Attribution Analysis of Seasonal Runoff in the Source Region of the Yellow River Using Seasonal Budyko Hypothesis

Previous studies mainly focused on quantifying the contribution rate of different factors on annual runoff variation in the source region of the Yellow River (SRYR), while there are few studies on the seasonal runoff variation. In this study, the monthly water storage and monthly actual evaporation of SRYR were calculated by the monthly ABCD model, and then a seasonal Budyko frame was constructed. Finally, the contribution rate of climatic and anthropic factors on the seasonal runoff variation in Tangnaihai hydrological station were quantitatively calculated. It turned out that: (1) The changing point of runoff data at Tangnaihai hydrological station is 1989. (2) The ABCD monthly hydrological model could well simulate the monthly runoff variation of Tangnaihai hydrological station. (3) Anthropic factors play a major role in runoff change in spring, summer, and winter, while climatic factors play a major role in runoff change in autumn.

Relative Contribution of the Xiaolangdi Dam to Runoff Changes in the Lower Yellow River

Human activities are increasingly recognized as having a critical influence on hydrological processes under the warming of the climate, particularly for dam-regulated rivers. To ensure the sustainable management of water resources, it is important to evaluate how dam construction may affect surface runoff. In this study, using Mann–Kendall tests, the double mass curve method, and the Budyko-based elasticity method, the effects of climate change and human activities on annual and seasonal runoff were quantified for the Yellow River basin from 1961–2018; additionally, effects on runoff were assessed after the construction of the Xiaolangdi Dam (XLD, started operation in 2001) on the Yellow River. Both annual and seasonal runoff decreased over time (p < 0.01), due to the combined effects of climate change and human activities. Abrupt changes in annual, flood season, and non-flood season runoff occurred in 1986, 1989, and 1986, respectively. However, no abrupt changes were seen after the construction of the XLD. Human activities accounted for much of the reduction in runoff, approximately 75–72% annually, 81–86% for the flood season, and 86–90% for the non-flood season. Climate change approximately accounted for the remainder: 18–25% (annually), 14–19% (flood season), and 10–14% (non-flood season). The XLD construction mitigated runoff increases induced by heightened precipitation and reduced potential evapotranspiration during the post-dam period; the XLD accounted for approximately 52% of the runoff reduction both annually and in the non-flood season, and accounted for approximately −32% of the runoff increase in the flood season. In conclusion, this study provides a basic understanding of how dam construction contributes to runoff changes in the context of climate change; this information will be beneficial for the sustainable management of water resources in regulated rivers.

The relevance of the past unsustainable increase of glacier runoff for large-scale basins in different climatological settings

&lt;p&gt;Depending on the seasonality of temperature and precipitation, mountain glaciers seasonally store and release large amounts of freshwater. Therefore, glaciers have a strong influence on water availability in many regions of the world. In an ongoing global climate change, glaciers have an additional impact on water availability, as the net amount of stored ice changes in an unsustainable way. This results in glaciers not only altering the seasonal runoff, but also adding a net input into the drainage system.&lt;br&gt;To better understand the interplay between seasonal and long-term storage changes, we suggest to split the monthly seasonal mass balance into a sustainable fraction, which is derived by balancing solid precipitation by ablation proportional to positive temperatures, and an unsustainable fraction, which causes long-term glacier mass change.&lt;/p&gt;&lt;p&gt;Similarly, we consider the effect of glacier area changes, allowing us to separate seasonal runoff into components attributable to (unsustainable) area change, (unsustainable) mass change, or the (sustainable) seasonal runoff from the glacier.&lt;/p&gt;&lt;p&gt;By applying the concept to a reconstruction of global glacier change, we illustrate how the glacier input into river basins in different climatological settings has been affected by the glacier mass loss during the 20th century.&amp;#160;&lt;/p&gt;

Future changes in snow and its influence on seasonal runoff and low flows in Czechia

