Rainfall Interception and Partitioning in Afromontane Rain Forests of the Eastern Arc Mountains, Tanzania: Implications for Water Conservation

MUNISHI, P. K. T. & SHEAR, T. H. 2005. RainfaU interception and partitioning in afromontane rain forests of the Eastern Arc Mountains, Tanzania: implications for water conservation. The aboveground components of the hydrologic cycle of rain forest are important processes that determine the hydrologic hehavioiir and dynamics of these ecosystems. Precipitation, throughfall, stem flow, canopy interception atid streamflow were tneastued and tiiodetled in two afromontane rain forests of the Eastern Arc Mountains of Tanzania. Meastirements were made daily for 50 months in the Ulugurus and 56 months in the Usamharas. Throughfall was 76% of the gross rainfall in the Usamharas and 79% in the Ulugurus. Stemflow was less than 2% of rainfall. Both parameters were correlated with gross rainfall (r'̂ = 0.97, 0.99, 0.86 and 0.94). Canopy interception was 22% of rainfall for the Usambaras and 20% for the Ulugurus. Streamflow was hest modelled using five months running mean rainfall iti the Ulugurus (r = 0.67) and three to four months in the Usarnbaras (r = 0.72). A high proportion of the gross rainfall is delivered as net precipitation. There is effective partitioning of rainfall on the forest canopy providing reasonable dumping effect of rainstorms. The slow response in streamflow to rainfall events shows the efficiency of the forests to mitigate storm water impacts and thus ensuring continuous water stipply. Further studies in effects of forest harvesting on water yield are pertinent to enable adequate planning of forest utilization.