Pseudo Global Warming Research Articles

Climatological representation of mesoscale convective systems in a dynamically downscaled climate simulation

This research assesses the utility and validity of using simulated radar reflectivity to detect potential changes in linear and nonlinear mesoscale convective system (MCS) occurrence in the Midwest United States between the early and late 21st century using convection‐permitting climate simulation output. These data include a control run and a pseudo‐global warming (PGW) run that is based on RCP 8.5. First, using a novel segmentation, classification, and tracking procedure, MCS tracks are extracted from observed and simulated radar reflectivity. Next, a comparison between observed and the control run MCS statistics is performed, which finds a negative summertime bias that agrees with previous work. Using a convolutional neural network to perform probabilistic predictions, the MCS dataset is further stratified into highly organized, quasi‐linear convective systems (QLCSs)—which can include bow echoes, squall lines, and line echo wave patterns—and generally less‐organized, non‐QLCS events. The morphologically stratified data reveal that the negative MCS bias in this region is largely driven by too few QLCSs. Although comparisons between the control run and a PGW run suggest that all MCS events are less common in the future (including QLCS and non‐QLCS events), these changes are not spatially significant, whereas the biases between the control run and observations are spatially significant. A discussion on the importance and challenges of simulating QLCSs in convection‐permitting climate model runs is provided. Finally, potential avenues of exploration are suggested related to the aforementioned issues.

Climate change impact on future photovoltaic resource potential in an orographically complex archipelago, the Canary Islands

It is widely accepted by the scientific community that in the coming decades the Earth's climate will undergo significant changes, which will affect the ecosystems and the population in various ways. In this work, climate change impacts on solar photovoltaic (PV) resources were evaluated in the Canary Islands, an orographically complex archipelago located in the sub-tropical Atlantic Ocean, using high resolution dynamical downscaling techniques. To alleviate the high computational cost of high resolution simulations, the pseudo-global warming technique was used to compute the initial and boundary conditions from a reanalysis dataset and from the monthly mean changes obtained by the simulations of fourteen global climate models included in the Coupled Model Intercomparison Project Phase 5 (CMIP5). Projections of annual-mean daily irradiation and PV potential were obtained for two future decades (2045–2054 and 2090–2099) and for two different greenhouse gas emission scenarios (RCP4.5 and RCP8.5), and the corresponding results were compared with those for a recent period (1995–2004). During winter, a generalized increase in PV potential is expected, as a consequence of a reduction in cloud cover. However, during summer, future simulations indicate a decrease in PV potential because of the rise of temperature and, therefore, a reduction in PV panel efficiency.

Benefit analysis of flood adaptation under climate change scenario

Typhoon Morakot of 2009 caused the worst flooding in the history of Taiwan. Because research on climate change has indicated that similar extreme disasters are expected to become more frequent, this study investigated adaptation projects for mitigating the impact of such disasters in the future. It used Typhoon Morakot as an example and applied the pseudo-global warming method for simulating the impact of a Morakot-level typhoon plus warming effects to analyze the flood losses caused by increasing precipitation. For this study, Tainan City, a city severely damaged by Typhoon Morakot in 2009, was chosen as a demonstration area to evaluate the optimal adaptation measures by cost–benefit analysis methods. The results showed that the precipitation will increase as much as 60% in the Tainan region at the end of this century and that in the future the inundation area in Tainan will see a 10.4% increase beyond the flooding caused by Typhoon Morakot. Fifteen combinations of adaptation projects were provided to reduce future flood losses. Finally, a composite adaptation project combining riverbed dredging and improved plans for evacuation and sheltering was determined to be the optimal option, as it could create a net benefit of as much as 27 million US dollars in the 60 years of engineering service life for Tainan City.

