Seasonal/Interannual Variations of Soil Moisture in the Former USSR and Its Relationship to Indian Summer Monsoon Rainfall

Abstract

Seasonal/interannual variations of soil moisture in the former USSR during the period from 1972 to 1985 are investigated by using in situ data. An index of soil moisture in central Eurasia is evaluated as the arithmetic mean of soil moisture normalized by the respective field capacity. This index exhibits a maximum at the end of April when the interannual variability of the index reaches a yearly minimum. It was found that snowmelt occurring around mid-April is responsible for this feature, which results in the least persistence of this index from March to April. Using this index, the relationships between land surface processes over central Eurasia and the following Indian summer monsoons are investigated from the viewpoint of the snow?hydrological effect. The seasonal march of this index and that of spatially averaged snow depth in central Eurasia are described. Based on the amount of Indian summer monsoon rainfall, two cases of good and two cases of poor monsoon years are selected. During these years, an apparent inverse relationship is found between April snow cover over central Eurasia and the subsequent Indian summer monsoon rainfall. Results indicate that during the warm phases of ENSO, the snow?hydrological effect does not hold, whereas it holds during other years. This result does not contradict former observational and modeling studies, and implies that variations in Indian summer monsoon rainfall are most strongly related to the anomalous circulation of the coupled ocean?atmosphere system, with some contribution from the snow?hydrological effect.