Assessing the impact of climate change on the severity and frequency of droughts in the western region of Saudi Arabia using the Standardized Precipitation Index (SPI) for the period (1959–2024)

Abstract

This study aims to demonstrate the impact of climate change on the change in monthly rainfall rates in the Makkah region, as any change in the rainfall pattern, whether an increase, decrease, or irregularity of rainfall, leads to clear repercussions on plants. This is based on the analysis of monthly rainfall rate data for a period of 66 years, which was divided into two time periods: the first extended from (1959-1991), and the second from (1992-2024), and extracting the monthly averages for the two periods. The results confirmed that there is a clear difference in rainfall rates between the two study periods in favor of the second period (1992-2024), as rainfall rates increased by a difference of 4.1 mm.

The data were then entered into the Drought Indices Calculator (DrinC) software to calculate the Standardized Precipitation Index (SPI) for estimating dry and wet years in the Makkah region, based on 12-month values over a 66-year period. The data were divided into two periods, each 33 years long, to understand the impact of climate change on rainfall patterns in the second period compared to the first, and how this affected the SPI levels. The results confirmed a clear impact of climate change on rainfall rates and amounts across all months. Rainfall increased in the second period compared to the first, by a difference of 4.1 mm. Monthly variations were observed, with months that previously recorded low rainfall, such as the summer months, experiencing higher amounts. Conversely, wet months saw a relative decrease in rainfall, leading to variations in drought levels across the two periods.

The results confirmed that near-average aridity was the most frequent condition during most months of the two study periods, and it was the dominant condition between the two periods. It occurred 86% of the time in the first period and decreased to 75% in the second, a difference of 11%. Average humidity was also more prevalent in the second period than in the first, by a difference of 1%. Very high humidity was also more frequent in the second period compared to the first, by a difference of 3%. Extremely high humidity also increased in the second period compared to the first, by a difference of 1%. These results indicate that the region tends towards wetter than dry conditions during the second period. A relative improvement in humidity was observed during the main rainy season, which is an indicator of continued vegetation growth due to improved humidity conditions in the region.