2.1 Study area: Emaerete sub-catchment
The study site (Figure 1) is located in the Monduli Highland area, east of the Northern Tanzanian Rift Valley, with an elevation ranging between 1746m and 2037m. The geology is from volcanic origin and the soils have evolved to loamy clay andosols on the upper slopes, and to the typical swelling clay vertisols in the lower topographic swales. The mean annual rainfall (MAR) ranges from 800 mm in the lower areas to 860 mm for the higher areas and was obtained from the global “CHELSA” dataset (Karger et al., 2017). The area has a typical bimodal wet season, with a short peak that occurs from November to December and a long peak between February and May, and one long dry season from June to October (Prins & Loth, 1988). Local and global climatic phenomena such as the El Nino Southern Oscillation and the Indian Ocean Dipole interlink to create a high interannual variation wherein the short rains can fail (droughts) or connect to the long rains (wet) (Nicholson, 1996). The natural vegetation is mostly an elevation-defined transition between savanna bushland and afro-montane rainforest. The landscape in many areas is characterized by severe surface denudation in open grazing land with notable rill and gully erosion by overland flow (Figure 1b).
The communities are predominantly Maasai and have a long history of assimilation and reciprocal influencing with other ethnic groups such as the waArusha and waMeru. Livelihoods in these communities continue to transition from nomadic pastoralism to sedentary agro-pastoralism driven by factors such as population growth, social and environmental human displacement. While traditional customs have gradually lost importance, they still exist, sometimes assimilated within local governance structures, or in parallel with formal governance. Much village land is still set aside for communal grazing, however, during transition to agro-pastoralism, large areas of land have been entrained into different ownership processes, and used for mixed agriculture. The rights to these lands mostly belong to the ‘original’ Maasai people although some of these plots are also being leased to farmers from other regions in Tanzania who pay for their tenure in crop-shares. Both processes have resulted in a conversion of semi-natural grazing lands to cropland. The dominant cropping system is intercropping of maize with common beans. However, there are other crops grown in the area such as wheat and horticultural products. These croplands areas are mostly located in the upper slopes of the landscape, while the grazing lands are mostly located in the lower areas and topographic swales.
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Figure 2: Emaerete catchment (a) broad land cover and (b) topography showing areas designated for agriculture (grey outline) where remainder is open land utilized for common grazing. Note areas of severe gully erosion and surface denudation.