Abstract
Under the influence of global climate change, the discharges of major global rivers directed into the ocean have undergone significant changes. To study the trends and causes in discharge variation, we selected 40 large rivers and analyzed their annual discharges near their estuaries from 1960 to 2010. The method of runoff variation attribution analysis based on the Budyko hypothesis for large-scale basins was developed, in which influencing factors of human activities and glacial melting factors were added to the formula. The contribution rate of climate factors and human activities to changes in discharge were quantitatively identified. Climatic factors include precipitation, evapotranspiration and glacial melting. Human activity factors include underlying surface and artificial water transfer. The contribution rate is determined by the elastic coefficient, which is obtained by the ratio of change rate of each factor and the change rate of runoff. The results indicated that the discharges predominantly showed downward trends with a few upward trends. Rivers in North America and Africa showed downward trends, and those in Europe principally showed upward trends. Climate was the main influencing factor of discharges changes, and only approximately 25% of river discharges were greatly affected by human activities. River discharges in 75% of the basins which mainly contains subtropical monsoon humid climate and savanna climate zones showed upward trends. In the four basins which are mainly contains tropical rainforest climate and tropical monsoon climate, they all showed downward trends. The trend of discharges in the temperate monsoon climate, temperate continental climate, and temperate maritime climate cannot be accurately judged because of irregular variation. The discharges in the mid-high latitudinal zones predominantly showed upward trends, while those in the mid-low latitudinal zones with the influence of human activities showed downward trends.
Highlights
The discharge of large rivers into the oceans constitutes an important component of the global hydrological cycle and an important link for the coupling between terrestrial and oceanic hydrological cycles
From the above analysis results, we found that the contribution rate of precipitation in all basins is above 29%, and the precipitation elastic coefficient in 27 basins is larger than other factors
In the seven basins where the discharge has a significant upward trend (Table 4), the δz values in the Lena River and the Yana River are less than 50%
Summary
The discharge of large rivers into the oceans constitutes an important component of the global hydrological cycle and an important link for the coupling between terrestrial and oceanic hydrological cycles. The global mean surface temperature (GMST) has continued to increase [1,2]. The frequency of extreme events such as heavy rainfall and drought has increased significantly in various regions of the world [2,3,4,5,6]. Combined with the impact of human activities, discharges may change significantly [7,8]. The environmental degradation of many estuaries in the world is a serious issue that poses a threat to water supply security, ecological environment safety, and sustainable socioeconomic development. Discharge directed into the ocean represents the final process in the complex water cycle, and its changes are comprehensive manifestations of climate change
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callMore From: International Journal of Environmental Research and Public Health
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
