Two-decade variations in hydrology of two river basins in the Usambaras of north-eastern Tanzania
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Date
1994
Authors
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Publisher
Duke University
Abstract
Quantifying local, regional, and global climatic and hydrologic changes is relatively
difficult due to high temporal and spatial variability, and to the length of time it takes for
these changes to be monitored and detected. The study of precipitation and river flow
patterns of two watersheds, Sigi and Soni Rivers, that drain the east and west Usambaras
in northeastern Tanzania over a two decades period 1965 to 1989, show that there were
varying patterns of precipitation and river flow on the Usambaras over the period. Though
a non-significant trend, precipitation increased by 2.7% in the east Usambaras while it
decreased by 7.7% in the west Usambaras during the period 1965-1990. The mean annual
discharge increased by 2.6% in the east and 44% in the west Usambaras. During
approximately two decades, discharge per unit of precipitation did not change significantly
in the east Usambaras whereas it appeared to increase at a rate of 0.02 m3 s“lyr"l in the
west Usambaras (P = 0.06). This is about 0.4 m3 s-1 yr-1 (1.2 cm ha-1 yr-1) more water
flowing into the river today compared to 1965.
There has been an increase in the proportion of precipitation reaching the rivers
especially in the west Usambaras, which seems to have started about in the mid-1960’s.
Such watershed response to rainfall may be attributed to climatic and land use factors. In
the Usambaras, changes in hydrologic response coincide with high rates of deforestation
and changes in land use patterns. It is recommended that the remaining catchment areas on
the Usambaras, and vegetation filter strips along river/stream banks should be protected. Appropriate reforestation work in degraded lands including agroforestry in farmlands should form the framework of conservation measures.
Description
Msc. Dissertation
Keywords
River flow, Watersheds, River basins-Usambaras, North-eastern Tanzania