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The Yellow River basin serves as an important economic belt and industrial base in China, featuring numerous industrial parks. However, alongside its economic significance, the basin struggles with significant water environmental challenges. This study analyzed the operational status, influent water quality, and energy consumption of 63 centralized wastewater treatment plants (WWTPs) from 54 major industrial parks in the Yellow River basin. The scale of these WWTPs was primarily within the range of 1 × 104~5 × 104 m3/d, with an average hydraulic loading rate of 53.8%. Aerobic treatment processes are predominant. The influent concentrations of chemical oxygen demand (COD), biochemical oxygen demand (BOD), ammonia nitrogen (NH3-N), total nitrogen (TN), and total phosphorus (TP) in the WWTPs exhibited a right-skewed distribution. The BOD/COD ratio of the WWTPs fluctuated between 0.1 and 1.6, and 75% of the WWTPs showed a COD/TN ratio lower than eight. The average BOD5/TN was 2.7, and the probability of influent BOD5/TP > 20 was 84.6%. A significant linear correlation exists between the influent BOD and COD concentrations, while moderate linear relationships are also observed among NH3-N, TN and TP, emphasizing the importance of maintaining appropriate nitrogen and phosphorus levels for efficient pollutant removal. The average electricity consumption of WWTPs in the Yellow River basin in 2023 was 1.1 kWh/m3. It is important to upgrade these WWTPs and reduce their energy consumption. Further strengthening the construction of industrial wastewater collection and treatment facilities based on regional characteristics is recommended to promote the high-quality development of industrial wastewater treatment in the Yellow River basin. [ABSTRACT FROM AUTHOR]

In this work, the largest tributary of the South Branch in the upper reaches of the Xiong'an New Area is selected as the study area. The impact-based critical areal rainfall indices for early flood warnings are proposed from the perspective of the impacts of floods on socio-economic factors. Specifically, four steps, including the determination of the damage-causing discharges, the establishment of the rainfall–discharge relationship, the computation of the critical areal rainfall and the validation of the early warning indices, were used to determine the critical areal rainfall for early flood warnings in the watershed. The results showed that the 1-day critical areal rainfall amounts were 31 mm, 63 mm, 92 mm and 160 mm for early flood warning levels 4, 3, 2 and 1, respectively, when the 1-day antecedent areal rainfall was ≤10 mm. The critical areal rainfall amounts were 20 mm, 54 mm, 87 mm and 160 mm for early flood warning levels 4, 3, 2 and 1, respectively, when the 1-day antecedent areal rainfall was >10 mm. The early warning effectiveness of the proposed critical indices was validated with historical catastrophic flood events and precipitation data during recent flood seasons. The results demonstrated that the impact-based critical indices had a high accuracy and could release warnings 1–2 days in advance, which could effectively avoid the occurrence of missed and underestimated warnings. [ABSTRACT FROM AUTHOR]

It is indisputable that global warming has triggered more frequent extreme weather and in turn led to severe flood disasters. To understand the trend of extreme rainfall under 1.5 °C and 2 °C warming, we investigated the historical variation and future trends in extreme rainfall for the Huai River basin, which has frequently been hit by floods, using recorded meteorological data and a projection of five General Circulation Models in the Coupled Model Intercomparison Project 6. We used the years 1995–2014 as the baseline period to study the temporal and spatial changes in extreme rainfall under 1.5 °C and 2.0 °C warming scenarios. The results indicated that (1) temperatures in the Huai River basin have risen significantly from 1995 to 2014, but there are insignificant variation trends in annual precipitation (AP), intensive precipitation (R95P), maximum daily precipitation (Rx1d) and heavy rain days (Rr50) during the same time span. (2) From 2015 to 2100, both temperature and extreme rainfall indices show increase trends, with a higher rate of increase under a higher emission scenario. (3) Under the warming scenario of 1.5 °C, AP, R95P, Rx1d and Rr50 in the basin will likely increase by 4.6%, 5.7%, 6.2% and 13.4%, respectively, compared with that in the baseline period. Under the warming scenario of 2.0 °C, AP, R95P, Rx1d and Rr50 will probably increase by 7.3%, 7.4%, 10.9% and 19.0%, respectively. (4) Spatially, the changes in extreme rainfall indices under the warming scenarios of 1.5 °C and 2.0 °C generally tend to increase from north to south. Higher intensity extreme rainfall will likely extend to the whole of the Huai River basin. It is therefore essential to study adaptive measures to cope with flooding in the Huai River basin induced by the increase in future rainfall extremes. [ABSTRACT FROM AUTHOR]

