CAB129-37 — Page 313

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Some of these points were further illustrated by a series of four gauges placed in February, 1948 at 2-mile intervals on an east-west line onpUnit 3. The three easterly gauges, on higher ground, showed similar readings and received rain on the same days and in comparable quantities. The westernmost gauge, on the slope leading to the Kinyasungwe depression, and facing the Chinene hills, was apparently being affected by an entirely different rainfall system, although the total was not very different from that received by the other gauges.

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In the coming season, rain gauges will be set up throughout the cleared area at the same density of one for 4 square miles in order to continue these studies and to provide the Unit staffs with more precise indications day by day of rainfall distribution.

Many visitors to Kongwa have commented on the supposedly marginal nature. of the Kongwa climate, particularly in respect of low total amount, seasonal variability and bad distribution of the rainfall. Evidence has been adduced from records at Dodoma both of rainfull and of famine and scarcity years in the Province.

It is true that of the three Tanganyika areas, Kongwa has the lowest and least certain rainfall. In assessing this matter, however, the following facts must be taken into account:

The rainfall situation in the production areas at Kongwa, as distinct from that at Dodoma, 50 miles to the west, is evidently influenced by the Chinene hills on the western boundary of the area. These hills are effective in intercepting rainfall carried on the prevailing rain-bearing easterly winds.

In the 1947-48 crop season, although African crops, particularly of maize, were largely a failure in the Kongwa area for lack of rain, maize and other grain crops of suitable varieties were successful in plantings made by the Scientific Department. This is in part due to better agricultural methods, but must also be influenced by the factors considered below.

Although at Kongwa total rainfall is low, it is compressed into a season of 4 to 5 months. The average rainfall per week is thus higher than might be assumed. The variability of rainfall may be expected to be offset to some extent by effective water conservation measures. Investigations on the Kongwa Experi- ment Station have shown that under standing bush the soil is dry in August to a depth of at least 6 feet. On the other hand, on cleared and contoured fields, down a long slope, most of which were not planted in 1947-48, and carried a dense growth of weeds through the season (until ploughed in late April), moisture was present at 4 feet depth in the upper fields, rising lower down to as little a 18 in. The average quantity present down the slope was shown by sampling to be equivalent approximately to 4 in. of rainfall. Therefore, by eliminating runoff, moisture can be stored in the soil at Kongwa, in spite of weed growth, which must have used far more water during the season than a well-kept crop of groundnuts would have done. If this general result is confirmed by more precise investigations, which are to be undertaken, it may well transform the estimation of the climatic possibilities at Kongwa, in regard to both crop production and water supplies.

Concern has been expressed, too, at the high winds of Kongwa itself during the 1948 dry season. These were far more severe than the winds in the produc- tion areas 7 miles and over to the north of Kongwa. It seems likely, therefore, that whether or not the gales are a regular annual phenomenon (which according to experience and observation is open to serious doubt), they are much intensified by the turbulence induced by Kiboriani mountain.

Urambo

The Urambo Region has a rainfall of 30 in. to 35 in. per year. It seems to have shared the relatively dry season experienced by Kongwa in 1947-48. Humi- dities appear to remain high during rainless periods, but it is not known whether

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