Inter-Annual Vegetation Changes in Response to Climate Variability in Rwanda

摘要

Comprehensive studies on how vegetative ecosystems respond to fluctuations in precipitation and temperature patterns are of great necessity for environmental risk assessment and land-use evaluations. The present study examined the annual trends in vegetation greenness in Rwanda from 2000-2015 and assessed the relationship between these dynamics and climate factors by means of MODIS NDVI, air temperature, SOI and precipitation datasets. Mann Kendal trend test has been utilized to determine the direction and the rates of changes, while Spearman’s rank correlation method has been used to determine the levels of associability between NDVI changes and climatic variables. The results indicate that approximately 11.9% of the country’s vegetation has significantly improved (р < 0.05) from slight to significant improvement while 10.4% of the vegetative cover degraded from slight to severe degradation and an estimated 77.6% of the country’s vegetation cover has remained relatively stable. Much of improvement has been detected in the lowlands of eastern province whereas much of degradation has been highlighted in the western highlands of the Congo Nile ridge and Kigali city. There was a weak correlation between NDVI anomalies and SOI anomalies (rs = 0.36) while near surface air temperature was moderately correlated (rs = 0.47) with changes in Mean NDVI. Precipitation was more significantly associated (r = 0.84) with changes in vegetation health in low plains of Eastern Province (Nyagatare District in particular) than in the high altitude regions of the Congo Nile ridge. A strong positive correlation with precipitation was found in rain fed croplands;mosaic vegetation;mosaic forest or shrubland, herbaceous vegetation/grass-land savannah and sparse vegetation. Identification of degradation hotspots could significantly help the government and local authorities galvanize efforts and foster results driven policies of environmental protection and regeneration countrywide.