Streamflow changes and its influencing factors in the mainstream of the Songhua River basin,Northeast China over the past 50 years

The Songhua River plays a key role in the national development of China, owing to its unique natural condition and resources. Recent changes in the streamflow in the Songhua River are important with regard to local sustainable development and management under the background of global warming and aggravating soil erosion. In order to detect changes in the streamflow, two streamflow series from 1955 to 2004 (observed at the Harbin and Jiamusi stations) in the mainstream of Songhua River basin were obtained, and methods of statistical analysis, wavelet transform, and double mass analysis were employed to analyze the data. Reasons for the changes to the streamflow are discussed with respect to natural and man-made drivers. The results show the following: (1) From 1955 to 2004, the streamflow series present obvious declining trends. (2) The streamflow series followed the pattern of a wet–dry–wet–dry cycle pattern over the past 50 years. In the mainstream of Songhua River, wet years mainly occurred during the periods of 1955–1966 and 1984–1993, while dry years mainly occurred in the 1970s and after 2000. (3) Within the 50-year scale, the streamflow series appeared in the main periods of circa 33-, 13- and 4-year, in which the 33-year periodicity is the strongest. (4) Precipitation and temperature directly influenced the streamflow in the mainstream of the basin. The discharge was positively correlated with the precipitation and negatively correlated with the temperature. In addition, human activity was another important driving factor for streamflow change. (5) In the mainstream of Songhua River basin, the influences on streamflow can be divided into three periods: 1955–1976, 1977–1997, and 1998–2004. In the first period climate change played a dominant role, and during the latter two periods human influences were enhanced significantly.     

The influence of 10 years of water conveyances on groundwater and juvenile Populus euphratica of the lower Tarim River

The changes in the depth of groundwater were studied from the period before water conveyance through 2010, and the TDS of groundwater was analyzed in the lower reaches of the Tarim River during the period 2001–2010. Besides, the numbers of juvenile P. euphratica were investigated in the lower reaches of the Tarim River during the period 2001–2010. The findings indicate that: (1) the hydrological environment of the lower reaches has slowly deteriorated again; and (2) few juvenile P. euphratica were observed along the channel. These results show that the positive influence of the ecological water conveyance project on the ecosystem of the lower Tarim River should be beneficial in the long term; however, the long-term stability of the ecosystem cannot be achieved by the current water diversion scheme.     

Joint pattern of seasonal hydrological droughts and floods alternation in China’s Huai River Basin using the multivariate L-moments

Under the current condition of climate change, droughts and floods occur more frequently, and events in which flooding occurs after a prolonged drought or a drought occurs after an extreme flood may have a more severe impact on natural systems and human lives. This challenges the traditional approach wherein droughts and floods are considered separately, which may largely underestimate the risk of the disasters. In our study, the sudden alternation of droughts and flood events (ADFEs) between adjacent seasons is studied using the multivariate L-moments theory and the bivariate copula functions in the Huai River Basin (HRB) of China with monthly streamflow data at 32 hydrological stations from 1956 to 2012. The dry and wet conditions are characterized by the standardized streamflow index (SSI) at a 3-month time scale. The results show that: (1) The summer streamflow makes the largest contribution to the annual streamflow, followed by the autumn streamflow and spring streamflow. (2) The entire study area can be divided into five homogeneous sub-regions using the multivariate regional homogeneity test. The generalized logistic distribution (GLO) and log-normal distribution (LN3) are acceptable to be the optimal marginal distributions under most conditions, and the Frank copula is more appropriate for spring-summer and summer-autumn SSI series. Continuous flood events dominate at most sites both in spring-summer and summer-autumn (with an average frequency of 13.78% and 17.06%, respectively), while continuous drought events come second (with an average frequency of 11.27% and 13.79%, respectively). Moreover, seasonal ADFEs most probably occurred near the mainstream of HRB, and drought and flood events are more likely to occur in summer-autumn than in spring-summer.     

