The detection of dry-wet variation (Ma et al., 2006)
The time series of 55 years (1951-2005) soil moisture in East China is generated by SRSM. The data then used to analyze the dry/wet trend in Eastern China, and the results are compared with commonly used drought-wetness indexes such as precipitation, surface humidity index and Palmer drought index (PDSI).
The trends of precipitation, Surface Humidity Index (SHI), PDSI and retrieved soil moisture at 50-60cm from 1951 to 2004 are analyzed with M-K method, and the results are shown in Fig. 7.20.
The spatial distributions of four trends are similar in Eastern China. But the location and scope of the most arid area generated by SRSM is different from those of other three indexes. The significant drying trends from precipitation, SHI and PSDI are likely to continue in Northeastern China, and trend from SRSM shows less prominent in the same area. For SRSM, the most significant drying trend region locates at the transition belt in Northern China, which the precipitation's been decreasing, though not significantly. The inconsistency of soil moisture and precipitation trends might be the results of surface air temperature rising, which causes the increase of potential evaporation at surface and further reduce the surface soil moisture. The severe dryness extends downward and induces the significant deeper soil drying. In center-south part of Northern China, which also shows notable regional warming, the decreasing precipitation is associated with deeper soil moisture reduction. The mechanisms controlling interactions between precipitation and soil moisture in different regions are complicated and need to be further analyzed with coupled climate and hydrology model.
negative value means decrease trend which express with diagonals; for precipitation: negative value means decreasing tendency, and positive value means increasing tendency; and for other three indexes: negative value means drying tendency, and positive value means wetting tendency; and the shaded parts reach 95% level significance test.)
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