Analyzing vegetation health dynamics across Across Western Kenya through Normalised Difference Vegetation Index (NDVI) and climatic variables

Abstract Climate change is one the most pressing challenges facing humanity in today’s world. It is primarily observed through the long-term, interconnected shifts in temperature, precipitation patterns, and an increase in extreme weather events such as floods and droughts. Climate change impacts communities in diverse ways ranging from the degradation of vegetation health thus affecting the sustainability of livelihoods in many communities Bungoma and Busia County of Kenya is endowed with various vegetation cover ranging from grasslands, forests and bamboo, however, the relationship between climatic changes and vegetation health remains under-researched. This study assesses the relationships between vegetation dynamics and climatic variations in Bungoma and Busia Counties from 1993 to 2023. Employing high-resolution Landsat data for Normalized Difference Vegetation Index (NDVI) assessments, integrated with climate variables from CHIRPS and TERRACLIMATE datasets, our approach leverages Google Earth Engine (GEE) and ArcGIS PRO 3.2 for efficient processing. It combines statistical methodologies, including linear regression, Mann–Kendall trend tests, Sen's slope estimator and partial correlation analyses. The study established a mean positive Mann Kendall Tau value of 0.100 for temperatures, and 0.0457 for precipitation. This reflects an increase in both precipitation and temperature of the study area and the increase trend was statistically significant at P = 0.0000. The study established a mean positive PDSI Tau value of 0.15 and an NDVI Tau value of 0.200 an indication of overall increase on vegetation cover and overall wetness of the region. The results revealed a negative relationship (r=-0.158469, P = 0.00029) between NDVI and LST, (r = 0.132497, P = 0.00249) between NDVI and Precipitation and a (r = 0.132478, P = 0.002494) between NDVI and Standardised Precipitation Index (SPI) of the study area, highlighting that precipitation as a primary driver of vegetation growth while increased temperatures drives vegetation degradation thus illustrating its crucial influence in Bungoma and Busia counties. Our investigation further revealed the complex association between vegetation health and climatic factors, which varies spatially across different parts of the county. There is need to mitigate rising temperatures while supporting increased precipitation in the region for enhanced vegetation health of the region.