities in the basin under study. Notwithstanding the possible adaptations analysed for power plants in Berlin, increased economic costs are expected due to declining streamflows and higher water temperatures.

Integrating water resources management in eco-hydrological modelling.

In this paper the integration of water resources management with regard to reservoir management in an eco-hydrological model is described. The model was designed to simulate different reservoir management options, such as optimized hydropower production, irrigation intake from the reservoir or optimized provisioning downstream. The integrated model can be used to investigate the impacts of climate variability/change on discharge or to study possible adaptation strategies in terms of reservoir management. The study area, the Upper Niger Basin located in the West African Sahel, is characterized by a monsoon-type climate. Rainfall and discharge regime are subject to strong seasonality. Measured data from a reservoir are used to show that the reservoir model and the integrated management options can be used to simulate the regulation of this reservoir. The inflow into the reservoir and the discharge downstream of the reservoir are quite distinctive, which points out the importance of the inclusion of water resources management.

An ensemble analysis of climate change impacts on streamflow seasonality across 11 large river basins

The paper investigates climate change impacts on streamflow seasonality for a set of eleven representative large river basins covering all continents and a wide range of climatic and physiographic settings. Based on an ensemble of nine regional hydrological models driven by climate projections derived from five global circulation models under four representative concentration pathways, we analyzed the median and range of projected changes in seasonal streamflow by the end of the twenty-first century and examined the uncertainty arising from the different members of the modelling chain. Climate change impacts on the timing of seasonal streamflow were found to be small except for two basins. In many basins, we found an acceleration of the existing seasonality pattern, i.e. high-flows are projected to increase and/or low-flows are projected to decrease. In some basins the hydrologic projections indicate opposite directions of change which cancel out in the ensemble median, i.e., no robust conclusions could be drawn. In the majority of the basins, differences in projected streamflow seasonality between the low emission pathway and the high emission pathway are small with the exception of four basins. For these basins our results allow conclusions on the potential benefits (or adverse effects) of avoided GHG emissions for the seasonal streamflow regime.

Adaptation strategies to global change for water resources management in the Spree river Catchment, Germany

Abstract Computer models for long‐term simulations of water resources management strategies are used in the analysis of water availability problems in river basins. Such models can also be used for the examination of global change impacts, which are characterised by changed natural water yield and water demand due to climate and socio‐economic changes. Already existing water quantity and water quality problems in the catchments of the river Spree and the river Schwarze Elster were analysed in the context of global change. The main water quantity issues are caused by the future development of the mining industry and climate change. The effects of these future developments were analysed using the long‐term water resources management model WBalMo. Subsequently, adaptation strategies were defined in co‐operation with the relevant stakeholders and their effects analysed with the same model. The results show that continuation of the existing water resources management strategy will not be able to compensate for the impacts of global change. However, a changed management strategy might compensate the impacts for some users.

Potential impacts of climate change and regional anthropogenic activities in Central European mesoscale catchments.

Abstract The Soil and Water Integrated Model (SWIM) was used to assess potential climate and land-use change impacts in the Central European catchments of Schwarze Elster, Spree and Lusatian Neisse which are heavily influenced by opencast lignite mining. To account for potential climate change, scenarios of two statistical regional climate models, STAR and WettReg, were used. Regional anthropogenic change was considered in terms of increasing cultivation of energy crops (oilseed rape, silage maize, sunflower and sorghum) and decreasing mining activities (decreasing groundwater depression cone). In the climate scenarios, decreased natural discharge, by up to 60% in the long-term average, was simulated. In simulations with climate scenarios and oilseed rape, this effect is halved; the other energy crops have a small additional impact on discharge. The decreasing groundwater depression cone slightly compensates for climate change impacts. Overall, potential impacts of regional anthropogenic activities are secondary to those of climate change. Editor Z.W. Kundzewicz; Guest editor M. White

Trend analysis for integrated regional climate change impact assessments in the Lusatian river catchments (north-eastern Germany)

Trend analysis on observations and model-based climate change simulations are two commonly used methods for climate change detection and impact analysis. Here we propose an integrated assessment and interpretation of climate change impacts as a prerequisite for stakeholder outreach and planning of suitable climate change adaptation measures. The assessment includes (i) identifying trends in meteorological and hydrological observations and their nature, (ii) analysing the relation between the meteorological drivers and generated run-off as an integrated catchment response and (iii) analysing how hitherto changes agree with the simulations by regional climate models (RCMs). The Lusatian river catchments of Spree and Schwarze Elster, characterised by high anthropogenic impact (e.g. mining activities) and low natural water yield, serve as study areas. The results of this study suggest that increases in observed temperature and potential evapotranspiration are robust while observed precipitation remained nearly unchanged (1963–2006). The RCMs agree on simulating a temperature increase but simulate opposing trends for precipitation for both past (1963–2006) and future (2018–2060) periods, the latter inducing differences in the hydrological response (actual evapotranspiration and run-off). For stakeholder outreach, we communicated a range of potential future climates and identified the statistical RCMs (STAR, WettReg) as warm and dry scenarios, and the dynamical RCMs (REMO, CCLM) as wet scenarios. Ultimately, the combined analysis of trends in observations and simulation models can be beneficial for stakeholder outreach and may increase their willingness to plan and implement suitable climate change adaptation strategies which are urgently needed within the Lusatian river catchments.

Relationship between irrigation water demand and yield of selected crops in Germany between 1902 and 2010: a modeling study

The demand for irrigation water is increasing worldwide, including regions in Germany with low precipitation and water-demanding crops. In this study, history of irrigation water demand (IWD) in the German nation states in relation to the yield of four crops (1) potato, (2) spring barley, (3) oat, and (4) winter wheat, during droughts between 1902 and 2010 was analyzed. The difficulties caused by the shifting borders of the German nation state over the past century were dealt with by dividing the data for the region into four time periods for the analysis. Low precipitation during droughts influenced crop yield in the German nation states. Analyses of droughts resulted in no clear conclusions; however, it appeared that after 1950, German nation states droughts had a negative influence on the yield of the four crops despite the important role irrigation played in German agriculture since 1960 in the German nation state. Lower yield because of weather conditions since 1950 was primarily attributable to the high-yield potential of improved crop varieties, for which yield potential is only reached under optimal growing conditions. In this study, the analysis of the modeled historical IWD in agriculture revealed the urgency with which the German crop production systems must adapt to extremes in a changing climate not only by improving irrigation systems via irrigation scheduling but also by greater higher diversification of crops.

Is climate change a threat to the growing importance of wind power resources in the energy sector in Germany

ABSTRACT Electricity generation by wind power plants is gaining importance all over the world. Climate change may increase or decrease the potential for wind power generation. An approach to assess the effects of climate change on wind power production is presented. Simulation results indicate small impacts of climate change on wind power generation in Germany. The northern areas seem to profit from climate change, while in small regions in the southern areas negative effects occur. According to the study’s analysis, climate change will not negatively affect wind power production. The overall effect will be surpassed by the expansion in wind power generation capacity.