Trends in short-term precipitation variability

Since long-term changes in precipitation variability are an important aspect of climate change, it is necessary to know whether and how they are changing. We consider two measures of short-term precipitation variability: (i) dry-to-wet and wet-to-wet transition probabilities; they are sufficient for the description of the other two probabilities (dry-to-dry and wet-to-dry) provided precipitation occurrence follows the two-state first-order Markovian process and (ii) mean duration of dry and wet spells, that is, sequences of days without and with measurable precipitation.

The daily precipitation data are taken from European Climate Assessment and Dataset project. We examine 395 precipitation station series from 1961 to 2010. Long-term trends of seasonal values of variability measures and their statistical significance are calculated by non-parametric methods (Mann-Kendall test, Kendall statistic). We found out that statistically significant trends of transition probabilities are more frequent in winter than in summer. In winter, there are positive trends of wet-to-wet probabilities and negative trends of dry-to-dry probabilities in northern Europe.