No abstract

Drought is one of the most overwhelming natural disasters that has a widespread impact on ecosystems, economies, and societies around the world. It has been a major concern for farmers in the South Wollo Zone, so better monitoring and assessment of agricultural drought with the help of earth observation data is critical. The main objective of this research is to characterize the spatiotemporal variation, frequency, and trends of agricultural drought from 2001 to 2021 using the earth observation-derived vegetation health index (VHI) and standardized precipitation evapotranspiration index (SPEI). The VHI and SPEI were developed using the following variables: potential evapotranspiration (MOD16A2GF), climatic hazards group infrared precipitation with stations (CHIRPS), surface temperature of the land and emissivity (MOD11A2), and normalized difference vegetation index (MOD13Q1 NDVI). As a result, SPEI and VHI were used to characterize the spatiotemporal agricultural drought variation in the South Wollo zone. Additionally, the Mann-Kendall (MK) trends analysis and Pearson correlation were used to identify the trends in the agricultural drought and the relationship between VHI and SPEI, respectively. SPEI and VHI were validated using crop yield data. According to the findings, there were agricultural droughts of varying severity in 2002, 2004, 2009, 2010, 2014, and 2015. Furthermore, the study found a significant increase in drought frequency over the years 2001–2021. The results demonstrated that there was a decreasing SPEI (87.5%) and VHI (57.4%) slope during July. The comparison between the SPEI and VHI was positive and significant on the seasonal scale (r = 0.56, p = 0.01). The regression analysis results showed that detrended crop yields agreed well with VHI (R2/r = 0.49/0.70, P < 0.01) and SPEI (R2/r = 0.34/0.58, P < 0.05). Hence, the findings of the present study illustrated the effectiveness and utility of the SPEI and VHI for agricultural drought evaluation, monitoring, and early warnings in the South Wollo administrative zone.