Hindcasting multidecadal predevelopment groundwater levels in the Floridan aquifer

Abstract

Establishing predevelopment benchmark groundwater conditions is challenging without long-term records to discern impacts of pumping and climate change on aquifer levels. Understanding periodic natural cycles and trends require 100 years or more data which rarely exist. Using limited records, we develop an approach to hindcast multidecadal levels and examine the temporal evolution of climatic and pumping impacts. The methodology includes a wavelet-aided statistical model, constrained by temporal scales of physical processes responsible for groundwater level variation, including rainfall, evapotranspiration and pumping stresses. The model and hindcasts are tested at three sites in Florida using traditional split calibration-verification methods for the period of record and with the documented historical drought and wet years for the period of no-record. The pumping impact is quantified over time and compared with regional groundwater models, revealing that withdrawals are responsible for 30 to 70% of the declines in levels since 1960s. Hindcasting yielding 110 years of monthly levels is used to assess the effect of climate change and pumping on the frequency of critical low levels. At all three sites, the frequencies of critical low levels increase significantly in the 1960 to 2015 period when compared to the 1904 to 1959 period. For example, at site 1, the return period of the critical low level is shortened by 3.9 years due to climate change and 2.2 years due to pumping.

Five Centuries of Groundwater Elevations Provide Evidence of Shifting Climate Drivers and Human Influences on Water Resources in North Central Florida

“…Comparing z scores for instrumental mean annual groundwater elevations at the Cross City and Newberry wells identifies strong similarities regarding interannual variability, but an increasing difference between groundwater elevations at the two sites over time that is more pronounced during years of low groundwater (Figures 8a and 8b). This pattern matches both observed and modeled impacts of groundwater withdrawals on regional groundwater elevations (Gordu & Nachabe, 2021). Using linear regression to remove the shared variance between the Cross City and Newberry wells further supports this notion, with a Durbin‐Watson test indicating significant trend in the residuals ( d = 1.08, p < 0.001) that is identical in slope to the residuals of the tree ring‐based reconstruction of elevations at the Newberry well (Figure 8c).…”

“…Third, widespread groundwater extraction for agricultural and municipal purposes is altering groundwater levels around the world (Bierkens & Wada, 2019), potentially introducing trends in groundwater levels that are unrelated to atmospheric conditions that would otherwise link patterns in tree growth to changes in groundwater levels (Ferguson & St. George, 2003). Despite these challenges, the potential value of expanding perspectives on groundwater variability over multiple centuries to better understand their human and climatic drivers is immense and worth pursuing (Gholami et al., 2017), particularly where oceanic‐atmospheric phenomena influence hydrologic conditions on time scales beyond the instrumental record (Gordu & Nachabe, 2021). This is the case in the southeastern United States, where growing populations are increasing demands on groundwater resources in a region where global sea surface temperatures (SST) strongly influence hydrologic conditions (Enfield et al., 2001; Schmidt et al., 2001).…”

Five Centuries of Groundwater Elevations Provide Evidence of Shifting Climate Drivers and Human Influences on Water Resources in North Central Florida

“…Comparing z scores for instrumental mean annual groundwater elevations at the Cross City and Newberry wells identifies an increasing difference between groundwater elevations at the two sites over time that is more pronounced during years of low groundwater (Figure 6a,6b). This pattern matches both observed and modeled impacts of manuscript submitted to Water Resources Research groundwater withdrawals on regional groundwater elevations (Gordu & Nachabe, 2021).…”

“…The implications for interpreting the overall reconstruction are substantial, but do not undermine the value of the results reported here. Given the relatively recent development of high-capacity wells in the vicinity of the USGS Newberry well, and supported by data from modeling efforts, it is likely that substantial human impacts on groundwater elevation began in the 1990s and have increased since that time (Gordu & Nachabe, 2021). This means the calibration dataset provides at least three decades of relatively stable relationships among climate, groundwater elevation, and tree growth.…”

“…Third, widespread manuscript submitted to Water Resources Research groundwater extraction for agricultural and municipal purposes is altering groundwater levels around the world (Bierkens & Wada, 2019), potentially introducing trends in groundwater levels that are unrelated to atmospheric conditions that would otherwise link patterns in tree growth to changes in groundwater levels (Ferguson & St. George, 2003). Despite these challenges, the potential value of expanding perspectives on groundwater variability over multiple centuries to better understand their human and climatic drivers is immense and worth pursuing (Gholami et al, 2017), particularly where oceanic-atmospheric phenomena influence hydrologic conditions on time scales beyond the instrumental record (Gordu & Nachabe, 2021). This is the case in the southeastern United States, where growing populations are increasing demands on groundwater resources in a region where global sea surface temperatures strongly influence hydrologic conditions (Enfield et al, 2001;.…”