&lt;p&gt;Mountains are often called as &amp;#8220;water towers&amp;#8221; because they substantially affect hydrology of downstream areas. However, snow storages are decreasing and snow melts earlier mainly due to air temperature increase. These changes largely affect seasonal runoff distribution, including summer low flows and thus influence the water availability. Therefore, it is important to investigate the future change in relation between snow and summer low flows, specifically to assess a wide range of hydrological responses to different climate predictions. Therefore, the main objectives of this study were 1) to simulate the future changes in snow storages for a large set of mountain catchments representing different elevations and to 2) analyse how the changes in snow storages will affect streamflow seasonality and low flows in the future reflecting a wide range of climate predictions. The predictions of the future climate from EURO-CORDEX experiment for 59 mountain catchments in Czechia were considered. These data were further used to drive a bucket-type catchment model, HBV-light, to simulate individual components of the rainfall-runoff process for the reference period and three future periods.&lt;/p&gt;&lt;p&gt;Future simulations showed a dramatic decrease in snow-related variables for all catchments at all elevations. For example, annual maximum SWE decreased by 30%-70% until the end of the 21&lt;sup&gt;st&lt;/sup&gt; century compared to the current climate. Additionally, the snow will melt on average by 3-4 weeks earlier in the future. The results also showed the large variability between individual climate chains and indicated that the increase in air temperature causing the decrease in snowfall might be partly compensated by the increase in winter precipitation. Expected changes in snowpack will cause by a month earlier period with highest streamflow during melting season in addition to lower spring runoff volume due to lower snowmelt inputs. The future climate scenarios leading to overall dry conditions in summer are associated with both lowest summer precipitation and seasonal snowpack. The expected lower snow storages might therefore contribute to more extreme low flow periods. The results also showed considerably smaller changes for the RCP 2.6 scenario compared to the RCP 4.5 and RCP 8.5 both in terms snow storages and seasonal runoff. The results are therefore important for mitigation and adaptation strategy related to climate change impacts in mountain regions.&lt;/p&gt;

ANALYSIS OF LONG-TERM VARIABILITY OF RIVER RUNOFF IN THE URAL RIVER BASIN

The hydrological zoning of the Ural River basin has been clarified in terms of synchronism and in-phase fluctuations in annual runoff. 5 hydrological regions have been identified. For 9 hydrological posts and 5 meteorological stations located in different parts of the basin, a detailed statistical analysis of long-term data was carried out. A single 1975 year of the beginning of hydro-meteorological changes in the basin was revealed. For each hydrological region, statistically significant changes in the annual and seasonal runoff were revealed. The assessment of the factors of change in runoff was carried out. Areas with a predominant influence on the change in runoff or anthropogenic load on water resources or climatic changes are identified.

Spatial and seasonal variations of hydrological responses to climate and land-use changes in a highly urbanized basin of Southeastern China

Climate and land-use changes are two major factors that significantly affect the watershed hydrology cycle. It is essential for regional water resource management to quantitatively assess the respective hydrological impact of these two factors. In this study, the Soil and Water Assessment Tool (SWAT) was constructed to quantify the contributions of climate and land-use changes to runoff at the annual and seasonal time scales in the Qinhuai River basin (QRB), where significant urbanization occurred from 1986 to 2015. Moreover, based on the partial least squares regression, the specific impact of individual land-use change on major hydrological components was evaluated at the sub-basin scale. The results showed that: (1) the predominant patterns of land-use change in the QRB included the transformations from paddy fields to urban areas and dry lands, forest to dry lands and dry lands to urban areas; (2) the flood seasonal precipitation series and all air temperature series had significant increasing trends over 1986–2015, and annual and seasonal runoff series had significant increasing trends and had an abrupt change point in 2001; (3) the average annual, flood seasonal, and non-flood seasonal runoff increased 238.5, 130.2 and 108.3 mm, of which land-use change was responsible for 77.6, 55.1, and 104.8% of the increases, respectively, while climate change was responsible for 22.4, 44.9, and −4.8%, respectively and (4) the hydrological response to land-use change showed an obvious decrease in actual evapotranspiration (ET) and significant increases in surface runoff and baseflow. The decrease of ET and increase of baseflow could be attributed to the conversion patterns from paddy fields and forest to dry lands, while the conversions from paddy fields and dry lands to urban areas caused a remarkable increase in surface runoff in the QRB. The study demonstrated that these practicable approaches were beneficial for the more unbiased views of the hydrological responses to climate change and land-use change in the highly urbanized basin, which were also critical for the sustainable development of regional water resource and future land-use planning.

INFLUENCE OF LARGE-SCALE ATMOSPHERIC PROCESSES ON SEASONAL RUNOFF OF LARGE SIBERIAN RIVERS

Based on daily runoff volumes of four large Siberian rivers (the Ob, Yenisei, Lena, and Kolyma) for 1936-2018, the regime and changes in the total annual and seasonal runoff are analyzed. High synchronous and asynchronous correlations between monthly river runoff and atmospheric circulation indices of hemispheric and regional scales are revealed. In recent decades, the total annual runoff and its variations have increased (the rate of increase is most pronounced for the Kolyma River). A change in water content within a year is heterogeneous: weak positive trends are characteristic of the spring flood runoff and the summer-autumn period, and a significant increase occurred in the winter months. High correlations with a 1-8-month shift made it possible to identify the most informative regions, the atmospheric circulation over which makes a certain contribution to the variance of river runoff.