Soil Moisture Variations and Their Relationships with Different Vegetation Types in The Upper Blue Nile River Basin

Código

I-EBHE0007

Autores

Sintayehu Adefires Abebe

Tema

WG 1.07: Understanding drivers & feedbacks of soil moisture variability

Resumo

The vegetation-soil moisture relationship is complex and nonlinear. On the one hand, vegetation activity determines the space-time distribution and availability of soil moisture. On the other hand, soil moisture influences vegetative actions. Therefore, understanding these key relationships is crucial for appropriate interventions. In this study the spatiotemporal patterns of vegetation response to soil moisture changes were explored using time series of NDVI and soil moisture datasets from 1982 through 2015. Non-parametric trend and correlation analyses were conducted to quantify the changes over time and the degree of relationship between soil moisture and vegetation response. Results show that shrublands in northwestern lowlands along the Ethio-Sudan border and southern Ethiopian highlands exhibit a significantly increasing trend. 32.3% of the NDVI pixels and 66.6% of the soil moisture pixels show a significant trend. The land cover types in these areas are mostly shrublands. On the other hand, the sparse grassland of the southwestern lowlands shows a decreasing vegetation activity trend. 28.8% of the valid pixels (excluding pixels of no data, cities and waterbodies) show a higher correlation (? > 0.7), whereas 49.7% indicate a correlation between 0.5 and 0.7, mainly in the shrubland, grassland and forested areas. A maximum correlation (? = 0.85) is observed in the croplands, while the mean correlation was 0.61. The bare lands show the weakest correlation. In general, cropped areas followed by shrublands show a higher correlation with soil moisture changes. Consequently, these vegetation types are considered to be highly vulnerable to climate variability and require more attention than others. The correlation between same month (lag0) NDVI and soil moisture is substantially higher than the subsequent previous month (lag1-lag5) soil moisture values. This quick response relates to croplands, shrublands and grasslands, confirming their sensitivity to short-term soil moisture changes. Forested areas of the basin didn't show an appreciable correlation with soil moisture fluctuations either in the same month (lag0) or subsequent previous month (lag1-lag5) soil moisture values. This resistance could partly be due to their deeper and well-developed rooting system, enabling them to access deep soil water resources.