Monitoring surface dryness using geostationary thermal observations

Abstract

This study introduces an operational land dryness index (DI) developed by the National Oceanic and Atmospheric Administration (NOAA)/National Severe Storms Laboratory (NSSL) to assist mainly in wildfire risk assessment and forecasting. The index is developed based on observations of daytime rise of surface radiative temperature from the geostationary operational environmental satellites (GOES). Thermal measurements of heating rates are normalized using solar radiation, also from GOES, to account for spatial changes in solar time. Maps of the DI are developed systematically over the continental US on a daily basis from cloud-free pixels. In addition, anomalies of the DI are evaluated with respect to a 5-year mean to further classify the extent of dryness.The DI is assessed using (1) the microwave-based soil moisture product from the National Snow and Ice Data Center (NSIDC), (2) estimates of soil moisture from the North American Land Data Assimilation System (NLDAS), that is based on the North American land surface model and (3) vegetation cover estimated from the normalized difference vegetation index (NDVI).An overall agreement is found between the DI and microwave-based estimates of soil moisture. The peak absolute correlation, which reached around 0.6, is found in late summer over scrubland. The correlation between the products also shows a seasonal pattern that needs to be corroborated with further observations. The consistency of the developed product with other independent measures implies its reliability and its potential in wildfire forecasting.