- Weather related danger regions in the Angora Goat Industry
|Last update: March 27, 2012 12:30:45 PM|
Weather related danger regions in the Angora Goat Industry
D I Rowswell
Grootfontein College of Agriculture
Private Bag X529
Middelburg Cape 5900
The correlation between adverse weather and Angora goat losses was studied in the 20 highest mohair-producing districts in South Africa. A representative sample of farmers from these districts (central Cape Province) supplied dates of Angora goat deaths caused by unfavourable weather conditions over the past 14 years. It was then possible to relate these dates to prevailing climatic conditions.
The limited research on weather-related deaths among goats has indicated that the primary cause of such losses is a drop in circulating blood glucose owing to cold stress (Fourie, 1984; Wentzel, Viljoen and Botha, 1979). In practice most fatalities result from cold stress caused by a combination of rain, wind and low temperature.
For the purpose of this study it was therefore accepted that rainfall, wind and temperature were the three main weather elements responsible for goat deaths. Average criteria for these elements were then determined for associated death incidences. All possible climatic data obtained from the Weather Bureau and Agro-meteorology for the region were used to calculate probability factors for each of the 26 weather stations in the Angora goat area (Table 1).
The survey, done by die Agro-meteorological Section, Grootfontein College of Agriculture, was dependent on the Angora goat farmer's response: his accuracy in observing and willingness to supply the required data.
The aim of the study was to arrive at realistic cut-off climatic values, which cause Angora goat deaths. These could be of assistance to the Weather Bureau in the visualized warning programme for the mohair farmer. A further objective was to accumulate as many death dates as possible to help the Weather Bureau to identify the general weather patterns responsible for the mortality rate of Angora goats. From the collected data a benchmark could be derived according to which farmers could, for instance, choose a generally "safe" time for shearing.
Angora goat farmers in the 20 highest mohair-producing districts in the country (Mohair Board, 1983) were requested to assist in the study by supplying dates of Angora goat deaths caused by adverse weather and other related information. The districts in question are depicted in Figures 1 to 3. Survey forms were then sent out annually to participating farmers to monitor goat losses and dates on which goats were brought to shelter owing to adverse weather conditions.
At a workshop held at the Agro-meteorological Section at Grootfontein in June 1984, it was concluded that goat deaths could result as soon as the minimum temperature dropped below 10° C with 5 mm of rainfall and a simultaneous wind run of 180 km/d (7,5 km/h). This lower limit of fatal weather conditions concurred with earlier research findings on goat deaths caused by simulated adverse weather conditions (Fourie, 1984).
The cut-off values: ≥ 5 mm rainfall, ≤ 10° C minimum temperature and ≥ 180 km/d wind run were therefore used to analyse each weather station's daily data to calculate the probability of these criteria occurring throughout the year (Figure 1).
When sufficient death dates were received from the farmers, it was decided to see how the criteria compared with the values measured at representative weather stations.
The data from each representative weather station were then analysed for each death date to calculate what the mean climatic values would be for the elements: temperature, rainfall and wind.
An analysis of climatic data was then done for the criteria: ≥ 5 mm rainfall and ≤10° C average daily temperature for each weather station in the Angora goat region to assess how the above-mentioned cut-off values affect the weather pattern in the region.
One hundred and twenty-two reports of goat deaths were received in 1984 dating back to 1970.
The analysis of daily climatic data for each weather station in and bordering the traditional Angora goat region was carried out using the criteria: ≥ 5 mm rainfall, ≤ 10° C minimum temperature and ≥ 180 km/d wind run. Figure 1 shows the yearly mean isolines while the average for the region amounted to 15,3 percent.
The mean conditions when goats died were calculated. It was found that there was a 73 percent correlation between the assumed criteria and the climatic data when goat deaths took place. The results are depicted in Graph 1.
From the calculated cut-off values of ≥ 5 mm rainfall and ≤ 10° C average daily temperature a further analysis was carried out to derive the probability factors for each weather station on a yearly basis (Figure 2). The yearly average was 11,9 percent.
