A hundred years of Caposele spring discharge measurements: trends and statistics for understanding water resource availa
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ORIGINAL PAPER
A hundred years of Caposele spring discharge measurements: trends and statistics for understanding water resource availability under climate change G. Leone1
•
M. Pagnozzi1 • V. Catani1 • G. Ventafridda2 • L. Esposito1 • F. Fiorillo1
Accepted: 14 October 2020 Ó Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract The 100 year discharge series of the Caposele karst spring in southern Italy enables insight into variations in water resource availability under climate change, given the length of the series, the systematic quality of the records and the absence of human-made alteration of the natural conditions of the aquifer. With this scope, frequency and trend analyses of hydrometeorological variables were conducted. Various three-parameter probability distribution functions were fitted to the data to calculate the Standardized Discharge Index, which describes spring discharge variations in a standardized manner. Common goodness-of-fit tests were applied to evaluate the performance of each distribution. In addition, a new criterion based on the frequency of events exceeding specific extreme Z values is proposed to quantify the deviation of the calculated index from the theoretical Standard Normal Distribution. The Weibull distribution was found to be best for calculating standardized series of spring discharge as it fits the extreme values of both tails well. The relationship between spring discharge and climatic variables was investigated by using least square linear regression, Mann–Kendall and Sen’s slope trend detection tests, applied to the entire series and to 30-year moving time series. A statistically significant decrease of spring discharge of -0.0045 m3 s–1/year has occurred over the last 100 years, whereas no statistically significant trends were found in annual or seasonal precipitation series. However, temperature has constantly been above the mean during the past two decades. An analysis of trends in the moving time series of all variables suggests a connection between the observed spring discharge decay and temperature increase, which can be considered common to other areas of centralsouthern Italy. Keywords Karst spring discharge Time series Weibull distribution Performance of fits Trends Southern Italy
1 Introduction As of the end of 2019, the discharge time series of Caposele spring in southern Italy covers a continuous period of 100 years of records. Such a lengthy spring discharge series is uncommon, and it allows investigation into statistical features of the time series and their relationship with climate variables. In particular, trends of the main climate variables, rainfall and temperature, have direct
& G. Leone [email protected] 1
Department of Sciences and Technologies, University of Sannio, Benevento, Italy
2
Acquedotto Pugliese S.P.A, Bari, Italy
control over groundwater storage conditions as well as spring discharge. Therefore, analyses of long spring discharge time series, combined with an analysis of time series of climate variables
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