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	Palmer Drought Severity Index	Rainfall-Runoff Modeling
分野	Disaster Studies	Disaster Studies
系統	Process / pipeline	Process / pipeline
提唱年	1965	1979
提唱者	Wayne C. Palmer (1965); self-calibrating variant by Wells, Goddard & Hayes (2004)	Keith J. Beven (Primer; TOPMODEL with M. J. Kirkby)
種類	Water-balance soil-moisture drought index	Process-based hydrologic simulation pipeline
原典	Palmer, W. C. (1965). Meteorological Drought. Research Paper No. 45, U.S. Department of Commerce, Weather Bureau, Washington, DC, 58 p.	Beven, K. J. (2012). Rainfall-Runoff Modelling: The Primer (2nd ed.). Wiley-Blackwell, Chichester. ISBN: 9780470714591
別名	PDSI, Palmer Index, Palmer Drought Index, Self-Calibrating PDSI (sc-PDSI)	Hydrological Modeling, Watershed Runoff Simulation, Catchment Hydrologic Modeling, Conceptual Rainfall-Runoff Models
関連	2	3
概要	The Palmer Drought Severity Index (PDSI), developed by Wayne Palmer in 1965, was the first comprehensive water-balance drought index and remains a benchmark in drought monitoring. Rather than tracking precipitation alone, the PDSI runs a two-layer soil-moisture accounting that balances precipitation against evapotranspiration, runoff, and recharge to gauge whether the moisture supply is abnormally short for the prevailing conditions. It compares actual precipitation to the 'climatically appropriate for existing conditions' (CAFEC) precipitation, converts the departure into a standardized moisture anomaly, and accumulates it over time so that the index reflects the persistence and severity of drought, typically on a scale from about −4 (extreme drought) to +4 (extreme wetness). Because Palmer's original empirical constants were calibrated to particular U.S. regions and limited its spatial comparability, Wells, Goddard, and Hayes introduced the self-calibrating PDSI (sc-PDSI) in 2004, which derives those constants from local data and makes the index far more consistent across climates.	Rainfall-runoff modeling simulates how precipitation falling on a catchment is transformed into streamflow at its outlet, accounting for the water that is intercepted, infiltrated, stored, evaporated, and routed through soils and channels. Models range from simple lumped conceptual stores (such as the unit hydrograph or bucket-type models) to spatially distributed, physically based representations of the catchment. Keith Beven's Rainfall-Runoff Modelling: The Primer is the standard reference, and his and Kirkby's 1979 TOPMODEL — built on a topographic wetness index that predicts where saturated, runoff-generating areas expand — remains one of the most influential conceptual formulations. Because real catchments are heterogeneous and only partly observable, calibration against gauged discharge and explicit treatment of parameter uncertainty (Beven's GLUE framework) are central. The models drive flood forecasting, water-resource planning, and assessment of land-use and climate change.