Trend and Attribution Analysis of Runoff Changes in the Weihe River Basin in the Last 50 Years

In recent years, the Weihe River basin has experienced dramatic changes and a sharp decrease in runoff, which has constrained the sustainable development of the local society, economy, and ecology. Quantitative attribution analysis of runoff changes in the Weihe River basin can help to illustrate reasons for dramatic runoff changes and to understand its complex hydrological response. In this paper, the trends of hydrological elements in the Weihe River basin from 1970 to 2019 were systematically analyzed using the M–K analysis method, and the effects of meteorological elements and underlying surface changes on runoff were quantitatively analyzed using the Budyko theoretical framework. The results show that potential evapotranspiration and precipitation in the Weihe River basin have no significant change in 1970–2019; runoff depth has an abrupt change around 1990 and then decrease significantly. The study period is divided into the base period (1970–1989), PΙ (1990–2009), and PII (2010–2019). Compared with the base period, the elasticity coefficients (absolute values) of each element show an increasing trend in PΙ and PII. The sensitivity of runoff to these coefficients is increasing. The sensitivity of the precipitation is the highest (2.72~3.17), followed by that of the underlying surface parameter (−2.01~−2.35); the sensitivity of the potential evapotranspiration is the weakest (−1.72~−2.17). In the PΙ period, the runoff depth decreased significantly due to the combination effects of precipitation and underlying surface with the values of 6.18 mm and 13.92 mm, respectively. In the PII period, rainfall turned to an increasing trend, contributing to the increase in runoff by 11.80 mm; the further increase in underlying surface parameters was the main reason for the decrease in runoff by 22.19 mm. The significant increase in runoff by 8.54 mm because of the increased rainfall, compared with the PΙ periods. Overall, the increasing underlying surface parameter makes the largest contribution to the runoff changes while the precipitation change is also an important factor.

Analyzing the Impact of Climate Change and Human Activities on Surface Runoff in the Changbai Mountain Area, Northeast China

Climate change and human activities are two important factors affecting surface runoff. In water resource management and planning, it is generally important to separate the contribution of these factors when assessing runoff changes. The Changbai Mountain area is rich in water resources and is an important hydropower energy base for Northeast China. This study used Sen’s slope estimator to explore trends in runoff precipitation and evapotranspiration from 1960 to 2016, and the results showed a downward trend in runoff and an upward trend in precipitation and evaporation in most areas. The mutation point of the annual time series for the observed runoff was estimated, and the time series was divided into the base period (1960–1975) and impact period (1976–2016). Based on the Budyko framework, we performed attribution analysis of the runoff changes, and analyzed the difference between the mountainous region and the whole basin. We determined that the impacts of climate change and human activities, on average, accounted for decreases in the runoff by 60.15% and 39.85%, respectively, for the Second Songhua River Basin; 73.74% and 26.26%, respectively, for the Tumen River Basin; 84.76% and 15.24%, respectively, for the Yalu River Basin; human activities were the main causes of runoff changes in the Changbai Mountain area; climate change was the main cause of runoff changes in mountainous regions. The results of this study show that the reasons for the change in runoff in mountainous regions and the whole basin in the same area are different, which has some illuminating significance for water resources management of different elevation areas.

Historical and future runoff changes in the Yangtze River Basin from CMIP6 models constrained by a weighting strategy

Based on the ERA5-Land datasets from 1981-2020, a decadal oscillation has been found in the variation of summer runoff in the middle and lower reaches of the Yangtze River Basin (MLYRB). The oscillation suggests that the MLYRB will experience increased runoff in the next few decades after 2020 which saw a record high runoff in the MLYRB. The decadal changes in summer runoff over the MLYRB under various climate change scenarios are then analyzed with direct runoff outputs from 28 general circulation models (GCMs) participating in the sixth phase of Coupled Model Intercomparison Project (CMIP6). Given that the equal-weighted multi-model ensemble mean could not well represent the historical runoff changes in MLYRB, in this paper we introduced a model weighting scheme that considers both the model skill and independence. It turns out that this scheme has well constrain the models to represent the observed decadal changes of summer runoff. The weighted mean projections suggest that the summer runoff in the MLYRB during 2015-2100 under all warming scenarios will be higher than the present-day; and 2021-2040 is likely to be a period with significantly increased summer runoff. Results of the present study are of great implication for flood control and effective water resources management over the MLYRB in the future, and the weighting approach used in this paper could be applied to a wide range of projections at both regional and global scales.

Temporal and Spatial Changes of Runoff Regime in the Yellow River Basin from 1956 to 2017

The Yellow River is one of the major rivers with severe runoff declines in China, but there are significant differences in runoff changes in the upper and lower reaches of the basin and among different tributaries. However, the characteristic of runoff change and its spatial heterogeneity are not well understood in the whole basin. In this paper, 48 hydrological stations located in the mainstream and major tributaries were selected, and the meteorological and runoff data from 1956 to 2017 were collected. The multi-year and intra-year changes in runoff were analyzed, and then the attribution of climate change and human activity to runoff change was quantified by the climate elasticity coefficients. The results showed that: (1) in the past 60 years, the runoff of the Yellow River showed a serious decrease trend of −8.25 mm/10a. Moreover, most tributaries decreased significantly in runoff with a rate of −1.42 mm/10a to −28.99 mm/10a; (2) for the whole basin, the contribution of climate change and human activity to runoff changes was 13% and 87%, respectively. Moreover, the contribution of the two factors varied considerably in different tributaries. Finally, focusing on different runoff regime and socioeconomic characteristics, this study provided corresponding water resources adaptive management suggestions.

