Hydrological changes: are they present at local scales?

Hydrological Mediterranean situation has undergone rapid changes over the last years. This fact causes heavy consequences for both regional water authorities and water utilities to properly plan the future groundwater management. This work analyzes the presence of hydrological changes at local scales, through the reconstruction and time series analysis of hydroclimatic variables (precipitation and temperature) in a coastal Tuscany watershed. For this purpose, the following statistical analyses were performed: (a) change point analysis; (b) Mann-Kendall and Sen's slope tests; (c) precipitation concentration index calculation; (d) analysis of anomalous data; (e) Autoregressive Integrated Moving Average model (ARIMA). The climate variation impact on the water cycle for the study area was then assessed. Although a significant temperature trend was not defined, it is possible to observe a growing trend starting from 1990, as confirmed by larger scale studies. The results of the Mann-Kendall test (p value = 7.3425e-06) and of the Sen's slope test (- 6.6) for annual precipitation show a statistically significant tendency to decrease, enough to cause a shift in rainfall regimes. The average monthly precipitation values fitted by the ARIMA model show a decrease in time with a maximum expected monthly precipitation of 170 mm (95% confidence level). This scenario reflects rainfall change pattern observed in the study area, where rainfall regime starts in 1990 from sub-humid climate system (annual precipitation between 600 and 1200 mm) to reach a semi-arid one today, with the annual precipitation ranging, at the present day, between 400 and 600 mm (about - 40% respect the previous 30 years).

Automated summary

The study analyzed the hydrological changes in a coastal Tuscany watershed, focusing on hydroclimatic variables such as precipitation and temperature. While no significant temperature trend was identified, there has been a growing trend in temperature since 1990. The Mann-Kendall and Sen's slope tests showed a statistically significant tendency for annual precipitation to decrease, leading to a shift in rainfall regimes.