PRECIPITATION RECYCLINGOVER THE NORTHERN CHINA

The precipitation recycling over the Northern China was evaluated using 20 years' NCEP reanalysis data. It is found that only 19% of the precipitation in the Yellow River basin comes from the local evaporation, while the other 81% comes from outside vapor. Precipitation over the upper reaches of the Huanghe River are mainly contributed by the strong vapor flow from the Tibet Plateau, so the recycling in the upper reaches is less than 15%. With the westerly winds, water vapor from evaporation in the upper reaches of the Huanghe River are brought into its lower reaches, combining with the moisture from the south and north, are contributed to the local precipitation, resulting in a elliptic region with high recycling rates over 30% in the lower reaches of the Huanghe River. The precipitation recycling varies obviously with seasons: it has the highest value of about 0.32 in August, while it does not reach 0.05 in November, December and January. Both evaporation and precipitation show good correspondence in spatial distribution and yearly variation, which reveals that evaporation is strongly influenced by local precipitation. Evaporation, precipitation and recycling ratios increase during the 20 years, which may be the effect of the climate warming.