River runoff in Switzerland in a changing climate –  changes in moderate extremes and their seasonality

Abstract. Future changes in river runoff will impact many sectors such as agriculture, energy production, or ecosystems. Here, we study changes in the seasonality, frequency, and magnitude of moderate low and high flows and their time of emergence. The time of emergence indicates the timing of significant changes in the flow magnitudes. Daily runoff is simulated for 93 Swiss catchments for the period 1981–2099 under Representative Concentration Pathway 8.5 with 20 climate model chains from the most recent transient Swiss Climate Change Scenarios. In the present climate, annual low flows typically occur in the summer half-year in lower-lying catchments (<1500 m a.s.l.) and in the winter half-year in Alpine catchments (>1500 m a.s.l.). By the end of the 21st century, annual low flows are projected to occur in late summer and early autumn in most catchments. This indicates that decreasing precipitation and increasing evapotranspiration in summer and autumn exceed the water contributions from other processes such as snowmelt and glacier melt. In lower-lying catchments, the frequency of annual low flows increases, but their magnitude decreases and becomes more severe. In Alpine catchments, annual low flows occur less often and their magnitude increases. The magnitude of seasonal low flows is projected to decrease in the summer half-year in most catchments and to increase in the winter half-year in Alpine catchments. Early time of emergence is found for annual low flows in Alpine catchments in the 21st century due to early changes in low flows in the winter half-year. In lower-lying catchments, significant changes in low flows emerge later in the century. Annual high flows occur today in lower-lying catchments in the winter half-year and in Alpine catchments in the summer half-year. Climate change will change this seasonality mainly in Alpine catchments with a shift towards earlier seasonality in summer due to the reduced contribution of snowmelt and glacier melt in summer. Annual high flows tend to occur more frequent, and their magnitude increases in most catchments except some Alpine catchments. The magnitude of seasonal high flows in most catchments is projected to increase in the winter half-year and to decrease in the summer half-year. However, the climate model agreement on the sign of change in moderate high flows is weak.

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Moderate runoff extremes in Swiss rivers and their seasonal occurrence in a changing climate

10.5194/hess-2020-667 ◽

2021 ◽

Author(s):

Regula Muelchi ◽

Ole Rössler ◽

Jan Schwanbeck ◽

Rolf Weingartner ◽

Olivia Martius

Keyword(s):

Climate Change ◽

21St Century ◽

Climate Models ◽

Climate Model ◽

Late Summer ◽

Climate Change Scenarios ◽

Low Flows ◽

Glacier Melt ◽

High Flows ◽

Alpine Catchments

Abstract. Future changes in runoff impact many sectors such as agriculture, energy production, or ecosystems. Therefore, assessments of runoff characteristics under climate change are crucial for decision-makers and water management planners. We study changes in moderate runoff extremes, i.e. low and high flows that occur once every year or season in today's climate. Daily runoff is simulated for 93 Swiss catchments for the period 1981–2099 under the Representative Concentration Pathway 8.5 using 20 downscaled regional climate models from the newest transient Swiss climate change scenarios. The magnitude of moderate annual low flows is projected to decrease in lower lying catchments and to increase in Alpine catchments. Seasonal low flows in summer are projected to decrease and seasonal low flows in winter to increase. Moderate annual high flows are projected to slightly increase in most catchments but to decrease in high Alpine catchments. However, the climate model agreement on the sign of change in moderate high flows is not robust. The projected decrease in Alpine catchments contradicts results for extreme high flows from previous studies. This difference may be due to different indicators used (moderate extremes vs. extremes). The time of emergence indicates the timing of significant changes in the flow magnitudes. For low flows the time of emergence is early in 21st century in high Alpine catchments due to early changes in winter low flows. In lower lying catchments, significant changes in low flows emerge later in the century. For moderate high flows, only few catchments indicate a significant change. Shifts in the seasonality of moderate low flows due to climate change are found in many catchments. By end of the 21st century, low flows are projected to occur in late summer and early autumn in most catchments indicating that the lack of precipitation in summer and autumn exceeds the contributions from other processes such as snow and glacier melt contributions. For moderate high flows, changes in seasonality are found in Alpine catchments with a shift towards earlier occurrence in summer due to a reduced contribution of snow and glacier melt in summer. In the projections, low flows occur more frequently in lower lying catchments and less frequently in Alpine catchments. For high flows the frequency increases slightly in most catchments, but models often disagree on the sign of change. Changes in the annual co-occurrence of moderate low and high flows are mainly due to changes in the frequency of low flows that increases in lower lying catchments and decreases in Alpine catchments.

