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The Afro-Asian summer monsoon (AfroASM) sustains billions of people living in many developing countries covering West Africa and Asia, vulnerable to climate change. Future increase in AfroASM precipitation has been projected by current state-of-the-art climate models, but large inter-model spread exists. Here we show that the projection spread is related to present-day interhemispheric thermal contrast (ITC). Based on 30 models from the Coupled Model Intercomparison Project Phase 6, we find models with a larger ITC trend during 1981-2014 tend to project a greater precipitation increase. Since most models overestimate present-day ITC trends, emergent constraint indicates precipitation increase in constrained projection is reduced to 70% of the raw projection, with the largest reduction in West Africa (49%). The land area experiencing significant increases of precipitation (runoff) is 57% (66%) of the raw projection. Smaller increases of precipitation will likely reduce flooding risk, while posing a challenge to future water resources management., (© 2022. The Author(s).)

The Tibetan Plateau (TP) has experienced "south drying‐north wetting" extreme precipitation changes over the past half century. The effects of water vapor transport at different timescales on TP extreme precipitation changes remain unexplored. Here, we utilize the reanalysis data sets to quantify the contributions of stationary and transient processes of water vapor transport to the long‐term changes in the extreme precipitation (R95p) during wet season (Jun‐Jul‐Aug‐Sep) over the TP and surrounding regions. We find that the daily scale transient processes dominate the dipole trend of extreme precipitation with a contribution of 55.1% in the northern and 79.5% in the southern TP, respectively, whereas the contribution of monthly scale stationary processes is of 19.0% and 20.5%. The long‐term changes in extreme precipitation are dominated by the transient dynamic component. We identified the synoptic circulation patterns affecting the changes of R95p over the northern and southern TP by using k‐means clustering. The patterns featured with a 500 hPa trough, 200 hPa wind divergence and low transient geopotential height are identified. The frequency of the dominant circulation patterns increases in the northern TP and decreases in the southern TP, which leads to the dipolar changes of extreme precipitation over the TP and surrounding regions. Plain Language Summary: The Tibetan Plateau (TP), known as the "Asian water tower," is facing a crisis of water resources imbalance. Extreme precipitation has attracted much attention because of its large amount and disastrous nature. A "south drying‐north wetting" pattern of extreme precipitation changes over the TP and surrounding regions is seen in recent decades. Understanding the contribution of water vapor transport at different timescales to this dipolar pattern is of vital importance for the water resources changes therein. Based on the state‐of‐the‐art reanalysis data sets, we show that the "south drying‐north wetting" of extreme precipitation over the TP and surrounding regions is dominated by the long‐term changes of transient processes, whereas stationary processes have the same effect but are smaller in magnitude. We also stress the dominant role of changes in the frequency of synoptic circulation patterns on the "south drying‐north wetting" pattern of extreme precipitation changes over the TP and surrounding regions. Our results highlight the strong link between changes in the frequency of synoptic‐scale processes and long‐term changes in extreme precipitation over the TP and surrounding regions. Key Points: The transient processes dominate the extreme precipitation changes over the TP with contributions of 55.1% (north) and 79.5% (south)The frequency changes of the synoptic circulation patterns are responsible for the extreme precipitation changes over the TP [ABSTRACT FROM AUTHOR]

