Variation Characteristics of Stable Isotopes in Precipitation and Response to Regional Climate Conditions during Pre-monsoon, Monsoon and Post-monsoon Periods in the Tianshui Area

Abstract

The stable isotopes in precipitation provide a new understanding for the mechanism study of water cycles in the Loess Plateau. However, there has never been an introduction for the Tianshui area, which is transitioning from semi-humid to semi-arid. We analyzed the time series changes of stable isotopes in precipitation at seven sampling points during pre-monsoon, monsoon and post-monsoon periods (April to October) in the Tianshui area. The results show that the temperature effect not only shows spatial differences but also seasonal changes and a weak precipitation effect is only found during the monsoon period. At the same time, the variation characteristics of precipitation isotopes before and after the monsoon clearly record the advancing and retreating time of the monsoon. We captured this important time node around 7 May and 21 September. Due to the influence of the regional microclimate formed by different natural conditions, the kinetic fractionation effect of isotopes in precipitation cause obvious differences in the slope and intercept of the meteoric water line in different natural regions, which shows that the stable isotopes in precipitation with high-resolution changes in a short period of time are of great significance to deeply explore the hydrological process of regional microclimates.

Below‐cloud evaporation effect on stable water isotopes in precipitation at the eastern margin of Qinghai‐Tibet Plateau

“…Based on the precipitation samples collected at the Maqu station from January to December in 2020, we established the LMWL (Figure 7) as δ 2 H = 4.97 δ 18 O – 28.25 ( r 2 = 0.862). The slope and intercept of LMWL are much lower than those of GMWL ( δ 2 H = 8 δ 18 O + 10), indicating that the falling raindrops are affected by the non‐equilibrium fractionation (Craig, 1961; Martina et al, 2017; Zhou et al, 2020). In addition, the LMWL slope ( S L ) and theoretical slope ( S T ) are also shown in Table 2.…”

“…Here we extracted stable isotope data from the C‐Isoscape product (Wang et al 2022), and mapped the δ 18 O values in precipitation (Figure 4e). Usually the strong below‐cloud evaporation leads to great enrichment of δ 18 O in precipitation (Zhou et al, 2020). From Figure 4e, it can be seen that the spatial pattern of δ 18 O and Δ δ 18 O are consistent, which indicates that the use of homogeneous assumption is still an effective way to evaluate the effect of below‐cloud evaporation across the Gannan Plateau.…”

“…In contrast, the stratification assumption is also mentioned in some cases (Crawford et al, 2017;Zhou et al, 2019), that is, the different heights have various meteorological settings for a falling raindrop. However, the atmospheric relative humidity and air temperature may have great uncertainty to the model which is involved in both measurements and reanalysis (Dai et al, 2011;Rieckh et al, 2018) (Zhou et al, 2020). From Figure 4e, it can be seen that the spatial pattern of δ 18 O and Δδ 18 O are consistent, which indicates that the use of homogeneous assumption is still an effective way to evaluate the effect of below-cloud evaporation across the Gannan Plateau.…”

Impacts of reducing scattering and absorbing aerosols on the temporal extent and intensity of South and East Asian summer monsoon

“…2 shows the wind fields over Asia continent during pre-monsoon (April-May), monsoon (June-August) and post-monsoon seasons (September-October). The selection of the different monsoonal periods follows previous studies (Vissa et al, 2013;Zeng et al, 2019;Zhou et al, 2020). Overall, the model captures the spatial features and temporal evolutions of the ASM horizontal circulations from upper to lower levels.…”

Feature Engineering of Geohazard Susceptibility Analysis Based on the Random Forest Algorithm: Taking Tianshui City, Gansu Province, as an Example

“…The study area covered 16.4 km 2 in total, 104 • 35 1 ~106 • 42 24 E (longitude), 34 • 4 57 35 • 10 18 N (latitude). Located at the eastern end of the Qilian orogenic belt, the transition zone between the Guanzhong Plain and the Loess Plateau, the terrain is high in the west and relatively low in the east [41], ranging from 736~3118 m. Fractures are distributed widely, among which the most typical ones are the West Qinling North Rim Fault [42], the Tongwei Fault, and the Qingshui Fault. As a result, tectonic activities take place frequently.…”