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The meteorological drought (MD) is the precursor of the hydrological drought (HD), and understanding the propagation process from MD to HD is of great significance for the early warning of HD. Based on the theory of run and Bayesian networks, this study uses the standardized precipitation index (SPI), standardized precipitation evapotranspiration index (SPEI) and standardized streamflow index (SSI) to explore the characteristics and propagation of MD and HD in the regions of eastern Gansu, China. The results indicate that: (1) The region was mainly wet (dry) and the wetness (dryness) was stronger before (after) 2000 when reflected by SSI. The frequency is higher based on SPI and SPEI than that based on SSI, while the duration and magnitude are lower than those based on SSI. (2) The propagation time from MD to HD is generally within 1–10 months. After the occurrence of a certain level of MD, it is most likely to propagate to HD events that are relatively weaker than the MD. Besides, the higher the intensity level of MD, the shorter the propagation time to HD, and the shorter for cumulative occurrence probability of HD to approach 1.0. (3) The increase in temperature and decrease in precipitation, runoff and runoff coefficient may contribute to the dryness after 2000. Moreover, the weakened propagation from MD to HD may be due to the rapid increase of water resource consumption caused by intensive anthropogenic activities in the study area. From the above results, this study found some propagation characteristics from MD to HD in a semi‐arid and semi‐humid watershed, which can provide a supplement for revealing the drought mechanism and can assist in the management and planning of water resources in China. [ABSTRACT FROM AUTHOR]

Based on the daily precipitation data of the Huai River basin (HRB) and NCEP/NCAR reanalysis data from 1960 to 2014, the study examines the spatio‐temporal characteristics of summer extreme precipitation (SEP), explores the statistical relationship between the changes of SEP in the HRB and the East Asian summer monsoon (EASM), and further investigates the circulation characteristics which are most conducive to extreme precipitation under different EASM backgrounds. The main results are as follows: (a) summer extreme precipitation indices (SEPI) of PNL90 and PQ90 mainly increased (although not significant) in the HRB from 1960 to 2014, and the weakening of EASM may be the reason for the upwards trend. (b) The characteristics of SEP are quite different between the north and the south of the HRB, and SEPI mainly negatively correlates with East Asian summer monsoon index (EASMI) in the south but positively correlates in the north. (c) Extreme precipitation may occur under both strong and weak summer monsoon backgrounds in the HRB, but the circulation configurations are different. The differences between high and low SEP are mainly associated with the intensity of western Pacific subtropical high (WPSH) for the weak EASM years, while the differences mainly lie in the position of WPSH for the strong EASM years. Extreme precipitation may occur under both strong and weak East Asian summer monsoon (EASM) backgrounds in the Huai River basin, but the circulation configurations are different. Four types of combinations (A, B, C, D) between summer extreme precipitation (SEP) and EASM are classified. The differences between high and low SEP mainly lie in the intensity of western Pacific subtropical high (WPSH) for the weak EASM years, while the differences mainly lie in the position of WPSH for the strong EASM years. [ABSTRACT FROM AUTHOR]

Due to the close relationship of climate change with reference evapotranspiration (ET), detecting changes in ET spatial distribution and its temporal evolution at local and regional levels is favorable to comprehensively understand climate change-induced impacts on hydrology and agriculture. In this study, the objective is to identify whether climate change has caused variation of ET spatial distribution in different analysis periods [i.e., long- (20-year), medium- (10-year), and short-term (5-year)] and to investigate its temporal evolution (namely, when these changes happened) at annual and monthly scales in Southwest China (SWC). First, we estimated ET values using the United Nations Food and Agriculture Organization (FAO) Penman-Monteith equation, based on historical climate data measured at 269 weather sites during 1973-2012. The analysis of variance (ANOVA) results indicated that the spatial pattern of annual ET had significantly changed during the past 40 years, particularly in west SWC for the long-term analysis period, and west and southeast SWC in both medium- and short-term periods, which corresponded to the percent area of significant differences which were 21.9, 58.0, and 48.2 %, respectively. For investigating temporal evolution of spatial patterns of annual ET, Duncan's multiple range test was used, and we found that the most significant changes appeared during 1988-2002 with the significant area of higher than 25.0 %. In addition, for long-, medium-, and short-term analysis periods, the spatial distribution has significantly changed during March, September, November, and December, especially in the corresponding periods of 1988-1997, 1983-1992, 1973-1977, and 1988-2002. All in all, climate change has resulted in significant ET changes in SWC since the 1970s. Knowledge of climate change-induced spatial distribution of ET and its temporal evolution would aid in formulating strategies for water resources and agricultural managements. [ABSTRACT FROM AUTHOR]