Spatiotemporal distribution of snow cover and its variation in the upper reaches of the Taolai River basin，Qilian Mountains北大核心CSCD

Snow is an important part of the cryosphere and plays an important role in the hydrological cycle and energy balance. Study of the spatiotemporal characteristics of snow cover and its change is the prerequisite for analyzing the formation,distribution and variation of runoff from mountains in inland river basins. In this study,we selected the upper reaches of the Taolai River basin of Qilian Mountains as the study area,used down⁃ scaling methods to obtain high-resolution snow depth data,and adopted methods of spatial statistics,sensitivity analysis and contribution separations to quantify snow cover distribution and variation influenced by terrain and the regional climate during the time period from 2002 to 2018. Results showed that basin early average snow depth ranged from 0 cm to 2. 5 cm,with variation from -0. 19 cm·a-1 to 0. 06 cm·a-1. The area of snow depth re⁃ duction during the study period accounted for 68. 30% of the total area. It was found that the snow depth increase more with altitude and less with the increase of slope. Variation of snow depth increased below 2 500 m a. s. l. and decreased above 2 500 m a. s. l. As the slope increases,it first increases and then decreases;the snow depth of each aspect decreases,especially in the northwest orientation. The sensitivity of snow depth to air tempera⁃ ture and solar radiation were found negative in general,while that of the precipitation was found positive. The precipitation in high-altitude areas has a relatively large contribution to the snow depth variation,while in the val⁃ ley areas,the contribution of temperature to snow cover is more significant. This work provides an example for the study of snow dynamics in the upper reaches of inland river watersheds,and benefits model simulation and prediction of mountain runoff and regional water management. © 2023 The Author(s).     

Seasonal variations of nitrogen,phosphorus and the nutrient characters in the shallow lakes along the middle and lower reaches of the Yangtze River

Lakes along the middle and lower reaches of the Yangtze River are unique shallow lake group faced with serious problems of eutrophication. In shallow lakes, there are strong interactions between surface sediment and overlying water, and the chemical, biol…     

Dynamic change of landscape pattern and hydrological ＆ geochemical characteristic analysis before and after the emergency water transportation in the lower reaches of the Tarim River, China

The Tarim River is the longest continental river in China. During the past five decades, intensive human exploitation of natural resources, especially water resources in this area has caused serious eco-environmental problems. The Green Corridor in the lower reaches of the Tarim River is situated on the brink of the grave. To save the Green Corridor, emergency water transportation measure was taken by the local government from the year 2000. The landscape pattem and hydrological ＆ geochemical characteristics had changed greatly after emergency water transportation in the lower reaches of the Tarim River. After processing the remote sensing images in the years 2000 and 2005 using ARCGIS 9.0 software, which present the landscape pattems before and after the emergency water transportation, characteristics of dynamic change of landscape pattem were analyzed. The landscape pattern change is described as follows： The forest land, waters, cultivated land and construction landscape area increased, particularly the forest land, which increased by 23.03% during the last 5 years. The water landscape change was only inferior to the forest land, which increased by 16.04%. The lawn, sand and Gobi saline-alkali land area was reducing; lawn and cultivated land had made the biggest contribution to the increase of forest land by 6.46% and 4.79%. In the year 2005, landscape diversity index, evenness index, ffactal dimension and general fragmentation values increased, but dominance index reduced. Furthermore, the eco-hydrological process, hydrological ＆ geochemical characteristics were analyzed based on the monitoring data in this paper. The results showed the hydrological ＆ geochemical characteristics changed greatly after emergency water transportation. Hydrological geochemical characteristics were influenced earlier in the upper part than in the lower part in the lower reaches of the Tarim River. Variations in the concentration of some major ions and hydrological chemical types are obvious.     

Seasonal variations of nitrogen, phosphorus and the nutrient characters in the shallow lakes along the middle and lower reaches of the Yangtze River

Lakes along the middle and lower reaches of the Yangtze River are unique shallow lake group faced with serious problems of eutrophication. In shallow lakes, there are strong interactions between surface sediment and overlying water, and the chemical, biological processes are complicated in the system. The mechanism of shallow lake eutrophication is still insufficient to instruct the harness practice. Water samples were collected quarterly in each lake center from 2000 to 2003. Chemical variables and ionic concentrations were measured in laboratory. This paper focused on the seasonal variations of NO2-N, NO3-N, NH4-N, DIP, chlorophyll a and TN ： TP ratios in 49 lakes along the middle and lower reaches of the Yangtze River. The cooperating mechanisms between N and P were investigated through the analysis of their relationships at different nutrient levels.     