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New Zealand River Hydrology under Late 21st Century Climate Change

Water ◽

10.3390/w12082175 ◽

2020 ◽

Vol 12 (8) ◽

pp. 2175

Author(s):

Daniel B. G. Collins

Keyword(s):

Climate Change ◽

New Zealand ◽

21St Century ◽

Climate Model ◽

Water Cycle ◽

Well Being ◽

Cultural Economic ◽

Low Flows ◽

Late 21St Century ◽

The Mean

Climate change is increasingly affecting the water cycle and as freshwater plays a vital role in countries’ societal and environmental well-being it is important to develop national assessments of potential climate change impacts. Focussing on New Zealand, a climate-hydrology model cascade is used to project hydrological impacts of late 21st century climate change at 43,862 river locations across the country for seven hydrological metrics. Mean annual and seasonal river flows validate well across the whole model cascade, and the mean annual floods to a lesser extent, while low flows exhibit a large positive bias. Model projections show large swathes of non-significant effects across the country due to interannual variability and climate model uncertainty. Where changes are significant, mean annual, autumn, and spring flows increase along the west and south and decrease in the north and east. The largest and most extensive increases occur during winter, while during summer decreasing flows outnumber increasing. The mean annual flood increases more in the south, while mean annual low flows show both increases and decreases. These hydrological changes are likely to have important long-term implications for New Zealand’s societal, cultural, economic, and environmental well-being.

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Evidence of river flow regulation loss over time in the Magdalena river basin

10.5194/egusphere-egu21-13716 ◽

2021 ◽

Author(s):

Diver E. Marín ◽

Juan F. Salazar ◽

José A. Posada-Marín

Keyword(s):

Climate Change ◽

Environmental Change ◽

River Basin ◽

River Flow ◽

Southern Oscillation ◽

Scaling Theory ◽

Scaling Properties ◽

Low Flows ◽

High Flows ◽

Magdalena River

<p>Some of the main problems in hydrological sciences are related to how and why river flows change as a result of environmental change, and what are the corresponding implications for society. This has been described as the Panta Rhei context, which refers to the challenge of understanding and quantifying hydrological dynamics in a changing environment, i.e. under the influence of non-stationary effects. The river flow regime in a basin is the result of a complex aggregation process that has been studied by the scaling theory, which allows river basins to be classified as regulated or unregulated and to identify a critical threshold between these states. Regulation is defined here as the basin&#8217;s capacity to either dampen high flows or to enhance low flows. This capacity depends on how basins store and release water through time, which in turn depends on many processes that are highly dynamic and sensitive to environmental change. Here we focus on the Magdalena river basin in northwestern South America, which is the main basin for water and energy security in Colombia, and at the same time, it has been identified as one of the most vulnerable regions to be affected by climate change. Building upon some of our previous studies, here we use data analysis to study the evolution of regulation in the Magdalena basin for 1992-2015 based on the scaling theory for extreme flows. In contrast to most previous studies, here we focus on the scaling properties of events rather than on long term averages. We discuss possible relations between changes in the scaling properties and environmental factors such as climate variability, climate change, and land use/land cover change, as well as the potential implications for water security in the country. Our results show that, during the last few decades, the Magdalena river basin has maintained its capacity to regulate low flows (i.e. amplification) whereas it has been losing its capacity to regulate high flows (i.e. dampening), which could be associated with the occurrence of the extremes phases of&#160; El Ni&#241;o Southern Oscillation (ENSO) and anthropogenic effects, mainly deforestation. These results provide foundations for using the scaling laws as empirical tools for understanding temporal changes of hydrological regulation and simultaneously generate useful scientific evidence that allows stakeholders to take decisions related to water management in the Magdalena river basin in the context of environmental change.</p>

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Future water temperature of rivers in Switzerland under climate change investigated with physics-based models

10.5194/hess-2021-194 ◽

2021 ◽

Author(s):

Adrien Michel ◽

Bettina Schaefli ◽

Nander Wever ◽

Harry Zekollari ◽

Michael Lehning ◽

...

