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Global climate change has altered the spatial-temporal regimes of hydro-meteorological variables. The impact of climate change on the risk transferability from meteorological to hydrological droughts needs to be investigated. Based on the gridded meteorological data and 19 global climate model simulations from the Coupled Model Inter-comparison Project Phase 5,the climate change scenarios were generated over 135 catchments in China for two future periods (2011—2055 and 2056—2100). The best performed hydrological model over four lumped models was selected for hydrological simulations. Based on precipitation scenarios and hydrological simulations,the Standard Precipitation Index (SPI) and the Standard Runoff Index (SRI) were respectively calculated for each catchment and time period. The meteorological and hydrological drought episodes were extracted based on the runoff theory. Finally,drought risks by incorporating the most likely selection into the Copula function were calculated,and the risk transferability from meteorological to hydrological droughts under the current and future climates were investigated. The results show that:① Meteorological and hydrological droughts are highly sensitive to future warming climates. Specifically,drought return periods are projected to lengthen in northern China,indicating mitigating risks,while they become shortened by 2 to 5 times over most catchments in central and southern China,indicating deteriorated conditions. ② The meteorological drought risks positively correlate with the hydrological drought risks under the current and future climates,with the Pearson correlation coefficients being higher than 0.99. ③ The sensitivity of hydrological to meteorological drought risks almost stay unchanged for each catchments for different future periods,whereas the co-occurrence of hydrological and meteorological droughts is projected to slightly increase over northern China under future warming climates. [ABSTRACT FROM AUTHOR]

Copula functions, which are flexible tools for the derivation of joint probability distributions, have been widely and effectively used to deal with multi variable analysis problems in the field of hydrology and water resources. Particularly in recent decades, this method has received great attention from researchers and engineers because of its advantages in multivariate analysis where the marginals of the data are not normally distributed. This paper provides a state-of-the-art review of the last decade of copula functions in multivariate hydrological frequency analysis, coinci dence and combination analysis of hydrological events, hydrological stochastic simulation, and hydrological modeling and forecasting, etc. More specifically, application issues such as parameter estimation, variable asymmetry, fitting optimization, tail characteristics, multivariable return period selection, and sampling error are described. Finally, the key points and development direction of Copula functions in the field of hydrology and water resources are consid ered, which provides guidance for the application of this method in the future. [ABSTRACT FROM AUTHOR]

The human activity and climate change have significantly altered the river flow and spatio- temporal distribution of flood process, which directly impact on design flood in the downstream section. The effects of upper reservoir construction and regulation on downstream hydrologic regime are reviewed, the main research contents of design flood theory and method in cascade reservoir operation period are proposed. We mainly discuss non- stationary flood frequency analysis method and the most likely flood regional combination method based on copula function, and compare their practicability. We recommend using design floods and flood control water level in reservoir operation period, and suggest further research references and directions. [ABSTRACT FROM AUTHOR]

Droughts have such essential features as long duration,large scope of influence,and spatio-temporal continuity,and a single variable or double variables were mostly considered in previous studies. By identifying arid patches and judging the continuity between two adjacent droughts based on the given threshold,a spatio-temporally continuous 3D identification method has been proposed for drought events,measuring a drought event in terms of 5 characteristic variables of duration,area,severity,intensity,and central location;the duration-area-severity frequency analysis method based on Copula function has been proposed. Taking Southwest China as an example,SPI drought indices are used to identify the drought events that lasted 3 months or longer in recent 52 years,which totaled 78. Among them,the most serious event from Aug. 2009 to Jun. 2010 has a recurrence period of 94 years. The comparison between the probability distribution function and the Copula function indicates that the 3 characteristic variables of duration,area and severity shall be simultaneously considered upon frequency analysis of drought events. [ABSTRACT FROM AUTHOR]