The Tibetan Plateau (TP) region, also known as the "Asian water tower", provides a vital water resource for downstream regions. Previous studies of water cycle changes over the TP have been conducted with climate models of coarse resolution in which deep convection must be parameterized. In this study, we present results from a first set of high-resolution climate change simulations that permit convection at approximately 3.3-km grid spacing, with a focus on the TP, using the Icosahedral Nonhydrostatic Weather and Climate Model (ICON). Two 12-year simulations were performed, consisting of a retrospective simulation (2008–20) with initial and boundary conditions from ERA5 reanalysis and a pseudo-global warming projection driven by modified reanalysis-derived initial and boundary conditions by adding the monthly CMIP6 ensemble-mean climate change under the SSP5-8.5 scenario. The retrospective simulation shows overall good performance in capturing the seasonal precipitation and surface air temperature. Over the central and eastern TP, the average biases in precipitation (temperature) are less than −0.34 mm d−1 (−1.1°C) throughout the year. The simulated biases over the TP are height-dependent. Cold (wet) biases are found in summer (winter) above 5500 m. The future climate simulation suggests that the TP will be wetter and warmer under the SSP5-8.5 scenario. The general features of projected changes in ICON are comparable to the CMIP6 ensemble projection, but the added value from kilometer-scale modeling is evident in both precipitation and temperature projections over complex topographic regions. These ICON-downscaled climate change simulations provide a high-resolution dataset to the community for the study of regional climate changes and impacts over the TP. [ABSTRACT FROM AUTHOR]

Cold extremes have large impacts on human society. Understanding the physical processes dominating the changes in cold extremes is crucial for a reliable projection of future climate change. The observed cold extremes have decreased during the last several decades, and this trend will continue under future global warming. Here, we quantitatively identify the contributions of dynamic (changes in large-scale atmospheric circulation) and thermodynamic (rising temperatures resulting from global warming) effects to East Asian cold extremes in the past several decades and in a future warm climate by using two sets of large-ensemble simulations of climate models. We show that the dynamic component accounts for over 80 % of the cold-month (coldest 5 % boreal winter months) surface air temperature (SAT) anomaly over the past 5 decades. However, in a future warm climate, the thermodynamic change is the main contributor to the decreases in the intensity and occurrence probability of East Asian cold extremes, while the dynamic change is also contributive. The intensity of East Asian cold extremes will decrease by around 5 °C at the end of the 21st century, in which the thermodynamic (dynamic) change contributes approximately 75 % (25 %). The present-day (1986–2005) East Asian cold extremes will almost never occur after around 2035, and this will happen 10 years later due solely to thermodynamic change. The upward trend of a positive Arctic Oscillation-like sea level pressure pattern dominates the changes in the dynamic component. The finding provides a useful reference for policymakers in climate change adaptation activities. [ABSTRACT FROM AUTHOR]

To connect a wide range of research communities including climate change mitigation and adaptation activities, the Intergovernmental Panel on Climate Change (IPCC) 6th assessment report (AR6) employs the Shared Socioeconomic Pathway (SSP) scenarios. The CORDEX East Asia calls for a dynamical downscaling of climate change projections under the new SSP scenarios. In this study, the state-of-the-art regional climate model RegCM4 with a horizontal resolution of 25 km was used to dynamically downscale future climate changes, which were derived from the global climate model FGOALS-g3, under multiple SSP scenarios over the CORDEX East Asia Phase II domain. Compared to the driving global model FGOALS-g3, the downscaling exhibited added value in the simulation of present-day mean and extreme rainfall over China in terms of both spatial pattern correlation and biases. The largest improvements were found over the Pearl River Basin and the Yangtze River Basin. For the period of 2081–2100 under the SSP2-4.5 scenario, the areas in China with increases in the projected mean and extreme rainfall generally overlapped with the areas with substantial climatological mean and extreme rainfall in both RegCM4 and FGOALS-g3, which highlights the importance of simulated climatology in projecting future rainfall changes. The moisture budget analyses indicated that the projected increases in summer mean rainfall were mainly attributed to thermodynamic processes associated with the increased moisture. The mean and extreme rainfall was most sensitive to the increased emission scenarios in the Northwest Interior River Basin and least sensitive in southern China. From SSP1-2.6 to SSP5-8.5, larger fractions of land area and population would be affected by greater increased and more intense rainfall. If the emissions were reduced from SSP5-8.5 to SSP1-2.6, over 80% of the impacts would be avoided over most regions in China. [ABSTRACT FROM AUTHOR]