Maps were then plotted for each month, except January and February, which had no days when the criteria were experienced at any weather station used. Figure 3 depicts the average situation for each of these months.
Figure 1 illustrates the average probability that the criteria (≤ 10° C minimum temperature, ≥ 5 mm precipitation and ≥ 180 km/d wind run) will be exceeded during any day. In the north east (Middelburg, the eastern parts of Cradock and Somerset East, Bedford, Adelaide and Cathcart) the chances are higher than normal for the cut -off values to occur. In the southern central area (Uniondale, Steytlerville, Uitenhage and the southern parts of Willowmore) a similar situation is found. In the extreme south there is a 100 percent chance of the criteria being experienced. An area to the north east of Beaufort West has an above average chance.
From the results of the average figures calculated from the death dates, Graph 1 illustrates that 8 percent of the maximum daily temperatures were above 20 C while 86 percent of the minimum daily temperatures were below 10° C. The 10 percent wind run below 50 km/d was due to the unreliable data reported by certain stations. From the rainfall statistics 21 percent occurred between 80 - 90 mm, which was mainly as a result of heavy rains in July 1983.
The rainfall average (51,2 mm) as depicted on the graph cannot be accepted as a cut-off value. The assumed value of 5 mm was therefore maintained.
Wind run, being an accumulative measurement, can be misleading. Strong winds encountered during part of the day can influence the daily average immensely even though night conditions were calm. It was also found that some stations had either no data or the data available was unreliable. For these reasons wind run was omitted from the criteria responsible for affecting the goats.
In the analysis of temperature data, it was observed that a 10° C daily minimum temperature as cut-off value could be experienced on many summer mornings with the afternoon temperature rising above 30° C. This situation could occur together with thunderstorm activity (5 mm rainfall) and a north westerly wind (180 km/d). From the average daily calculated temperature of 9,6 C (Graph 1) it seems that this value is a far more realistic figure for the temperature criterion. Therefore, using 10° C as the mean daily value, the minimum would have to be less and the maximum would not be much higher than this figure. This situation lends itself to cool or cold conditions with a likelihood of associated rain - typical frontal system weather. Thunderstorm conditions will be the product of higher temperatures in the latitudes: 31° to 34° south.
It was therefore deduced that a criteria of ≥ 5 mm rainfall and ≤10° C average daily temperature will give a realistic picture as to what extent the goats will be adversely affected.
In Figure 2 yearly averages illustrate the cut-off values: ≤10 °C average daily temperature and ≥ 5 mm rainfall for each station. It may be noted that this chart compares closely to Figure 1 where the other criteria were used. The similar areas i.e. the north eastern, southern central and in the case of Figure 2 the extreme north-western part of the region show this pattern. In Figure 2 it may also be observed that there is a higher than 50 percent chance of the cut-off factors being experienced in the northern mountainous area of Adelaide and Fort Beaufort as well as in the southern part of Willowmore and eastern pan of Uniondale.
The maps plotted for each month when the criteria were experienced illustrate how the monthly average percentage value for the likelihood of adverse weather (criteria ≥ 5 mm rainfall and ≤ 10° C average daily temperature) fluctuates. The monthly figures illustrate the encroachment of high probability isolines on large areas during the July - August period. Trouble free zones are also shown; these are the areas between the 0 percent isolines.
Weather patterns responsible for the adverse weather affecting the mohair industry have been correlated with goat death data received from Angora goat farmers. This has promoted a better understanding of the causes of weather-related deaths. The cut-off weather values, which have been calculated from these data, may in future assist in forecasting adverse weather for the Angora goat farmer.
The monthly probability isoline maps provide information to the Angora goat farmer with respect to the safety of his goats in his particular climatic situation. The charts also supply guidelines as to when the best time would be to shear his goats.
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MOHAIR BOARD, 1982 - 1983. Seventh Annual Report.
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WENTZEL D, VILJOEN K S & BOTHA L J J, 1979. Physiological and endocrinological reactions to cold stress in the Angora goat. Agroanimalia. II, 19 - 22.
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