Vegetation net primary productivity (NPP) reveals the plants capability to transform solar energy to photosynthesis. It can be used as an indicator of status of environmental processes affected by climate changes and human activities, especially in degraded areas such as Gadarif State, Sudan, where vegetation degradation has progressively taken place. In this study, three types of net primary productivity from 2000 to 2017 were used to assess the relative roles of climate variables and human activities on vegetation variability in the eastern part of Sudan (Gadarif State) by ordinary least-square regression technique. The three types of NPP are the actual NPP derived from MODIS data, potential NPP estimated using Thornthwaite memorial model and human-related NPP, the difference between the Potential NPP and actual NPP. The correlations between NPP and climate variables are calculated using Pearson’s correlation coefficient. The results revealed that 91.7% of the study area has experienced vegetation degradation caused by human activities with a variation of 97.95% in NPP. In contrast, 8.3% of the study area has a recovery by 2.05% of increase in NPP favored by climate change. The main driving forces of vegetation degradation are human activities, and the dominant factor for vegetation reversion is climate. No clear interaction between the two factors (climate change and human activities) was observed in the study area throughout the period of study. Thus, we concluded that NPP is a good indicator for assessing the relative roles of climate changes and human activities in vegetation cover dynamics that has obviously occurred in almost all districts of Gadarif, Sudan.

Using net primary productivity (NPP) as an indicator to desertification driving factor and expansions is one of the importance tools in the assessment of the contribution of climate change and human activity in desertification. In this study we used three types of net primary productivity; the actual NPP, Potential NPP and HNPP (human appropriation of NPP) to discriminate the relative role of climate change and human activities in desertification from 2000 to 2008 in Northern Kordofan province-Sudan. The results showed, 63.75% of the study area experienced desertification expansion. Within which, 67.32% was induced by Human activities compared with 32.03% caused by climate change and 0.65% caused by a combination of the two factors. By contrast, climate change is the dominant factor of desertification reversion, 2.3% of desertification reversion caused by human activities compared with 97.7% induced by climate change and there isn’t interaction between climate change and human activities in reversion area. The largest area of expansion and reversion occurred in northeast and western parts of the study area respectively. We developed two propositions in the study area. First, the desertification expansion was induced by human activities, whereas desertification reversion was induced by climate change as typified in north south part, central part and western part. Second, both desertification expansion and reversion was induced by climate change as typified in northeast part of study area.