The ecosystem and societal development in arid Central Asia are highly vulnerable to climate change. During the past five decades, significant warming occurs in Central Asia, but whether the influence of anthropogenic forcing is detectable remains unclear. Therefore, we employ the optimal fingerprinting method to address the question in this study. The observed annual mean temperature (°C) over Central Asia significantly increases by 1.33 from 1961 to 2005, which mainly concentrates in summer (0.90), autumn (1.22), and winter (2.48). The influence of anthropogenic forcing, particularly the greenhouse gases (GHG) forcing, on both the annual and seasonal significant warming trends are robustly detected. GHG increases the annual, summer, autumn, and winter mean temperature (°C) by 1.25 (0.52–2.00), 1.11 (0.32–1.92), 1.11 (0.40–1.83), and 2.50 (0.91–4.34), respectively. Attribution results demonstrate an underestimation (overestimation) of CMIP5 models in simulating the annual and winter (summer and autumn) historical warming trend in Central Asia, implying a potential bias of the future temperature projections reported in IPCC AR5. Thus, we adjust the projections based on the attributed scaling factors, showing that the projected annual, summer, autumn, and winter mean temperature would significantly increase at a rate (°C decade−1) of 0.32 (0.16–0.49), 0.20 (0.06–0.35), 0.24 (0.10–0.38) and 0.58 (0.24–0.93) under RCP4.5, while 0.74 (0.36–1.12), 0.48 (0.14–0.84), 0.58 (0.25–0.91), and 1.25 (0.53–2.02) under RCP8.5, respectively, demonstrating large annual variation. To the end of twenty-first century, the annual (winter) mean temperature (°C) over Central Asia would increase by 7.00 (11.75) under RCP8.5, 0.85 (5.17) higher than the unadjusted results. [ABSTRACT FROM AUTHOR]

An integrated picture of the future changes in the water cycle is provided focusing on the global land monsoon (GLM) region, based on multimodel projections under the representative concentration pathway 8.5 (RCP8.5) from phase 5 of the Coupled Model Intercomparison Project (CMIP5). We investigate the reservoirs (e.g., precipitable water, soil moisture) and water fluxes (e.g., precipitation P, evaporation E, precipitation minus evaporation P − E, and total runoff) of the water cycle. The projected intensification of the water cycle with global warming in the GLM region is reflected in robust increases in annual-mean P (multimodel median response of 0.81% K−1), E (0.57% K−1), P − E (1.58% K−1), and total runoff (2.08% K−1). Both surface (−0.83% K−1) and total soil moisture (−0.26% K−1) decrease as a result of increasing evaporative demand. Regionally, the Northern Hemispheric (NH) African, South Asian, and East Asian monsoon regions would experience an intensified water cycle, as measured by the coherent increases in P, P − E, and runoff, while the NH American monsoon region would experience a weakened water cycle. Changes in the monthly fields are more remarkable and robust than in the annual mean. An enhanced annual cycle (by ~3%–5% K−1) with a phase delay from the current climate in P, P − E, and runoff is projected, featuring an intensified water cycle in the wet season while little changes or slight weakening in the dry season. The increased seasonality and drier soils throughout the year imply increasing flood and drought risks and agricultural yields reduction. Limiting global warming to 1.5°C, the low warming target set by the Paris Agreement, could robustly reduce additional hydrological risks from increased seasonality as compared to higher warming thresholds. [ABSTRACT FROM AUTHOR]

Extreme heat (EH) over North China (NC) is affected by both large scale circulations and local topography, and could be categorized into foehn favorable and no-foehn types. In this study, the performance of a regional coupled model in simulating EH over NC was examined. The effects of regional air-sea coupling were also investigated by comparing the results with the corresponding atmosphere-alone regional model. On foehn favorable (no-foehn) EH days, a barotropic cyclonic (anticyclonic) anomaly is located to the northeast (northwest) of NC, while anomalous northwesterlies (southeasterlies) prevail over NC in the lower troposphere. In the uncoupled simulation, barotropic anticyclonic bias occurs over China on both foehn favorable and no-foehn EH days, and the northwesterlies in the lower troposphere on foehn favorable EH days are not obvious. These biases are significantly reduced in the regional coupled simulation, especially on foehn favorable EH days with wind anomalies skill scores improving from 0.38 to 0.47, 0.47 to 0.61 and 0.38 to 0.56 for horizontal winds at 250, 500 and 850 hPa, respectively. Compared with the uncoupled simulation, the reproduction of the longitudinal position of Northwest Pacific subtropical high (NPSH) and the spatial pattern of the low-level monsoon flow over East Asia are improved in the coupled simulation. Therefore, the anticyclonic bias over China is obviously reduced, and the proportion of EH days characterized by anticyclonic anomaly is more appropriate. The improvements in the regional coupled model indicate that it is a promising choice for the future projection of EH over NC. [ABSTRACT FROM AUTHOR]

