Active Flagship Pilot Studies

URBan environments and Regional Climate Change (URB-RCC)

Cities play a fundamental role on climate at local to regional scales through modification of heat and moisture fluxes, as well as affecting local atmospheric chemistry and composition, alongside air-pollution dispersion. Vice versa, regional climate change impacts urban areas and is expected to more severely affect cities and their citizens in the upcoming decades. Simultaneously, the share of the population living in urban areas is growing, and is projected to reach about 70% of the world population up to 2050. This is especially critical in connection to extreme events, for instance heat waves with extremely high temperatures exacerbated by the urban heat island effect, in particular during night-time, with significant consequences for human health. Additionally, from the perspective of recent regional climate model developments with increasing resolution down to the city scale, proper parameterization of urban processes is starting to play an important role to understand local/regional climate change. The inclusion of the individual urban processes affecting energy balance and transport (i.e. heat, humidity, momentum fluxes) via special urban land-use parameterization of distinct local processes becom es vital to simulate the urban effects properly. This will enable improved assessment of climate change impacts in the cities and inform adaptation and/or mitigation options by urban decision-makers, as well as adequately prepare for climate related risks (e.g. heat waves, smog conditions etc.). Cities are becoming one of the most vulnerable environments under climate change. In 2013, the CORDEX community identified cities to be a prime scientific challenge. Though, until now no major collaborative efforts have happened, therefore increased cooperation dedicated to these aspects is highly relevant to the CORDEX community.

The main goal of this FPS is to understand the effect of urban areas on the regional climate, as well as the impact of regional climate change on cities, with the help of coordinated experiments with urbanized RCMs. This clearly complies with the first CORDEX FPS criterion to address regional to local scales problems and effects with local impacts, which cannot be addressed by the GCMs and is not included in the standard CORDEX framework. The proposed activities require the specific data, both for specific land-use parameterization and the observational data, which are available from the previous campaigns, to make the expected simulations and their validation complying with the second CORDEX FPS criterion. This FPS action can be supported by – and contributing to – Special IPCC Assessment Report planned for cities after AR6, WCRP Grand Challenges – Weather and Climate Extremes – on local scale, and SDG (Sustainable Development Goal) on sustainable cities (#11), climate action (#13) and health (#3), providing information for risk management in these aspects to urban stakeholders, which corresponds to the third CORDEX FPS criterion. As for the fourth criterion, urbanization is important for many groups participating in CORDEX activities and going across the CORDEX domains as big cities appear in each of them. Clearly, careful selection of targeted coordinated simulations have to be performed.

Dynamical downscaling experiments and hydrological modelling for Canada and Mexico

Weak (strong) thermal gradient and intense (weak) convective activity characterizes the tropical (extra tropical) atmosphere. For the tropics, the release of latent heat is the primary source of energy in the circulations of the region; while for the extra-tropics are the thermal gradients, Coriolis and the momentum fluxes associated to perturbations of all scales.

Earth System Models (ESMs) are a useful tool to contribute to the understanding of global circulation and generate climate change scenarios for the following decades. The resolution of these models is adequate to describe global circulation patterns, but not enough to describe the subcontinental processes important to North America, such as the effects of their abrupt orography or atmospheric processes at scales smaller than 10 km. That gap is filled up by performing dynamical downscaling, which requires regional models with the potential to increase to higher spatial resolutions.

Based on the contrasting nature of the tropics and the extra-tropics, this study proposes to carry out a dynamical downscaling experiment for North America (Mexico, the United States and Canada), using two of the CMIP6 ESMs with the “best performance” for the regions, in agreement with statistical metrics (Colorado et al., 2018), forcing the RegCM and WRF models, and evaluating their capabilities. The regional models will run under low resolution (45 km), medium resolution (15 km) and high-resolution (5 km) nesting grids, with the highest resolution covering two domains, one over a group of river basins located in the tropical zone of Mexico (namely Actopan, Antigua, Jamapa and Nautla) and a second one over a group of river basins located in the southern province of Quebec in Canada (namely Du Nord, Doncaster, Matawin, L´Assomption, Noire, Maskinonge, Du Loup and Taureau).

