Innovative polygon trend analysis application for rainfall trends analysis in the Mekerra watershed (northwest of Algeria)

In semiarid climates, precipitation is the most important hydrometeorological event, as it remains the main source of water. In the context of climate change, the analysis of its spatio-temporal trends provides useful information for effective planning and management of water resources. Daily rainfall data collected from 12 meteorological stations in the downstream Mekkera Basin, Northwest Algeria, between 1975 and 2011 were analyzed using the innovative polygon trend analysis method. The analysis focused on trends in average monthly rainfall, average number of rainy days, average daily intensity, maximum daily rainfall, and maximum number of dry days per month. The results reveal a contrasting trend in monthly precipitation averages between dry and wet season months. Precipitation drops by 55 times during the spring months, with a significant decrease in February and March. In winter, there was a less noticeable decrease, though the intensity of maximum daily events increased. August and September show a significant increase in maximum daily precipitation across all stations, consistent with the overall 52 detected cases of increasing rainfall in the dry season. In addition, 70% of time series show that an increase in rainy days led to a decrease in the maximum number of dry days, whereas 52% of time series with fewer rainy days experienced more dry days. These findings offer crucial insights that can assist water managers in developing adaptive strategies to tackle the changing precipitation patterns in the region.