Search Results (3)

Patterns of stable isotopes of water (¹⁸O and ²H) in precipitation have been used as tracers for analyzing environmental processes which can be changed by factors such as the topography or meteorological variables. In this study, we investigated the isotopic data in precipitation for one year in the low mountain range of North Hesse, Germany, and analyzed mainly for altitude, rainfall amount, and air temperature effects on a regional scale. The results indicate that the isotopic composition expressed an altitude effect with a gradient of −0.14‰/100 m for δ¹⁸O, −0.28‰/100 m for δ²H and 0.83‰/100 m for Deuterium excess. Patterns of enrichment during warmer months and depletion during colder months were detected. Seasonal correlations were not consistent because the altitude effect was superimposed by other processes such as amount and temperature effects, vapor origins, orographic rainout processes, moisture recycling, and sub-cloud secondary evaporation. Precipitation was mostly affected by secondary evaporation and mixing processes during the summer while depleted moisture-bearing fronts and condensation were more responsible for isotope depletion during winter. In autumn and spring, the amount effect was more prominent in combination with moisture recycling, and large-scale convective processes. The altitude effect was also detected in surface water. The investigated elevation transect with multiple stations provided unique insights into hydrological and climatic processes of North Hesse on a regional scale. The spatial heterogeneity and mixing of different processes suggest that multiple rainfall stations are required when rainfall isotopes serve as forcing data for hydrological applications such as transit time assessments in complex terrains. Full article

Fractionation of stable isotopes in precipitation runs through the water cycle, and deuterium excess is a second-order parameter linking water-stable oxygen and hydrogen isotopes. It is strongly influenced by under-cloud evaporation in unsaturated air, especially in arid climates. Based on the improved Stewart model, this study used 670 precipitation stable isotope data and measured meteorological element data from 11 sampling points from January 2018 to September 2019 to verify the existence of sub-cloud secondary evaporation in the Shiyang river basin and quantitatively calculate the intensity of sub-cloud secondary evaporation and its influence on precipitation stable isotopes. The study used the vapor flux and the improved Lagrangian model to track the moisture source of precipitation and analyze the influence of the moisture source of different paths on the stable isotopes of precipitation. Therefore, this study is helpful to understand the evapotranspiration loss mechanism and recharge mechanism of moisture in the watershed. The results showed that there is sub-cloud secondary evaporation in the Shiyang River Basin, and from the seasonal scale, the sub-cloud secondary evaporation is stronger in spring and summer, but weaker in autumn and winter, which makes heavy isotopes enriched in spring and summer and depleted in autumn and winter. From the perspective of spatial distribution, the sub-cloud secondary evaporation is stronger in the midstream and downstream of the Shiyang river, resulting in more enrichment of heavy isotopes. In the vertical direction, the sub-cloud secondary evaporation at 850–700 hPa is the strongest, which enriches the heavy isotope in this layer and reduces the deuterium excess. In addition, the main moisture source of precipitation in the Shiyang River Basin is the westerly air mass, and the mid and high-latitude land sources contribute more moisture to the precipitation. However, the supply of the sea source is very limited, which makes the deuterium excess of precipitation higher and does not show regional consistency and seasonality well. Full article

The stable isotopes (²H, ¹⁸O) of precipitation change due to the sub-cloud secondary evaporation during raindrop fall. The study of the temporal and spatial variation of sub-cloud secondary evaporation and its causes by using hydrogen and oxygen stable isotopes is of great significance to the study of the regional water cycle process. Based on the hourly meteorological data of 648 meteorological stations in 17 provinces (cities) of the Yangtze River Basin from March 2018 to February 2019, we analyzed the temporal and spatial characteristics of precipitation excess deuterium variation (Δd) in the region, based on the improved Stewart model. We discuss the various influence factors under different magnitude Δd value change and the impact factor of each partition sub-cloud secondary evaporation influence of the difference. The results show the following: (1) In terms of hourly variation, the sub-cloud secondary evaporation in the daytime is stronger than that at night. In terms of monthly variation, different regions of the study area have different characteristics; that is, the effect of sub-cloud secondary evaporation is more significant in summer and autumn in the northern subtropics and south temperate zones, and in spring and summer in the mid-subtropics and plateau climate zones. (2) There were significant spatial differences in the study area in different seasons, and the effect of sub-cloud secondary evaporation was the most significant in the plateau climate area throughout the year. (3) When the rainfall is 0–5 mm, the temperature is >30 °C, the vapor pressure is <3 hPa, the relative humidity is 50–60%, and the raindrop diameter is 0.5–1 mm; the sub-cloud secondary evaporation effect is the most obvious. Full article