Changes in Hurricanes from a 13-Yr Convection-Permitting Pseudo–Global Warming Simulation

Abstract Tropical cyclones have enormous costs to society through both loss of life and damage to infrastructure. There is good reason to believe that such storms will change in the future as a result of changes in the global climate system and that such changes may have important socioeconomic implications. Here a high-resolution regional climate modeling experiment is presented using the Weather Research and Forecasting (WRF) Model to investigate possible changes in tropical cyclones. These simulations were performed for the period 2001–13 using the ERA-Interim product for the boundary conditions, thus enabling a direct comparison between modeled and observed cyclone characteristics. The WRF simulation reproduced 30 of the 32 named storms that entered the model domain during this period. The model simulates the tropical cyclone tracks, storm radii, and translation speeds well, but the maximum wind speeds simulated were less than observed and the minimum central pressures were too large. This experiment is then repeated after imposing a future climate signal by adding changes in temperature, humidity, pressure, and wind speeds derived from phase 5 of the Coupled Model Intercomparison Project (CMIP5). In the current climate, 22 tracks were well simulated with little changes in future track locations. These simulations produced tropical cyclones with faster maximum winds, slower storm translation speeds, lower central pressures, and higher precipitation rates. Importantly, while these signals were statistically significant averaged across all 22 storms studied, changes varied substantially between individual storms. This illustrates the importance of using a large ensemble of storms to understand mean changes.

The Simulated Impact of the Snow Albedo Feedback on the Large-Scale Mountain–Plain Circulation East of the Colorado Rocky Mountains

Abstract The Front Range mountain–plain circulation (FRMC) is a large-scale diurnally driven wind system that occurs east of the Colorado Rocky Mountains in the United States and affects the weather both in the Rocky Mountains and Great Plains. As the climate warms, the snow albedo feedback will amplify the warming response in the Rocky Mountains during the spring, increasing the thermal contrast that drives the FRMC. In this study, the authors perform a 7-yr pseudo–global warming (PGW) regional climate change experiment along with an idealized PGW “fixed albedo” experiment to test the sensitivity of the FRMC to the snow albedo feedback (SAF). The authors find a mean increase in the springtime FRMC strength in the PGW experiment that is primarily driven by the snow albedo feedback. Furthermore, interannual variability of changes in FRMC strength is strongly influenced by interannual variability in the SAF. An additional case study experiment configured with a much higher resolution is performed to examine the finescale details of how the SAF and the FRMC interact. This experiment includes a passive tracer to investigate subsequent impacts on pollution transport. The case study reveals that loss of snow cover causes an increase in the strength of the FRMC. Advection by the strengthened FRMC increases the concentration of tracers emitted over the Great Plains in the boundary layer over the Front Range mountains.

The response of land-falling tropical cyclone characteristics to projected climate change in northeast Australia

Land-falling tropical cyclones along the Queensland coastline can result in serious and widespread damage. However, the effects of climate change on cyclone characteristics such as intensity, trajectory, rainfall, and especially translation speed and size are not well-understood. This study explores the relative change in the characteristics of three case studies by comparing the simulated tropical cyclones under current climate conditions with simulations of the same systems under future climate conditions. Simulations are performed with the Weather Research and Forecasting Model and environmental conditions for the future climate are obtained from the Community Earth System Model using a pseudo global warming technique. Results demonstrate a consistent response of increasing intensity through reduced central pressure (by up to 11 hPa), increased wind speeds (by 5–10% on average), and increased rainfall (by up to 27% for average hourly rainfall rates). The responses of other characteristics were variable and governed by either the location and trajectory of the current climate cyclone or the change in the steering flow. The cyclone that traveled furthest poleward encountered a larger climate perturbation, resulting in a larger proportional increase in size, rainfall rate, and wind speeds. The projected monthly average change in the 500 mb winds with climate change governed the alteration in the both the trajectory and translation speed for each case. The simulated changes have serious implications for damage to coastal settlements, infrastructure, and ecosystems through increased wind speeds, storm surge, rainfall, and potentially increased size of some systems.

