Fluctuations of continuous soil moisture evaporation under different rainfall conditions during the growing period of the non-monsoon season, the eastern Loess Plateau

Soil moisture is an important link between material and energy exchange between the land and atmosphere, and its evaporation loss is crucial to sustainable development of agriculture. Based on observations of long-term stable isotopes of soil moisture in the eastern Loess Plateau (ECLP) during the non-rainy season growing period, this study systematically explored soil water evaporation loss at different soil depths using the Craig-Gordon model and revealed the internal relationship between soil evaporation loss and environmental elements. Main findings included: (1) The soil moisture content showed a gradual decreasing trend, with a weak soil moisture δ¹⁸O fluctuation appearing in April, whereas a stronger fluctuation was observed in June. (2) A significant vertical spatial heterogeneity was observed in soil moisture δ¹⁸O of each soil layer. Enriched soil moisture δ¹⁸O values appeared in the 0-20 cm soil layer, and the minimum value appeared in the 40-60 cm soil layer. (3) A significant spatial and temporal heterogeneity was observed in the soil moisture evaporation loss fraction (<i>f</i>) (0-23.35%), with weaker values at the beginning of the study period and larger values between mid-late May and mid-June. The largest soil evaporation loss was observed in the 0-20 cm soil layer (average value of 8.97%), a fluctuating decreasing trend appeared with increasing soil depth. (4) Regional soil moisture evaporation loss was positively correlated with regional air temperature (T) and potential evapotranspiration (ET₀) and negatively correlated with soil water content (SWC) and relative humidity (RH). The correlation between soil moisture evaporation loss and environmental elements gradually weakened with increasing soil depth. (5) The environmentally driven model of continuous evaporation of soil moisture was suitable for larger amounts, especially for the surface soil layers. The results of this study have important implications for water resource management, ecosystem stability, and sustainable regional agriculture in the ECLP.