Aeolian desertification and its causes in the Zoige Plateau of China’s Qinghai–Tibetan Plateau

Studies and efforts to control aeolian desertification in China have focused on the arid and semiarid lands in the north. However, the aeolian desertification that is occurring on the high-altitude Qinghai–Tibetan Plateau, which has a cold and humid climate, has received attention only in recent years. In this paper, we report the results of monitoring this aeolian desertification between 1975 and 2005 and of our analysis of its causes on the Zoige Plateau, which is located in the northeastern part of China’s Qinghai–Tibetan Plateau. Aeolian desertified lands expanded at a compound annual rate of 4.07% between 1975 and 2005. They expanded most rapidly between 1975 and 1990, at an annual rate of 7.73%. Factors responsible for this expansion include increasing temperature, decreasing precipitation, over-grazing, drainage of water systems, and land reclamation for agriculture. Increasing temperature, over-grazing, and the drainage of water systems were the key factors. The climatic variations between 1975 and 2005 were not sufficient by themselves to lead to aeolian desertification. Human disturbances such as over-grazing and drainage of water systems must thus have been primarily responsible for the observed changes, and human behavior must be adjusted to control the expansion of aeolian desertification and rehabilitate the desertified lands.     

Behavior and budget of dissolved uranium in the lower reaches of the Yellow (Huanghe) River: Impact of Water–Sediment Regulation Scheme

The Water–Sediment Regulation Scheme (WSRS) is an important water conservancy project in the Yellow River basin, which is usually operated annually from June to July to control water and sediment release from the Xiaolangdi Reservoir in the middle reaches. As a greatly concentrated period of delivering terrigenous materials from the Yellow River to the sea, the WSRS can serve as a natural laboratory to examine the geochemical behavior of elements during their transport along the river. Uranium isotopes (²³⁴U and ²³⁸U) were measured in Yellow River waters at stations Xiaolangdi (located in the middle reaches of the Yellow River) and Lijin (the last hydrologic station near the Yellow River estuary) during the WSRS 2012. Compared with station Xiaolangdi, dissolved uranium concentration at station Lijin was markedly higher, showing a significant impact from the WSRS. Budget calculation for dissolved uranium during the WSRS indicated that two major sources of new added dissolved uranium in the section of the Yellow River between Xiaolangdi and Lijin: suspended particles (46%) and porewater of bottom sediment (45%). The flux of dissolved uranium from the Yellow River to the sea was estimated to be 2.40 × 10⁷ g during the WSRS 2012.     

Assessment of nutrient sources and paleoproductivity during the past century in Longgan Lake, middle reaches of Yangtze River, China

A 63-cm sediment core documents that the concentrations of nutrients in sediment, such as organic carbon, nitrogen and phosphorous, continually increased during the last century in Longgan Lake, middle reaches of the Yangtze River, China. C/N ratio and δ^13Corg revealed that organic matter in the sediment derived mainly from aquatic and terrestrial sources is a minor contributor. Excess phosphorous is related to human activities marked by utilization of phosphoric fertilizers since 1952 A.D. The increase of δ^13Corg towards the sediment surface, together with increasing of OC and N accumulation, indicated the elevation of lake primary productivity due to excess phosphorous loading caused by utilization of phosphoric fertilizer. The decrease of δ^15N during the primary productivity elevation process, especially after 1952, can be attributed to the discharged of nitrogen with lower δ^15N into the lake.     

Review on transboundary aquifers in People’s Republic of China with case study of Heilongjiang-Amur River Basin

Groundwater, as a precious resource hidden underground, is an important component of the global water system. Transboundary aquifers containing substantial amount of groundwater often carry crucial ecological and social implications. Yet, it is unfortunate that transboundary aquifers have hardly been in the forefront of political and scientific discussions, and have not received due attention by policymakers. This article attempts to summarize the investigation on the eight transboundary aquifers that China shares with the neighboring countries. An overview on the groundwater resources in China, including its distribution, exploitation and challenges is also provided. Hydrogeological condition of the Heilongjiang-Amur River Basin aquifer, which is one of the eight major aquifers, is further elaborated. Cooperative activities carried out by China and Russia on monitoring and management of this aquifer are also presented.     

Temporal stability of soil water storage and its influencing factors on a forestland hillslope during the rainy season in China’s Loess Plateau

