Remotely Sensed Observational Analyses
In addition to LSM-derived drought-related analyses, research supported by various agencies (including NOAA) has led to the development of new strategies for using satellite data to monitor droughts (and floods), which can provide an assessment of drought characteristics independent of LSM analyses. Like most current LSMs, the NLDAS models do not include a dynamical vegetation component, and therefore do not capture the reduction in evaporation that can arise from vegetation changes caused by drought (e.g., crop damage or delay).
A key success in this area has been the expansion of near-real time satellite-based analyses that are relevant to drought, particularly those describing vegetation and evapotranspiration. For example, the evaporative stress index (ESI) (Otkin et al. 2013) provides a thermal infrared satellite-based index to estimate evapotranspiration deficits, and may provide complementary information to the NLDAS systems. In addition, these products add to the information resources that can be utilized for characterizing current droughts as part of the USDM. For example, rapid-onset droughts are typically driven by warm air temperatures and low humidity and clear skies, and often with high winds that enhance evaporation and dry soils. The remotely sensed ESI captures these phenomena and can provide an early warning of drought impacts on agricultural systems in some cases, whereas an integrated multivariate drought monitoring system may be slower to depict rapid changes because of inherent lags in some of the component analyses.