Abstract
In recent decades, strong human activities have not only brought about climate change including both global warming and shifts in the weather patterns but have also caused anomalous variations of hydrological elements in different basins all around the world. Studying the mechanisms and causes of these hydrological variations scientifically is the basis for the management of water resources and the implementation of ecological protection. Therefore, taking the Yongding River mountain area as a representative watershed in China, the changes of different observed and simulated hydro-meteorological variables and their possible causes are analyzed on an inter-annual scale based on ground based observations and remotely sensed data of hydrology, meteorology and underlying surface characteristics from 1956 to 2016. The results show that the annual natural runoff of Guanting hydrological station in the main stream of the Yongding River, Cetian hydrological station and Xiangshuibao hydrological station in the tributary of the Yongding River all have a significant decreasing trend and abrupt changes, and all the abrupt change points of the annual natural runoff series of the three hydrological stations appear in the early 1980s. On the inter-annual scale, the water balance model with double parameters is unable to effectively simulate the natural surface runoff after the abrupt change points. The annual average precipitation after the abrupt change points decreases by no more than 10%, compared with that before the abrupt change points. However, the precipitation from July to August, which is the main runoff-production period, decreases by more than 25%, besides the intra-annual temporal distribution of precipitation becoming uniform and a significant decrease in effective rainfall, which is the source of the runoff. Meanwhile, the NDVI in the basin show an increasing trend, while the groundwater level and land water storage decrease significantly. These factors do not lead only to the continuous reduction of the annual natural runoff in the Yongding River mountain area from 1956 to 2016, but also result in significant changes of the hydro-meteorological relationship in the basin.
Highlights
IntroductionDue to the strong human activities, hydrological elements in many regions show an increasing or decreasing trend
The variabilities of the annual natural runoff series of the Guanting hydrological station, the Cetian hydrological station and the Xiangshuibao hydrological station are tested at the 95% confidence level by using the diagnosis system for hydrological variability
This study analyses the changes of natural runoff in the main and tributaries of the Yongding River from 1956 to 2016, reveals the change of the hydro-meteorological relationship in the basin around the 1980s, and comprehensively analyzes the important driving mechanism leading to the significant decline of the natural runoff and the change of the hydro-meteorological relationship from three aspects, including the intra-annual temporal distribution of precipitation, the change of vegetation cover and the groundwater exploitation
Summary
Due to the strong human activities, hydrological elements in many regions show an increasing or decreasing trend This leads to the sharp decrease in river runoff in some arid areas, which will bring challenges to the management of water resources and ecological protection in the basin at present or in the future [6,7,8,9] it is of great significance to analyze the variability and causes for the changes in different hydro-meteorological variables in order to understand the climate change induced changes of the hydrological cycle, as well as to improve the hydrological prediction, water-resource evaluation methods, water-resource planning and management, etc.
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