Changes in the convective population and thermodynamic environments in convection-permitting regional climate simulations over the United States

Novel high-resolution convection-permitting regional climate simulations over the US employing the pseudo-global warming approach are used to investigate changes in the convective population and thermodynamic environments in a future climate. Two continuous 13-year simulations were conducted using (1) ERA-Interim reanalysis and (2) ERA-Interim reanalysis plus a climate perturbation for the RCP8.5 scenario. The simulations adequately reproduce the observed precipitation diurnal cycle, indicating that they capture organized and propagating convection that most climate models cannot adequately represent. This study shows that weak to moderate convection will decrease and strong convection will increase in frequency in a future climate. Analysis of the thermodynamic environments supporting convection shows that both convective available potential energy (CAPE) and convective inhibition (CIN) increase downstream of the Rockies in a future climate. Previous studies suggest that CAPE will increase in a warming climate, however a corresponding increase in CIN acts as a balancing force to shift the convective population by suppressing weak to moderate convection and provides an environment where CAPE can build to extreme levels that may result in more frequent severe convection. An idealized investigation of fundamental changes in the thermodynamic environment was conducted by shifting a standard atmospheric profile by ± 5 °C. When temperature is increased, both CAPE and CIN increase in magnitude, while the opposite is true for decreased temperatures. Thus, even in the absence of synoptic and mesoscale variations, a warmer climate will provide more CAPE and CIN that will shift the convective population, likely impacting water and energy budgets on Earth.

Changes in Winter North Atlantic Extratropical Cyclones in High-Resolution Regional Pseudo–Global Warming Simulations

The present study investigates changes in the location, frequency, intensity, and dynamical processes of North Atlantic extratropical cyclones with warming consistent with the IPCC Fifth Assessment Report (AR5) representative concentration pathway 8.5 (RCP8.5) scenario. The modeling, analysis, and prediction (MAP) climatology of midlatitude storminess (MCMS) feature-tracking algorithm was utilized to analyze 10 cold-season high-resolution atmospheric simulations over the North Atlantic region in current and future climates. Enhanced extratropical cyclone activity is most evident in the northeast North Atlantic and off the U.S. East Coast. These changes in cyclone activity are offset from changes in eddy kinetic energy and eddy heat flux. Investigation of the minimum SLP reached at each grid point reveals a lack of correspondence between the strongest events in the current and future simulations, indicating the future simulations produced a different population of storms. Examination of the percent change of storms in the storm-track region shows a reduction in the number of strong storms (i.e., those reaching a minimum SLP perturbation of at least −51 hPa). Storm-relative composites of strong and moderate storms show an increase in precipitation, associated with enhanced latent heat release and strengthening of the 900–700-hPa layer-average potential vorticity (PV). Other structural changes found for cyclones in a future climate include weakened upper-level PV for strong storms and a weakened near-surface potential temperature anomaly for moderate storms, demonstrating a change in storm dynamics. Furthermore, the impacts associated with extratropical cyclones, such as strong near-surface winds and heavy precipitation, strengthen and become more frequent with warming.

SST Ensemble Experiment-Based Impact Assessment of Climate Change on Storm Surge Caused by Pseudo-Global Warming: Case Study of Typhoon Vera in 1959

To evaluate future changes in storm surge caused by global warming, dynamical downscaling was conducted using the Weather Research and Forecasting model for Typhoon Vera under present- and future-climate conditions and storm surge simulation using the Coupled Model of Surge, Wave, and Tide. The present-climate experiment entailed dynamical downscaling using data from the Japanese 55-year Reanalysis project as the initial and boundary conditions, and the future-climate experiments entailed downscaling considering future changes simulated through sea-surface temperature ensemble experiments using the Meteorological Research Institute Atmosphere General Circulation Model. The characteristics of the downscaled typhoon agreed well with the Best Track, and the future changes in the typhoon characteristics were as follows: intensification of the central pressure, delayed decline in the high-latitude area, and westward track migration. Present-climate storm surge simulation executed using these downscaling results after correcting for the track error agreed with the observed surge, but the storm surges under future-climate conditions were underestimated because of differences in the typhoon track and surface roughness. Storm surge simulations were conducted using an empirical typhoon model; the results suggest a storm surge of 26 cm (average of the ensemble) at Nagoya Port, which is located in the innermost region of Ise Bay.

