scholarly journals Estimating design hydrologic extremes in a warming climate: alternatives, uncertainties and the way forward

2021 ◽  
Vol 379 (2195) ◽  
pp. 20190623 ◽  
Author(s):  
Ashish Sharma ◽  
Suresh Hettiarachchi ◽  
Conrad Wasko
Keyword(s):  
Climate Model ◽  
Flash Flood ◽  
Design Guidelines ◽  
Design Flood ◽  
The Future ◽  
Flood Magnitude ◽  
Urban Catchments ◽  
Climate Model Simulations ◽  
Hydrologic Design ◽  
The Impact

It is now well established that our warming planet is experiencing changes in extreme storms and floods, resulting in a need to better specify hydrologic design guidelines that can be projected into the future. This paper attempts to summarize the nature of changes occurring and the impact they are having on the design flood magnitude, with a focus on the urban catchments that we will increasingly reside in as time goes on. Two lines of reasoning are used to assess and model changes in design hydrology. The first of these involves using observed storms and soil moisture conditions and projecting how these may change into the future. The second involves using climate model simulations of the future and using them as inputs into hydrologic models to assess the changed design estimates. We discuss here the limitations in both and suggest that the two are, in fact, linked, as climate model projections for the future are needed in the first approach to form meaningful projections for the future. Based on the author's experience with both lines of reasoning, this invited commentary presents a theoretical narrative linking these two and identifying factors and assumptions that need to be validated before implementation in practice. This article is part of a discussion meeting issue ‘Intensification of short-duration rainfall extremes and implications for flash flood risks’.

Future changes in heatwaves over Africa at the convection-permitting scale

2021 ◽  
Author(s):  
Cathryn Birch ◽  
Lawrence Jackson ◽  
Declan Finney ◽  
John Marsham ◽  
Rachel Stratton ◽  
...  
Keyword(s):  
Climate Model ◽  
Daily Rainfall ◽  
Shortwave Radiation ◽  
Daily Maximum ◽  
Future Change ◽  
Driving Mechanisms ◽  
The Future ◽  
Convective Scale ◽  
Climate Model Simulations ◽  
The Impact

<p>Mean temperatures and their extremes have increased over Africa since the latter half of the 20th century and this trend is projected to continue, with very frequent, intense and often deadly heatwaves likely to occur very regularly over much of Africa by 2100. It is crucial that we understand the scale of the future increases in extremes and the driving mechanisms. We diagnose daily maximum wet bulb temperature heatwaves, which allows for both the impact of temperature and humidity, both critical for human health and survivability. During wet bulb heatwaves, humidity and cloud cover increase, which limits the surface shortwave radiation flux but increases longwave warming. It is found from observations and ERA5 reanalysis that approximately 30% of wet bulb heatwaves over Africa are associated with daily rainfall accumulations of more than 1 mm/day on the first day of the heatwave. The first ever pan-African convection-permitting climate model simulations of present-day and RCP8.5 future climate are utilised to illustrate the projected future change in heatwaves, their drivers and their sensitivity to the representation of convection. Compared to ERA5, the convection-permitting model better represents the frequency and magnitude of present-day wet bulb heatwaves than a version of the model with more traditional parameterised convection. The future change in heatwave frequency, duration and magnitude is also larger in the convective-scale simulation, suggesting CMIP-style models may underestimate the future change in wet bulb heat extremes over Africa. The main reason for the larger future change appears to be the ability of the model to produce larger anomalies relative to its climatology in precipitation, cloud and the surface energy balance.</p>

scholarly journals On the Choice of Ensemble Mean for Estimating the Forced Signal in the Presence of Internal Variability

2018 ◽  
Vol 31 (14) ◽  
pp. 5681-5693 ◽  
Author(s):  
Leela M. Frankcombe ◽  
Matthew H. England ◽  
Jules B. Kajtar ◽  
Michael E. Mann ◽  
Byron A. Steinman
Keyword(s):  
Regional Differences ◽  
Climate Model ◽  
Surface Air Temperature ◽  
Internal Variability ◽  
Single Model ◽  
Sea Level Pressure ◽  
Model Simulations ◽  
Ensemble Mean ◽  
Climate Model Simulations ◽  
The Impact