ABSTRACT To account for CO2 impacts on the vegetation leaf area index ( LAI) and the different responses of stomatal conductance in various vegetation species, the modified Soil and Water Assessment Tool ( SWAT) model is calibrated in the Xinjiang Basin with the measured daily streamflow from 1961 to 1970, showing that SWAT accurately reproduces monthly and annual streamflow from 1971 to 2005 and actual evapotranspiration ( AET) from 1983 to 2005. AET and streamflow in the basin for the 21st century are assessed using a multi-model ensemble approach in which downscaled and bias corrected outputs are compared to the baseline (1971-1999) and used to drive the SWAT model. The ensemble average annual precipitation decreases in the three scenarios, with maximum decreases of 7.61% during 2011-2050 and 4.80% during 2051-2090 in scenario A2. In contrast, the ensemble average annual and monthly temperature (minimum and maximum) increase by different amounts during the two periods in each scenario. For each emissions scenario, the ensemble average annual AET will increase, while the average annual streamflow will decrease. Under the A2 scenario, the maximum changes of average annual AET (streamflow) are +18.31% (−20.93%) and +20.93% (−23.43%) during 2011-2050 and 2051-2090, respectively. Compared to the baseline, the ensemble average annual minimum streamflow during 2011-2050 will decrease by approximately 20% under the A1B and A2 scenarios and by 7% in the B1 scenario. Thus, the ensemble average annual maximum streamflow will decrease under each scenario during the two periods, except for a 6.42% increase in the A1B scenario during 2051-2090. A Generalized Extreme Value ( GEV) analysis, simultaneously, suggests that the maximum annual streamflow will decrease during the two periods under each scenario, with exception during 2051-2090 in the scenario A1B, and the magnitudes will decrease for 2-, 5-, 10-, 20- and 50-year return periods. [ABSTRACT FROM AUTHOR]

The Yangtze River Delta is one of the most developed regions in China and the rapid development of urbanization have greatly influenced regional hydrology and water resources. Taking several typical urbanizing areas in the Yangtze River Delta as examples, this paper probes into the impacts of urbanization on hydrologic cycle and hydrological process with the support of RS, GIS and hydrological model. The research centers on the impacts of urbanization on precipitation, hydrological process, river networks, and water environment in some typical cities. The results show that: (1) Urban rain island effect is not evident when the process of urbanization is slow, while the differences of annual precipitation and flood season precipitation between urban and suburban areas increased to a certian extent in the booming stage of urbanization. (2) The annual runoff depth and the runoff coefficient increased with the development of urbanization, and the effect will be more notable when the urban areas expand to a certain size; (3) River network systems, especially low-grade rivers have been greatly destroyed in the process of urbanization, which increases the risk of flood and water degradation, so it is very important to protect natural river systems. Based on the results, some proposals of sustainable utilization and protection of water resources is also addressed. [ABSTRACT FROM AUTHOR]

Extreme hydrometeorological events have far-reaching impacts on our daily life and may occur more frequently with rising global temperatures. The probability of the concurrence of these extreme events in the upper reaches of the river network is of particular importance for the lower reaches, which is referred to as the encounter probability of extreme events, and may have even stronger socio-economic impacts. In this study, the Rao River basin in China is selected as an example to explore the encounter probability and risk of future flood and drought based on the encounter probability model. The reference period was 1971–2000, and the future prediction periods were 2020–2049 and 2070–2099. The calibrated and validated statistical downscaling model (SDSM) was used to generate future daily precipitation and daily mean temperature. The calibrated and validated Xin'anjiang model was used to predict future daily mean streamflow in the basin. In addition, the encounter probability model was established using the joint distribution of occurrence dates and magnitudes of daily mean streamflow to investigate the encounter probabilities of flood and drought under future climate change. Results show that, for flood occurrence dates, the encounter probability during the flood season would decrease in the two future periods while the dates would generally be earlier. For flood magnitudes, the encounter probability of the two tributaries' floods and the probability of flood at each tributary would decrease (e.g., the encounter probability with the same-frequency of 100-years would reduce by 53% to 95%), which indicates reduced risk of future major floods in the study area. For drought occurrence dates, the encounter probability during the non-flood season would decrease. For drought magnitudes, the encounter probability would decrease (e.g., the encounter probability with the same-frequency of 100-years would reduce by 18% to 33%), even though the probability of future drought at each tributary would increase. Such analyses provide important probabilistic information to help us prepare for the upcoming extreme events. [ABSTRACT FROM AUTHOR]

This paper explores the influences of human activities on water level changes of Taihu Lake basin based on indicators of hydrologic alteration method. The results indicated that: First, the water levels of 1990s to 2000s are significantly higher than those of 1970s to 1980s and the increasing in non-flood season (October to April of next year) is bigger than that of flood season (May to September). Second, the hydrologic changes are the most significant in the highest and lowest water levels and the average water level from January to March among all the indicators of hydrologic alteration. Human activities represented by urbanization are the main factors causing these changes. [ABSTRACT FROM AUTHOR]