A new approach to construct representative future forcing data for dynamic downscaling

Climate downscaling using regional climate models (RCMs) has been widely used to generate local climate change information needed for climate change impact assessments and other applications. Six-hourly data from individual simulations by global climate models (GCMs) are often used as the lateral forcing for the RCMs. However, such forcing often contains both internal variations and externally-forced changes, which complicate the interpretation of the downscaled changes. Here, we describe a new approach to construct representative forcing for RCM-based climate downscaling and discuss some related issues. The new approach combines the transient weather signal from one GCM simulation with the monthly mean climate states from the multi-model ensemble mean for the present and future periods, together with a bias correction term. It ensures that the mean climate differences in the forcing data between the present and future periods represent externally-forced changes only and are representative of the multi-model ensemble mean, while changes in transient weather patterns are also considered based on one select GCM simulation. The adjustments through the monthly fields are comparable in magnitude to the bias correction term and are small compared with the variations in 6-hourly data. Any inconsistency among the independently adjusted forcing fields is likely to be small and have little impact. For quantifying the mean response to future external forcing, this approach avoids the need to perform RCM large ensemble simulations forced by different GCM outputs, which can be very expensive. It also allows changes in transient weather patterns to be included in the lateral forcing, in contrast to the Pseudo Global Warming (PGW) approach, in which only the mean climate change is considered. However, it does not address the uncertainty associated with internal variability or inter-model spreads. The simulated transient weather changes may also be unrepresentative of other models. This new approach has been applied to construct the forcing data for the second phase of the WRF-based downscaling over much of North America with 4 km grid spacing.

Future Enhancement of Heavy Rainfall Events Associated with a Typhoon in the Midlatitude Regions

In August 2016, eastern Hokkaido in northern Japan had unusual typhoon landfalls and experienced heavy rainfall events that caused severe disasters. To understand the impact of global warming on typhoon-related rainfall in such midlatitude regions, numerical experiments on one of the typhoons in August 2016, Typhoon Chanthu, were conducted by using a high-resolution three-dimensional atmosphere–ocean coupled regional model in current and pseudo-global warming (PGW) climates. The amount, intensity, and duration of rainfall in eastern Hokkaido associated with the typhoon increased in the warming climate. The PGW typhoon traveled northward with relatively slower translation speed and resulted in a delay in the landfalls for 6 h. Furthermore, large amounts of near-surface water vapor > 22 g kg−1 from the southern sea increased the convective instability around eastern Hokkaido and caused tall and intense updrafts. As a result, significant predecessor rainfall events with intense rainfall developed about 24 h before the typhoon landfall. Increased near-surface water vapor in the warming climate also enhanced rainfall associated with the typhoon passage over a widespread area. These results suggest that attention should be paid to future enhancement of heavy rainfall events in the midlatitude regions under global warming.

Future Projections of Typhoon Intensity Change by Pseudo-global Warming Simulations

Future Projections of Typhoon Intensity Change by Pseudo-global Warming Simulations

The Simulated Response of Diurnal Mountain Winds to Regionally Enhanced Warming Caused by the Snow Albedo Feedback

Abstract The snow albedo feedback (SAF) is an important climate feature of mountain regions with transient snow cover. In these regions, where patterns of snow cover are largely determined by the underlying terrain, the SAF is highly variable in space and time. Under climate warming, these variations may affect the development of diurnal mountain winds either by altering the thermal contrast between high and low elevations or by increasing boundary layer mixing. In this study, high-resolution regional climate modeling experiments are used to investigate and characterize how the SAF modulates changes in diurnal wind systems in the Rocky Mountains of Colorado and Utah during the spring when SAF strength is at a maximum. Two separate 7-yr pseudo–global warming climate change experiments with differing model configurations are examined. An evaluation of the control simulations against a mesoscale network of observations reveals that the models perform reasonably well at simulating diurnal mountain winds within this region. In the experiment with a strong SAF, there is a clear increase in the strength of daytime upslope flow under climate warming, which leads to increased convergence and cloudiness near the snow margin. Additionally, there is a decrease in the strength of nighttime downslope flows. In the simulation with a weaker SAF, the results are generally similar but less pronounced. In both experiments, an altered thermal contrast, rather than increased boundary layer mixing, appears to be the primary mechanism driving changes in diurnal mountain wind systems in this region.

