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Evapotranspiration (ET) is an important process of water and energy exchanges between land and atmosphere. In this study, a processed-based GLEAM (global land-surface evaporation: the Amsterdam methodology) satellite assimilation product has been validated in the Yangtze River valley on the observations of flux and the water balance method. The changes of total ET and its components, well as the associated dynamics, have been analyzed for the period of 1980–2014. The total ET shows significant increasing trends especially in the middle and lower reaches of the Yangtze River valley, which is mostly due to the increase of transpiration. The spatial and temporal dynamics of total ET are analyzed with respect to temperature, precipitation, and solar radiation. The spatial pattern of total ET in the Yangtze River valley is found to be jointly determined by temperature and precipitation. As for the temporal dynamics, precipitation plays the dominant role in total ET in the source regions of the valley. While in the most regions, solar radiation is suggested to be a main controller, in the positive manner, of total ET. This may provide an in-depth understanding of ET changes in the warming climate, and form a basis for water resource management in the Yangtze River valley.

Based on the daily observational precipitation data at 147 stations in the Yangtze River Basin during 1960–2005 and projected daily data of 79 grid cells from the ECHAM5/ MPI-OM model in the 20th and 21st century, time series of precipitation extremes which contain AM (Annual Maximum) and MI (Munger Index) are constructed. The distribution feature of precipitation extremes is analyzed based on the two index series. Three principal results were obtained, as stated in the sequel. (i) In the past half century, the intensity of extreme heavy precipitation and drought events was higher in the mid-lower Yangtze than in the upper Yangtze reaches. Although the ECHAM5 model still can’t capture the precipitation extremes over the Yangtze River Basin satisfactorily, spatial pattern of the observed and the simulated precipitation extremes are much similar to each other. (ii) For quantifying the characteristics of extremely high and extremely low precipitation over the Yangtze River Basin, four probability distributions are used, namely: General Extreme Value (GEV), General Pareto (GPA), General Logistic (GLO), and Wakeby (WAK). It was found that WAK can adequately describe the probability distribution of precipitation extremes calculated from both observational and projected data. (iii) Return period of precipitation extremes show spatially different changes under three greenhouse gas emission scenarios. The 50-year heavy precipitation and drought events from simulated data during 1951–2000 will become more frequent, with return period below 25 years, for the most mid-lower Yangtze region in 2001–2050. The changing character of return periods of precipitation extremes should be taken into account for the hydrological design and future water resources management.

In this paper, we explored the trends of the atmospheric moisture budget, precipitation, and streamflow in summer during 1961 to 2005 and possible correlations between them by using the linear regression method in the Yangtze River basin, China. The results indicate that: (1) increasing tendencies can be detected in the atmospheric moisture budget, precipitation and streamflow in the Yangtze River basin; however, the significant increasing trends occur only in the atmospheric moisture budget and precipitation in the middle and lower Yangtze River basin; (2) both the ratio of summer moisture budget to annual moisture budget and the ratio of summer precipitation to annual precipitation exhibit a significant increasing trend in the Yangtze River basin. The ratio of summer streamflow to annual streamflow is in a significant increasing trend in Hankou station. Significant increasing summer precipitation can be taken as the major controlling factor responsible for the higher probability of flood hazard occurrences in the Yangtze River basin. The consecutively increasing summer precipitation is largely due to the consistently increasing moisture budget; (3) the zonal geopotential height anomaly between 1991 and 2005 and 1961 and 1990 is higher from the south to the north, which to a large degree, limits the northward propagation of the summer monsoon to north China. As a result, the summer moisture budget increases in the middle and lower Yangtze River basin, which leads to more summer precipitation. This paper sheds light on the changing properties of precipitation and streamflow and possible underlying causes, which will be greatly helpful for better understanding of the changes of precipitation and streamflow in the Yangtze River basin.

Daily precipitation data of 148 measuring stations in the Yangtze River basin (P.R. China) for the period from 1961 to 2002 have been analyzed to detect quasi periodicities in the frequency of occurrence of extreme precipitation events. Extreme precipitation events of duration 1-day and 10-day were defined in terms of 90th percentile threshold exceedances for each station. The time series were standardized, averaged and detrended for each subbasin. Distinct temporal agglomerations of Gaussian peaks in the smoothed time series for all subbasins were detected for certain years. Quasi periodicities features in the time series were analyzed by means of spectrum analyses. Characteristic differences were found for the subbasins with typical significant quasi periodicities in the 2–3 and 3–4 year ranges. Wavelet analyses revealed that the stability of the observed quasi periodicities over time also varied between the subbasins. This results in various degrees of confidence that can be placed on the future extrapolation of Fourier emulations. Our extrapolations suggest occurrences of peaks in the frequencies of extreme precipitation events for most subbasins around the years 2012–2013 and 2017–2018 even though major differences between the subbasins are expected.

For the upper and mid-lower Yangtze River basin trends of pan evaporation and reference evapotranspiration are analysed from 1961 to 2000 using daily data of 115 stations. Both pan evaporation and reference evapotranspiration decreased during the summer months contributing most to the total annual reduction. This trend is more significant in the mid-lower than in the upper Yangtze reaches. The decreasing trends can be associated with trends in net radiation and wind speed. Results are compared with the 20th century evaporation simulated by the general circulation model (GCM, ECHAM5/MPI-OM). Also the GCM’s actual evaporation decreases contrasting an overall increase in air temperature.

The present study is an analysis of the observed extreme temperature and precipitation trends over Yangtze from 1960 to 2002 on the basis of the daily data from 108 meteorological stations. The intention is to identify whether or not the frequency or intensity of extreme events has increased with climate warming over Yangtze River basin in the last 40 years. Both the Mann-Kendall (MK) trend test and simple linear regression were utilized to detect monotonic trends in annual and seasonal extremes.

Climate variability and flood events in the Yangtze Delta, which is a low-lying terrain prone to flood hazards, storm tides and typhoons, are studied in terms of a trend and detrended fluctuation analysis of historical records. The data used in this paper were extracted from historical records such as local annuals and chronologies from 1000–1950 and supplemented by instrumental observations since 1950. The historical data includes frequencies of floods, droughts and maritime events on a decadal basis. Flood magnitudes increase during the transition from the medieval warm interval into the early Little Ice Age. Fluctuating climate changes of the Little Ice Age, which are characterised by arid climate events, are followed by wet and cold climate conditions with frequent flood hazards. For trend analysis, the Mann-Kendall test is applied to determine the changing trends of flood and drought frequency. Flood frequency during 1000–1950 shows a negative trend before 1600 A.D. and a positive trend thereafter; drought frequency increases after 1300. The detrended fluctuation analysis of the flood and drought frequencies reveals power law scaling up to centuries; this is related to long-term memory and is similar to the river Nile floods.

Monthly precipitation trends of 160 stations in China from 1951–2002 have been analysed and interpolated. The Mann-Kendall trend test was applied to examine the monthly precipitation data. Significant positive and negative trends at the 90, 95, and 99 percent confidence levels were detected for numerous stations. The number, distribution, and direction of the trends varied from month to month.