Application of sequential trend analysis for discharge characterisation of Vipava karstic springs, Slovenia

The discharge of Vipava springs and precipitation data of their recharge area have been statistically analyzed and presented in this paper to provide some additional insight into the hydrological regime of the aquifer. Monotone and sequential trends have been evaluated and interpreted based on a 45-year data measurement period between 1960 and 2004. The springs have a typical karstic regime with short-term periods of high discharge and long-term periods of mean and low discharge values. The ratio of low, mean and high discharges is about 1:10:100. The majority of the springs’ groundwater comes from precipitation in the recharge area. Supplementation of two different statistical analyses for sequential trend detection was applied to annual decile discharge values (1960–2004) due to the subjectivity of results interpretation. The first method involved the use of rescaled adjusted partial sums (RAPS) and the second non-parametric sequential Mann-Kendall trend detection. The purpose of the investigation was to determine if and to what extent the length and trend line direction of sub-periods differ between different annual decile values of Vipava springs and to what extent decile values are related to annual precipitation. Sequential trend analysis confirmed similarity in hydrological conditions between some neighbouring discharge decile values but not in others. This analysis also showed that the length of sub-periods and their linear trend direction differed with respect to low, mean and high annual decile discharge values