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Potential evapotranspiration (PET) plays a pivotal role in resource management and drought assessment. However, future PET estimates remain underexplored in the African region. This study employs twenty General Circulation Models (GCMs) to estimate past (1979–2014) and future PET changes across near-term (2021–2040), mid-term (2061–2080), and long-term (2081–2100) periods, considering four Shared Socioeconomic Pathways (SSPs) including SSP1–2.6, SSP2–4.5, SSP3–7.0, and SSP5–8.5. The research assesses the impact of various climatic factors on PET across Africa and its sub-regions using the Penman-Monteith model. The analysis reveals that Penman-Monteith estimates for PET during 1979–2014 exhibit an increase of 0.68 mm per year (mm/a) across Africa. Notably, the Northern region (NAF), Sahara (SAH), Southern region (SAF), and Eastern region (EAF) experience higher PET changes of 1.78 mm/a, 1.75 mm/a, 1.09 mm/a, and 0.12 mm/a, respectively. Conversely, the Western region (WAF) and Central region (CAF) exhibit negative trends of −0.03 mm/a, and − 0.28 mm/a. Future PET in whole Africa is projected to increase by 0.05 mm/a in SSP1–2.6 and SSP2–4.5, and 0.07 mm/a in higher emissions for 2021–2040, by 0.02 mm/an under SSP1–2.6, 0.07 in SSP2–4.5, 0.09 mm/a, and 0.16 mm/a, in SSP3–7.0 and SSP5–8.5 for 2061–2080, and by −0.01 mm/a in SSP1–2.6, 0.05 mm/a SSP2–4.5, 0.10 mm/a SSP3–7.0, and 0.18 mm/a SSP5–8.5 for 2081–2100. Furthermore, higher emissions are anticipated to drive PET increases in various regions during 2081–2100, with NAF, SAH, and SAF projected to rise by 0.17 mm/a, 0.16 mm/a, and 0.23 mm/a, respectively. WAF, CAF, and EAF are expected to experience increases of 0.20 mm/a, 0.19 mm/a, and 0.15 mm/a, respectively. Contribution analysis indicates that solar radiation played a major factor in PET over Africa as well as in WAF, CAF, and EAF. Maximum temperatures were pivotal in NAF, SAH, and SAF. In future periods (2021-2040, 2061-2080, and 2081-2100), maximum temperatures take precedence to Africa's PET, and at varying percentages to different sub-regions. The findings underscore the significance of PET estimation, particularly in the context of drought evaluation locally and regionally. • PET estimates an increase of 0.68 mm/annum across Africa from 1979 to 2014. • PET is projected to increase under all scenarios, shows stronger in high forcing scenario. • Solar radiation contributed to PET in the past andmaximum temperatures in future but varies across periods and regions. • The study underscores the implications of PET estimations for drought evaluation. [ABSTRACT FROM AUTHOR]

The simulation results of CMIP5 (Coupled Model Inter-comparison Project phase 5) multi-model ensemble in the Indus River Basin (IRB) are compared with the CRU (Climatic Research Unit) and APHRODITE (Asian Precipitation-Highly-Resolved Observational Data Integration Towards Evaluation) datasets. The systematic bias between simulations and observations is corrected by applying the equidistant Cumulative Distribution Functions matching method (EDCDFm) and high-resolution simulations are statistically downscaled. Then precipitation and temperature are projected for the IRB for the mid-21st century (2046–2065) and late 21st century (2081–2100). The results show that the CMIP5 ensemble captures the dominant features of annual and monthly mean temperature and precipitation in the IRB. Based on the downscaling results, it is projected that the annual mean temperature will increase over the entire basin, relative to the 1986–2005 reference period, with greatest changes in the Upper Indus Basin (UIB). Heat waves are more likely to occur. An increase in summer temperature is projected, particularly for regions of higher altitudes in the UIB. The persistent increase of summer temperature might accelerate the melting of glaciers, and has negative impact on the local freshwater availability. Projections under all RCP scenarios show an increase in monsoon precipitation, which will increase the possibility of flood disaster. A decreasing trend in winter and spring precipitation in the IRB is projected except for the RCP2.6 scenario which will cause a lower contribution of winter and spring precipitation to water resources in the mid and high altitude areas of the IRB. [ABSTRACT FROM AUTHOR]

