Evaluation of the water budget technique for the determination of the effective length of the growing season under different climatic conditions in Malawi
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Date
1998
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Sokoine University of Agriculture
Abstract
A study was conducted in Malawi, with the objective of evaluating the potential of the
water budget technique, for the determination of the effective length of the growing
season under different soil and climatic conditions. Two criteria were used to achieve the
objective. One was the rainfall criterion, where rainfall was the only input and the other
was the water budget criterion, where climatic data, soil and plant characteristics were
major inputs.
Historical rainfall data were tested for homogeneity and statistical distribution using
RAINBOW computer programme. All the stations, except Dedza, were homogeneous (P
= 0.05). The coefficient of determination (R^) suggested that the onset and end of the
growing season can be approximated by normal distribution whilst the annual rainfall
can be approximated by lognormal distribution.
Three years of historical rainfall data were used to calibrate IRSIS as a predictor of daily
runoff. Very good and consistent performance (R2=0.86) was obtained in predicting
runoff. The calibration of the rainfall criterion using the water budget criterion indicated
that the onset of the growing season could be defined as, a day when a running total of
30mm of rain is accumulated in a decade with no dry spell of more than 10 days
occurring in the following 30 days. The results of the start and end of the growing season
indicate that the rainfall criterion used in this study can be adapted for Chitedze and
Makoka. The water budget criterion predicted onset dates closer to when farmers usually
plant maize than the rainfall criterion. Both criteria revealed that Mangochi, Ngabu,
Makhanga and Chileka have short growing seasons and high occurrence of dry spells within the growing season. Water conservation measures and / or supplemental irrigation
should be advocated in these areas for sustainable crop production.
Using runoff plots, the study also showed that the Curve Number (CN) value in plain
plot was higher than in contour plot.
It is recommended that the rainfall criterion which does not require a lot of input data
should be calibrated using a more accurate approach (water budget) to establish
appropriate threshold and conditions for different stations.
Description
Degree 0f Master of Science (Agricultural Engineering)
Keywords
Water budget technique, Growing season, Climatic conditions, Malawi