Developing rainfall erosivity equations for use in Tanzania with limited rainfall intensity data
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Date
2013
Authors
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Publisher
Sokoine University of Agriculture
Abstract
Soil erosion by water is a growing problem in Tanzania particularly in semi-arid
areas and on the mountain steep slopes. The potential for soil erosion is based on
many factors. One of the factors limiting erosion control in the country is the
availability of rainfall erosivity information. The study focused on developing
rainfall erosivity equations for use in Tanzania using limited available rainfall
intensity data. The rainfall intensity charts from 13 selected rain gauge stations were
used to calculate the daily, monthly and annual rainfall erosivity (EI30) values. The
calculated annual EI30 ranged from 570 (MJ-mm/ha-h-y) to 10 568 (MJ-mm/ha-h-y)
which are typical rainfall erosivity values in the tropics. The linear, logarithmic and
power equations relating the calculated annual rainfall erosivity to annual rainfall
volume and Fournier index were developed for each of the 13 selected rain gauge
stations. An equation relating rainfall erosivity to annual rainfall volume for all the
13 rainfall gauge stations showed to be the most accurate based on coefficient of
determination (R2) and the standard error of estimate. The Linear equation which had
an R2 value of 0.95 and standard error of estimate equal to 505.85, resulting from
combined data sets for all stations showed to be the best and was thus recommended
to be used for calculating rainfall erosivity in Tanzania. The recommended equation
was used to calculate R- values of 278 rain gauge stations and for developing rainfall
erosivity map for Tanzania. The ARC VIEW GIS using Inverse Distance Weighted
(IDW) interpolation method was used to develop the Iso- erodent map of Tanzania.
The predicted average long term annual rainfall erosivity ranged from about 1 140
MJ-mm/ha-h-y to 12 118 MJ-mm/ha-h-y. The highest rainfall erosivity values were for the areas receiving highest amount of rainfall volumes including some parts of the
Lake Victoria, Uluguru Mountain, part of northern and southern highlands and
Zanzibar islands. The Central semi-arid areas and part of the northern highlands of
the country having low annual rainfall volumes have low rainfall erosivity.
Description
Dissertation
Keywords
Soil erosion, Rainfall erosivity information