Daily Hydrologic Drought Assessment Using GPS: Improving Drought Management with the United States GPS-Based Drought Index (US-GDI)

Anthropologically, drought intensity is measured not by how strongly the rain falls over a few days but by how dry the land becomes over a specific period of time. The duration and intensity of this drying period, affects hydrologic pools (i.e. rivers, lakes, and groundwater) uniquely based on the characteristics of their respective drainage basins. Contrarily, drought management techniques currently rely heavily on meteorologically derived drought indices (e.g., the Standardized Precipitation Evapotranspiration Index), which offer valuable insights into the amount of water entering the system but provide no information about water retention levels. As such, currently only GPS-based drought indices provide direct characterization of hydrologic drought with both high spatial resolution, and daily temporal resolution. To assist in the retention of hydrologic resources, we present an update on the status of the United States GPS-Based Drought Index (US-GDI). Our methodology advances those presented by Young et al, 2024. We leverage the availability of the data provided by the Nevada Geodetic Laboratory, and produce a framework which provides rapid US-GDI hydrologic drought assessment solutions with a latency of ~48 hours. Final solutions are expected within 10-14 days. Solutions for the full study period are calculated daily, with hydrologic load estimates, GDI evaluations between one day and 48 months, and step offsets in the vertical component updated daily. To assess the sensitivity of the US-GDI to hydrologic resources, we present an analysis of the correlation between US-GDI timescales and to stream discharge, surface-reservoir storage/elevations, and groundwater across specific hydrologic units across the United States. To facilitate the distribution of the results, we introduce a webpage which provides direct access to all solutions provided by the US-GDI (including both hydrologic loading estimates, and GDI time scale solution. The US-GDI represents an opportunity to significantly improve hydrologic resource preservation and maintenance during periods of sustained hydrologic drought.