Trend and Variability Analysis of CHIRPS-Based Rainfall in Riau, Indonesia

Abstract

Adequate surface rainfall observation data remains a challenge in Riau Province, both in terms of the number of stations and the length of homogeneous records. This study aims to analyze the trend and variability of rainfall in Riau Province for the period 1990–2024 using CHIRPS (Climate Hazards group InfraRed Precipitation with Stations) satellite data as an alternative climate data source to support water resource planning, agriculture, and hydrometeorological disaster mitigation in the region. Annual and monthly CHIRPS rainfall data were extracted via Google Earth Engine and analyzed using descriptive statistics, linear regression, the non-parametric Mann-Kendall trend test, coefficient of variation (CV), and standard-deviation-based year classification. The results show a mean annual rainfall of 2,811.7 mm with a standard deviation of 325.5 mm and a CV of 11.6%, indicating relatively low interannual variability typical of Sumatra. The linear trend shows a slight increase of 7.4 mm/year but is not statistically significant (p = 0.178; Mann-Kendall p = 0.102), suggesting that rainfall variation is dominated by cyclic interannual factors rather than a long-term trend. The years 1997, 2015, and 2019 were identified as dry years, while 2007, 2008, and 2022 were wet years. The seasonal pattern shows a rainfall peak in October–January and a relatively dry period in June–July. This characterization of the trend, variability, and seasonal pattern of rainfall provides a quantitative basis for planting schedule planning, water resource management, and drought and flood preparedness in Riau Province.