Motivated by the Paris Agreement, this study aims to investigate the changes in precipitation extremes across South Asia and its five climatic zones for each 0.5 °C of warming above the pre-industrial level from 1.5 °C to 3.0 °C. In this regard, 20 global climate model outputs from the latest CMIP6 under four combinations of SSP-RCP scenarios (SSP1–2.6, SSP2–4.5, SSP3–7.0, and SSP5–8.5) are used. Four widely used extreme precipitation indices such as number of consecutive wet days (CWD), number of heavy precipitation days (R10mm), maximum consecutive 5-day precipitation (RX5day), and the number of very wet days (R99pTOT) defined by the Expert Team on Climate Change Detection and Indices (ETCCDI) are applied to detect the extreme events. To ensure reduced uncertainty, we used bias-corrected and multi-model ensemble outputs. Results indicate that as the degree of global warming increases, the changes in magnitudes of extreme events are projected to intensify (except for CWD) and the largest growth is found under 3.0 °C in the entire domain and its five climatic zones. The polar climatic zone is anticipated to experience the highest magnitude of changes for extreme events under all the warming scenarios. The largest percentage of area with significant increase is found under the highest warming level (3.0 °C), especially for R95pTOT (95.5% of the entire domain). For an additional 0.5 °C (2.0–1.5 °C) of warming, the anticipated precipitation-related extremes will increase by 3.5%, (RX5day), 3.6% (R10mm) and 6.6% (R99pTOT), as mitigation targets set out in the Paris Agreement. The projected intense sea surface temperature over the Arabian Sea, and large water vapor content over South Asian landmass are expected to influence precipitation-related extreme events. Notably, considering all aspects of our analysis, R99pTOT is expected to be the most predominant extreme precipitation index across the domain with continued warming. So, our findings strongly support the Paris Agreement target to limit global warming to 1.5 °C and provide a scientific basis. • Precipitation extremes over South Asia will intensify with continued warming. • The polar climatic zone will experienceprecipitation-related extremes largely. • Extra 0.5 °C (2.0–1.5 °C) will increase the extreme event by 3.5%, (RX5day), 3.6% (R10mm) and 6.6% (R99pTOT). • R99pTOT is expected to be the most predominant event for South Asia. [ABSTRACT FROM AUTHOR]

Understanding the patterns of dryness/wetness in the warming context is important for stakeholders to formulate adaptation strategies to minimize the impacts of floods and droughts. Spatial and temporal characteristics of regional temperature, precipitation, potential evapotranspiration (PET) and dryness/wetness variation were investigated for the period from 2015 to 2100 under SSPs-RCPs in Northwest China. Results show that annual mean temperature, precipitation and PET are projected to increase during 2015–2100, with increases higher in the long-term (2081–2100) than the near-term (2021–2040) and mid-term (2041–2060). Increase rate under SSP5–8.5 and SSP3–7.0 will significantly higher than other scenarios. Relative to the reference period (1995–2014), annual SPEI12 is projected to show a decreasing trend during 2015–2100. Trend will decrease highest under SSP5–8.5 scenario whereas the lowest under SSP1–1.9 and SSP1–2.6 scenarios. The state of drought in Northwest China is near normal during the reference period, drought will significantly escalate and moderate and severe drought will dominate the most of Northwest China with the increase of radiative forcing under SSPs-RCPs during 2015–2100. SSP5–8.5 will have the largest drought area than other scenarios. Observation shows Northwest China characterized a warmer and humid trend during 1961–2014, while GCMs projected that Northwest China will experience significant dryness trend during 2015–2100 under SSPs-RCPs, and SSP3–7.0, SSP4–3.4, SSP4–6.0 and SSP5–8.5 scenarios will be much drier than SSP1–1.9, SSP1–2.6 and SSP2–4.5 scenarios. • Bias corrected results can reasonably reproduce the spatio-temporal variations in temperature and precipitation for original output of GCMs from CMIP6. • Multi-model Ensemble projected that annual mean temperature, annual precipitation and potential evapotranspiration will increase in Northwest China during 2021–2100. • Annual SPEI12 in Northwest China exhibits decreasing trends during 2021–2100 relative to the reference period (1995–2014), with declining tendency about 0.10/10a under SSPs-RCPs. • Drought will significantly escalate with moderate and severe droughts dominate most of Northwest China during 2021–2100 under SSPs-RCPs. [ABSTRACT FROM AUTHOR]

