ABSTRACT
The standard suite of indicators currently used in operational drought monitoring režects anomalous conditions in several major components of the hydrologic budget-representing de–cits in precipitation, soil moisture content, runoff, surface and groundwater storage, snowpack, and streamžow. In principle, it is useful to have a diversity of indices because drought can assume many forms (meteorological, agricultural, hydrological, and socioeconomic), over broad ranges in timescale
7.1 Introduction .................................................................................................. 145 7.2 TIR-Based Modeling of Evapotranspiration ................................................ 147 7.3 Evaporative Stress Index ............................................................................... 150 7.4 Precipitation-Based Drought Metrics ........................................................... 152
7.4.1 Palmer Indices .................................................................................. 152 7.4.2 Standardized Precipitation Index ..................................................... 152 7.4.3 U.S. Drought Monitor ....................................................................... 153 7.4.4 Standardized Anomalies and Seasonal Composites ......................... 154
7.5 Drought Index Intercomparison ................................................................... 154 7.5.1 Seasonal Anomalies.......................................................................... 154 7.5.2 Monthly Comparisons ...................................................................... 156 7.5.3 Spatiotemporal Correlations between Indices .................................. 157
7.6 Limitations and Future Work ....................................................................... 160 7.7 Conclusions ................................................................................................... 162 Acknowledgments .................................................................................................. 164 References .............................................................................................................. 164
(weeks to years), and with varied impacts of interest to different stakeholder groups. Farmers, for example, may be principally interested in soil moisture de–cits, river forecasters will focus on streamžow žuctuations, and water managers will be concerned with longer-term stability in municipal water supply and reservoir levels. Only recently has actual evapotranspiration (ET) been considered as a primary indicator of drought conditions (e.g., Anderson et al., 2007b; Labedzki and KaneckaGeszke, 2009; Li et al., 2005; Mo et al., 2010). ET is a valuable drought indicator because it režects not only moisture availability but also the rate at which water is being consumed. Because transpiration (T) and carbon uptake by vegetation are tightly coupled through stomatal exchange, ET anomalies are indicative of vegetation health and growing conditions. In addition, the importance of so-called žash droughts is becoming increasingly evident, where hot, dry, and windy atmospheric conditions can lead to unusually rapid soil moisture depletion and, in some cases, devastating crop failure. Such events cannot be easily identi–ed using local precipitation anomalies but should have a detectable ET signature.
