Vadose Zone Recharge Studies In Arid and Semi-Arid Northern China.

The Hanford studies led by Dr. Glendon Gee were influential to the experimental design of the first vadose zone recharge investigations undertaken in northwestern China. It was our great fortune that this classic and illuminating work had been undertaken within analogous cold semiarid climate conditions. This presentation will highlight methodologies and key results of field recharge investigations in the central Loess Plateau (semi-arid) and the Badan Jilin Desert (arid). Both studies relied heavily on environmental tracer techniques in view of the dry climate and low subsurface flux rates. In the Loess Plateau, moisture dynamics in thick silty vadose zone profiles were examined in order to assess recharge variability under the influence of land use change (agriculture and soil conservation practices). Integration of environmental tracer methodologies with soil physics monitoring allowed current and previous deep drainage conditions to be contrasted. In the Badan Jilin Desert, results from environmental tracers in the vadose zone determined the role of diffuse recharge in a desert water balance and uncovered a multi-decadal relationship between deep drainage rates and the East Asian Summer Monsoon. Innovative methodologies which integrate vadose zone tracer data with remote sensing, physical monitoring and numerical modeling have great potential for improving assessment of recharge rates on challenging spatial and temporal scales.