Linear and Nonlinear Trend Analyzes in Global Satellite-Based Precipitation, 1998-2017

Precipitation varies spatio-temporally in amount, intensity, and frequency. Although, much research has been conducted on analyzing precipitation patterns and variation at the global scale, trend types have still not received much attention. This study developed a new polynomial-based model for detecting nonlinear and linear trends in a satellite precipitation product (TRMM 3B43) for the 1998-2017 period at a near-global scale. We used an automated trend classification method that detects significant trends and classifies them into linear and nonlinear (cubic, quadratic, and concealed) trend types in satellite-based precipitation at near-global, continental, and climate zone scales. We found that 12.3% of pixel-based precipitation time series across the globe have significant trend at 0.05 significance level (50% positive and 50% negative trends). In all continents except Asia, decreasing trends were found to cover larger areas than corresponding increasing trends. Regarding climate zone and precipitation trend change, our results indicate that a linear trend is dominant in the warm temperate (77.7%) and equatorial climates (80.4%) while the least linear change was detected in the polar climate (68.9%). The combined results of continental and climate zone scales indicate significant increasing trends in Asia and arid climate over the last 20 yr. Furthermore, positive trends were found to be more significant at the continental scale, particularly, in Asia relative to the climate zone scale. Linear change in precipitation (80%) was the most dominant trend observed as opposed to nonlinear (quadratic [11%] and cubic [9%]) trend types at the global scale.

Automated summary

The study developed a new model to detect trends in satellite precipitation data, finding that 12.3% of pixel-based precipitation time series show significant trends, with a dominance of linear trends across continents. Decreasing trends cover larger areas than increasing trends except in Asia, and linear trends dominate in warm temperate and equatorial climates.