In the discussion of climate impacts, 1.5 and 2 °C have become iconic values. This study examines the impacts of 1.5 and 2 °C global warming on water availability, runoff seasonality, and extreme monthly and daily runoff in two catchments, using the semi-distributed hydrological model Hydrologiska Byråns Vattenbalansavdelning-D, based on a combination of five global climate models (GCMs) and four representative concentration pathways (RCPs). Subsequently, quantitative assessments were made for projection uncertainties from GCMs and RCPs. The two catchments are the Yiluo River catchment (YLC) in northern China and the Beijiang River catchment (BJC) in southern China. The results indicate wetter flood seasons for YLC and warmer mean annual temperatures, drier springs, and more severe floods over long return periods (25 and 50 years) for both catchments. The change magnitude of most indicators is expected to be larger in YLC than in BJC. Mean annual temperatures in both catchments are expected to have smaller changes under the 1.5 °C scenario than under the 2.0 °C scenario. However, the change magnitude of the other hydrological variables is projected to be approximately equivalent for both catchments under both scenarios. Uncertainties of projected impacts from GCMs are generally larger than those from RCP scenarios, for both catchments and warming scenarios, with the exception of mean annual temperature of BJC. These findings indicate that effective measures are required to address increasing annual temperatures, more severe flood events (25- and 50-year return periods), and drier spring seasons in both catchments and wetter flood seasons in YLC.

Land use and land cover change (LUCC) and water resource utilization behavior and policy (WRUBAP) affect the hydrological cycle in different ways. Their effects on streamflow and hydrological balance components were analyzed in the Yiluo River Basin using the delta method and the Soil and Water Assessment Tool (SWAT). The multivariable (runoff and actual evapotranspiration) calibration and validation method was used to reduce model uncertainty. LUCC impact on hydrological balance components (1976–2015) was evaluated through comparison of simulated paired land use scenarios. WRUBAP impact on runoff was assessed by comparing natural (simulated) and observed runoff. It showed that urban area reduction led to decreased groundwater, but increased surface runoff and increased water area led to increased evaporation. LUCC impact on annual runoff was found limited; for instance, the difference under the paired scenarios was <1 mm. Observed runoff was 34.7–144.1% greater than natural runoff during November–June because of WRUBAP. The effect of WRUBAP on wet season runoff regulation was limited before the completion of the Guxian Reservoir, whereas WRUBAP caused a reduction in natural runoff of 21.6–35.0% during the wet season (July–October) after its completion. The results suggest that WRUBAP has greater influence than LUCC on runoff in the Yiluo River Basin. Based on existing drought mitigation measures, interbasin water transfer measures and deep groundwater exploitation could reduce the potential for drought attributable to predicted future climate extremes. In addition to reservoir regulation, conversion of farmland to forestry in the upstream watershed could also reduce flood risk.

An assessment of the impact of climate change on regional hydrological processes is vital for effective water resources management and planning. This study investigated the potential effects of climate change on water availability, seasonal runoff, flooding, and water stress in the Yellow River and Pearl River basins in China over the next 30 years, using a semi-distributed hydrological model based on a combination of five general circulation models with four Representative Concentration Pathway scenarios and five Shared Socioeconomic Pathways. The results indicated annual mean temperature could rise higher in the Yellow River Basin than the Xijiang River Basin during 2021–2050. Higher risks of small floods and some big floods, but lower risks of rare big floods are projected for both basins. Water scarcity will continually threaten the Yellow River Basin, especially during the dry season and around 2025. In comparison with the effects of climate change, population variation was expected to have a greater impact on water scarcity. A longer and drier dry season is projected for the Pearl River Basin, which could aggravate water stress and saltwater intrusion into the Pearl River delta. Although the present findings have implications for water resource management planning, caution should be observed because of the neglect of reservoir/dam operations and inherent projection uncertainty.

This study assesses present-day extreme climate changes over China by using a set of phase 6 of the Coupled Model Intercomparison Project (CMIP6) statistical downscaled data and raw models outputs. The downscaled data is produced by the adapted spatial disaggregation and equal distance cumulative distribution function (EDCDF) method at the resolution of 0.25° × 0.25° for the present day (1961–2014) and the future period (2015–2100) under the Shared Socioeconomic Path-way (SSP) 2-4.5 than SSP5-8.5 emission scenario. The results show that the downscaling method improves the spatial distributions of extreme climate events in China with higher spatial pattern correlations, Taylor Skill Scores and closer magnitudes no matter single model or multi model ensemble (MME). In the future projections, large inter-model variability between the downscaled models still exists, particular for maximum consecutive 5-day precipitation (RX5). The downscaled MME projects that total precipitation (PTOT) and RX5, will increase with time, especially for the northwest China. The projected heavy precipitation days (R20) also increase in the future. The region of significant increase in R20 locates in the south of river Yangtze. Maxi-mum annual temperature (TXX) and percentage of warm days (TX90p) are projected to increase across the whole country with larger magnitude over the west China. Projected changes of minimum annual temperature (TNN) over the northeastern China is the most significant area. The higher of the emission scenario, the more significant of extreme climates. This reveals that the spatial distribution of extreme climate events will become more uneven in the future.

This study investigated the potential impacts of climate change on water scarcity and hydrological extremes in the Yellow River Basin in the near-term (2026–2050), mid-term (2051–2075), and long-term (2076–2100) periods under three combined pathways of Shared Socioeconomic Pathways (SSPs) and Representative Concentration Pathways (RCPs) SSP1–2.6, SSP2–45, and SSP5–8.5 relative to the reference period (1986–2010), based on the runoff simulation through the Huayuankou hydrological station using the HBV-D hydrological model, which was forced by a statistically downscaling dataset. The results indicate that water shortage would still threaten the Yellow River because annual runoff will remain below 1000 m³/year, although water scarcity would be alleviated to some degree. More and larger floods will happen in summer in the 21st century, especially in the long-term period under the SSP5–8.5 scenario. More Hydrological droughts will occur during July–October, and some extreme droughts would likely exceed the historical largest magnitudes in July and August in the long term under the SSP5–8.5 scenario.