Abstract
Precipitation during the period 2001–2016 over the northern and central part of Tuscany was studied in order to characterize the rainfall regime. The dataset consisted of hourly cumulative rainfall series recorded by a network of 801 rain gauges. The territory was divided into 30 × 30 km2 square areas where the annual and seasonal Average Cumulative Rainfall (ACR) and its uncertainty were estimated using the Non-Parametric Ordinary Block Kriging (NPOBK) technique. The choice of area size was a compromise that allows a satisfactory spatial resolution and an acceptable uncertainty of ACR estimates. The daily ACR was estimated using a less computationally expensive technique, averaging the cumulative rainfall measurements in the area. The trend analysis of annual and seasonal ACR time series was performed by means of the Mann–Kendall test. Four climatic zones were identified: the north-western was the rainiest, followed by the north-eastern, northcentral and south-central. An overall increase in precipitation was identified, more intense in the north-west, and determined mostly by the increase in winter precipitation. On the entire territory, the number of rainy days, mean precipitation intensity and sum of daily ACR in four intensity groups were evaluated at annual and seasonal scale. The main result was a magnitude of the ACR trend evaluated as 35 mm/year, due mainly to an increase in light and extreme precipitations. This result is in contrast with the decreasing rainfall detected in the past decades.
Highlights
In recent decades, there has been a gradual increase in the average temperature of the atmosphere.Global warming has determined a higher water vapor concentration and an increase in global precipitation [1]
The analysis of daily Average Cumulative Rainfall (ACR) time series showed an increase in extreme events, in this case, in agreement with the results obtained for the previous years [5,7]
The size of the areas had to be large enough to contain a sufficient number of rain gauges in order to perform an acceptably accurate ACR estimate
Summary
There has been a gradual increase in the average temperature of the atmosphere. Griffith et al [21] used geosynchronous visible or infrared satellite imagery to estimate rainfall over large space and time scales All these techniques are characterized by lower spatial and temporal resolution. The estimation of ACR degrades the spatial resolution compared to rain gauge measurements but it allows the amount of rainfall to be assessed on a selected area. In this context, the Tuscany territory was divided into square areas where the ACR was estimated. The analysis showed higher rainfall in the north-western area, and an overall increase during the period, more pronounced on the Tyrrhenian coast. The analysis of daily ACR time series showed an increase in extreme events, in this case, in agreement with the results obtained for the previous years [5,7]
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