Some numerical experiments will be made with 2.5 km resolution over the group of river basins located in Mexico and Canada.

We propose to carry on a process-oriented verification in both subregions, considering its different regional processes, but applying the same methodologies to analyze the contributions of regional mechanisms under contrasting conditions that allow the understanding of high/low frequency atmospheric dynamics, acquiring a better-understanding of processes in contrasted environments.

Evaluating how well the models can reproduce the observations under different conditions is challenging since there are different modes of response to forcing with scales on the order of hours, days, months and years.

In the project, dynamical downscaling with the highest spatial resolution of 5 km using the “convection permitting” option will be applied, for the historical period: 1981-2010, near future: 2020-2049 and far future: 2070-2099, under two extreme climate change scenarios: SSP5-8.5 and SSP1-2.6, estimating the temporal and spatial variability over the two regions.

Some statistical downscaling techniques based on bias correction (such as Bias Correction/Constructed Analogues and Bias-Correction Spatial Disaggregation) and Perfect Prognosis will be applied to compare with the dynamical downscaling simulations. Comparisons with existing CORDEX simulations over the NAM and CAM domains will also be carried out.

And finally, the HYDROTEL distributed hydrological model will be run to better investigate the use of convection-permitting climate simulation outputs for the simulation of streamflows.

North America: Assessing the Use of Regional Models in a Storyline Framework for Understanding Climate Hazards

Physical storylines are a physically self-consistent unfolding of past events or of plausible future events and pathways (Shepherd et al. 2018). They generally consist of both a recreation of a past event or period and an exploration of future analogue events that may arise under different future climate change scenarios. In short, storylines are a way to frame a problem in terms of 1) a geographic region, 2) an event, and 3) a set of process drivers for that event. Extreme events and/or climate hazards, particularly those that have had a resounding effect on stakeholder and policymaker decisions, are natural candidates for examination using physical storylines.

We propose to leverage the storyline framework for understanding model performance and future projected changes across multiple extreme weather and climate events or periods of interest to our project stakeholders.

Eight different types of weather/climate extremes that took place over the contiguous U.S. (CONUS) will be examined. The 2018 California wildfire season, atmospheric river events on the West Coast, the 2015 spring season of repeated mesoscale convective system (MCS) occurrence in the southern U.S. Plains that led to widespread flooding, Hurricane Irma, the 1996 rain-on-snow flooding event in the Susquehanna River basin, strong Northeast U.S. windstorms caused by both extratropical cyclones and derechos, and Northeast U.S. droughts.

These eight different physical storylines will be drawn on as test cases for assessing if regional models can reproduce these rare events at high to very high resolution in a manner that is consistent with observations, allow us to better understand the processes behind the events, and assess how these extreme events may look in the future. Two different methods for producing projections will be applied here, depending on the hazard in question. A pseudo-global warming approach will be applied in most, but for some, e.g. the atmospheric rivers, future analogs will be identified via the mining of simulation ensembles. This provides us with an opportunity to examine two different methods for generating event projections.

For this FPS, we will distill the information gained from the use of these storylines into actionable information for the international regional modeling community and potential interested stakeholders.

