The monthly accumulated precipitation and monthly average temperature of 117 meteorological stations in Song-Liao River Basin (SLRB) were used to calculate the Standardized Precipitation Evapotranspiration Indices (SPEI) to analyze the drought characteristics, including long-term trends, drought affected area, climate abrupt change, intensive drought occurrence regions, and drought durations during 1964–2013 with the support of GIS. The Area Drought Severity (ADS), a comprehensive index, is proposed to assess both the variations of drought degree and the extent of the drought affected area. The results revealed that (1) the drought happening probability and degree are rising and the affected areas of all degrees of drought have an increasing trend during the last 50 years; (2) there is a climate abrupt change which occurred in around 1994, and the area with declining SPEI is larger than that with declining SPI, which could be due to the rising temperature after the climate abrupt change; (3) all degrees of drought occurrence probability increased, and the intensive drought occurrence regions altered from the northern SLRB to the southwestern SLRB after the climate abrupt change; (4) the drought duration increased from 1994, and the increased drought durations occurred in most parts of SLRB.

The Northwest of Yellow River Basin (YRB) is an arid and semi-arid region. This study employs wavelet analysis, dry area coverage, drought frequency, and Mann–Kendall test trend to investigates the evolution characteristics of drought in the Northwest of YRB and the impact of macro climatic conditions on drought. The scale of season and year Standardized Precipitation Evapotranspiration Index (SPEI) was mostly represented as alternating dry and wet weather in this region. SPEI decreased significantly in each season, indicating increased drought. The drought situation changed abruptly in 1968, and the change was more obvious around 2000. Drought trend in autumn is more noticeable than in the other three seasons. The average annual dry area covers 34%. The drought frequency in each station at the annual scale was between 30.78% and 46.15%, its high values are mainly concentrated in the western region. The main cycles of annual SPEI changes are 37 and 5 years; spring is 45 and 10 years; summer is 20 and 5 years; autumn is 36, 10, and 5 years; winter is 45, 22, and 5 years. Furthermore, drought occurrence and changes are closely related to large-scale climatic factors, with El Niño-Southern Oscillation having the greatest impact on drought.

The sequence of reservoir operations has a profound influence on the regulation and storage capacity of reservoir groups to effectively utilise the natural water inflow and external water transfer in the basin, especially for reservoir groups with water supply tasks. This study establishes the reservoir operation sequence (ROS) of four reservoir group modes, aiming at national economic and ecological water consumption, constructs a model of ROS-based multi-objective ecological operation of the reservoir group, and uses the particle swarm optimisation (PSO) method to optimise the solution. Analysing the results of the three schemes in two scenarios at the Yinma River Basin (YRB) indicates that after the Central Jilin Water Supply Project is put into operation, not only will the production and living water be effectively improved, but also the ecological water in the basin. Then, we compared the optimisation results of different water supply sequences in series and parallel reservoirs, which illustrates that the ROS of the four modes formulated in this research is the optimal water supply sequence.

Regarding the gross water resources security and sustainable development in Ningxia, water resources ecological footprint model (EFw model) is adopted to analyze the temporal and spatial variations of EFw and threshold changing trends of available water resources in Ningxia. The research demonstrate that the period from 2002 to 2019 witnessed a decrease in fluctuation of EFw, a high year-to-year variability of water resources ecological carrying capacity (ECw), and a high supply pressure. On the whole, the water resource utilization efficiency has a remarkble improvement. The water-saving effect of is also conspicuous in agriculture and industry, but urban water consumption is conspicuously increased. In the aspect of space, the water resources ecological footprint in Ningxia is mainly concentrated in Yinchuan and Wuzhong, where water consumption in agriculture is large. In accordance to the macro water resources allocation of the Yellow River, Ningxia’s macro water resources are still in loss, while the ecological losses of macro water resources in Wuzhong and Zhongwei are more serious. Therefore, the improvement of agricultural and industrial water utilization efficiency in accordance to water supply and demand is necessary; besides, the problem of low efficiency of water consumption in tertiary industry and residents also needs to be addressed; lastly, the adjustment of the industrial structure and water resources allocation, and implement practical and effective methods are both essential. Guided by ‘determining city development and industries by water’, the goal of the water resources sustainable development in Ningxia will be realized.

Drought is one of the most devastating natural disasters, especially in China. In drought assessment, the PDI has high robustness, is easier to obtain than indices such as SPEI and PDSI, and is more advantageous in regions with sparse stations. The present study employs the annual PDI with the precipitation and temperature data from 830 meteorological stations to systematically study the interannual variation characteristics of drought and humidity in China during 1970–2019. The results showed the following: (1) 26.6% of the total statistics from meteorological stations showed significant (p < 0.05) increases in annual PDI values throughout China during 1970–2019. (2) Air temperature plays a more remarkable role than precipitation in assessing the drying trend with PDI throughout China. (3) About 71% of stations experienced more drought events (PDI > 1) than humidity events (PDI < −1), 14% of stations experienced more humidity events than drought events. (5) All stations experienced drought events (PDI > 1) with a frequency range from 6% to 32% and humidity events (PDI < −1) with a frequency range from 8% to 36%. Most of the stations experienced extreme drought events (PDI > 3) with a frequency range from 2% to 10%, while only 177 stations experienced extreme humidity events (PDI < −3) with a frequency range from 2% to 4%. (6) More than 67% of stations experienced drought conditions during both periods of 1972–1974 and 2000–2002 and even exceeded 80% in the three years 1972, 2000, and 2001. Both periods of 1976–1983 and 1985–1999 can be considered to be a humidity period throughout China. In conclusion, the PDI successfully expresses the interannual variation characteristics of drought and humidity events throughout China previously captured by other prominent, recommended drought indices.