Large-scale vegetation restoration in China’s Loess Plateau has been initiated by the central government to control soil and water losses since 1999. Knowledge of the spatio-temporal distribution of soil water storage (SWS) is critical to fully understand hydrological and ecological processes. This study analysed the temporal stability of the SWS pattern during the rainy season on a hillslope covered with Chinese pine (Pinus tabulaeformis Carr.). The soil water content in eight soil layers was obtained at 21 locations during the rainy season in 2014 and 2015. The results showed that the SWS at the 21 locations followed a normal distribution, which indicated moderate variability with the coefficients of variation ranging from 14 to 33%. The mean SWS was lowest in the middle slope. The spatial pattern of SWS displayed strong temporal stability, and the Spearman correlation coefficient ranged from 0.42 to 0.99 (p < 0.05). There were significant differences in the temporal stability of SWS among different soil layers (p < 0.01). The spatial patterns of SWS distribution showed small differences in different periods. The best representative locations of SWS were found at different soil depths. The maximum RMSE and MAE at 0–1.6 m soil depth for the rainy season were 4.27 and 3.54 mm, respectively. The best representative locations determined during a short period (13 days) can be used to estimate the mean SWS well for the same rainy season, but not for the next rainy season. Samples of SWS collected over a fortnight during the rainy season were able to capture the spatial patterns of soil moisture. Roots were the main factor affecting the temporal stability of SWS. Rainfall increased the temporal stability of the soil water distribution pattern. In conclusion, the SWS during the rainy season had a strong temporal stability on the forestland hillslope.     

Characteristics and influencing factors of runoff changes in the upper Shule River basin from 1954 to 2016北大核心CSCD

River runoff is an important water resource in the arid region of northwest China. Under the back⁃ ground of climate change,the exploration on change characteristics and influencing factors of river runoff is of great significance for understanding the law of river hydrological change. Based on the daily discharge of Chang⁃ mabao hydrological station,the observation materials from meteorological stations and radiosonde stations,and the first and second Chinese glacier inventory,the variation characteristics and possible influencing factors of runoff in the upper Shule River were systematically analyzed by using the linear trend,empirical mode decompo⁃ sition and hierarchical multiple regression. The results show that the annual runoff of the upper Shule River showed a significant increasing trend during 1954-2016,with a rate of 1. 00×108 m3·（10a）-1. Both runoff in flood period and non-flood period also showed a similar increasing trend. The runoff suddenly changed in 1999 and had two oscillation periods of about 15a and 7a,among them the 15a oscillation period was the most signifi⁃ cant. Both cumulative positive temperature and precipitation were the main climatic factors affecting the runoff in the upper Shule River,which can explain more than 80% of the runoff change. There was a significant posi⁃ tive correlation between the summer runoff in the upper Shule River and the height of 0 ℃ layer. It means that the height changes of 0 ℃ layer can be used to predict the runoff change of the river in flood period,which provides an important reference for evaluating the runoff change of glacial melt recharge rivers in the arid re⁃ gion of northwest China. From 1966 to 2006,the ice volume in the upper Shule River basin decreased by about 5. 77 km3,indicating that glacier changes play a crucial role in the change and regulation of runoff in the basin. © Journal of Glaciology and Geocryology 2022.     

Salts in the clay playas of China’s arid regions: gone with the wind

In China’s arid regions, aeolian salts are transported along with dust aerosols, but their contents and the emission rates are poorly understood. Using samples with undisturbed surfaces and artificially disrupted surfaces (to simulate human disturbances such as reclamation, planting, trampling by animals, and other activities), the transport rates for windblown material and the salt contents of clay playa surfaces were investigated in a wind tunnel. The results showed that under wind velocities ranging from 8 to 22 m/s, wind erosion rates ranged between 0.009 and 0.066 g/m²/s for the undisturbed surfaces and between 0.011 and 0.048 g/m²/s for the artificially disrupted playa surfaces. Although the amount of wind-transported material that was captured was too small to allow an analysis of individual salt contents using the available equipment, electrical conductivity measurements and correlation analysis revealed mean total salt contents of 9.59 g/kg in the transported materials collected above the sealed playa surfaces versus 3.38 g/kg in materials from the same surfaces that were artificially cracked after testing the sealed surfaces. Given the large areas containing clay playas in China’s arid regions, these results will improve our understanding of aeolian salt transport in arid China and will facilitate interpretation of the sources of aeolian salts.     