Subtropical anticyclones dominate the subtropical ocean basins in summer. Using the multimodel output from phase 5 of the Coupled Model Intercomparison Project (CMIP5), the future changes of the subtropical anticyclones as a response to global warming are investigated, based on the changes in subsidence, low-level divergence, and rotational wind. The subtropical anticyclones over the North Pacific, South Atlantic, and south Indian Ocean are projected to become weaker, whereas the North Atlantic subtropical anticyclone (NASA) intensifies, and the South Pacific subtropical anticyclone (SPSA) shows uncertainty but is likely to intensify. Diagnostic analyses and idealized simulations suggest that the projected changes in the subtropical anticyclones are well explained by the combined effect of increased tropospheric static stability and changes in diabatic heating. Increased static stability acts to reduce the intensity of all the subtropical anticyclones, through the positive mean advection of stratification change (MASC) over the subsidence regions of the subtropical anticyclones. The pattern of change in diabatic heating is dominated by latent heating associated with changes in precipitation, which is enhanced over the western North Pacific under the 'richest get richer' mechanism but is reduced over subtropical North Atlantic and South Pacific due to a local minimum of SST warming amplitude. The change in the diabatic heating pattern substantially enhances the subtropical anticyclones over the North Atlantic and South Pacific but weakens the North Pacific subtropical anticyclone. [ABSTRACT FROM AUTHOR]

Changes in precipitation characteristics directly affect society through their impacts on drought and floods, hydro-dams, and urban drainage systems. Global warming increases the water holding capacity of the atmosphere and thus the risk of heavy precipitation. Here, daily precipitation records from over 700 Chinese stations from 1956 to 2005 are analyzed. The results show a significant shift from light to heavy precipitation over eastern China. An optimal fingerprinting analysis of simulations from 11 climate models driven by different combinations of historical anthropogenic (greenhouse gases, aerosols, land use, and ozone) and natural (volcanic and solar) forcings indicates that anthropogenic forcing on climate, including increases in greenhouse gases (GHGs), has had a detectable contribution to the observed shift toward heavy precipitation. Some evidence is found that anthropogenic aerosols (AAs) partially offset the effect of the GHG forcing, resulting in a weaker shift toward heavy precipitation in simulations that include the AA forcing than in simulations with only the GHG forcing. In addition to the thermodynamic mechanism, strengthened water vapor transport from the adjacent oceans and by midlatitude westerlies, resulting mainly from GHG-induced warming, also favors heavy precipitation over eastern China. Further GHG-induced warming is predicted to lead to an increasing shift toward heavy precipitation, leading to increased urban flooding and posing a significant challenge for mega-cities in China in the coming decades. Future reductions in AA emissions resulting from air pollution controls could exacerbate this tendency toward heavier precipitation. [ABSTRACT FROM AUTHOR]

