Quantifying the contribution of evaporation from Lake Taihu to precipitation with an isotope-based method

ABSTRACT Moisture recycling plays a crucial role in regional hydrological budgets. The isotopic composition of precipitation has long been considered as a good tracer to investigate moisture recycling. This study quantifies the moisture recycling fractions (f r) in the Lake Taihu region using spatial variations of deuterium excess in precipitation (d P) and surface water vapour flux (d E). Results show that d P at a site downwind of the lake was higher than that at an upwind site, indicating the influence of lake moisture recycling. Spatial variations in d P after sub-cloud evaporation corrections were 2.3, 1.4 and 3.2 ‰, and d E values were 27.4, 32.3 and 31.4 ‰ for the first winter monsoon, the summer monsoon and the second winter monsoon, respectively. Moisture recycling fractions were 0.48 ± 0.13, 0.07 ± 0.03 and 0.38 ± 0.05 for the three monsoon periods, respectively. Both using the lake parameterization kinetic fractionation factors or neglecting sub-cloud evaporation would decrease f r, and the former has a larger influence on the f r calculation. The larger f r in the winter monsoon periods was mainly caused by lower specific humidity of airmasses but comparable moisture uptake along their trajectories compared to the summer monsoon period.