Quantifying Future Drought Intensity and Frequency: A Multi-Scenario Study Using SPI, PDSI, and LPDF in the Mid-Atlantic Region of the US

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Abstract
Drought is a natural hazard characterized by gradual onset and prolonged precipitation deficit. With climate change intensifying precipitation variability, accurate drought assessment is critical for effective water resource management and mitigation. Focusing on Maryland in the Mid-Atlantic region of the United States, this study computes and analyzes drought indices to assess both near (2021–2060) and late (2061–2100) drought conditions, in the context of climate variability. We employed three distinct objectives to enhance drought assessment and monitoring capabilities under projected climate scenarios: (1) calculation of the Standardized Precipitation Index (SPI) reflecting meteorological conditions using precipitation data from seven GCMs across three SSPs for two future periods (2021–2060 and 2061–2100); (2) integration of both precipitation and temperature projections in the Palmer Drought Severity Index (PDSI) (implemented here as a simplified PDSI based on a standardized Z-index) to reflect combined hydrological and thermal influences (i.e., Hydrological indices); and (3) a Low Precipitation Duration–Frequency Analysis (LPDF) as indicator of both meteorological and hydrological conditions to quantify and compare the frequency and severity of low precipitation events across different SSPs. These objectives were achieved by fitting a gamma distribution for SPI and an Extreme Value Type I distribution for LPDF, and applying Z-index (i.e., long-term moisture abnormalities) and weighting factors representing the ratio of precipitation to evapotranspiration. Results reveal notable variability in SPI values, with a general trend toward increased extreme wet conditions, especially under high emission scenarios (i.e., SSP585) in the latter half of the century (2061–2100). Meanwhile, PDSI analysis indicated a subtle shift toward drier conditions despite increases in precipitation, particularly under SSP126 and SSP245, suggesting that temperature rises may offset precipitation gains. In addition, LPDF values indicated a reduced frequency of prolonged low-precipitation events under SSP585 compared to SSP126 and SSP245; this reflects higher total precipitation and should not be interpreted as resilience to drought, since the concurrent rise in temperature-driven evaporative demand can still intensify hydrological and agricultural drought stress. These results highlight the importance of incorporating climatic variables in drought assessments to understand future meteorological and hydrological scenarios under climate change projections. The study can help water resource managers and illustrates how such integrations can enhance our understanding of future drought scenarios under different climate change projections.

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