The realistic simulation and projection of the Amundsen Sea Low (ASL) are essential for understanding the Antarctic climate and global climate change. Using 14 models that participated in phase 6 of the Coupled Model Intercomparison Project (CMIP6), this study evaluates the climatological characteristics of ASL with comparison to the ERA5 reanalysis and their CMIP5 versions and assesses the future change of ASL under 1.5 °C–4 °C global warming. The climatological spatial distribution of ASL is captured reasonably but with underestimated intensity by CMIP6 multi-model ensemble (MME). Among the CMIP6 models, EC-Earth3 has most accurate representation of ASL according to the pattern correlation and biases. The seasonal variation of the ASL depth and location are found to be reasonably reproduced by the CMIP6 models. CMIP6 MME has higher skills in simulating the seasonal cycle of absolute depth and zonal migration of the ASL center. The relative central pressure of ASL is underestimated in all seasons and there is a 4-degree northward shift bias of the ASL center in austral winter, which were also evident in the CMIP5. The semiannual cycle of ASL absolute depth with two deepest pressure in April and October is also captured by CMIP6 MME. However, the observed peak of pressure between the two months occurs in June, while it delays one month and appears until July in CMIP6 MME. Compared with CMIP5, CMIP6 MME exhibit evident reduced uncertainties and overall improvement in simulating absolute depth and location of the ASL center, which might be attributed to models' capability of representing the location of Southern Hemisphere westerlies, while the biases in relative depth become even large in CMIP6 MME. In response to future warming from 1.5 °C to 4 °C above pre-industrial levels, the absolute depth of ASL will very likely deepen with larger amplitude in all seasons, while the relative depth might enhance only under high-level warmer world in austral autumn to winter. The CMIP6 MME also projects that the ASL will shift poleward constantly in austral summer and migrate southwestward during austral autumn with the rising global mean temperature. Among all the seasons, the most prominent future changes in intensity and location of ASL are found in autumn. The enhancement and poleward movement of ASL could also be identified during the Ross Sea ice advance season under 1.5 °C–4 °C global warming. The results reveal the potential of CMIP6 models in the ASL study and the impact of ASL on Antarctic climate under different global warming levels. • Latest CMIP6 models exhibit generally better representation and reduced uncertainties in reproducing Amundsen Sea Low (ASL) than CMIP5. • The improvement in ASL of CMIP6 models might be associated with more robust simulation of Southern Hemisphere westerlies. • ASL will very likely deepen and migrate poleward constantly under 1.5 °C to 4 °C global warming above pre-industrial levels. [ABSTRACT FROM AUTHOR]

In this paper, future drought characteristics (frequency, duration and intensity) over China are analysed by using four climate models from CMIP6 under the seven SSP-RCP (shared socioeconomic pathway-representative concentration pathway) scenarios (SSP119, SSP126, SSP434, SSP245, SSP460, SSP370, and SSP585) for three defined periods of 2021–2040 (near-term), 2041–2060 (mid-term) and 2081–2100 (long-term). The corresponding four climate models output from CMIP5 are also used to conduct a comparison analysis between CMIP5 and CMIP6 to address the improvements added to CMIP6 in terms of drought identification. The drought characteristics are identified by applying the standardized precipitation-evapotranspiration index (SPEI) at a 12-month timescale and run theory. The results show that CMIP6 has a robust capability to capture historical (1986–2005) drought characteristics. For the future period of 2021–2040, the decrease in precipitation and increase in potential evapotranspiration will lead to continuous dry conditions in the upper and middle Yangtze River basin and eastern Pearl River basin. Relative to the reference period, drought events will be more frequent and severe with longer durations in the Northwest River basins and middle Yangtze River basin. Furthermore, higher emissions signify a greater increase in drought frequency and intensity in the long-term period. Except for the SSP585 scenario, the lower emission scenario corresponds to the higher drought duration soon and in the mid-21st century (2021–2060). This finding is regarded as a "strange phenomenon", which cannot be detected by the previous CMIP5-based emission scenarios (RCP2.6, RCP4.5 and the unlikely pathway RCP8.5). Therefore, additional "possible future"-based scenarios (SSP119, SSP126, SSP434, SSP245, SSP460, and SSP370) should be included in extreme climate studies, especially for the near future and mid-21st century. Notably, compared with CMIP5, the reduced biases in drought characteristics are more likely associated with improvements in the representation of physical processes in climate models from CMIP6. The results of this study could provide a basis for the development of drought adaptation measures over China. • Latest CMIP6 climate models and seven SSP-RCP scenarios are used to analyze the possible changes in droughts over China. • More robust projections will be presented by CMIP6 than CMIP5, due to the better representations in physical processes. • The higher emission signifies shorter drought duration, lower precipitation and PET in mid-21st century over China. [ABSTRACT FROM AUTHOR]

