This paper examines the relationships between soil moisture anomalies and precipitation. The physical mechanisms of summer precipitation regimes over the United States and Mexico are examined using the NCEP-NCAR reanalysis, the North American Regional Reanalysis (NARR) and the North American Land Data Assimilation based on the Noah model. The relationships between soil moisture and precipitation are regional dependent.

Over the Southwest and the North American Monsoon Core region, rainfall is largely controlled by the large scale circulation anomalies. The moisture fluxes have larger influence on rainfall anomalies than soil moisture.

Over the Great Plains east of 100W, the coupling between soil moisture and precipitation is strong. The increase in soil moisture is associated with the changes in the Bowen ratio. The decrease in sensible heat leads to cooler temperature in the region. The impact of soil moisture on precipitation is realized only if soil moisture anomalies are strong enough to change the large scale low level circulation anomalies. The largest impact depends on the location of soil moisture and can be recognized locally or over the areas downstream along the path of the Great Plains low level jet. The local land-atmosphere interaction also can feedback to the maintenance of drought in the region.