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In this study, the temporal variation of actual evapotranspiration (AE) over China during 1980–2015 is analysed based on an ensemble of six reanalyses and a complementary‐relationship‐based AE dataset. The results reveal that annual mean AE in China increases significantly, and the major regime shift occurred around 1998. Accordingly, long‐term mean AE changes from 1999–2015 relative to 1980–1997 are computed to quantify the spatial pattern of AE trends. In general, annual AE increases significantly in southern and northwestern China but decreases significantly in northeastern China and eastern Tibetan Plateau. Then we examine the primary cause for changes in AE using the Budyko framework, in which the change of climate is represented by changes in precipitation and potential evapotranspiration and the shift in landscape characteristics is represented by the parameter n. Overall, increasing potential evapotranspiration is the main contributor to the increase of AE in southeastern China. Increasing potential evapotranspiration and the parameter n are the main contributors to the increase of AE in southwestern China. Decreasing AE in northeastern China and eastern Tibetan Plateau are respectively caused by changes in precipitation and the parameter n, whereas the combination of these two factors has led to increasing AE in northwestern China. It is shown here that the contribution of the parameter n is comparable to that of climate change in western China. A positive correlation is found between vegetation coverage and the parameter n; however, vegetation type, catchment slope, irrigation practices, and glacial meltwater also have an impact on regional n. A concurrent occurrence of the negative contribution of parameter n and positive vegetation coverage change is found in the forest land of northeastern and southeastern China. Decreasing irrigation water is likely the main reason for the negative contribution of n in cropland of the North China Plain. [ABSTRACT FROM AUTHOR]

By using the hindcast and forecast data from the National Centers for Environmental Prediction Climate Forecast System version 2 (NCEP CFSv2) for the 1982–2018 period, we investigate the forecasting skills of the mid‐summer (July and August) surface air temperature (SAT) at interannual timescales in this study. Although CFSv2 predictions show a warm bias for the climatological mean SAT over the Yangtze River valley (25°–32°N, 105°–122°E), they show a consistent and great performance in predicting the interannual variability of the mid‐summer SAT over this region until 4 months in advance, where the linear correlation coefficient between the predicted and observed time series reaches +0.65, +0.51 and + 0.68 for 4, 2 and 0 months in advance, respectively. The CFSv2 predictions well simulate the linkage between the SAT anomalies over the Yangtze River valley and the anomalous atmospheric circulation aloft, including the circumglobal teleconnection and zonal extension of the Western Pacific Subtropical High. However, CFSv2 has trouble in simulating the associated vertical velocity, cloud cover and solar radiation anomalies, except for 0 months in advance. The persistent forecasting skills result from the accurate response of the circumglobal teleconnection and Western Pacific Subtropical High to the El Niño/Southern Oscillation and sea surface temperature (SST) anomalies over the mid‐latitude North Atlantic. Correspondingly, the forecasting skill, signal and signal‐to‐noise ratio are effectively improved in the years with strong mid‐summer SST anomalies over the tropical central‐eastern Pacific or mid‐latitude North Atlantic. These results are useful for understanding the predictability of the mid‐summer SAT over the Yangtze River valley. [ABSTRACT FROM AUTHOR]

This study explores the near‐surface air temperature (TAS) prediction skills at different time scales via coupled climate models that were involved in the Coupled Model Intercomparison Project phase 5 (CMIP5). The simulation skills of the global mean TAS are first assessed between the observations and models; then, the temporal variability is separated into three parts (the linear trend, decadal variability and inter‐annual variability), and each part is compared with the observations. It is found that the global mean TAS anomaly and the decadal variability are well captured by the model, while the inter‐annual variability is poorly presented. In all the three parts of different time scales, there are larger differences among the 18 models, and the ensemble mean of CMIP5 is the closest to the observations. Besides, the TAS decadal variability is better presented for global ocean than for global land. In the assessment of climate oscillation, it is found that the models can well reproduce the TAS decadal variation patterns correlated with the Pacific Decadal Oscillation (PDO) and the inter‐annual variation patterns correlated with El Niño–Southern Oscillation (ENSO) but poor for the decadal variation patterns related to the Atlantic Multidecadal Oscillation (AMO). This study provides a reference assessing the simulation skills of climate models and an indicator evaluating the advantage of CMIP6 in comparison with CMIP5. [ABSTRACT FROM AUTHOR]

The aim of this study is to explore the long‐term trends in the distribution of global monsoon precipitation over recent decades using the Global Precipitation Climatology Project (GPCP) data set. In addition, the potential4 mechanisms are examined by applying the atmospheric moisture budget decomposition method to the outputs from the ERA‐Interim medium‐range weather forecasting reanalysis produced by the European Centre for Medium‐Range Weather Forecasts (ECMWF). Changes in global monsoon precipitation are primarily thermodynamically caused by changes in specific humidity and dynamically caused by changes in circulation, as well as by changes in moisture transport that are driven by transient eddies and local evaporation. The results show that the increasing trends in global summer monsoon precipitation from 1979 to 2016 were dominated by contributions from the southern Asian, South African, and North American monsoon regions and were driven by the response of atmospheric circulation to the enhanced east–west thermal contrast in the tropical Pacific. We find that changes in the sea surface temperature (SST) patterns promote increased low‐level vertical velocities in monsoon regions, leading to moisture convergence through divergent circulation anomalies when combined with the climatological humidity field. Hence, the processes result in increasing trends in monsoon precipitation. In addition, evaporation makes increasing contributions to monsoon precipitation throughout the world, except in the South American monsoon region. Moreover, subtropical regions in the East Pacific (the Atlantic) may be major sources of water vapour that have supported increases in precipitation over the southern Asian and North American monsoon regions (the South African monsoon region) in recent decades. Linear trends in (a) precipitation, (b) the moisture convergence term, (c) evaporation, and (d) residual term (precipitation minus the divergence of vertically integrated moisture transport term and evaporation) in local summer (May–September in the Northern Hemisphere and November–March in the Southern Hemisphere) from 1979 to 2016 (unit: mm day−1 year−1). The black curves depict the monsoon domains. Stippled regions indicate statistical significance at the 95% level or higher, as determined using the Mann–Kendall trend test. [ABSTRACT FROM AUTHOR]