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The variations in the reference evapotranspiration (ET0) are closely related to meteorological factors. The purpose of this study is to explore the relationships between the meteorological factors and the ET0. Based on meteorological data from 26 meteorological stations in the Yiluo River Basin (YLRB) and its surrounding areas from 1958 to 2020, in this study, the temporal and spatial variations and driving factors of the ET0 in the YLRB are investigated. The results are as follows. Spatially, the annual ET0 decreases from the northeast to the southwest in the YLRB. Temporally, the annual ET0 exhibits a fluctuating decreasing trend rather than a monotonic decreasing trend during the entire period. The trend of the ET0 contains two mutation points, in 1972 and 1994. Thus, the research period can be divided into three periods. It is concluded that the variations in the ET0 are the most sensitive to the relative humidity, but the driving factor that contributes the most to the variations in the ET0 is the wind speed. The driving factors are closely related to the rates of relative change of the meteorological factors.

The vegetation and ecosystem in the source region of the Yangtze River and the Yellow River (SRYY) are fragile. Affected by climate change, extreme droughts are frequent and permafrost degradation is serious in this area. It is very important to quantify the drought–vegetation interaction in this area under the influence of climate–permafrost coupling. In this study, based on the saturated vapor pressure deficit (VPD) and soil moisture (SM) that characterize atmospheric and soil drought, as well as the Normalized Differential Vegetation Index (NDVI) and solar-induced fluorescence (SIF) that characterize vegetation greenness and function, the evolution of regional vegetation productivity and drought were systematically identified. On this basis, the technical advantages of the causal discovery algorithm Peter–Clark Momentary Conditional Independence (PCMCI) were applied to distinguish the response of vegetation to VPD and SM. Furthermore, this study delves into the response mechanisms of NDVI and SIF to atmospheric and soil drought, considering different vegetation types and permafrost degradation areas. The findings indicated that low SM and high VPD were the limiting factors for vegetation growth. The positive and negative causal effects of VPD on NDVI accounted for 47.88% and 52.12% of the total area, respectively. Shrubs were the most sensitive to SM, and the response speed of grassland to SM was faster than that of forest land. The impact of SM on vegetation in the SRYY was stronger than that of VPD, and the effect in the frozen soil degradation area was more obvious. The average causal effects of NDVI and SIF on SM in the frozen soil degradation area were 0.21 and 0.41, respectively, which were twice as high as those in the whole area, and SM dominated NDVI (SIF) changes in 62.87% (76.60%) of the frozen soil degradation area. The research results can provide important scientific basis and theoretical support for the scientific assessment and adaptation of permafrost, vegetation, and climate change in the source area and provide reference for ecological protection in permafrost regions. [ABSTRACT FROM AUTHOR]

Forest-sediment relationship is a hot and important issue in Ecohydrology studies. China has implemented many large-scale reforestation programmes in the last decades to address the growing soil erosion and desertification. In this study, we made statistical and graphic analyses on the long-term hydrological data of the 39 watersheds in the rocky mountain area of the North China, and then we were able to analyze the effect of forest on sediment yield. Our results show that the effect is weak in the lees-precipitation regions (when MAP < 500 mm). And in the more-precipitation regions(when MAP >500 mm), the impact of forest on reducing sediment yield is different with the varied forest coverage (f), the relationship between the sediment yield and forest coverage show a quadratic polynomial.

Under the influence of global climate change and intense human activities, the world is facing water issue and crisis in varying extent. It is considered to be strategically important to study the relation between land-use change and water environment of the only surface water source of Beijing (a city facing severe water shortage). In this article, the quantitative relation between land-use structure and water environment quality of Chaobai River Basin was discussed. GIS spatial analysis function and Markov transition matrix were used to calculate the composition and changes of land use. Meanwhile the correlation between land-use structure and water quality index was analysed by means of correlation analysis, redundancy analysis (RDA) and other mathematical statistics. The land-use impact on water quality was also investigated. The result indicated that the main means of land use in Chaobai River Basin were forest land, farmland, construction land and waters. The major shifted land during 1995 and 2005 was farmland while during 2005 and 2015 was forest land. The indexes of water quality were deeply influenced by the means of land use, of which the deterioration of water quality was significantly affected by construction land. Water quality could be drastically improved by the spatial distribution of forest land, which was especially sensitive to ammonia and potassium permanganate index. The correlation between farmland area variation and water quality was not remarkable. RDA proved the effect of the land-use forms on water environment of Chao River and Bai River in different years. The results could be used to provide a scientific basis for the land optimization and water pollution control of Chaobai River Basin, as well as guide the policy decision of space development and water environment protection of Chaobai River Basin. [ABSTRACT FROM AUTHOR]