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Accueil du site → Doctorat → États-Unis → 2022 → Drought Monitoring in the Southwestern United States : Analysis of Seasonal Precipitation, Multiscalar Indices, and Soil Water

University of Arizona (2022)

Drought Monitoring in the Southwestern United States : Analysis of Seasonal Precipitation, Multiscalar Indices, and Soil Water

McKellar, Trevor

Titre : Drought Monitoring in the Southwestern United States : Analysis of Seasonal Precipitation, Multiscalar Indices, and Soil Water

Auteur : McKellar, Trevor

Université de soutenance : University of Arizona

Grade : Doctor of Philosophy (PhD) 2022

Résumé partiel
Drought is a complex, natural hazard that can cause widespread socioeconomic and environmental impacts. Drought can be defined as a water deficit that arises compared to normal conditions and lasts long enough to cause a lasting hydrological imbalance ; however, what constitutes normal conditions varies based on the local climate regime and water source being studied. It is therefore that drought can be subjective to the observer and accounting for the correct environmental drivers is important to accurately assess drought impacts. In water-limited ecosystems like the Southwestern United States, hereby referred to as the Southwest, monitoring drought conditions presents unique challenges as annual potential evapotranspiration is significantly greater than precipitation. Primary production of Southwestern vegetation is adapted to the timing and magnitude of soil water recharge from seasonal precipitation. Variations in precipitation timing and magnitude can thus lead to lasting drought impacts and therefore tracking soil water at different depths is key for understanding overall ecosystem health. Studies have monitored soil water availability by placing Time Domain Reflectometry (TDR) probes at different depths within a soil profile. However, varying measurements between TDR probes due to differences in soil properties, calibration complications, and maintenance issues have led to the lack of long-term, reliable soil water datasets. This has restricted drought analysis using soil water data to a more local scale. As an alternative approach, land managers and decisions makers use meteorological drought indices as proxies for soil water availability. Meteorological drought indices are numerical timeseries that convey the frequency and magnitude of meteorological indicators, such as precipitation and temperature. Examples of meteorological drought indices are the Standardized Precipitation Index (SPI) and Standardized Precipitation-Evapotranspiration Index (SPEI), which use monthly total precipitation and water balance values, respectively, to communicate drought conditions. A key feature of the SPI and SPEI is the ability to be calculated at any monthly timescale length (‘multiscalar’), allowing for drought conditions of different water sources, such as shallow soil water, to be evaluated. Furthermore, the SPI and SPEI require minimal data inputs and are simple to calculate. It is therefore that the SPI and SPEI are commonly used by land managers for drought monitoring and decision making. Using SPI and SPEI timescales to estimate soil water in the semi-arid Southwest can be complicated as not all falling precipitation can be assumed to infiltrate into a soil profile.

Mots clés : Climate Drought Index Monitoring Soils Southwest

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Page publiée le 16 novembre 2022