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Peru is already facing a number of challenges related to climate change, including retreating glaciers and more severe droughts and floods. Therefore, a countrywide analysis of current and future hydroclimatic conditions is crucial to formulate adaptation strategies in water resource development. This study aims to evaluate the effects of climate change on the distribution of water budget components and streamflow variability across Peru. For that, we bias-adjusted and statistically downscaled CMIP6 climate projections of 10 climate models under two Shared Socioeconomic Pathways (SSP1-2.6 and SSP5-8.5) to obtain a range of possible future regional climatic conditions. These selected scenarios span a range of possible future options from the sustainable pathway (SSP1-2.6, with 2.6 W/m2 by the year 2100) to fossil-fueled development (SSP5-8.5, with 8.5 W/m2 by the year 2100). The adjusted climate data were fed into the hydrological model, Soil and Water Assessment Tool (SWAT), to simulate and analyze future hydroclimatic conditions. SWAT was calibrated and validated at 72 discharge stations against mean, high and low water flows. Climate projections suggest a warmer climate and diverging changes in precipitation, with a drier response over the lowlands of the Upper Amazon related to a substantial reduction in precipitation during June-November and a wetter response over the tropical Andes due to precipitation increases during September-March. Projected changes in hydrological conditions show lower water availability over lowlands and higher water availability along the Andean basins in the future. The projections for hydrological extremes indicate that Peru might face excessive water exposure during floods along the Andean catchments and water scarcity during droughts over the Amazon lowlands in the future, particularly under the fossil-fueled development (SSP5-8.5) scenario. The results of this study provide information to planners and decision-makers for formulating adaptation strategies for sustainable water management under climate change in Peru. Keywords: water resources, climate change, CMIP6, hydrological extremes, Peru, Andes, Amazon

Burundi is one of the poorest countries in the world with about 65% of the population living below the poverty line and suffering from alarming food insecurity. Its population is highly dependent on rain-fed agriculture, which makes them extremely sensitive to climate variability and extremes for their subsistence. During the last decades, heavy rains, floods, and landslides suffered by Burundi’s population have led to severe famines, death, conflicts, and internal displacement among other fatalities, indicating the high vulnerability of this region to extreme events. Therefore, it is of vital importance to provide detailed information about the potential impacts of climate change in order to enhance adaptation options and preparedness in a country for which little information about climate projections and hydro-climatic impacts is available.In this work, we investigated the changes in future climate over Burundi projected by a set of 13 regional climate models, for two future periods, under RCP4.5 and RCP8.5. The projections from CORDEX models have been used as forcing climate for the eco-hydrological Soil and Water Integrated Model (SWIM) in order to assess future changes in mean and extreme river discharge and water availability across Burundi.Our results indicate that unabated climate change will lead to faster and more severe warming over Burundi than the global mean. Precipitation will increase in the north of Burundi despite a possible prolongation of the dry season, and will decrease in the south, with the exception of the months core of the rainy season that show the highest rise along the year and across the country. The increase in the frequency, magnitude, and intensity of extreme climate events (daily temperature, dry and wet events) will characterize the future climate in this region according to CORDEX models.These changes get translated into increases of discharge in North Burundi across the whole year in all future scenarios and periods (up to 196% in annual streamflow in small catchments and 40% in larger ones), and slight decreases in the south from February to October (up to 7%). The increase of daily and annual extreme river discharges, their probabilities of exceedance, and the decrease in their recurrence intervals implies a higher risk of floods in magnitude and frequency.These findings indicate the critical importance of adaptation of land and water management to changing hydro-climatic conditions in Burundi to improve food security and support its development.

Changes in weather persistence are of particular concern in the context of climate change as periods of longer persistence can reinforce weather extremes. In our study we apply structural image recognition methods to global ERA5 reanalysis data to identify when, where and how long isolines of atmospheric geopotential height fields run in similar tracks. We identify regions and episodes around the world in which, retrospectively, unusually long-lasting weather patterns repeatedly occurred. Concerning the temperature and precipitation meteorological fields, we derive a connection between the occurrence of weather persistence and hydro-climatic extreme events.Based on our new method we find that weather persistence has been particularly increasing in Northern Hemisphere mid-latitudes in summer confirming earlier studies. Here, highly populated regions like Central Europe have experienced long-term increases in persistent weather conditions of up to 4-5% between 1981 and 2019 amplifying the risk of prolonged heat waves and droughts. Further, we show that climate models tend to have difficulties in capturing the dynamics of weather persistence and thus may severely underestimate the frequency and magnitude of future extremes events in their climate projections.

In our first study on possible flood damages under climate change in Germany, we reported that a considerable increase in flood-related losses can be expected in a future warmer climate. However, the general significance of the study was limited by the fact that outcome of only one global climate model (GCM) was used as a large-scale climate driver, while many studies report that GCMs are often the largest source of uncertainty in impact modelling. Here we show that a much broader set of global and regional climate model combinations as climate drivers show trends which are in line with the original results and even give a stronger increase of damages.

This study aims to compare impacts of climate change on streamflow in four large representative African river basins: the Niger, the Upper Blue Nile, the Ubangi and the Limpopo. We set up the eco-hydrological model SWIM (Soil and Water Integrated Model) for all four basins individually. The validation of the models for four basins shows results from adequate to very good, depending on the quality and availability of input (observed climate, soils, land use, water management) and calibration (discharge) data. For the climate impact assessment we drive the model with outputs of five bias-corrected Earth System Models of Coupled Model Intercomparison Project Phase 5 (CMIP5) for the Representative Concentration Pathways (RCPs) 2.6 and 8.5. This climate input is put into the context of climate trends of the whole African continent and compared to a CMIP5 ensemble of 19 models in order to test their representativeness. Subsequently, we compare the trends in mean discharges, seasonality and hydrological extremes in the 21st century. The uncertainty of results for all basins is high, mainly due to the climate input. Still, climate change impact is clearly visible for mean discharges but also for extremes in high and low flows. The uncertainty of the projections is the lowest in the Upper Blue Nile, where an increase in streamflow is most likely. In the Niger and the Limpopo Basins, the magnitude of trends in both directions is high and has a wide range of uncertainty. In the Ubangi, impacts are the least significant. Our results confirm partly the findings of previous continental impact analyses for Africa. However, contradictory to these studies we find a tendency for increased streamflows in three of the four basins (not for the Ubangi). Guided by these results, we argue for attention to the possible risks of increasing high flows in the face of the dominant water scarcity in Africa. In conclusion, the study shows that impact intercomparisons have added value to the adaptation discussion and may be used for setting up adaptation plans in the context of a holistic approach.

This article describes a modelling study on nitrogen transport from diffuse sources in the Nuthe catchment, representing a typical lowland region in the north-eastern Germany. Building on a hydrological validation performed in advance using the ecohydrological model SWIM, the nitrogen flows were simulated over a 20-year period (1981-2000). The relatively good quality of the input data, particularly for the years from 1993 to 2000, enabled the nitrogen flows to be reproduced sufficiently well, although modelling nutrient flows is always associated with a great deal of uncertainty. Subsequently, scenario calculations were carried out in order to investigate how nitrogen transport from the catchment could be further reduced. The selected scenario results with the greatest reduction of nitrogen washoff will briefly be presented in the paper.