RC2: Review for "Changes in extremely hot days under stabilized 1.5oC and 2.0oC global warming scenarios as simulated by the HAPPI multi-model ensemble"

Abstract Summer season has lengthened substantially across Northern Hemisphere (NH) land over the past decades, which has been attributed to anthropogenic greenhouse gas increases. This study examines additional future changes in summer season onset and withdrawal under 1.5℃ and 2.0℃ global warming conditions using multiple atmospheric global climate model (AGCM) large-ensemble simulations from the Half a degree Additional warming, Prognosis and Projected Impacts (HAPPI) project. Five AGCMs provide more than 100 runs of 10-year length for three experiments: All-Hist (current decade: 2006-2015), Plus15, and Plus20 (1.5℃ and 2.0℃ above pre-industrial condition, respectively). Results show that with 1.5℃ and 2.0℃ warmer conditions summer season will become longer by a few days to weeks over entire NH lands, with slightly larger contributions by delay in withdrawal due to stronger warming in late summer. Stronger changes are observed more in middle latitudes than high latitudes and largest expansion (up to three weeks) is found over East Asia and the Mediterranean. Associated changes in summer-like day frequency is further analyzed focusing on the extended summer edges. The hot days occur more frequently in lower latitudes including East Asia, USA and Mediterranean, in accord with largest summer season lengthening. Further, difference between Plus15 and Plus20 indicates that summer season lengthening and associated increases in hot days can be reduced significantly if warming is limited to 1.5℃. Overall, similar results are obtained from CMIP5 coupled GCM simulations (based on RCP8.5 scenario experiments), suggesting a weak influence of air-sea coupling on summer season timing changes.

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Intensification of extreme snowfall under future warming

10.5194/egusphere-egu21-10589 ◽

2021 ◽

Author(s):

Lennart Quante ◽

Sven Willner ◽

Robin Middelanis ◽

Anders Levermann

Keyword(s):

Climate Change ◽

Global Warming ◽

Observational Data ◽

Climate Models ◽

Hydrological Cycle ◽

Freezing Point ◽

Model Ensemble ◽

Northern Latitudes ◽

Coupled Climate Models ◽

Future Warming

Due to climate change the frequency and character of precipitation are changing as the hydrological cycle intensifies. With regards to snowfall, global warming thereby has two opposing influences. Increasing humidity enables potentially intense snowfall, whereas warming temperatures decrease the likelihood of snowfall in the first place. Here we show an intensification of extreme snowfall under future warming, which is robust across all global coupled climate models when they are bias-corrected with observational data. While mean daily snowfall decreases drastically in the model ensemble, both the 99th and the 99.9th percentiles of daily snowfall increase strongly in the next decades. Additionally, the magnitude of high snowfall events increases, which is likely to pose considerable challenge to municipalities in mid to high northern latitudes. We propose that the almost unchanged occurrence of temperatures just below the freezing point of water in combination with the strengthening of the hydrological cycle enables this intensification of extreme snowfall. Thus extreme snowfall events are likely to become an increasingly important impact of climate change on society in the next decades.

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Spatiotemporal Changes in Headwater Flow Contributions to Major Rivers of Germany under Changing Climate

10.5194/egusphere-egu2020-7639 ◽

2020 ◽

Author(s):

Akash Koppa ◽

Thomas Remke ◽

Stephan Thober ◽

Oldrich Rakovec ◽

Sebastian Müller ◽

...

Keyword(s):

