Quantifying the below-cloud evaporation of raindrops using near-surface water vapour isotopes: Applications in humid and arid climates in East Asia

Abstract

In global hydrological circulation, evaporation widely occurs from the land, the oceans, and other water surfaces. Compared to the evaporation from open water, the below-cloud evaporation of falling raindrops is more difficult to quantify. As an alternative to the traditional microphysical model, the difference in stable water isotopes between water vapour and precipitation provides a new perspective to estimate the raindrop mass loss. According to the recent observations of stable isotopes in near-surface water vapour and precipitation in five sampling stations from humid to arid climates in East Asia, we quantified the below-cloud evaporation of raindrops using both a microphysical model and an isotope inversion model. The results indicate that the isotope inversion model, relative to the microphysical model, usually underestimates the impact of below-cloud evaporation on precipitation, especially in arid inland. The sensitivity test of the two models to errors in climatic factors shows that the microphysical model was more sensitive to errors in temperature and relative humidity than the isotope inversion model. We also plot the ranges that the isotope inversion model has solutions under various meteorological and isotope inputs. The findings are useful for understanding the atmospheric processes below the cloud base and the comparability of different methods in quantifying below-cloud evaporation.