Climate change has substantial impacts on regional hydrology in the major river basins. To figure out such latent hydrological impacts of changing climate, more reliable hydrological simulations are imperative. In this study, we evaluated the impacts of climate change on hydrological regime in the Upper Yangtze River Basin based on four downscaled and bias-corrected Global Climate Model outputs from Coupled Model Intercomparison Project Phase 5 under four Representative Concentration Pathways (RCP2.6, RCP4.5, RCP6.0, and RCP8.5) driving three hydrological models. Two model evaluation approaches were applied: simple and comprehensive. The comprehensive approach was used to evaluate models in the historical period, optimizing objective function at four gauges, and hydrological models were weighted for impact assessment based on their performance. In such a way, projected streamflow time series are obtained under different emission scenarios. Results show that the annual average discharge is projected to increase by 4.1–10.5% under the RCP scenarios at the end of twenty-first century relative to the reference period (1970–1999). Moreover, the high flow is projected to increase and the low flow to decrease indicating a higher probability of flood and drought occurrence in the basin. The severity of floods and droughts may increase. In comparison with the simple one-site model evaluation approach, the comprehensive method reveals that the anticipated extreme flow events would be less severe, and annual mean discharge slightly lower. The projected results imply that application of the comprehensive model evaluation approach could narrow the simulated spreads of projections significantly, and might provide more credible results. [ABSTRACT FROM AUTHOR]

Droughts are major, large‐scale, weather‐driven natural disasters, on the rise in the changing climate. We project changing population exposure to drought in two vulnerable, adjacent, basins of large rivers, the Tarim River Basin (TRB) and the Indus River Basin (IRB), for the future horizon 2021–2065. Drought events are assessed based on the outputs of multiple Global Climate Models, by applying the Standardized Precipitation Evapotranspiration Index (SPEI) and the Intensity‐Area‐Duration method (IAD). Future population exposure to droughts is evaluated by combining the drought events under three RCP scenarios (RCP2.6, RCP4.5, and RCP8.5) with the projected population from Shared Socioeconomic Pathways (SSPs), acknowledging the recent two‐child policy in China. Results show that frequency of drought events in both river basins could increase in the future, while increase in the TRB is stronger than in the IRB. The areal coverage of drought events in both river basins is projected to be greater in 2021–2065 than in 1961–2005. Increase of frequency and areal coverage in both basins is especially strong for the class of extreme drought events. According to the ensemble mean of multi‐GCMs, population exposure to droughts was 25.0% and 20.9% of the total population in the TRB and the IRB, respectively, in 1961–2005, and it is projected to increase by over 60% for the TRB and to increase by over 30% for the IRB, in 2021–2065. Plain Language Summary: As a major, large‐scale, weather‐driven natural disaster, drought may occur in all climatic zones and cause significant losses in human and natural systems. Both the Tarim River Basin and the Indus River Basin are vulnerable to drought, but changing characteristics of population exposure to drought is unknown for the two basins under the climate and population dynamics scenarios. We analyze the changing frequency and areal coverage of drought events in 2021–2065 relative to 1961–2005 and then quantify the population exposure to drought in both two river basins. It was found that frequency and areal coverage of drought in both river basins could increase in the future. Increase of frequency and areal coverage in both basins is especially strong for extreme drought events. Population exposure to droughts was 25.0% and 20.9% of the total population in the Tarim and the Indus River Basin, respectively, in 1961–2005, and it is projected to increase by over 60% for the Tarim River Basin and by over 30% for the Indus River Basin in 2021–2065. Key Points: This research combine the Representative Concentration Pathways and the Shared Socioeconomic Pathways scenarios in the drought exposure assessmentThis research project drought events in river basins of the Tarim and the Indus, based on the multiple GCM outputs and the Intensity‐Area‐Duration methodDrought is projected to be more severe in the TRB than in the IRB, while population exposed to droughts in the IRB has been and will be larger than in the TRB [ABSTRACT FROM AUTHOR]

The present paper examines flood risk (composed of hazard, exposure, and vulnerability) in a range of spatial perspectives – from the global to the local scale. It deals with observed records, noting that flood damage has been increasing. It also tackles projections for the future, related to flood hazard and flood losses. There are multiple factors driving flood hazard and flood risk and there is a considerable uncertainty in our assessments, and particularly in projections for the future. Further, this paper analyses options for flood risk reduction in several spatial dimensions, from global framework to regional to local scales. It is necessary to continue examination of the updated records of flood-related indices, trying to search for changes that influence flood hazard and flood risk in river basins. [ABSTRACT FROM AUTHOR]