The reproducibility and future changes of the onset of the Asian summer monsoon were analyzed based on the simulations and projections under the Representative Concentration Pathways (RCP) scenario in which anthropogenic emissions continue to rise throughout the 21st century (i.e. RCP8.5) by all realizations from four Chinese models that participated in the Coupled Model Intercomparison Project Phase 5 (CMIP5). Delayed onset of the monsoon over the Arabian Sea was evident in all simulations for present-day climate, which was associated with a too weak simulation of the low-level Somali jet in May. A consistent advanced onset of the monsoon was found only over the Arabian Sea in the projections, where the advanced onset of the monsoon was accompanied by an increase of rainfall and an anomalous anticyclone over the northern Indian Ocean. In all the models except FGOALS-g2, the enhanced low-level Somali jet transported more water vapor to the Arabian Sea, whereas in FGOALS-g2 the enhanced rainfall was determined more by the increased wind convergence. Furthermore, and again in all models except FGOALS-g2, the equatorial SST warming, with maximum increase over the eastern Pacific, enhanced convection in the central West Pacific and reduced convection over the eastern Indian Ocean and Maritime Continent region, which drove the anomalous anticyclonic circulation over the western Indian Ocean. In contrast, in FGOALS-g2, there was minimal (near-zero) warming of projected SST in the central equatorial Pacific, with decreased convection in the central West Pacific and enhanced convection over the Maritime Continent. The broader-scale differences among the models across the Pacific were related to both the differences in the projected SST pattern and in the present-day simulations. [ABSTRACT FROM AUTHOR]

Multi-decadal high resolution simulations over the CORDEX East Asia domain were performed with the regional climate model RegCM3 nested within the Flexible Global Ocean-Atmosphere-Land System model, Grid-point Version 2 (FGOALS-g2). Two sets of simulations were conducted at the resolution of 50 km, one for present day (1980-2005) and another for near-future climate (2015-40) under the Representative Concentration Pathways 8.5 (RCP8.5) scenario. Results show that RegCM3 adds value with respect to FGOALS-g2 in simulating the spatial patterns of summer total and extreme precipitation over China for present day climate. The major deficiency is that RegCM3 underestimates both total and extreme precipitation over the Yangtze River valley. The potential changes in total and extreme precipitation over China in summer under the RCP8.5 scenario were analyzed. Both RegCM3 and FGOALS-g2 results show that total and extreme precipitation tend to increase over northeastern China and the Tibetan Plateau, but tend to decrease over southeastern China. In both RegCM3 and FGOALS-g2, the change in extreme precipitation is weaker than that for total precipitation. RegCM3 projects much stronger amplitude of total and extreme precipitation changes and provides more regional-scale features than FGOALS-g2. A large uncertainty is found over the Yangtze River valley, where RegCM3 and FGOALS-g2 project opposite signs in terms of precipitation changes. The projected change of vertically integrated water vapor flux convergence generally follows the changes in total and extreme precipitation in both RegCM3 and FGOALS-g2, while the amplitude of change is stronger in RegCM3. Results suggest that the spatial pattern of projected precipitation changes may be more affected by the changes in water vapor flux convergence, rather than moisture content itself. [ABSTRACT FROM AUTHOR]

A flexible regional ocean-atmosphere-land system coupled model [Flexible Regional Ocean Atmosphere Land System (FROALS)] was developed through the Ocean Atmosphere Sea Ice Soil, version 3 (OASIS3), coupler to improve the simulation of the interannual variability of the western North Pacific summer monsoon (WNPSM). The regionally coupled model consists of a regional atmospheric model, the Regional Climate Model, version 3 (RegCM3), and a global climate ocean model, the National Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics (LASG)/Institute of Atmospheric Physics (IAP) Climate Ocean Model (LICOM). The impacts of local air-sea interaction on the simulation of the interannual variability of the WNPSM are investigated through regionally ocean-atmosphere coupled and uncoupled simulations, with a focus on El Niño's decaying summer. Compared with the uncoupled simulation, the regionally coupled simulation exhibits improvements in both the climatology and the interannual variability of rainfall over the WNP. In El Niño's decaying summer, the WNP is dominated by an anomalous anticyclone, less rainfall, and enhanced subsidence, which lead to increases in the downward shortwave radiation flux, thereby warming sea surface temperature (SST) anomalies. Thus, the ocean appears as a slave to atmospheric forcing. In the uncoupled simulation, however, the atmosphere is a slave to oceanic SST forcing, with the warm SST anomalies located east of the Philippines unrealistically producing excessive rainfall. In the regionally coupled run, the unrealistic positive rainfall anomalies and the associated atmospheric circulations east of the Philippines are significantly improved, highlighting the importance of air-sea coupling in the simulation of the interannual variability of the WNPSM. One limitation of the model is that the anomalous anticyclone over the WNP is weaker than the observations in both the regionally coupled and the uncoupled simulations. This results from the weaker simulated climatological summer rainfall intensity over the monsoon trough. [ABSTRACT FROM AUTHOR]

