The Use of the Evaporative Stress Index for Monitoring Drought over California
Tuesday, April 21, 2015
Christopher Hain, Earth System Science Interdisciplinary Center, COLLEGE PARK, MD, United States, Martha C. Anderson, Agricultural Research Service Beltsville, Beltsville, MD, United States, Jason Otkin, Cooperative Institute for Meteorological Satellite Studies, Madison, WI, United States, Xiwu Zhan, NOAA-NESDIS, College Park, MD, United States and Li Fang, NOAA, Boulder, CO, United States
Abstract:
Drought monitoring is a complex and multi-faceted endeavor, warranting use of multiple indicators. The utility and reliability of standard meteorological drought indices based on measurements of precipitation is limited by the spatial distribution and quality of currently available rainfall data. Furthermore, precipitation-based indices only reflect one component of the surface hydrologic cycle, and cannot readily capture non-precipitation based moisture inputs to the land-surface system (e.g., irrigation, shallow groundwater tables) that may temper drought impacts. Vegetation indices have been shown to be useful for drought monitoring, as vegetation health degrades, signatures in these indices start to appear due to a decrease in vegetation greenness. An additional indicator currently used for monitoring drought are satellite-based observations of land surface temperature (LST). In comparison, LST is a fast-response variable, with the potential for providing early warning of crop stress reflected in increasing canopy temperatures. One particular LST-based indicator, the Evaporative Stress Index (ESI) represents anomalies in the ratio of actual-to-potential ET, generated with the Atmosphere-Land Exchange Inverse surface energy balance model. It has been demonstrated that ESI maps over the continental US show good correspondence with standard drought metrics and with patterns of antecedent precipitation, but can be generated at significantly higher spatial resolution due to a limited reliance on ground observations. Unique behavior is observed in the ESI in regions where the evaporative flux is enhanced by moisture sources decoupled from local rainfall, for example in areas where drought impacts are being mitigated by intense irrigation or shallow water tables. Because precipitation is not used in construction of the ESI, this index provides an independent assessment of drought conditions and will have particular utility for real-time monitoring in regions with sparse rainfall data or significant delays in meteorological reporting. This presentation will focus on applications of ESI for California through the assessment of ESI performance over past droughts and provide a framework for using ESI in an operational setting.
