Is Standardized Precipitation Index (SPI) a Useful Indicator to Forecast Groundwater Droughts? — Insights from a Karst Aquifer

Abstract

The study sought to understand the relationships between meteorological and groundwater droughts on water levels and spring discharges in Edwards Aquifer, Texas. Standardized Precipitation Index (SPI)‐styled Standardized Groundwater Index (SGI) was used to quantify groundwater droughts. SGI time series signal was delayed and damped, while SPI was volatile. SGI values correlated well with SPI values that were observed five to eight months ago. Dynamic regression models with lagged SPI terms and autoregressive integrated moving average errors indicated a statistically significant yet weak relationship between Lag‐1 SPI and SGI. The utility of SPI for groundwater drought forecasting was minimal in this aquifer. Nonseasonal and seasonal autoregressive terms played an important role in forecasting SGI and highlighted the need for long‐term, high‐resolution monitoring to properly characterize groundwater droughts. Spring flows exhibited stronger and quicker responses to meteorological droughts than changes in storage. In aquifers with spring discharges, groundwater monitoring programs must make efforts to inventory and monitor them. Groundwater drought contingency measures can be initiated using SPI but this indicator is perhaps inappropriate to remove groundwater drought restrictions.

Long-Term Drought Trends in Ethiopia with Implications for Dryland Agriculture

“…In such an instance, the use of a simpler drought index (e.g., one based on precipitation alone) would be validated and deemed reasonable for trend detection. If different drought indices exhibit diverging trends, then additional insights with regards to the underlying mechanisms driving droughts can be ascertained [27]. Identification of such underlying factors are helpful to guide future data collection activities and identify mechanistic shifts in drought-producing processes [28].…”

Comparison of Meteorological- and Agriculture-Related Drought Indicators across Ethiopia

“…Previous studies have indicated that agricultural and meteorological droughts need not be coincident [6]. However, agricultural drought indicators may correlate to lagged values of a meteorological indicator or vice-versa.…”

“…However, the relationships between meteorological, agricultural, and hydrological droughts are not always straightforward. The onset and cessation of agricultural and hydrological droughts do not typically coincide with meteorological droughts, as the former are affected by other factors (e.g., soil and watershed characteristics) that control the rate of water movement and storage in soil, surface water, and groundwater compartments [6].…”

Economic and Ecological Impacts of Increased Drought Frequency in the Edwards Aquifer

“…These states represent the full spectrum of recharge possibilities, and lower recharge years are used in this study to represent drought. The drought defined here is meteorological since recharge in a karst aquifer correlates well with rainfall variation [16]. Subsequently, EDSIM has been used to study climate change effects [33], regional water planning [34], El Niño-Southern Oscillation (ENSO) effects [12], and elevation dependent management [35].…”

“…Habitat for several endangered species is supported by springflows [15]. The aquifer is karstic and does not retain water as it fell greatly in the year after the large recharge events [16].…”