1. College of Water Resources and Architectural Engineering, Northwest Agriculture and Forestry Sci-Tech Univ.; Yangling 712100 China
2. Beijing Hydrology Center; Beiwaxili No. 51, Haidian Beijing 100089 China
3. Dep. of Soil and Physical Sciences, Faculty of Agriculture and Life Science; Lincoln Univ.; Lincoln Canterbury 7647 New Zealand
4. Univ. of Saskatchewan; Saskatoon SK S7N3H5 Canada