Abstract:
For improving sustainable water resources management and planning at local and
regional scales, specifically in small islands, long-term and recent rainfall trends due to
temporal shifts in major climatic drivers should be investigated based on dense and longrunning
ground data series — as done in this research work for the North Atlantic
Portuguese island of Madeira (741 km2). Monthly, wet season and annual rainfall trends
have been obtained via the non-parametric Mann-Kendall (MK) and the Sen’s slope
estimator tests for 41 rain gauges spanning from 1940/41 to 2016/17 (77 hydrological
years, each starting on October 1). By means of the Sequential Mann-Kendall (SQMK)
test, abrupt temporal shifts in the wet season and annual rainfall, and in the North Atlantic
Oscillation index (NAOI) series have been identified on the late 1960’s—sandwiched by
two subperiods with clearly opposite trends. In general, the results suggest considerably
and statistically significant decreases in rainfall, exacerbated in recent years at the central
region of the island — one of the most important locations in terms of fresh water
security. Additionally, this work provides a solid basis to explain the climate change
effects on the Madeira rainfall, suggesting that abrupt changes of the island’s rainfall
variability can be directly linked to those of the North Atlantic Oscillation (NAO) climatic
driver based on the strong established teleconnection. These findings are expected to
contribute to the improvement of actions towards sustainable water management in the
island, and of some other small islands with climatic characteristics influenced as well by
large-scale circulation patterns.
