Assessing Rainfall Variability in A Tropical Monsoon Watershed: Evidence from The Brantas Watershed, Indonesia

The aim of this study is to address the limited understanding of spatial-temporal climate change dynamics in the tropical monsoon watershed, which is critical for effective watershed management and climate resilience planning. The aim of this study is to assess rainfall variability in the tropical monsoon watershed with a case study in the Brantas watershed, Indonesia. The research was conducted in the Brantas Watershed, East Java, Indonesia. Data collection for rainfall data used CHIRPS (Climate Hazards Group InfraRed Precipitation with Station Data) with 5 km resolution. The analysis of rainfall trends was carried out using regression analysis, while the analysis of differences between rainfall in the two decades 2005-2014 and 2015-2024 was carried out using the t-test. Results indicate rainfall variability was high but not statistically significant, suggesting complex dynamics influenced by monsoonal cycles and ENSO phenomena. Rainfall data show that from 2005 to 2024, there is an increasing trend. These findings highlight the urgent need for integrating adaptive watershed governance, including community-based climate resilience strategies, into local water resource management policies to mitigate climate change impacts on the Brantas Watershed.