In this paper, the intensity, area and duration of future droughts in China are analyzed using the Standardized Precipitation Index (SPI) and the Standardized Precipitation Evapotranspiration Index (SPEI). The SPI and SPEI are used to evaluate the simulation ability of drought characteristics with the regional climate model COSMO-CLM (CCLM). The projected intensity and duration of future drought events are analyzed for the period 2016-2050 under three different respective concentration pathways (RCPs). The simulated and projected drought events are analyzed by applying the intensity-area-duration method. The results show that CCLM has a robust capability to simulate the average drought characteristics, while some regional disparities are not well captured, mainly the simulation of more drought events of shorter duration in Northwest China. For the future period 2016-2050, more intense dryness conditions are projected for China. An increase in evapotranspiration is found all over China, while a reduction in precipitation is apparent in the southern river basins. The increase in evapotranspiration plays an important role in the changes of future droughts over the northern river basins and southern river basins. Under RCP2.6, drought events of longer duration and with higher frequency are projected for the southwest and southeast of China. Under RCP4.5 and RCP8.5, a continuing tendency to more dry conditions is projected along a dryness band stretching from the southwest to the northeast of China. More frequent drought events of longer duration are projected in the southwestern river basins. For all future droughts, larger extents are projected, especially for events with long-term duration. The projected long-term drought events will occur more often and more severe than during the baseline period, and their central locations will likely shift towards Southeast China. The results of this study can be used to initiate and strengthen drought adaptation measures at regional and local scale, especially in the south of China. [ABSTRACT FROM AUTHOR]

Understanding the reasons for past changes in soil moisture conditions is key to improving forecasts of this extremely important variable coupling land and atmosphere. To contribute to this understanding, we analyzed the variability of soil moisture and its relationship to regional climate features. In this study we focused on the Poyang Lake basin, which is located on the southern bank of the Yangtze River at the junction of its middle and lower reaches in Jiangxi Province. Using in situ soil moisture observations from Nankang and Hukou stations for the period from 1998 to 2012, we tested the regional applicability of the high-resolution long-term Essential Climate Variable (ECV) soil moisture (SM) dataset (1978–2013) by means of trend and correlation analyses. We only used the ECV SM product here that is based on passive microwave technology. Both observed and ECV SM data show the same variations on monthly and inter-annual time scales including identical trend direction and strong correlations. To investigate the relationship between soil moisture conditions in the Poyang Lake basin and the Western Pacific Subtropical High (WPSH), correlation coefficients were calculated between the ECV SM data, the strength index ( I S ), and the northern limit index ( I N ) of the WPSH. The I S of the last autumn and winter shows a strong positive correlation with soil moisture during the subsequent rainy season. A strong WPSH in the preceding autumn and winter could result in more humid climate conditions in the Poyang lake basin during the following rainy season. The I N shows a strong negative correlation with concurrent soil moisture from July to September. The further the WPSH extends towards the north, the drier the area. [ABSTRACT FROM AUTHOR]

In this study, the intensity, area, and duration of droughts in China are analyzed using the Standardized Precipitation Index (SPI). The SPI was calculated on monthly data for 530 meteorological stations in China for the period 1960-2013. The time series were analyzed for ten major hydrological regions of China, respectively. The relationships between the intensity and the area of droughts for a specific duration were analyzed by the intensity-area-duration method. The results show that areas with a significant trend in dryness can be found in a band reaching from the southwest to the northeast of China, while areas with significant trends in wetness are especially detected in the northern river basins in recent decades. In addition, for recent years (2000-2013), most of the ten major hydrological regions show opposite trends in the SPI when compared to the whole study period (1960-2013) except for the central and southwestern parts of China. This dryness/wetness trends are related to the intensity and duration of drought events, which have been stronger and lasted longer in the detected dryness band except for some northern river basins. A regional shift of drought centers is found from the northwest to the southeast within Central China. Moreover, a decreasing trend in drought area is observed, which might be related to the regional changes in precipitation pattern associated with the atmosphere-ocean interaction. Changes in the SST of the Tropical Pacific and the Tropical Indian Ocean may have resulted in frequent severe drought events of small areal extent in the central and southwestern parts of China. For the study period, the most severe droughts that covered large areas mainly occurred in the north and west of China during the mid-to-late twentieth century. However, in the early twenty-first century, the most severe droughts were located in the southwest of China covering areas less than 0.7 million km. Conclusively, drought areas show a decreasing tendency, while more intense droughts of longer duration have been experienced, especially in the south of China, in the last decades. [ABSTRACT FROM AUTHOR]