Africa: Modelling the Southeast African regional Climate

Southeastern Africa is a region with a population of ~270 million people who are strongly affected by the local climate. Hence, it is important to get a better understanding of the regional climate, how it has changed in the past, and how it is likely to change in the future. An important question is whether and how the rainfall over southeastern Africa responds to anthropogenic forcings as well as natural climate variability. Dominant atmospheric phenomena in this region include the intertropical convergence zone (ITCZ), the tropical monsoon and El Niño-Southern Oscillation (ENSO). Furthermore, it is important to revise and update climate knowledge based on local climate scientists. There is already scientific literature on climate change studies for southern Africa, but work remains in evaluating the model projections and calibrating their output with in-situ observations. Southeastern Africa is experiencing a climate change where trends in mean precipitation may be due to changes in the occurrence of rainy days or rain intensity. It is important to understand the causes of these trends. Likewise, it is important to understand how the local temperature responds to changing large-scale conditions. Such questions can be explored through downscaling the southeast African regional climate from global climate models (GCMs) experiments in CORDEX – Africa. The research will involve analysis of local observations, reanalysis, historical and data from regional climate models (RCMs) and empirical-statistical downscaling (ESD) to study dependencies between large-scale conditions and local variability in the rain and temperature statistics. ESD and RCM simulations will be combined to provide reliable future projections, for instance, by using RCMs as pseudo-reality and the statistical models to emulate seasonally aggregated high-resolution RCM output for a large ensemble of multi-model ensembles (CMIP). Local observations will also be used in the model evaluation to assess the added value of regional downscaling for both ESD and RCMs. The proposed Flagship Pilot Study (FPS) is tailored to investigate the connections between changes and trends, and special attention will be on the rainy season(s) and its/their duration. Identified dependencies will be utilised for making reliable future projections (ESD). The proposed study will also enable an investigation into the importance of regional scale forcings (aerosols, land-use change, vegetation etc) for the southeast African region. The results will be presented as aggregated statistics for daily temperature and precipitation together with assessments of the models.

Central Asia- East Asia: High resolution climate modelling with a focus on convection and associated precipitation over the Third Pole region

The Third Pole (TP) is the Tibetan Plateau and all the mountain ranges that surround it. It has the world’s largest store of ice and snow outside the Arctic and Antarctic regions. The TP plays a significant role in the global climate system and is highly sensitive to humaninduced climate change. More than 10 major rivers originate from the TP, and the dramatic changes in the cryosphere have a great impact on water cycle, ecosystem and society over the TP and the surrounding regions. Due to the complex topography and harsh environment, ground-based observations are scarce over the TP, making the study of regional climate and its impact on other systems such as water and ecosystem difficult. Horizontal resolution of prevailing global reanalysis datasets is generally coarser than 30 km, which is not sufficient to examine convection and other mesoscale systems over the TP. High-resolution regional downscaling is badly needed for understanding processes and improve projections. This project aims at enhancing our understanding of the regional characteristics of water cycle changes over the TP region with a special focus on the convection and precipitation. The spatial scale of annual precipitation is generally small. Convection system contributes significantly to the total precipitation over the TP, and is therefore a key to understand the water cycle of the region. Thus, we will investigate the impact of convection system on the water cycle, especially precipitation. The contribution of Mesoscale Convective Systems (MCSs) to the precipitation over the TP will be addressed by using the Rain Cell Tracking method. A multi-model and/or multischeme approach will be utilized to assess the ability of regional climate model (RCM) in simulating convective precipitation over the TP, with the aid of satellite observations and water isotope observations. The targeted resolution is 2-9 km with a focus on convectionpermitting simulations (2-4 km). The simulations from different models or model configurations will be intercompared. We will start with a test simulation of one year. When this is done successfully, we plan to run a subset of models/model setups for a multi-year period between 1979 and 2018. The exact number of years will depend on the evaluation of the one year test and the computing resources available. The outcomes of the project are expected to enhance our understanding of processes relevant for cloud and precipitation formation, convection, MCS, and local wind system. They should also be useful to future high resolution regional climate modeling and regional reanalysis over the TP. Other studies, such as the water cycle will also benefit from the results of this project. An international was established for this project, including experts in regional climate modeling, relevant observation, statistical analysis, water isotope modeling and observations, as well as regional cryosphere and climate studies. Most of the teams have been actively engaged in or are in leading positions for an international research program the Third Pole Environment (TPE) which calls for such an effort. This project has a great potential to be successful and useful to WCRP in general and CORDEX in particular.

Active Flagship Pilot Studies

At the moment there are
5 endorsed active CORDEX Flagship Pilot Studies.

CORDEX Experiment Guide

Active Flagship Pilot Studies

At the moment there are 5 endorsed active CORDEX Flagship Pilot Studies.

CORDEX Experiment Guide

At the moment there are
5 endorsed active CORDEX Flagship Pilot Studies.