Streamflow trends and climate linkages in the source region of the Yellow River, China

Abstract

Abstract:Much of the discussion on hydrological trends and variability in the source region of the Yellow River centres on the mean values of the mainstream flows. Changes in hydrological extremes in the mainstream as well as in the tributary flows are largely unexplored. Although decreasing water availability has been noted, the nature of those changes is less explored. This article investigates trends and variability in the hydrological regimes (both mean values and extreme events) and their links with the local climate in the source region of the Yellow River over the last 50 years . This large catchment is relatively undisturbed by anthropogenic influences such as abstraction and impoundments, enabling the characterization of widely natural, climate-driven trends. A total of 27 hydrological variables were used as indicators for the analysis. Streamflow records from six major headwater catchments and climatic data from seven stations were studied. The trend results vary considerably from one river basin to another, and become more accentuated with longer time period. Overall, the source region of the Yellow River is characterized by an overall tendency towards decreasing water availability. Noteworthy are strong decreasing trends in the winter (dry season) monthly flows of January to March and September as well as in annual mean flow, annual 1-, 3-, 7-, 30-and 90-day maxima and minima flows for Maqu and Tangnag catchments over the period . The hydrological variables studied are closely related to precipitation in the wet season (June, July, August and September), indicating that the widespread decrease in wet season precipitation is expected to be associated with significant decrease in streamflow. To conclude, decreasing precipitation, particularly in the wet season, along with increasing temperature can be associated with pronounced decrease in water resources, posing a significant challenge to downstream water uses.

Effects of Permafrost Degradation on the Hydrological Regime in the Source Regions of the Yangtze and Yellow Rivers, China

“…In this study, a common increase in the time-lag between summer precipitation and the following cold-season monthly discharge for the two periods (before 1985 and after 1985) was also detected (Figure 3), which implied that permafrost degradation may affect the redistribution of summer precipitation towards the following winter discharge via increasing the soil storage capacity and delaying the release of water into streams. For the source regions of the Yangtze and Yellow rivers, a decline in summer precipitation is noticeable in the majority of the stations as shown in Figure 4, which is consistent with other researchers [35]. In order to validate the above results (as shown in Figures 3 and 4), we turn to precipitation (July-September), DEM (SRTM3), latitude, and longitude data of 36 meteorological stations in and around the source regions ( Figure S1).…”

“…According to the statistics in the late 1980s [49], there are about 5300 lakes in the source region of Yellow River, and about 80% of them are located in catchment 9, including the two largest fresh water lakes in the source regions (Eling and Zhaling). Summer precipitation in this catchment mainly contributes to groundwater instead of direct surface water due to the widespread lakes and wetlands [35,49], which makes an important supply for the following winter discharge. A positive correlation between the average recession coefficient and permafrost coverage, the average ratio of Q max /Q min and permafrost coverage was also detected, which implied that permafrost degradation could allow more water storage to support winter discharge and smooth out the seasonal distribution of discharge at catchment scale to some extent.…”

“…A deeper active layer allows additional water storage and pathways for transferring water, resulting in the dependence of winter discharge on the timing and amount of summer precipitation [50]. In the source region of Yellow River, the correlation analysis between monthly discharge and precipitation suggested that the monthly discharge was often the result of a combined effect of the precipitation in the current and previous months [35]. At the boundary of continuous and discontinuous permafrost of the lower Yenisei River, a common increase in the time-lag between precipitation events and stream discharge was detected between 1970s and 1980s [50].…”

“…With the geographical boundary of about 95°51′-103°28′ E and 32°12′-36°06′ N, the source region of Yellow River covers an area of 12.2 × 10 4 km 2 , and yields a mean annual runoff of 168 mm (about 35% of total runoff of Yellow River) [35]. Located between 90°30′-97°20′ E and 32°30′-35°40′ N, the source region of the Yangtze River is generally defined as the upstream catchment above the Zhimenda Discharge Station (Figure 1, Table 1), and covers an area of 13.7 × 10 4 km 2 .…”

“…This meteorological dataset has been subject to strict quality control by the National Meteorological Information Center, and has been used widely as the official meteorological data [35,[41][42][43]. In this study, the monthly precipitation data (July-September) at 11 meteorological stations were complete, and the average precipitation for each catchment was obtained by taking the average precipitation value for all stations within the specific catchment or nearby the discharge stations [35,[41][42][43].…”