  This paper investigates the impacts of climate change on groundwater droughts
making use of regional projections and standardized indices: the Standardized
Precipitation Index (SPI), the Standardized Precipitation Evapotranspiration
Index (SPEI) and the Standardized Groundwater Index (SGI). The method adopted,
using historical precipitation and temperature data and water levels collected
in monitoring wells, first investigates the possible correlations between
meteorological and groundwater indices at each well. Then, if there is a
correlation, a linear regression analysis is used to model the relationships
between SGIs and SPIs, and SGIs and SPEIs. The same relationships are used to
infer future SGIs from SPI and SPEI projections obtained by means of an
ensemble of Regional Climate Models (RCMs), under different climate scenarios
(RCP 4.5 and RCP 8.5). This methodology has been applied to data collected in
Tuscany (Italy), where historical series of daily climate variables (since
1934) and daily records for 16 wells, covering the period 2005-2020, are
available. The impacts on groundwater have been computed in the short
(2006-2035), medium (2036-2065) and long term (2066-2095). The analysis
indicates that, in the historical period and for most of the monitoring wells,
there is a good correlation between SGIs and SPIs or SPEIs. In a global warming
scenario, the influence of temperature on evapotranspiration phenomena cannot
be overlooked so the SGI-SPEI relationships seem more suitable to forecast
groundwater droughts. According to these relationships, negative effects on
groundwater levels in almost all wells are estimated for the futureDue to the
type of data required and its simplicity, this methodology can be applied to
different areas of interest for a quick estimate of groundwater availability
under climate change scenarios.
