Soil moisture has a direct influence on vegetation health. Plants suffer moisture stress when soil moisture falls below normal levels. In the extreme case (wilting point), they lose the ability to extract water from the soil. An earlier post (mapping-climate-change) looked at trends in surface temperature and precipitation over the past 30 years using data from a global circulation model (CFSv2 reanalysis). Soil moisture is also available from these models.
The map shows 2-metre soil moisture trends in Asia during March-April-May for the period 1982-present. Some areas show strong drying e.g. Mongolia, Caspian Sea ~ -10 g m -2 y -1. The desert provinces of western China appear to be getting wetter, while most of the fertile eastern provinces are getting drier.
Is China drying out?
To see what is happening in China more clearly, soil moisture trends can be summarised in terms of an average for each province (which can be displayed using Google Chart Tools thanks to the googleVis package in R). Mouse-over to see the wetting or drying trend (in g m -2 y -1) for each province.
The chart below shows the annual data along with the linear regression lines. Changes in soil moisture levels over the past 30 years are comparable to or exceed the annual variability in several cases.