Research to detect changes in precipitation variables has become a topic of particular interest to understand modifications in water resources availability. The review is focused on the Italian territory, outlining the “state of the art” of changes in precipitation regime through a review of 54 published studies on observed rainfall trend analyses, in the period 1999–2018. The aim is to combine a large body of knowledge in a single review and to explain the main patterns of rainfall changes occurred in Italy over the last decades. The analysis focused on the Total Precipitation (TP) and the number of Wet Days (WDs) indices at the annual and seasonal scale. A weight factor is introduced to take into account the differences among studies in geographical area, time series length, and number of stations. The review is accompanied by the discussion of other rainfall related variables, that is, precipitation intensity, extreme rainfall events and meteorological droughts, which are useful to provide a broader picture of rainfall changes. Overall, there is an agreement about the tendency of a decrease in wet days on the entire Italy, with limited discrepancies in the various regions. A decrease in wet days is accompanied by a negative trend (although less evident) in total precipitation, especially in winter. Nevertheless, a univocal direction of trends (or lack of thereof) in annual total precipitation and mostly hydrological extreme events is difficult to achieve.

中文翻译：

---

意大利观测降水趋势研究综述

了解降水量变化的研究已经成为了解水资源可利用性变化的特别感兴趣的话题。这篇综述着重于意大利领土，通过对1999-2018年间发表的54篇关于观测到的降雨趋势分析的研究进行了概述，概述了降水状况变化的“最新技术”。目的是在一次综述中结合大量知识，并解释过去几十年来意大利发生的降雨变化的主要模式。该分析着眼于年度和季节尺度的总降水量（TP）和湿天数（WDs）指数。引入权重因子是为了考虑到地理区域，时间序列长度和台数之间的研究差异。审查期间还讨论了其他与降雨有关的变量，即降水强度，极端降雨事件和气象干旱，这些变量有助于更广泛地了解降雨变化。总体而言，就整个意大利的湿天减少趋势达成了一致，各个地区之间的差异有限。湿天减少伴随着总降水量的消极趋势（尽管不那么明显），尤其是在冬季。然而，很难实现年度总降水量趋势（或缺乏趋势）的明确方向（主要是水文极端事件）。总体而言，就整个意大利的湿天减少趋势达成一致，各个地区之间的差异有限。湿天减少伴随着总降水量的消极趋势（尽管不那么明显），尤其是在冬季。然而，很难实现年度总降水量趋势（或缺乏趋势）的明确方向（主要是水文极端事件）。总体而言，就整个意大利的湿天减少趋势达成一致，各个地区之间的差异有限。湿天减少伴随着总降水量的消极趋势（尽管不那么明显），尤其是在冬季。然而，很难实现年度总降水量趋势（或缺乏趋势）的明确方向（主要是水文极端事件）。