Abstract In this paper we examine various options for the calculation of the forced signal in climate model simulations, and the impact these choices have on the estimates of internal variability. We find that an ensemble mean of runs from a single climate model [a single model ensemble mean (SMEM)] provides a good estimate of the true forced signal even for models with very few ensemble members. In cases where only a single member is available for a given model, however, the SMEM from other models is in general out-performed by the scaled ensemble mean from all available climate model simulations [the multimodel ensemble mean (MMEM)]. The scaled MMEM may therefore be used as an estimate of the forced signal for observations. The MMEM method, however, leads to increasing errors further into the future, as the different rates of warming in the models causes their trajectories to diverge. We therefore apply the SMEM method to those models with a sufficient number of ensemble members to estimate the change in the amplitude of internal variability under a future forcing scenario. In line with previous results, we find that on average the surface air temperature variability decreases at higher latitudes, particularly over the ocean along the sea ice margins, while variability in precipitation increases on average, particularly at high latitudes. Variability in sea level pressure decreases on average in the Southern Hemisphere, while in the Northern Hemisphere there are regional differences.

scholarly journals Selection of Bias Correction Methods to Assess the Impact of Climate Change on Flood Frequency Curves

Water ◽  
2019 ◽  
Vol 11 (11) ◽  
pp. 2266 ◽  
Author(s):  
Enrique Soriano ◽  
Luis Mediero ◽  
Carlos Garijo
Keyword(s):  
Climate Change ◽  
Bias Correction ◽  
Climate Models ◽  
Climate Model ◽  
Control Period ◽  
Flood Frequency ◽  
Climate Projections ◽  
The Future ◽  
Flood Quantiles ◽  
The Impact

Climate projections provided by EURO-CORDEX predict changes in annual maximum series of daily rainfall in the future in some areas of Spain because of climate change. Precipitation and temperature projections supplied by climate models do not usually fit exactly the statistical properties of the observed time series in the control period. Bias correction methods are used to reduce such errors. This paper seeks to find the most adequate bias correction techniques for temperature and precipitation projections that minimizes the errors between observations and climate model simulations in the control period. Errors in flood quantiles are considered to identify the best bias correction techniques, as flood quantiles are used for hydraulic infrastructure design and safety assessment. In addition, this study aims to understand how the expected changes in precipitation extremes and temperature will affect the catchment response in flood events in the future. Hydrological modelling is required to characterize rainfall-runoff processes adequately in a changing climate, in order to estimate flood changes expected in the future. Four catchments located in the central-western part of Spain have been selected as case studies. The HBV hydrological model has been calibrated in the four catchments by using the observed precipitation, temperature and streamflow data available on a daily scale. Rainfall has been identified as the most significant input to the model, in terms of its influence on flood response. The quantile mapping polynomial correction has been found to be the best bias correction method for precipitation. A general reduction in flood quantiles is expected in the future, smoothing the increases identified in precipitation quantiles by the reduction of soil moisture content in catchments, due to the expected increase in temperature and decrease in mean annual precipitations.

Flood recurrence under climate change: a probabilistic flood risk assessment of critical infrastructure in the Danube basin

2020 ◽  
Author(s):  
Michel Wortmann ◽  
Kai Schröter
Keyword(s):  
Flood Risk ◽  
Climate Model ◽  
Critical Infrastructure ◽  
Insurance Industry ◽  
Danube River ◽  
Detailed Model ◽  
Flood Level ◽  
Basin Scale ◽  
The Future ◽  
The Impact

