Seasonal Rainfall Concentration Variability and Its Impact on Vegetation Cover Density in Chamchamal District within the Semi-Humid Region of Northern Iraq

Abstract

Abstract

This study examined the seasonal concentration of rainfall and its impact on vegetation cover density in Chamchamal District within the semi-humid region of northern Iraq, based on data from three virtual rainfall stations and vegetation-cover maps derived from the NDVI index. The results showed that winter concentration was the most frequent pattern at Station 1, occurring in 20 years out of 36, and at Station 2 in 17 years, whereas spring concentration was the dominant pattern at Station 3, also occurring in 17 years. The findings also revealed 29 common years among the three stations sharing the same concentration season, including 14 years of winter concentration, 14 years of common spring concentration, and only one year of common autumn concentration, namely 1994–1995. Years with a relatively balanced rainfall distribution were limited to 4 years only, representing 11.1% of the study period.

  The results further indicated that the representative year for autumn concentration recorded a mean seasonal rainfall of 349.41 mm, with autumn contributing 38.41% of the total, whereas the representative year for winter concentration recorded only 44.03 mm, yet winter accounted for 92.69% of the seasonal rainfall, representing the highest seasonal concentration observed. The representative year for spring concentration recorded a mean of 229.30 mm, with spring contributing 57.36%, while the representative year for the balanced distribution pattern recorded 295.09 mm, distributed as 35.57% in autumn, 29.40% in winter, and 35.00% in spring.

  Regarding vegetation cover, the NDVI maps showed that the best vegetation response occurred in 2019, the year representing the winter concentration pattern, where dense and very dense vegetation together reached 40.35%, while barren land declined to only 9.97%. In contrast, 2015 represented the weakest vegetation condition, with weak vegetation classes covering 91.46% of the area. Pearson correlation coefficients also showed that winter rainfall and total seasonal rainfall had the strongest relationship with dense vegetation classes, with correlation coefficients of 0.868 for winter rainfall and 0.989 for total seasonal rainfall. The study concluded that the type of seasonal rainfall concentration is more influential than rainfall amount alone, and that winter and spring concentration patterns are more effective in enhancing vegetation cover density than autumn concentration or balanced rainfall distribution not accompanied by sufficient rainfall amounts