Search

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.

The relationships between soil respiration and environmental factors determine the effect of warming soil on the carbon balance in temperate forest ecosystems and on changes in atmospheric [CO.sub.2] concentrations. Here, we used 3 years of data regarding soil respiration rates ([R.sub.s]), soil temperature ([T.sub.s]), and soil volumetric water content (q) from a 50-year-old mature cedar (Platycladus orientalis L.) plantation at Jiufeng Mountain, Beijing, China, to demonstrate the seasonal and interannual variation of [R.sub.s] dependence on [T.sub.s] and q throughout the period 2008-2010. We used the exponential model to calculate the temperature sensitivity indicator [Q.sub.10] and we examined the annual and seasonal patterns of [R.sub.s] and [Q.sub.10]. The [R.sub.s] correlated with [T.sub.s] annually (p < 0.05). The [R.sub.s]-[T.sub.s] exponential relationship was significant in the autumn and winter (p < 0.05), while the combined [T.SUB.s] and q relationships with [R.sub.s] were significant in the spring and summer (p < 0.001). The spring [R.sub.s] anomalies caused by drought appeared to have carryover effects that translated to [R.sub.s] anomalies in the following summer. Finally, the summer [R.sub.s], which was influenced by the coincident precipitation and q anomalies, determined the magnitude of the annual total amount of soil respiration. This result has implications for how abiotic factors may drive shifts in seasonal patterns of soil respiration under a changing climate. Resume: Les relations entre la respiration du sol et les facteurs environnementaux determinent l'effet du rechauffement du sol sur le bilan du carbone dans les ecosystemes forestiers temperes et sur les modifications de la concentration de [CO.sub.2] atmospherique. Nous avons utilise trois annees de donnees portant sur le taux de respiration [(R.sub.s]), la temperature [(T.sub.s]) et l'humidite volumique du sol (q) provenant d'une plantation mature de thuya d'Orient (Platycladus orientalis L.) agee de 50 ans et situee au mont Jiufeng, a Beijing en Chine pour demontrer les variations saisonniere et interannuelle de la dependance de [R.sub.s] a [T.sub.s] et q au cours de la periode 2008-2010. Nous avons utilise le modele exponentiel pour calculer l'indicateur de sensibilite a la temperature [Q.sub.10] et nous avons etudie les patrons saisonniers et annuels de [R.sub.s] et [Q.sub.10]. Les valeurs de [R.sub.s] et [T.sub.s] etaient correlees sur une base annuelle (p < 0,05). La relation exponentielle entre [R.sub.s] et [T.sub.s] etait significative a l'automne et en hiver (p < 0,05), tandis que les relations combinees de [T.sub.s] et q avec [R.sub.s] etaient significatives au printemps et en ete (p < 0,001). Les anomalies de [R.sub.s] au printemps causees par la secheresse semblaient avoir des effets remanents qui se traduisaient par des anomalies de [R.sub.s] l'ete suivant. Finalement, durant l'ete [R.sub.s] etait influence par la precipitation coincidente et les anomalies de q determinaient l'ampleur de la quantite annuelle totale de respiration du sol. Ce resultat a des consequences sur la fa?on dont les facteurs abiotiques peuvent determiner les changements dans les patrons saisonniers de respiration du sol dans le contexte des changements climatiques. [Traduit par la Redaction], Introduction It has been widely documented that ongoing climate change exerts a great influence on the seasons and phenology (Cleland et al. 2007). The impact of these seasonal and phenological [...]

Differences in the net soil loss and apportionment of wind from water erosion on hillslopes were analyzed and evaluated quantitatively through resident 137Cs deficit approach across those Northern Loess Hilly Areas in China. The long-term averaged rates of erosion at hilltops, north- and south-facing slopes can be roughly estimated, which are about 64, 25 and 51 t ha−1 a−1, respectively. For north-facing slope, the erosion rate is about twice higher than that of south-facing one, indicating that wind erosion takes up about 51% of the total erosion amount, and greatly affect erosion rate distribution on the north-facing slopes in this area. [ABSTRACT FROM AUTHOR]