Keyword(s):

Climate Change ◽

21St Century ◽

Temperature Increase ◽

Emission Scenarios ◽

River Temperature ◽

Alpine Regions ◽

Low Emission ◽

High Emission ◽

Swiss Plateau ◽

Alpine Catchments

Abstract. Rivers are ecosystems highly sensitive to climate change and projected future increase in air temperature is expected to increase the stress for these ecosystems. Rivers are also an important socio-economical factor. In addition to changes in water availability, climate change will impact the temperature of rivers. This study presents a detailed analysis of river temperature and discharge evolution over the 21st century in Switzerland, a country covering a wide range of Alpine and lowland hydrological regimes. In total, 12 catchments are studied. They are situated both in the lowland Swiss Plateau and the Alpine regions and cover overall 10 % of the country’s area. This represents the so far largest study of climate change impacts on river temperature in Switzerland. The impact of climate change is assessed using a chain of physics-based models forced with the most recent climate change scenarios for Switzerland including low, mid, and high emissions pathways. A clear warming of river water is modelled during the 21st century, more pronounced for the high emission scenarios and toward the end of the century. For the period 2030–2040, median warming in river temperature of +1.1 °C for Swiss Plateau catchments and of +0.8 °C for Alpine catchments are expected compared to the reference period 1990–2000 (similar for all emission scenarios). At the end of the century (2080–2090), the median annual river temperature increase ranges between +0.9 °C for low emission and +3.5 °C for high emission scenarios for both Swiss Plateau and Alpine catchments. At the seasonal scale, the warming on the Swiss Plateau and in the Alpine regions exhibits different patterns. For the Swiss Plateau, the spring and fall warming is comparable to the warming in winter, while the summer warming is stronger but still moderate. In Alpine catchments, only a very limited warming is expected in winter. A marked discharge increase in winter and spring is expected in these catchments due to enhanced snowmelt and a larger fraction of liquid precipitation. Accordingly, the period of maximum discharge in Alpine catchments, currently occurring during mid-summer, will shift to earlier in the year by a few weeks (low emission) or almost two months (high emission) by the end of the century. In summer, the marked discharge reduction in Alpine catchments for high emission scenarios leads to an increase in sensitivity of water temperature to low discharge, which is not observed in the Swiss Plateau catchments. In addition, an important soil warming is expected due to glacier and snow cover decrease. These effects combined lead to a summertime river warming of +6.0 °C in Alpine catchments by the end of the century for high emission scenarios. Two metrics are used to show the adverse effects of river temperature increase both on natural and human systems. All results of this study along with the necessary source code are provided with this manuscript.

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Key drivers of ozone change and its radiative forcing over the 21st century

Atmospheric Chemistry and Physics ◽

10.5194/acp-18-6121-2018 ◽

2018 ◽

Vol 18 (9) ◽

pp. 6121-6139 ◽

Cited By ~ 6

Author(s):

Fernando Iglesias-Suarez ◽

Douglas E. Kinnison ◽

Alexandru Rap ◽

Amanda C. Maycock ◽

Oliver Wild ◽

...

Keyword(s):

Climate Change ◽

21St Century ◽

Radiative Forcing ◽

Climate Model ◽

Stratospheric Ozone ◽

Atmospheric Composition ◽

Climate Conditions ◽

Radiative Balance ◽

Radiative Forcings ◽

Year 2000

Abstract. Over the 21st century changes in both tropospheric and stratospheric ozone are likely to have important consequences for the Earth's radiative balance. In this study, we investigate the radiative forcing from future ozone changes using the Community Earth System Model (CESM1), with the Whole Atmosphere Community Climate Model (WACCM), and including fully coupled radiation and chemistry schemes. Using year 2100 conditions from the Representative Concentration Pathway 8.5 (RCP8.5) scenario, we quantify the individual contributions to ozone radiative forcing of (1) climate change, (2) reduced concentrations of ozone depleting substances (ODSs), and (3) methane increases. We calculate future ozone radiative forcings and their standard error (SE; associated with inter-annual variability of ozone) relative to year 2000 of (1) 33 ± 104 m Wm−2, (2) 163 ± 109 m Wm−2, and (3) 238 ± 113 m Wm−2 due to climate change, ODSs, and methane, respectively. Our best estimate of net ozone forcing in this set of simulations is 430 ± 130 m Wm−2 relative to year 2000 and 760 ± 230 m Wm−2 relative to year 1750, with the 95 % confidence interval given by ±30 %. We find that the overall long-term tropospheric ozone forcing from methane chemistry–climate feedbacks related to OH and methane lifetime is relatively small (46 m Wm−2). Ozone radiative forcing associated with climate change and stratospheric ozone recovery are robust with regard to background climate conditions, even though the ozone response is sensitive to both changes in atmospheric composition and climate. Changes in stratospheric-produced ozone account for ∼ 50 % of the overall radiative forcing for the 2000–2100 period in this set of simulations, highlighting the key role of the stratosphere in determining future ozone radiative forcing.