Actual evaporation in the Yangtze River basin is calculated by the complementary relationship approach-that is, the advection-aridity (AA) model with parameter validation from 1961 to 2007-and simulated by the general circulation model (GCM) ECHAM5-Max Planck Institute Ocean Model (MPI-OM) from 1961 to 2000. Trends of annual and seasonal estimated actual evaporation and air temperature, net radiation, saturation vapor pressure deficit, wind speed, and precipitation are examined by the linear regression method and nonparametric Mann-Kendall test. The stepwise regression method is used to analyze the significance to reference evapotranspiration of independent variables. Results show that a significant decreasing trend in annual reference evaporation is caused by a significant decline in wind speed. The annual actual evaporation decreases in the upper and midlower Yangtze reaches; more significantly in the AA model [-9.3 mm (10 yr)−1] than in the GCM [−3.6 mm (10 yr)−1]. Significant negative trends are found in spring and autumn, but they show reverse trends in summer and winter within the two methods, which is caused by the different contributors to the seasonal actual evaporation in the two methods. Decreasing net radiation is the main contributor to annual and spring actual evaporation in the two methods. Decreasing precipitation and net radiation are the main contributors to decreasing autumn actual evaporation in the AA model and the GCM. Increasing net radiation and decreasing precipitation are the main contributors to summer and winter actual evaporation in the GCM. Decreasing net radiation and increasing precipitation are the main contributors to decreasing summer and increasing winter actual evaporation in the AA model. [ABSTRACT FROM AUTHOR]

Low flow is a seasonal phenomenon which is a critical requirement for utilization of water resources under rapidly changing environmental conditions. The operation of the Three Gorges Dam (TGD) has had a great influence on downstream low flow in the Yangtze River. In this paper, the characteristics of low flow in the main Yangtze River were analyzed during the dry season before and after the TGD operation during the period of 1956–2016. The results show that: (1) the operation of the TGD has changed the spatial and temporal distribution of streamflow in the middle and lower Yangtze River and the annual mean low flow has increased significantly since the TGD operation. (2) The operation of the TGD could advance the date of the start of dry season in the lower Yangtze River basin. The start dates of the dry season in the Yichang, Hankou and Datong stations were advanced by 14 days, 10 days and 9 days, respectively. (3) The minimum streamflow in the lower Yangtze River has increased notably since the TGD operation. The minimum streamflow was raised by 42.91%, 13.76% and 6.06% at the Yichang, Hankou and Datong stations, respectively. The increasing number of dams in the world might have the potential effects on downstream low flow. More attention should be paid to investigating the influence of dam construction on low flow in rivers all over the world. [ABSTRACT FROM AUTHOR]