Climate Change ◽

Global Warming ◽

Soil Moisture ◽

Climate Models ◽

Climate Model ◽

Regional Climate ◽

Regional Climate Models ◽

Model Ensemble ◽

Hydrologic Models ◽

River Temperature

Headwater systems are a major source of water, sediments, and nutrients (including nitrogen and carbon di-oxide) for downstream aquatic, riparian, and inland ecosystems. As precipitation changes are expected to exhibit considerable spatial variability in the future, we hypothesize that headwater contribution to major rivers will also change significantly. Quantifying these changes is essential for developing effective adaptation and mitigation strategies against climate change. However, the lack of hydrologic projections at high resolutions over large domains have hindered attempts to quantify climate change impacts on headwater systems.Here, we overcome this challenge by developing an ensemble of hydrologic projections at an unprecedented resolution (1km) for Germany. These high resolution projections are developed within the framework of the Helmholtz Climate Initiative (https://www.helmholtz.de/en/current-topics/the-initiative/climate-research/). Our modeling chain consists of the following four components:Climate Modeling: We statistically downscale and bias-adjust climate change scenarios from three representative concentration pathway (RCP) scenarios derived from the EURO-CORDEX ensemble - 2.6, 4.5, and 8.5 to a horizontal resolution of 1km over Germany (i.e, a total of 75 ensemble members). The EURO-CORDEX ensemble is generated by dynamically downscaling CMIP-5 general circulation models (GCM) using regional climate models (RCMs). Hydrologic Modeling: To account for model structure uncertainty, the climate model projections are used as forcings for three spatially distributed hydrologic models - a) the mesocale Hydrologic model (mHM), b) Noah-MP, and c) HTESSEL. The outputs that will be generated in the study are soil moisture, evapotranspiration, snow water equivalent, and runoff. Streamflow Routing: To minimize uncertainty from river routing schemes, we use the multiscale routing model (mRM v1.0) to route runoff from all the three models. River Temperature Modeling: A novel river temperature model is used to quantify the changes in river temperature due to anthropogenic warming.The 225-member ensemble streamflow outputs (75 climate model members and 3 hydrologic models) are used to quantify the changes in the contribution of headwater watersheds to all the major rivers in Germany. Finally, we analyze changes in soil moisture, snow melt, and river temperature and their implications for headwater contributions. Previously, a high-resolution (5km) multi-model ensemble for climate change projections has been created within the EDgE project1,2,3,4. The newly created projections in this project will be compared against those created in the EDgE project.&#160; The ensemble used in this project will profit from the higher resolution of the regional climate models that provide a more detailed land orography.References[1] Marx, A. et al. (2018). Climate change alters low flows in Europe under global warming of 1.5, 2, and 3 C. Hydrology and Earth System Sciences, 22(2), 1017-1032.[2] Samaniego, L. et al. (2019). Hydrological forecasts and projections for improved decision-making in the water sector in Europe. Bulletin of the American Meteorological Society.[3] Samaniego, L. and Thober, S., et al. (2018). Anthropogenic warming exacerbates European soil moisture droughts. Nature Climate Change, 8(5), 421.[4] Thober, S. et al. (2018). Multi-model ensemble projections of European river floods and high flows at 1.5, 2, and 3 degrees global warming. Environmental Research Letters, 13(1), 014003.&#160;&#160;&#160;

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Evaluation of the contribution of tropical cyclone seeds to changes in tropical cyclone frequency due to global warming in high-resolution multi-model ensemble simulations

Progress in Earth and Planetary Science ◽

10.1186/s40645-020-00397-1 ◽

2021 ◽

Vol 8 (1) ◽

Author(s):

Yohei Yamada ◽

Chihiro Kodama ◽

Masaki Satoh ◽

Masato Sugi ◽

Malcolm J. Roberts ◽

...

Keyword(s):

Global Warming ◽

Survival Rate ◽

High Resolution ◽

Tropical Cyclone ◽

Model Simulation ◽

Tropical Cyclone Genesis ◽

Model Intercomparison ◽

Model Ensemble ◽

Intercomparison Project ◽

Cyclone Genesis

AbstractPrevious projections of the frequency of tropical cyclone genesis due to global warming, even in terms of sign of the change, depends on the chosen model simulation. Here, we systematically examine projected changes in tropical cyclones using six global atmospheric models with medium-to-high horizontal resolutions included in the sixth phase of the Coupled Model Intercomparison Project/High-Resolution Model Intercomparison Project. Changes in the frequency of tropical cyclone genesis could be broken down into the contributions from (i) the tropical cyclone seed, a depression having a closed contour of sea level pressure with a warm core and (ii) the survival rate, the ratio of the frequency of tropical cyclone genesis to that of tropical cyclone seeds. The multi-model ensemble mean indicates that tropical cyclone genesis frequencies are significantly decreased during the period 1990–2049, which is attributable to changes in tropical cyclone seeds. Analysis of the individual models shows that although most models project a more or less decreasing trend in tropical cyclone genesis frequencies and seeds, the survival rate also contributes to the result in some models. The present study indicates the usefulness of decomposition into the frequency of the tropical cyclone seeds and the survival rate to understand the cause of uncertainty in projected frequencies of tropical cyclone genesis.

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