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Assessment of extreme flows and uncertainty under climate change: disentangling the uncertainty contribution of representative concentration pathways, global climate models and internal climate variability

Hydrology and Earth System Sciences ◽

10.5194/hess-24-3251-2020 ◽

2020 ◽

Vol 24 (6) ◽

pp. 3251-3269 ◽

Cited By ~ 3

Author(s):

Chao Gao ◽

Martijn J. Booij ◽

Yue-Ping Xu

Keyword(s):

Climate Change ◽

Climate Variability ◽

River Basin ◽

Climate Models ◽

Global Climate ◽

Global Climate Models ◽

Internal Climate Variability ◽

Low Flows ◽

Uncertainty Sources ◽

High Flows

Abstract. Projections of streamflow, particularly of extreme flows under climate change, are essential for future water resources management and the development of adaptation strategies to floods and droughts. However, these projections are subject to uncertainties originating from different sources. In this study, we explored the possible changes in future streamflow, particularly for high and low flows, under climate change in the Qu River basin, eastern China. ANOVA (analysis of variance) was employed to quantify the contribution of different uncertainty sources from RCPs (representative concentration pathways), GCMs (global climate models) and internal climate variability, using an ensemble of 4 RCP scenarios, 9 GCMs and 1000 simulated realizations of each model–scenario combination by SDRM-MCREM (a stochastic daily rainfall model coupling a Markov chain model with a rainfall event model). The results show that annual mean flow and high flows are projected to increase and that low flows will probably decrease in 2041–2070 (2050s) and 2071–2100 (2080s) relative to the historical period of 1971–2000, suggesting a higher risk of floods and droughts in the future in the Qu River basin, especially for the late 21st century. Uncertainty in mean flows is mostly attributed to GCM uncertainty. For high flows and low flows, internal climate variability and GCM uncertainty are two major uncertainty sources for the 2050s and 2080s, while for the 2080s, the effect of RCP uncertainty becomes more pronounced, particularly for low flows. The findings in this study can help water managers to become more knowledgeable about and get a better understanding of streamflow projections and support decision making regarding adaptations to a changing climate under uncertainty in the Qu River basin.

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The Scenario Model Intercomparison Project (ScenarioMIP) for CMIP6

Geoscientific Model Development ◽

10.5194/gmd-9-3461-2016 ◽

2016 ◽

Vol 9 (9) ◽

pp. 3461-3482 ◽

Cited By ~ 251

Author(s):

Brian C. O'Neill ◽

Claudia Tebaldi ◽

Detlef P. van Vuuren ◽

Veronika Eyring ◽

Pierre Friedlingstein ◽

...

Keyword(s):

Climate Change ◽

Land Use ◽

21St Century ◽

Integrated Assessment ◽

Climate Model ◽

Model Intercomparison ◽

Wide Range ◽

Scenario Model ◽

Intercomparison Project

Abstract. Projections of future climate change play a fundamental role in improving understanding of the climate system as well as characterizing societal risks and response options. The Scenario Model Intercomparison Project (ScenarioMIP) is the primary activity within Phase 6 of the Coupled Model Intercomparison Project (CMIP6) that will provide multi-model climate projections based on alternative scenarios of future emissions and land use changes produced with integrated assessment models. In this paper, we describe ScenarioMIP's objectives, experimental design, and its relation to other activities within CMIP6. The ScenarioMIP design is one component of a larger scenario process that aims to facilitate a wide range of integrated studies across the climate science, integrated assessment modeling, and impacts, adaptation, and vulnerability communities, and will form an important part of the evidence base in the forthcoming Intergovernmental Panel on Climate Change (IPCC) assessments. At the same time, it will provide the basis for investigating a number of targeted science and policy questions that are especially relevant to scenario-based analysis, including the role of specific forcings such as land use and aerosols, the effect of a peak and decline in forcing, the consequences of scenarios that limit warming to below 2 °C, the relative contributions to uncertainty from scenarios, climate models, and internal variability, and long-term climate system outcomes beyond the 21st century. To serve this wide range of scientific communities and address these questions, a design has been identified consisting of eight alternative 21st century scenarios plus one large initial condition ensemble and a set of long-term extensions, divided into two tiers defined by relative priority. Some of these scenarios will also provide a basis for variants planned to be run in other CMIP6-Endorsed MIPs to investigate questions related to specific forcings. Harmonized, spatially explicit emissions and land use scenarios generated with integrated assessment models will be provided to participating climate modeling groups by late 2016, with the climate model simulations run within the 2017–2018 time frame, and output from the climate model projections made available and analyses performed over the 2018–2020 period.

