Use of Groundwater, Baseflow and SPEI to Evaluate Water Resources in Michigan, USA

Abstract

Precipitation and evaporation are commonly used to assess and forecast droughts. However, surface and groundwater respond to both land surface processes, land use, and climatic variables, and should be integrated into water management decisions. Water trend analysis near the Great Lakes is limited due to fluctuating cycles and data scarcity. In this study, we examine daily discharge data from 46 surface water gauges with high baseflow contributions and groundwater elevation from 28 observation wells in Michigan. Using established hydrograph separation techniques, we determined baseflow and standardized both annual average baseflow levels (SDBF) and groundwater levels (SDGW) from 1960 to 2022. These results are compared to the widely used Standardized Precipitation-Evapotranspiration Index (SPEI). SPEI is a widely used drought indicator that integrates both precipitation and potential evapotranspiration, offering a more comprehensive measure of water balance. While the SPEI suggests that Michigan is becoming wetter, the SDBF shows a mix of both wet and dry conditions. Interpreting SDGW is more challenging due to incomplete records, but it indicates varying groundwater stability across the state. In some areas, SDGW mirrors the trends seen in SDBF, while in others, it takes 3 to 4 years for groundwater levels to reflect the same changes observed in baseflow. Overall, SDBF provides a better understanding of surface processes and responses to changing climatic variables.