This study compared statistical downscaling model (SD) and dynamical downscaling model (DD) for changes in extreme temperature and precipitation indices, driven by the same global climate model output, in the 1.5 and 2 °C warmer climates in China. Simple bias correction (BC) methods were used to correct the climatology of temperature and precipitation in both models. After BC, both models show comparable performance in reproducing the spatial distributions of the extreme temperature and precipitation indices. Corrected model data were used to analyze future changes. Changing patterns of the extreme temperature indices are similar in the two models. Compared with the 2 °C warmer climate, warming 0.5 °C less can help reduce about 6% of summer day (SU) and 11% of tropical night (TR) increases (relative to 1986–2005) in China. Specifically, the reduced values of TR in northwest and northeast China are larger than 30% and 70%, respectively, in both models. Extreme wet indices will increase in most parts of China in the warmer climates. In DD, 5‐day maximum precipitation (RX5day) will increase by approximately 10% and 14% in the 1.5 and 2 °C warmer climates, respectively, with maximal values (17% and 28%, respectively) occurring in north China. In SD, differences in extreme wet indices between the two warmer climates are small, and RX5day will increase more than 20% in northeast China. In DD, specific humidity will increase, and the East Asian summer monsoon will be enhanced in the warmer climates, favoring a larger increase in wet extremes in north China compared to other parts of east China. Key Points: Statistical and dynamical downscaling methods are used to analyze extreme climate event changes in China in the 1.5 and 2 °C warmer climatesBias correction methods aimed at correcting the climatology of temperatures and precipitation are applied to both modelsChanging patterns of temperature indices are similar between the two models in the two warmer climates [ABSTRACT FROM AUTHOR]

The combined effects of externally forced change and natural climate variability determine the climate anomalies. Internal variability has a great impact on climate change at various spatial-temporal scales. Characterizing and quantifying internal variability is of fundamental importance not only for purposes of detection and attribution, but also for reliability of climate projections. Therefore, the estimated internal variability of near-surface air temperature is compared using three widely adopted methods (pre-industrial control (piControl) simulations, polynomial fit method and analysis of variance method), based on 37 models from the Coupled Model Intercomparison Project Phase 5 (CMIP5) and 40 large-ensemble simulations from the Community Earth System Model (CESM). The associated influences on the time of emergence (TOE) of near-surface air temperature in future climate projections are also quantified. The results show that for the multimodels from CMIP5, the estimated internal variability is comparable based on the piControl simulations and the polynomial fit method, while that estimated by the analysis of variance method is exaggerated in terms of the magnitude due to its inclusion of model uncertainty. Polar amplification is evident in the spatial distribution of estimated internal variability of surface temperature, with considerably larger magnitudes in the mid- to high-latitudes than the low-latitudes. The internal variability of surface temperature does not vary significantly with time or emission scenarios, except for that in the tropics estimated by the analysis of variance method. Moreover, the estimated internal variability shows high consistency among the three methods based on large-ensemble simulations from CESM. The different estimated internal variability further affects the TOE in future climate projections, mainly in the North Atlantic Labrador Sea and the Weddell and Ross Seas in the Southern Ocean where ocean deep overturning circulations occur. Specifically, the internal variability is estimated to be less than 15% of the forced signals over China based on all the three methods in the CESM large-ensemble simulations. This result is comparable to those estimated by the piControl simulations and polynomial fit method based on the CMIP5 multimodels, but tends to be overestimated by the analysis of variance method. [ABSTRACT FROM AUTHOR]