Early detection of drought onset using near surface temperature and humidity observed from space

Drought is associated with severe societal impacts ranging from shortages of water for human consumption to agricultural failure and famine. An important aspect of drought forecast is determining the onset, which is critical for early warning efforts and water resources and agriculture planning. Indices of precipitation shortage have been widely used to detect the onset of drought because precipitation deficits often lead to shortages in other hydrologic variables such as soil moisture and runoff. The present work demonstrates that atmospheric temperature and humidity observations from the Atmospheric Infrared Sounder (AIRS) contain information that can be used to detect drought onset earlier than that obtained from precipitation deficit. By calculating the standardized indices for precipitation, near-surface temperature, vapour pressure deficit, and relative humidity, we show that in many regions of the world signals of drought onset can be detected from near-surface temperature and humidity data a few months earlier than those obtained from precipitation deficit. In particular, vapour pressure deficit showed higher effectiveness than relative humidity or temperature only. The outcome was generally consistent for the three- and six-month accumulations studied here. Further analysis using 65years (1960-2014) of monthly temperature and humidity data derived from the Parameter-elevation Regressions on Independent Slopes Model (PRISM) data set over the continental United States suggests that there is a good agreement between drought early detection signals obtained from AIRS and that from ground stations during the overlapped (2003-2014) period. Analysis using longer record suggests that the frequency of successful early detection of drought onset using temperature and humidity data shows regional shift towards eastern United States in the recent years.