Temporal Trend Possibilities of Annual Rainfall and Standardized Precipitation Index in the Central Highlands, Vietnam

Abstract

This paper employed the Şen’s innovative trend analysis (ITA) method to identify overall and partial trends in annual rainfall records over the Central Highlands of Vietnam. Additionally, the lowest values of Standardized Precipitation Index (SPI) for 3 and 12 months were subjected to the analysis to reveal potential changes in the greatest intensity of meteorological drought. The outcomes from a preliminary assessment by applying the normal (Gaussian) probability distribution functions (PDFs) indicate significant increases in standard deviation values of the second half subseries (current climate), thereby implying greater level of rainfall variability. The results from temporal trend analysis show that there is high domination of neutral and decreasing trends in annual rainfall records, with the estimated ITA slopes varying mainly from − 10 to − 14 mm/year. Furthermore, the low value sub-groups are mainly characterized by significant decreasing trends, which is an evident indication of possible increases in drought intensity. These results were further demonstrated by evaluating the ITA plots for the lowest values of SPI in both 3-month and 12-month timescales. The lowest values of SPI are mainly lower than − 1.5 and − 2.0 corresponding to severe and extreme drought categories, and most of the scatter points in low SPI cluster are accumulated in the lower triangular area of 1:1 line. Generally, it is expected that these findings will contribute various well-founded foundations to manage water–use activities and natural hazards associated with rainfall shortages.