Analysis of climate change from dry to wet phase in NW China with an aridity-wetness homogenized index

Based on 1960-2003 rainfall and small-sized evaporation pan measurements from 131 stations in NW China, an aridity-wetness homogenized index is proposed of rainfall and evaporation as the crucial components of hydrological equilibrium, whereupon research is made of space/time characteristics of the climate that may change from a warm, dry to warm, wet phase in this region. Results show that 1) a regional consistent anomaly serves as the paramount mode of the 1960- 2003 yearly dry and wet features, as well as the opposite feature in the NW (NE) to the SE (SW) is also the important modes for the annual dry and wet abnormality; 2) the space patterns for the arid and moist anomaly include the westerly, tableland and monsoon climates; 3) the annual arid and wet features display greatly humidification trends in the whole NW, westerly and tableland climate zones, with the westerly climate humidification stronger than and the trend of the tableland sub-zone, their abrupt change from arid to moist in the mid 1970s while the area on the fringe of monsoon climate in the southeast of NW China shows a trend of aridification, which is rather weak, however.