Assessing Precipitation Trends Between 1960 and 2021 Using Multiple Trend Indexes in the GOIÁS State and Federal District, Brazil

Abstract

Climate change is reshaping the global climate patterns with varying effects, necessitating a thorough analysis of historical precipitation trends. This study aimed to assess precipitation trends over 60 years in Goiás State and the Federal District of Brazil using data from 21 precipitation gauges maintained by the National Water and Basic Sanitation Agency of Brazil. The Mann–Kendall test was applied to evaluate the precipitation trend significance (α = 5%) from 1960 to 2021, and Sen's slope was applied for trend magnitude. The Standardised Anomaly Index (SAI), Rainfall Anomaly Index (RAI) and Standard Precipitation Index (SPI) were used. The region had a mean (max-min) annual precipitation of 1462 (2007–915) mm, concentrated between October and April. The Mann–Kendall test showed that 76% of sites had a significant reduction in rainfall, with Sen's slope reaching −60.42 mm decade⁻¹. Only Goiânia showed a positive trend of 1.15 mm decade⁻¹, but with no significant trend at 5% by the Mann–Kendall test. The results indicate that precipitation decreases in September, October and spring. The RAI and SAI highlighted rainfall reduction in October, moving to drier classes, whereas the other months remained stable. The SPI showed a decreasing trend at 3, 6, 12 and 24 months, whereas no significant trend was observed at 1 month. The SPI for 12 and 24 months showed intensification of drier classes in the recent period (2011–2021). The results indicated consistent rainfall reduction over the region, mainly in September, October and summer. Furthermore, the SPI indicated meteorological droughts of low intensity and increased hydrological droughts. This has wide-ranging implications, particularly for groundwater reservoirs, affecting urban areas, hydroelectric power generation and irrigation systems, increasing conflict and requiring an urgent plan for water use.