Future projections of wind resource in a mountainous archipelago, Canary Islands

Large-scale atmospheric patterns and near-surface winds are expected to be modified in the future due to climate change, altering the availability of wind resources on a regional scale. These possible changes are especially important in isolated power systems, as is the case for a great percentage of the islands. High-resolution climate regionalization is therefore necessary to assess the future projections of wind resource, mainly in the case of orographically complex territories, such as The Canary Islands. In this work, WRF was used to perform a dynamic regionalization in this Archipelago, using the pseudo-global warming technique to compute the initial and boundary conditions from a reanalysis dataset and from the monthly mean changes obtained from the simulations of fourteen global climate models included in the Coupled Model Intercomparison Project Phase 5 (CMIP5). Projections of mean wind, wind energy density and extractable wind power were obtained for two future decades (2045–2054 and 2090–2099) and for two different greenhouse gas scenarios (RCP4.5 and RCP8.5) and the results were compared with those for 1995–2004. Statistically significant changes in wind resource were found in some areas, mainly during summer. Most of these areas correspond to zones where at present wind farms are located.

The Realization of Extreme Tornadic Storm Events under Future Anthropogenic Climate Change

Abstract This research seeks to answer the basic question of how current-day extreme tornadic storm events might be realized under future anthropogenic climate change. The pseudo global warming (PGW) methodology was adapted for this purpose. Three contributions to the CMIP5 archive were used to obtain the mean 3D atmospheric state simulated during May 1990–99 and May 2090–99. The climate change differences (or Δs) in temperature, relative humidity, pressure, and winds were added to NWP analyses of three high-end tornadic storm events, and this modified atmospheric state was then used for initial and boundary conditions for real-data WRF Model simulations of the events at high resolution. Comparison of an ensemble of these simulations with control simulations (CTRL) facilitated assessment of PGW effects. In contrast to the robust development of supercellular convection in each CTRL, the combined effects of increased convective inhibition (CIN) and decreased parcel lifting under PGW led to a failure of convection initiation in many of the experiments. Those experiments that had sufficient matching between the CIN and lifting tended to generate stronger convective updrafts than CTRL, although not in proportion to the projected higher levels of convective available potential energy (CAPE) under PGW. In addition, the experiments with enhanced updrafts also tended to have enhanced vertical rotation. In fact, such supercellular convection was even found in simulations that were driven with PGW-reduced environmental wind shear. Notably, the PGW modifications did not induce a change in the convective morphology in any of the PGW experiments with significant convective storminess.

Climate change impact on the roles of temperature and precipitation in western U.S. snowpack variability

AbstractWe employ dynamical downscaling and pseudo global warming methodologies to evaluate climate change impact on the roles of temperature and precipitation in spring snowpack (S) variability across the western United States (U.S.). The negative correlation between S and temperature weakens linearly with elevation, whereas the correlation between S and precipitation increases asymptotically with elevation. The curvilinear relationship in the latter case was not visible in prior studies because of the observation networks' limited range. In our historical validation, there is a range of threshold elevations (1580–2181 m) across six mountainous regions, above which precipitation is the main driver of snowpack variability and below which temperature is the main driver. Under a moderate end‐of‐century climate change scenario, these thresholds increase by 191 to 432 m. These rising thresholds indicate increasing spatial and elevational vulnerability of western U.S. spring snowpack along with associated impacts to hydrologic and ecologic systems.

Effects of global warming on the impacts of Typhoon Mireille (1991) in the Kyushu and Tohoku regions

Typhoon Mireille (1991) caused devastation over Japan. Assessing the impacts of such an extreme typhoon under global warming is an important task to prevent and mitigate future natural disasters. This study investigated the influences of global warming on the strong winds of Typhoon Mireille by conducting pseudo-global warming (PGW) experiments with a regional model. Since significant damages to forest areas occurred in Kyushu and Tohoku, we compared the typhoon impacts in these two regions. It was demonstrated that on average the mean wind speeds induced by Typhoon Mireille become stronger in Kyushu and weaker in Tohoku under the PGW conditions than under the September 1991 conditions. The difference between the two regions in the future is due to the simulated typhoons under PGW being stronger at lower latitudes and weakening more rapidly at higher latitudes. Thus, the impacts of Typhoon Mireille under a warmed climate are considered to be more severe at a lower latitude and weaker at a higher latitude.