Using the online-coupled Global/Regional Assimilation and Prediction System coupled with the Chinese Unified Atmospheric Chemistry Environment (GRAPES_CUACE) model, numerical experiments are conducted to compare the impacts of three planetary boundary layer (PBL) schemes—Medium Range Forecast (MRF), Yonsei University (YSU), and Mellor-Yamada-Janjic (MYJ)—on PM 2.5 simulations and their responses to aerosol-radiation feedback (ARF), under different terrain and weather conditions. The baseline experiments without ARF with all three PBL schemes can reproduce the spatial and temporal distribution characteristics of surface PM 2.5 on the whole and show that the model can capture the PM 2.5 variation better in unstable conditions (clean days) than in stable conditions (pollution days). The three PBL schemes show differences in the simulations of meteorological factors, e.g., the MRF scheme produces the best 10-m wind speed, the MYJ scheme produces the best 2-m temperature, and the YSU scheme produces the lowest PBL height (PBLH) and vertical diffusivity. Consequently, there is no significant difference among the three PBL schemes in surface PM 2.5 simulations due to the combined action of the surface and the PBL structure. However, all the baseline experiments massively underestimate PM 2.5 during severe pollution days. The online computing of ARF in the three PBL schemes can substantially improve the underestimation of PM 2.5 by reducing sensible heat fluxes, 2-m temperature, friction velocity, and the PBL height. More importantly, the response intensity of three PBL schemes to ARF is very different. For PM 2.5 simulations, MYJ has the weakest response, whereas MRF and YSU have similar responses. During the heavy pollution days with more intense aerosol-radiation effect, the increase of PM 2.5 induced by ARF in MRF and YSU is about twice that in MYJ, making the PM 2.5 simulated by MRF and YSU more consistent with the observations. This result shows the ARF dependence on the PBL processes and suggests the importance of PBL-ARF interaction to the PM 2.5 numerical prediction during haze episodes. • The variation of PM 2.5 is affected by the interaction between land surface and atmospheric boundary layer. • Aerosol-radiation feedback substantially improves the underestimation of PM 2.5 during heavy haze pollution. • Aerosol-radiation feedback strongly depends on the boundary layer processes. [ABSTRACT FROM AUTHOR]

Droughts reflect the extent of water deficit on the land surface, and can be quantified by various indices. In current study, potential evapotranspiration (PET), which is one of factors that have great influence on the drought condition, is estimated by a set of models. The set consists of four temperature-decisive models (Hamon, Hargreaves-Samani, Oudin, Thornthwaite), two radiation-decisive models (Energy-Only and Priestley-Taylor) and two synthesis models (Penman and Penman-Monteith). Subsequently, Standardized Precipitation Evapotranspiration Index (SPEI) is applied to assess the spatial and temporal distributions of droughts for the arid, the semi-arid and semi-humid, as well as the humid climatic zones in China for 1961–2017. The results show that: (1) Taking China as a whole, annual PET estimated by Penman-Monteith (P-M) formula is about 1000 mm, which is in the middle of the range of results from eight algorithms. Annual PET values estimated by radiation-decisive methods are relatively close to those obtained by P-M, while temperature-decisive methods yield lower values and the largest disparity among the different PET models can be up to 2.5 fold. (2) Comparing to drought records, both P-M and Thornthwaite are suitable for assessing drought condition on the national scale, but the drought assessed by the Thornthwaite method is worse than that by the P-M method in 1990–2017 when warming is faster than before in the arid region. (3) Increase first and then decrease of values of the SPEI index are detected in China for 1961–2017 by all PET estimations. Averaged over entire China, the wetting trend has changed to drying in the early 1990s by P-M-based SPEI. More meteorological stations are found to experience droughts after the early 1990s, particularly in the western humid region and the central semi-arid and semi-humid region. In contrast, a wetness tendency is found in the arid region. (4) Patterns of the drought frequency and duration by all PET algorithms maintain relatively good correspondence in the semi-arid and semi-humid region as well as the humid region. But in the arid region, drought frequency obtained by P-M is lower than for radiation-decisive and temperature-decisive models, while drought duration is longer. • Eight algorithms clustered into three groups are used to estimate potential evapotranspiration (PET) for China in 1961–2017. • A wetness trend is detected by synthesis and radiation-decisive models based SPEI, while getting drier by temperature-decisive models in the arid region. • A case study in China shows that choice of potential evapotranspiration formulas influences largely on drought assessment. [ABSTRACT FROM AUTHOR]