Attribution Analysis of Runoff Variation in Kuye River Basin Based on Three Budyko Methods

The Loess Plateau is the main soil erosion area within the Yellow River Basin. Quantifying the contribution rate of climate change and human activities to runoff change can provide support for water resources management in the Yellow River Basin. Kuye River Basin is located in the Loess Plateau. As a first-class tributary of the Yellow River, it was selected as the study area. Runoff from the Kuye River Basin has decreased significantly since the 1990s owing to climate change and anthropogenic coal mining. The main objective of this study was to quantify the contribution and sensitivity of climate change and anthropogenic activities to runoff changes using three popular Budyko and elasticity coefficient methods, as well as to compare the similarities and differences among the three methods. The results show that: (1) Through four mutation point test methods, the change point of runoff in the study period of Kuye River Basin is 1997. (2) The elasticity coefficients calculated by the three Budyko methods showed that during the study period, the runoff was more sensitive to changes in precipitation, followed by the catchment surface characteristic parameters and the potential evapotranspiration. (3) All three Budyko methods can yield reasonable contributions of climate change and human activity to runoff changes. The three methods together indicate that the influence of the catchment surface characteristic parameters is the most important factor for the runoff variation in the Kuye River.

Dynamics of the Natural Afforestation Process of a Small Lowland Catchment and Its Possible Impact on Runoff Changes

Changes in land use have an impact on changes in renewable water resources. Land use especially in the context of urbanization has been and continues to be widely studied. The role of the forests in ecosystems is well known but there is not much research investigating the impact of natural afforestation on water resources. This paper shows the results of the quantitative changes in the use of the lowland catchment in the last 50 years on the example of the Zagożdżonka river located in central Poland. The results show that the impact of climatic factors on the reduction of water resources in the Zagożdżonka catchment is compounded by socio-economic changes in agriculture, and the positive role of forest areas in the catchment depends on the water demand of the stand. The interactions between forest ecosystems and water retention are strong and, depending on the habitat conditions, they may reduce ground runoff and deepen the water deficit in the catchment area in dry periods.

Quantifying the Relative Contribution of the Climate Change and Human Activity on Runoff in the Choshui River Alluvial Fan, Taiwan

Climate factors and human activities are the leading causes of changes in the hydrological cycle. In addition to being an important part of the hydrological cycle, runoff is also an important indicator for assessing the amount of available water. Therefore, it is necessary to explore the reasons that have caused changes in runoff. In this study, the causes of runoff changes in the alluvial fan of the Choshui River from 1980–2018 are explored. Two simple methods, including a decomposition method based on the Budyko structure and a method based on climate elasticity, for which the necessary data are easy to obtain, are used to quantify the impact of climate factors and human activities on runoff changes. The results show that the runoff in the long term shows a significant transition point in 2003, where climate factors have contributed more than 90% of the change, while the influence of human activities on the changes in runoff appears to be relatively small. Moreover, the Budyko method and the Normalized Difference Vegetation Index (NDVI) show that the vegetation cover has decreased. In addition to providing a simple method to assess the causes of changes in runoff, this study also analyzes the causes of changes in the runoff of the alluvial fan of the Choshui River to provide a reference for water resource policy and land use management.

Evaluation of the Impacts of Climate Change on Runoff in Dadu River Basin Based on CORDEX Regional Climate Model

Owing to the rich water resources, the Dadu River basin is an important hydroelectric resources development area in Sichuan Province over China. The climate change will have a great impact on the runoff change in the Dadu River Basin. The prediction of the future runoff in the Dadu River Basin can effectively improve the utilization rate of water resources, and provide a reference for hydropower dispatching. At first, to reduce the uncertainties from climate model, this paper used Stepwise Clustering Analysis to calibrate and validate the CORDEX regional climate model ensemble data from 1970 to 2005 and projected the climate change trend of Dadu River basin from 2035 to 2065. Then the Dadu River watershed scales of SWAT model was established, using the SWAT-CUP for calibration and verification. Finally, the corrected future climate data are used to drive the SWAT model to realize the future runoff forecast in the Dadu River Basin. The results show that under the scenario of RCP4.5 and RCP8.5, the variation range of rainfall is small, and the maximum and minimum temperatures show an overall increasing trend. The maximum (minimum) temperature will increase about 0.6℃ (1.0℃) under the scenarios of RCP4.5 and 0.9℃ (1.4℃) under the scenario of RCP8.5. Compared with the baseline period, the future (2035-2065) annual runoff under RCP4.5 and RCP8.5 scenarios will increase by about 8.6% and 8.2%, respectively. Under the future climate change, the inter-annual runoff in the Dadu River Basin will change greatly, and the trend of runoff fluctuation is not consistent before and after 2050. Before 2050, runoff changes are small, however, after 2050, runoff changes under the two scenarios will increase by about 12%. On the one hand, this trend may be due to the impact of iceberg melting on runoff caused by temperature changes around 2050, on the other hand, it may be due to the combined effect of local plant evapotranspiration and ecological regulation.