Drought–flood variation and its correlation with runoff in three headstreams of Tarim River, Xinjiang, China

The Tarim River lies in the inland area of Northwest China, which has a semiarid or arid climate. Because of relatively scarce precipitation in this area, the main water resource is runoff from a mountainous drainage basin. It is very important to ascertain variations of regular hydrologic and meteorological time series data. Through the use of monthly precipitation and hydrologic data in the three headstream mountain areas of the Tarim River over the past 50 years, this work analyzes the variation of a drought–flood index and annual runoff volume, along with spatio-temporal structures of the index related to runoff at multiple time scales, via non-parametric testing and a wavelet transform method. Wavelet transform can clearly demonstrate many characteristics of the time series, including trend, shift, and major periods. Based on the analysis, the following conclusions can be drawn: (1) the drought–flood indices showed increasing trends for the Aksu and Yarkand rivers, and rose non-significantly for Hotan River. The indices of the three headstreams changed remarkably (p < 0.05) in 1986. The curves of wavelet variance show that significant periods of the indices are 4 and 8 years for Aksu and Hotan rivers, and 8 and 10 years for Yarkand River; (2) runoff of the Aksu and Hotan rivers had significant periods of 6 and 8 years, plus 3 and 9 years for Hotan River; (3) there was significant correlation between the drought–flood indices and annual runoff volume in the three headstreams. The results provide important information toward achieving predictability of flood and drought in Northwest China.     

Using LMDI method to analyze the influencing factors of carbon emissions in China’s petrochemical industries

China’s petrochemical industries are playing an important role in China’s economic development. However, the industries consume large amounts of energy and have become primary sources of carbon emission. In this paper, the change in carbon emissions from China’s petrochemical industries between 2000 and 2010 was quantitatively analyzed with the Log-Mean Divisia Index method, which was decomposed into economic output effect, industrial structural effect and technical effect. The results show that economic output effect is the most important factor driving carbon emission growth in China’s petrochemical industries; industrial structural effect has certain decrement effect on carbon emissions; adjustment of industrial structure by developing low-carbon emission industrial sectors may be a better choice for reducing carbon emissions; and the impact of technical effect varies considerably without showing any clear decrement effect trend over the period of year 2000–2010. The biggest challenge is how to make use of these factors to balance the relationship between economic development and carbon emissions. This study will promote a more comprehensive understanding of the inter-relationships of economic development, industrial structural shift, technical effect and carbon emissions in China’s petrochemical industries and is helpful for exploration of relevant strategies to reduce carbon emissions.

     

Using LMDI method to analyze the influencing factors of carbon emissions in China’s petrochemical industries

China’s petrochemical industries are playing an important role in China’s economic development. However, the industries consume large amounts of energy and have become primary sources of carbon emission. In this paper, the change in carbon emissions from China’s petrochemical industries between 2000 and 2010 was quantitatively analyzed with the Log-Mean Divisia Index method, which was decomposed into economic output effect, industrial structural effect and technical effect. The results show that economic output effect is the most important factor driving carbon emission growth in China’s petrochemical industries; industrial structural effect has certain decrement effect on carbon emissions; adjustment of industrial structure by developing low-carbon emission industrial sectors may be a better choice for reducing carbon emissions; and the impact of technical effect varies considerably without showing any clear decrement effect trend over the period of year 2000–2010. The biggest challenge is how to make use of these factors to balance the relationship between economic development and carbon emissions. This study will promote a more comprehensive understanding of the inter-relationships of economic development, industrial structural shift, technical effect and carbon emissions in China’s petrochemical industries and is helpful for exploration of relevant strategies to reduce carbon emissions.     

About the variability in thunderstorm and rainfall activity over India and its association with El Niño and La Niña

Thunderstorms are of much importance in tropics, as this region is considered to have central role in the convective overturn of the atmosphere and play an important role in rainfall activity. It is well known that El Niño and La Niña are well associated with significant climate anomalies at many places around the globe. Therefore, an attempt is made in this study to analyze variability in thunderstorm days and rainfall activity over Indian region and its association with El Niño and La Niña using data of thunderstorm day’s for 64 stations well distributed all over India for the period 1981–2005 (25 years). It is seen that thunderstorm activity is higher and much variable during pre-monsoon (MAM) and southwest monsoon (JJAS) than the rest of the year. Positive correlation coefficients (CCs) are seen between thunderstorms and rainfall except for the month of June during which the onset of the southwest monsoon sets over the country. CCs during winter months are highly correlated. Composite anomalies in thunderstorms during El Niño and La Niña years suggest that ENSO conditions altered the patterns of thunderstorm activity over the country. Positive anomalies are seen during pre-monsoon (MAM) and southwest monsoon months (JAS) during La Niña years. Opposite features are seen in southwest monsoon during El Niño periods, but El Niño favors thunderstorm activity during pre-monsoon months. There is a clear contrast between the role of ENSO during southwest monsoon and post-monsoon on thunderstorm activity over the country. Time series of thunderstorms and precipitation show strong association with similarities in their year-to-year variation over the country.