Impacts of Climatic Variation and Human Activity on Runoff in Western China

Hydrological cycle is sensitively affected by climatic variation and human activity. Taking the upper- and middle-stream of the Weihe River in western China as an example, using multiple meteorological and hydrological elements, as well as land-use/land-cover change (LUCC) data, we constructed a sensitivity model of runoff to climatic elements and human activities based on the hydro-thermal coupling equilibrium equation, while a cumulative slope was used to establish a comprehensive estimation model for the contributions of climatic variation and human activities to the changes of runoff. The results showed that the above function model established could be well applied to quantitatively study the elasticity of runoff’s response to climatic variation and human activities. It was found that the annual average precipitation, evaporation, wind velocity, sunshine hours, relative humidity and runoff showed decreasing trends and that temperature increased. While in the hydrological cycle, precipitation and relative humidity had a non-linear positive driving effect on runoff, while temperature, evaporation, sunshine hours, wind velocity, and land-use/land-cover change (LUCC) have non-linearly negatively driven the variation of runoff. Moreover, runoff has a strong sensitive response to precipitation, evaporation and LUCC. In areas with strong human activities, the sensitivity of runoff to climatic change was decreasing, and runoff has a greater elastic response to underlying surface parameters. In addition, the analysis showed that the abrupt years of climate and runoff changes in the Weihe River Basin were 1970, 1985 and 1993. Before 1985, the contribution rate of climatic variation to runoff was 68.3%, being greater than that of human activities to runoff, and then the contribution rates of human activities to runoff reached 75.1%. The impact of natural climate on runoff was weakened, and the effect of human activities on runoff reduction increased. Under 30 hypothetical climatic scenarios, the evaluation of runoff in the future showed that the runoff in the Weihe River Basin will be greatly reduced, and the reduction will be more significant during the flood season. Comparing the geographically fragile environments and intense human activities, it was believed that climatic variation had a dramatic effect on driving the water cycle of precipitation and evaporation and affected regional water balance and water distribution, while human activities had driven the hydrological processes of the underlying surface, thus becoming the main factors in the reduction of runoff. This study provided scientific tools for regional climate change and water resources assessment.

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.

Comprehensive evaluation of the water environment carrying capacity of a river basin: a case study of the Weihe River Basin in China

By combining the analytic hierarchy process (AHP) and system dynamics (SD) models, a compound index system is established for simulating and evaluating the water environment carrying capacity (WECC) of the Weihe River Basin. The development tendencies of the population, economy, water resource demand and supply, water environment, water pollution, and water management were obtained from 2005 to 2040 by applying the five scenarios designed in this study. The results indicate that the comprehensive solution scenario was the optimal scenario, and the WECC would upgrade from a ‘general’ status to a ‘good’ status. Moreover, the blind pursuit of rapid economic growth is inadvisable, and it will compromise the sustainability of the river basin area. The river basin area should divert local development modes toward increased sustainability, emphasizing the coordinated development of society, the economy, and the environment.

Sustainable Development Evaluation and Its Obstacle Factors of the Weihe River Basin in Shaanxi Province, China

The contradiction between economic growth, social development, and water environment deterioration represent significant challenges for river basin sustainable development. By constructing an indicator system of river basin sustainable development, the entropy method is adopted to conduct a quantitative evaluation of the cities sustainable development level for the Weihe River Basin in Shaanxi Province from 2009 to 2018, and the standard deviational ellipse is used to analyze the evolution of spatial distribution pattern of sustainable development in the study area. Furthermore, the obstacle degree model is applied to analyze the main obstacle factors restricting the improvement of river basin sustainable development. The results show that the sustainable development level of the Weihe River basin in Shaanxi Province improved slowly during the study period and significant regional differences among cities. This study provides a novel approach for future evaluation on sustainable development of the Weihe River basin and even the arid region in Northwest China, to achieve a win-win situation between economic and social development and ecological environment protection.

Spatial-Temporal Change of Actual Evapotranspiration and the Causes Based on the Advection–Aridity Model in the Weihe River Basin, China

Evapotranspiration is a key process between the atmospheric hydrological cycle and the energy cycle, which has a great significance in understanding climate change and the rational use of water resources, especially for the Weihe River basin (WRB) (a basin in China experiencing a shortage of water resources). We investigated the spatial-temporal change of actual evapotranspiration (ETa) based on the daily meteorological variables of 22 meteorological stations and the annual streamflow of three hydrological stations from 1970 to 2018 in the WRB. The contributions of key meteorological variables to ETa changes and the sensitivity coefficient are also quantified. The temporal trends of ETa showed an increasing trend from 1970 to 2018, and the spatial distribution of ETa increased from northwest to southeast in the WRB. Increasing trends were detected in the multi-year average, spring, and winter, but only a few stations passed the significance test. Summer and autumn showed a decreasing trend, but this trend was not significant. Solar radiation is the most sensitive meteorological variable, followed by vapor pressure, wind speed, and mean temperature. Vapor pressure contributes the most to ETa changes, followed by solar radiation. In general, vapor pressure (relative humidity) is the dominant meteorological factor affecting ETa in the WRB. In addition to meteorological factors, the ETa is also affected by combined and complicated factors caused by precipitation and human activities. As an important part of the hydrological cycle, ETa has important research significance for water resources management, economy, agriculture, and ecology and results of this study may be helpful to further clarify the climate change and human activities impacts on the basin hydrological cycle.