High-Resolution Future Projections of Temperature and Precipitation in the Canary Islands

Abstract The complex orography of the Canary Islands favors the creation of microclimates, which cannot be studied using global climate models or regional models with moderate resolution. In this work, WRF is used to perform a dynamic climate regionalization in the archipelago, using the pseudo–global warming technique to compute the initial and boundary conditions from a reanalysis dataset and from results of 14 global climate models. The simulations were performed for three decades, one at present (1995–2004) and two in the future (2045–54 and 2090–99), and for two different greenhouse gas scenarios (RCP4.5 and RCP8.5), defined in phase 5 of the Coupled Model Intercomparison Project. The obtained results, at a 5-km horizontal resolution, show a clear dependence of temperature increase with height and a positive change in diurnal temperature range, which is mainly due to a reduction in soil moisture and a slight decrease in cloud cover. This negative change in soil moisture is mainly a consequence of a decrease in precipitation, although the evaluation of simulated reduction in precipitation does not show statistical significance in most of the Canary Islands for the analyzed periods and scenarios.

Characterization of the Simulated Regional Snow Albedo Feedback Using a Regional Climate Model over Complex Terrain

Abstract Midlatitude mountain regions are particularly sensitive to climate change because of an active snow albedo feedback (SAF). Here, the SAF is characterized and quantified over the complex terrain of the Colorado Headwaters region using high-resolution regional climate model simulations. A pair of 7-yr control and pseudo-global warming simulations is used to study the regional climate response to a large-scale thermodynamic climate perturbation. Warming is strongly enhanced in regions of snow loss by as much as 5°C. Linear feedback analysis is used to quantify the strength of the SAF within the Headwaters region. The strength of the SAF reaches a maximum value of 4 W m−2 K−1 during April when snow loss coincides with strong incoming solar radiation. Simulations using 4- and 12-km horizontal grid spacing show good agreement in the strength and timing of the SAF, whereas a 36-km simulation shows discrepancies that are tied to differences in snow accumulation and ablation caused by smoother terrain. Energy budget analysis shows that transport by atmospheric circulations acts as a negative feedback to regional warming, damping the effects of the SAF. On the mesoscale, the SAF nonlocally enhances warming in locations with no snow, and enhances snowmelt in locations that do not experience snow cover change. The methods presented here can be used generally to quantify the role of the SAF in simulated regional climate change, illuminating the causes of differences in climate warming between models and regions.

Application of the Pseudo Global Warming Dynamic Downscaling Method to the Tokai Heavy Rain in 2000

The Tokai region in central Japan often receives heavy rainfall because of typhoons. Furthermore, because of global warming, the intensity of heavy rainfall events is expected to increase in the future. Therefore, assessment of possible differences in such events between the present and future is important. In this study, a record heavy rainfall event in the Tokai region on 11 September 2000, the so-called Tokai Heavy Rain (THR), was numerically simulated by weather research and forecasting model with triple nesting grid system of 50-, 10-, and 2-km horizontal resolution. Simulated results present characteristics of rainfall and atmospheric conditions similar to the actual event. Thus, the simulation is considered valid for reproducing rainfall processes of the THR. In addition, variations of heavy rainfall events in future climate scenarios are investigated using numerical simulations based on pseudo global warming (PGW) conditions, constructed using third-phase results of Coupled Model Intercomparison Project multi-model global warming experiments. Under certain future climate scenarios, the Tokai region may experience heavy rainfall events in which maximum hourly rainfall and extent of heavy rainfall areas increases. Such variations are mainly attributed to increased specific humidity in the lower troposphere. In some PGW runs, there was no significant rainfall around the Tokai region. There was increased specific humidity in these runs, and the horizontal distribution of lower atmospheric air temperature was favorable for the formation of a mesoscale convergence zone, as seen in PGW runs with heavy rainfall. However, vertical profiles of equivalent potential temperature and saturated equivalent potential temperature showed unsaturated and stable atmospheric stratifications that are unfavorable for convective activity. Even in cases with increased atmospheric temperature and specific humidity caused by global warming, differences in their spatial distributions and vertical profiles could lead to contrasting effects of global warming on a specific extreme weather event.