Pre-monsoon Drought and Heat Wave in India Observed from Space

The vagary of summer monsoon onsets in India is revealed by sharp increase in precipitation observed by Tropical Rain Measuring Mission (TRMM), Global Precipitation Mission (GPM) and soil moisture by Soil Moisture and Ocean Salinity (SMOS) and the Aquarius missions, with sharp drop in land temperature measured by Atmospheric Infrared Sounders (AIRS). The monsoon season coincides with satellite observations of integrated moisture transport across the coast from the Arabian Sea onto land and outflow to the Bay of Bengal; the net moisture transport agree in phase and magnitude with precipitation on land. During the weeks before the monsoon onsets, India has the driest and hottest periods that often cause health and economic disasters. We will support our hypothesis that the pre-monsoon drought and heat waves are caused by the net loss of moisture, with moisture advected out to the Bay of Bengal before coming in from the Arabian Sea. The phase difference of moisture advection on the two sides of the subcontinent is caused by the earlier start of summer monsoon in the Bay of Bengal than Arabian Sea caused by instability resulted from sea surface temperature rise. The effect of the pre-monsoon drought is accentuated by the delay of monsoon onset on land, from year to year. Using various methods to estimate river runoff (from land surface model adjusted to gauge measurements and from radar altimeter), and the mass change measured by Gravity Recovery and Climate Experiment (GRACE), we also show the seasonal change of water balance in the subcontinent.