<p>Consistent information on fluvial flood risks in large river basins is typically sparse. This is especially true for the Danube River basin covering up to 14 countries and creating a patchwork of flood risk information across a populous and flood-prone region. As climatic changes have shown to increase flooding in the future, consistent basin-scale assessments prove vital to the insurance industry as well as municipal and infrastructural planning. The Future Danube Model (FDM) was designed to fill this gap complying to both insurance industry and climate science standards. That is, allowing for a reasonably detailed model scale (based on a 25m digital elevation model), stochastic sampling to create a large number of extreme events and flood event footprints (10k years), a thorough calibration and validation as well as the use of an ensemble of climate model output to drive the model under scenario conditions. The model is here used to assess the impact on critical infrastructure across the basin. Results indicate a marked increase in flood risk has already occurred when comparing the current climate period (2006-2035) to the reference period (1970-1999). Further increases are projected under a moderate and a business as usual scenario for the next climate period (2020-2049) and the end of the century (2070-2099). In large parts of the basin, the historical 100-year flood level, often used as a critical protection level for infrastructure, is projected to be equalled or exceeded every 50–10 years, while areas with a 100-year flood risk are projected to increase by 6-19%.</p>

scholarly journals Trends in Downward Solar Radiation at the Surface over North America from Climate Model Projections and Implications for Solar Energy

2015 ◽  
Vol 2015 ◽  
pp. 1-7 ◽  
Author(s):  
Gerardo Andres Saenz ◽  
Huei-Ping Huang
Keyword(s):  
United States ◽  
North America ◽  
Solar Radiation ◽  
Solar Energy ◽  
Climate Model ◽  
Global Climate Model ◽  
The United States ◽  
Model Simulations ◽  
Climate Model Simulations ◽  
The Impact

The projected changes in the downward solar radiation at the surface over North America for late 21st century are deduced from global climate model simulations with greenhouse-gas (GHG) forcing. A robust trend is found in winter over the United States, which exhibits a simple pattern of a decrease of sunlight over Northern USA. and an increase of sunlight over Southern USA. This structure was identified in both the seasonal mean and the mean climatology at different times of the day. It is broadly consistent with the known poleward shift of storm tracks in winter in climate model simulations with GHG forcing. The centennial trend of the downward shortwave radiation at the surface in Northern USA. is on the order of 10% of the climatological value for the January monthly mean, and slightly over 10% at the time when it is midday in the United States. This indicates a nonnegligible influence of the GHG forcing on solar energy in the long term. Nevertheless, when dividing the 10% by a century, in the near term, the impact of the GHG forcing is relatively minor such that the estimate of solar power potential using present-day climatology will remain useful in the coming decades.

scholarly journals Decline in Terrestrial Moisture Sources of the Mississippi River Basin in a Future Climate

2020 ◽  
Vol 21 (2) ◽  
pp. 299-316 ◽  
Author(s):  
Imme Benedict ◽  
Chiel C. van Heerwaarden ◽  
Ruud J. van der Ent ◽  
Albrecht H. Weerts ◽  
Wilco Hazeleger
Keyword(s):  
River Basin ◽  
Mississippi River ◽  
Climate Model ◽  
Low Frequency ◽  
Future Climate ◽  
Mississippi River Basin ◽  
Moisture Source ◽  
Moisture Sources ◽  
Climate Model Simulations ◽  
The Impact

AbstractAssessment of the impact of climate change on water resources over land requires knowledge on the origin of the precipitation and changes therein toward the future. We determine the origin of precipitation over the Mississippi River basin (MRB) using high-resolution (~25 km) climate model simulations for present and future climate (RCP4.5). Moisture resulting in precipitation over the MRB is tracked back in time using Eulerian offline moisture tracking, in order to find out from where this water originally evaporated (i.e., the moisture sources). We find that the most important continental moisture sources are the MRB itself and the area southwest of the basin. The two most relevant oceanic sources are the Gulf of Mexico/Caribbean and the Pacific. The distribution of sources varies per season, with more recycling of moisture within the basin during summer and more transport of moisture from the ocean toward the basin in winter. In future winters, we find an increase in moisture source from the oceans (related to higher sea surface temperatures), resulting in more precipitation over the MRB. In future summers, we find an approximately 5% decrease in moisture source from the basin itself, while the decrease in precipitation is smaller (i.e., lower recycling ratios). The results here are based on one climate model, and we do not study low-frequency climate variability. We conclude that Mississippi’s moisture sources will become less local in a future climate, with more water originating from the oceans.