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Potential escalation of heat-related working costs with climate and socioeconomic changes in China

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1521828113 ◽

2016 ◽

Vol 113 (17) ◽

pp. 4640-4645 ◽

Cited By ~ 24

Author(s):

Yan Zhao ◽

Benjamin Sultan ◽

Robert Vautard ◽

Pascale Braconnot ◽

Huijun J. Wang ◽

...

Keyword(s):

Climate Change ◽

21St Century ◽

Radiative Forcing ◽

Socioeconomic Development ◽

Climate Model ◽

Global Climate ◽

Mainland China ◽

Labor Cost ◽

Labor Costs ◽

Socioeconomic Changes

Global climate change will increase the frequency of hot temperatures, impairing health and productivity for millions of working people and raising labor costs. In mainland China, high-temperature subsidies (HTSs) are allocated to employees for each working day in extremely hot environments, but the potential heat-related increase in labor cost has not been evaluated so far. Here, we estimate the potential HTS cost in current and future climates under different scenarios of socioeconomic development and radiative forcing (Representative Concentration Pathway), taking uncertainties from the climate model structure and bias correction into account. On average, the total HTS in China is estimated at 38.6 billion yuan/y (US $6.22 billion/y) over the 1979–2005 period, which is equivalent to 0.2% of the gross domestic product (GDP). Assuming that the HTS standards (per employee per hot day) remain unchanged throughout the 21st century, the total HTS may reach 250 billion yuan/y in the 2030s and 1,000 billion yuan/y in 2100. We further show that, without specific adaptation, the increased HTS cost is mainly determined by population growth until the 2030s and climate change after the mid-21st century because of increasingly frequent hot weather. Accounting for the likely possibility that HTS standards follow the wages, the share of GDP devoted to HTS could become as high as 3% at the end of 21st century.

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Influence of future climate and cropland expansion on isoprene emissions and tropospheric ozone

Atmospheric Chemistry and Physics ◽

10.5194/acp-14-1011-2014 ◽

2014 ◽

Vol 14 (2) ◽

pp. 1011-1024 ◽

Cited By ~ 23

Author(s):

O. J. Squire ◽

A. T. Archibald ◽

N. L. Abraham ◽

D. J. Beerling ◽

C. N. Hewitt ◽

...

Keyword(s):

Climate Change ◽

Land Use ◽

Land Use Change ◽

21St Century ◽

Tropospheric Ozone ◽

Climate Model ◽

Anthropogenic Emissions ◽

Change Scenario ◽

Dynamic Global Vegetation Model ◽

The Tropics

Abstract. Over the 21st century, changes in CO2 levels, climate and land use are expected to alter the global distribution of vegetation, leading to changes in trace gas emissions from plants, including, importantly, the emissions of isoprene. This, combined with changes in anthropogenic emissions, has the potential to impact tropospheric ozone levels, which above a certain level are harmful to animals and vegetation. In this study we use a biogenic emissions model following the empirical parameterisation of the MEGAN model, with vegetation distributions calculated by the Sheffield Dynamic Global Vegetation Model (SDGVM) to explore a range of potential future (2095) changes in isoprene emissions caused by changes in climate (including natural land use changes), land use, and the inhibition of isoprene emissions by CO2. From the present-day (2000) value of 467 Tg C yr−1, we find that the combined impact of these factors could cause a net decrease in isoprene emissions of 259 Tg C yr−1 (55%) with individual contributions of +78 Tg C yr−1 (climate change), −190 Tg C yr−1 (land use) and −147 Tg C yr−1 (CO2 inhibition). Using these isoprene emissions and changes in anthropogenic emissions, a series of integrations is conducted with the UM-UKCA chemistry-climate model with the aim of examining changes in ozone over the 21st century. Globally, all combined future changes cause a decrease in the tropospheric ozone burden of 27 Tg (7%) from 379 Tg in the present-day. At the surface, decreases in ozone of 6–10 ppb are calculated over the oceans and developed northern hemispheric regions, due to reduced NOx transport by PAN and reductions in NOx emissions in these areas respectively. Increases of 4–6 ppb are calculated in the continental tropics due to cropland expansion in these regions, increased CO2 inhibition of isoprene emissions, and higher temperatures due to climate change. These effects outweigh the decreases in tropical ozone caused by increased tropical isoprene emissions with climate change. Our land use change scenario consists of cropland expansion, which is most pronounced in the tropics. The tropics are also where land use change causes the greatest increases in ozone. As such there is potential for increased crop exposure to harmful levels of ozone. However, we find that these ozone increases are still not large enough to raise ozone to such damaging levels.

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