Data for the period 1821 to 2003 from 126 rain gauges, 41 temperature gauges, eight river discharge gauges and 239 wells, located in southern Italy, have been analysed to characterize the effect of recent climate change on availability of water resources, focusing on groundwater resources. Regular data are available from 1921 to 2001. Many analysis methods are used: principal component analysis, to divide the study area into homogenous portions; trend analysis, considering the Mann-Kendall, Student-t and Craddock tests, autocorrelation and cross-correlation analyses, and seasonal, annual and moving-average variables, applying the spatial analysis to each variable with a geographical information system approach. A widespread decreasing trend of annual rainfall is observed over 97% of the whole area. The decreasing trend of rainfall worsens or decreases as mean annual rainfall increases; the spatial mean of trend ranges from -0.8 mm/a in Apulia to -2.9 mm/a in Calabria. The decrease in rainfall is notable after 1980: the recent droughts of 1988-1992 and 1999-2001 appear to be exceptional. On a seasonal basis, the decreasing trend is concentrated in winter; a slight positive trend is observed in summer, the arid season in which the increase is useless as it is transformed into actual evapotranspiration. The temperature trend is not significant and homogeneous everywhere if the temperature increase seems to prevail, especially from about 1980. Net rainfall, calculated as a function of monthly rainfall and temperature, shows a huge and generalized negative trend. The trend of groundwater availability is so negative everywhere that the situation can be termed dramatic for water users, due not only to the natural drop in recharge but also to the increase of discharge by wells to compensate the non-availability of surface water tapped by dams, as a direct effect of droughts.
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