• Annual variations are more significant than inter-annual variations for AHG exponent. • Ice regimes significantly contribute to the seasonal changes of AHGs. • The stability of AHG increases with the increase of stream order and drainage area. To be able to precisely estimate discharges in un-gaged streams and reconstruct hydrological features in river systems, the temporal and spatial variations of at-a-station hydraulic geometry (AHG) and their impacting factors need to be detected. To this end, the Yalong River and Upper Jinsha River, which located in southeast Qinghai-Tibet Plateau, are selected as case study. This investigation explores quantitative data on the magnitude of spatial and temporal variations in AHGs over a period of 10 years for 38 mountain reaches with drainage areas ranging from 0.53 × 103 to 259.18 × 103 km2. Effects of ice regime and drainage area on AHG were discussed and the stability of AHG was analyzed. 42.1% of the reaches have flow velocity exponents that are greater than the river width and flow depth exponents combined. No significant spatial variation tendency is observed for AHG exponents while significant temporal variations are reported. Larger fluctuations are found for AHG exponents in annual variations compared with those in inter-annual variations. Ice regimes significantly contribute to the seasonal changes of AHGs. The relative differences of AHG coefficients (a , c , k) and exponents (b , f , m) with and without ice vary between −49.4 to 80.8% and −70.1% to 22.6%, respectively. Compared with no ice regime, the reaches with border ice and slush ice run have smaller exponents m and Froude Number and larger coefficients c and exponents f. Besides, coefficients a and exponents m increase while coefficients k and exponents b decrease with the increase of drainage area. However, coefficients c and exponents f exhibit no tendency with drainage area changes. AHG stabilities increase with the increased stream order and drainage area. Results of this study can enrich the AHG database for mountain rivers and provide a preliminary understanding of ice effects on AHG variations. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, the spatio-temporal variation and trend of daily actual evapotranspiration (ETa) are calculated for the Haihe River Basin from 1961 to 2010. The methodology is based on the complementary relationship approach, i.e. the advection–aridity (AA) model with parameter validation from 1961 to 2010, which allows the determination of ETa that cannot be instrumentally measured. Daily data on mean/maximum/minimum temperature, air pressure, actual water vapor pressure, sunshine hours, wind speed, sunshine duration and cloud cover from 31 meteorological stations from 1961 to 2010 are used in order to identify the main drivers of changes in evapotranspiration. The trend tests applied in this study are the linear regression method and the nonparametric Mann–Kendall test (MKtest). The results show: 1) the Haihe River Basin has an annual ETa at about 484 mm/yr. The highest ETa occurs in summer, followed by autumn. From 1961 to 2010, the annual ETa, the ETa in summer and the ETa in autumn show a significant negative trend in the Haihe River Basin. The ETa varies insignificantly in spring and winter; 2) the ETa shows distinct spatial variability in the Haihe River Basin. It closely follows the topography and increases with greater distance from the sea, but varies significantly during the seasons; 3) the central plain area of the Basin around the capital city of Beijing shows the highest occurrence of negative trends of ETa with a decrease of ETa of 40 mm for the time series. 4) negative trends of ETa in summer are related to multiple factors: decreasing relative humidity and decreasing reduced sunshine duration under increasing surface temperatures in summer. Increases in surface temperature include the mean, maximum and minimum daily temperature. The decline of ETa in autumn can be explained by a negative trend of relative humidity. The decreasing ETa suggests a reduction in water availability and cycle in seasons with highest water demand. [Copyright &y& Elsevier]

In this paper, future drought characteristics (frequency, duration and intensity) over China are analysed by using four climate models from CMIP6 under the seven SSP-RCP (shared socioeconomic pathway-representative concentration pathway) scenarios (SSP119, SSP126, SSP434, SSP245, SSP460, SSP370, and SSP585) for three defined periods of 2021–2040 (near-term), 2041–2060 (mid-term) and 2081–2100 (long-term). The corresponding four climate models output from CMIP5 are also used to conduct a comparison analysis between CMIP5 and CMIP6 to address the improvements added to CMIP6 in terms of drought identification. The drought characteristics are identified by applying the standardized precipitation-evapotranspiration index (SPEI) at a 12-month timescale and run theory. The results show that CMIP6 has a robust capability to capture historical (1986–2005) drought characteristics. For the future period of 2021–2040, the decrease in precipitation and increase in potential evapotranspiration will lead to continuous dry conditions in the upper and middle Yangtze River basin and eastern Pearl River basin. Relative to the reference period, drought events will be more frequent and severe with longer durations in the Northwest River basins and middle Yangtze River basin. Furthermore, higher emissions signify a greater increase in drought frequency and intensity in the long-term period. Except for the SSP585 scenario, the lower emission scenario corresponds to the higher drought duration soon and in the mid-21st century (2021–2060). This finding is regarded as a "strange phenomenon", which cannot be detected by the previous CMIP5-based emission scenarios (RCP2.6, RCP4.5 and the unlikely pathway RCP8.5). Therefore, additional "possible future"-based scenarios (SSP119, SSP126, SSP434, SSP245, SSP460, and SSP370) should be included in extreme climate studies, especially for the near future and mid-21st century. Notably, compared with CMIP5, the reduced biases in drought characteristics are more likely associated with improvements in the representation of physical processes in climate models from CMIP6. The results of this study could provide a basis for the development of drought adaptation measures over China. • Latest CMIP6 climate models and seven SSP-RCP scenarios are used to analyze the possible changes in droughts over China. • More robust projections will be presented by CMIP6 than CMIP5, due to the better representations in physical processes. • The higher emission signifies shorter drought duration, lower precipitation and PET in mid-21st century over China. [ABSTRACT FROM AUTHOR]