Water contribution of fog drip to surface runoff in Chishui forest region during the dry season

To enable a detailed investigation of the runoff recharge sources in the Chishui forest region and the contribution of fog drip in Chishui forest region during the dry season, water samples (including fog drip water, spring water and stream water) were collected in December 2014 from three major streams. A comparison of D and ¹⁸O isotopic water sample results with isotopic data for precipitation in Zunyi, showed that fog drip is distinctly more enriched in heavy isotopes than precipitation. The isotopic composition of spring and stream water was plotted, together with that of November/December precipitation, with results showing that stream water has similar isotopic composition to spring water, distributed along the local meteoric water line(LMWL). Isotopic data indicate that runoff is mainly recharged by groundwater, which is a mixture of early intermittent precipitation and continuous fog drip. Fog drip is an important surface runoff source in the Chishui forest region during the dry season, but it does not recharge surface runoff directly. The average contribution of fog drip reached 24.1% in the Sidonggou, Shizhangdong, and Yanziyan sampling areas (when calculated by δD, when calculating results by δ¹⁸O, the corresponding proportion was 20.0%).