Simulating the impact of future climate change on runoff processes in selected catchments of Slovakia

2021 ◽  
Author(s):  
Roman Výleta ◽  
Milica Aleksić ◽  
Patrik Sleziak ◽  
Kamila Hlavcova
Keyword(s):  
Climate Change ◽  
Air Temperature ◽  
Climate Model ◽  
Hydrological Cycle ◽  
Future Climate Change ◽  
Time Horizons ◽  
The Future ◽  
The Impact ◽  
Impacts Of Climate Change

<p>The future development of the runoff conditions, as a consequence of climate change, is of great interest for water managers. Information about the potential impacts of climate change on the hydrological regime is needed for long-term planning of water resources and flood protection.</p><p>The aim of this study is to evaluate the possible impacts of climate change on the runoff regime in five selected catchments located in the territory of Slovakia. Changes in climatic characteristics (i.e., precipitation and air temperature) for future time horizons were prepared by a regional climate model KNMI using the A1B emission scenario. The selected climatic scenario predicts a general increase in air temperature and precipitation (higher in winter than in summer). For simulations of runoff under changed conditions, a lumped rainfall-runoff model (the TUW model) was used. This model belongs to a group of conceptual models and follows a structure of a widely used Swedish HBV model. The TUW model was calibrated for the period of 2011 – 2019. We assumed that this period would be similar (to recent/warmer climate) in terms of the average daily air temperatures and daily precipitation totals. The future changes in runoff due to climate change were evaluated by comparing the simulated long-term mean monthly runoff for the current state (1981-2010) and modelled scenarios in three time periods (2011-2040, 2041-2070, and 2071-2100). The results indicate that changes in the long-term runoff seasonality and extremality of hydrological cycle could be expected in the future. The runoff should increase in winter months compared to the reference period. This increase is probably related to a rise in temperature and anticipated snowmelt. Conversely, during the summer periods, a decrease in the long-term runoff could be assumed. According to modelling, these changes will be more pronounced in the later time horizons.</p><p>It should be noted that the results of the simulation are dependent on the availability of the inputs, the hydrological/climate model used, the schematization of the simulated processes, etc. Therefore, they need to be interpreted with a sufficient degree of caution</p>

Exposure analysis of Chinese railways under the Change of Extreme-Precipitation in the future

2020 ◽  
Author(s):  
Jing Zhao ◽  
Kai liu ◽  
Ming Wang
Keyword(s):  
Global Warming ◽  
Return Period ◽  
Extreme Precipitation ◽  
Climate Model ◽  
Precipitation Amount ◽  
Extreme Rainfall ◽  
Railway Planning ◽  
The Future ◽  
Railway System ◽  
Climate Model Simulations

<p>Abstract: Rainfall-induced disaster is the most frequent disaster affected Chinese Railway System. Climate change will lead to more extreme rainfall in the future. A better understanding of extreme precipitation in the future and the exposure of railway infrastructures to extreme precipitation will facilitate railway planning and disaster risk management. This paper employs climate model simulations to calculate the changes of the extreme precipitation under different global warming scenarios. The return periods of the present 50-yr/100-yr return-period precipitation amount in the future are obtained. Based on this, the changes of the exposure of Chinese railways to extreme precipitation are analyzed. The results reveal that 58.61% (55.46) of China’s region will experience an increase in the 50-yr(100-yr) return-period precipitation under 1.5°C warming in comparison with the present period (2001–2020), the value will be 64.44% and 59.53% due to the additional 0.5°C warming. By calculating the exposure of Chinese railways, we found that 28.49% (32.15) of China's railways are in the region where 50-yr return-period rainfall at this stage will occur less than 20 years under 1.5°C (2.0°C) warming, and 36.85% (41.39)of China's railways are in the region where 100-yr return-period rainfall at this stage will occur less than 50 years under 1.5°C (2.0°C) warming in the future. This study quantified the exposure of China’s railway to extreme precipitation under the 1.5°C/2.0°C global warming. The results provided in this study have profound significance for the fortification planning of China's railway system for rainfall-induced disasters and provide useful experience for other countries.</p>

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