Seasonal Weather Forecast talk show on Capricorn and North West FM

Transcription

1 Seasonal Weather Forecast talk show on Capricorn and North West FM Categories of Weather Forecast Nowcast (0-6 hours) DETERMINISTIC Short-term (1-7 days) DETERMINISTIC Medium-term (up to 30 days) DETERMINISTIC/PROBABILISTIC Seasonal (3 months) PROBABILISTIC What is a Deterministic Forecast? Seasonal weather forecasts can be simplified by firstly looking at two common methods of weather forecasting which are Deterministic and Probabilistic in nature. For example, the deterministic forecast in South Africa will be the day-to-day forecasts produced by the South African Weather Service in the sense that they provide specific details regarding the weather with respect to location and time (e.g. heavy storm will reach Durban around noon on Sunday ). While great steps have been made in recent years in extending the range of forecasts, for fundamental reasons deterministic forecasts have not demonstrated any skill in predicting the weather weeks or months ahead. What is a Probabilistic Forecast? Seasonal forecasts take a different approach: they predict the climate, or more accurately the deviation from the average climate for the coming season. They are probabilistic in nature (e.g. there is an 80% probability that the season will be drier than average) and always relative to a mean climate. If the coming season is average, the seasonal forecast may not be particularly useful. However, a forecast that can correctly identify the future occurrence of large departures or anomalies from the average has considerable potential. The key to the success of a seasonal forecast lies in the correct identification and modelling of the system or factors that push the climate away from the average. What is an Above or Below-Normal Forecast? Figure 1: Climatic conditions for Louwna weather station in North West Province 1

2 Figures 1 and 2 illustrate the importance of understanding the climatic conditions of a specific area of farming activities. It is advisable to use the seasonal forecast with the necessary caution as the major climate drivers which govern the climate system of our region and the knowledge of local climatic data is also very important for accurate decision making. It is also recommended that shorter time-scale forecasts be monitored for the development of conditions that may change the current forecast as some of the climate drivers may have a greater influence over the current weather pattern in a relatively short period. Figure 2: Climatic conditions for Polokwane weather station in Limpopo Province Seasonal Forecast for July to September 2013 in North West and Limpopo Province Probabilities for below-normal rainfall conditions over Limpopo Province (LP) and the northeastern and southwestern parts of North West Province (NWP) are forecast during the period from July to September. The forecasting system indicates greater probabilities for below-normal rainfall conditions over NWP during August to October, whilst in early spring it indicates raised probabilities for above-normal rainfall conditions over the northeastern parts of LP (Figure 3). The likelihood is forecast of mid-winter maximum temperatures (day temperatures) becoming above normal for both LP and NWP. The tendency of warmer maximum temperatures is gradually expanded from the west of NWP during early spring whilst LP will continue to experience belownormal maximum temperatures during early spring (see Figure 4 left panel). The minimum temperature (night temperature) forecast system is indicating warmer conditions than normal for most of LP and NWP, with the exception of the southwestern parts of NWP for which cooler conditions are expected during July to September (see Figure 4 right panel). 2

3 Figure 3: Probabilistic above-normal (left panel) and below-normal (right panel) rainfall forecast for three overlapping seasons valid for the period of July to September

4 Figure 4: Probabilistic maximum (left panel) and (right panel) minimum temperature forecasts for the three overlapping seasons valid for the period of July to September 2013 Maize production in Limpopo and North West Province Table 1: Water and temperature impacts on maize production CLIMATIC IMPACTS Maize Minimum Range Precipitation Dry Land Water Requirements Critical Growing Stage Crop Damage During Drought Vegetative Pollination Stage Soft and Hard Dough Irrigation Critical Growing Stage Water requirements Soft and Vegetative Pollination Hard Stage Dough Minimum Summer Temperatures Extreme Requirements During Extreme Requirements During Long Days Germination All Growth Stages Maximum Summer Temperatures Germination All Growth Stages Temperature Requirements ( C) Germination Vegetative Pollination Stage Stage 2-3% Crop mm 7-10% Crop 4.5% Crop 5-19 C C Damage Damage Damage 4mm per per mm 5.7 mm Below 10 C 26 C per Wilting per Wilting day Wilting Day Day Day 13 C 30 C Summer Summer Summer Day Length Soft and Hard Dough Winter Short Days Drying of Kernels Winter Water and temperature play a major role in maize production. The minimum water requirements for maize production under dryland range from mm of rainfall and under irrigation the range is from mm per day during pollination stage. Why is this explanation and Seasonal Weather Forecasts of critical importance? 1. Climate largely determines the success or failure of food production. 2. More than 70% of the food and nutrition insecure people are rural and therefore directly or indirectly dependent on agriculture as their livelihood. Seasonal weather forecasts as a planning tool can largely change food and nutrition insecurity to food and nutrition security. 4

5 Growth originating in agriculture is almost three times more effective in reducing poverty than growth in any other sector of the economy. This was reiterated during a 2013 international Food Security Futures Conference. You are the farmers; you have the responsibility not only of food production but of food security, poverty reduction, and of economic growth in South Africa. The rural population is expected to peak between 2020 and 2050 which could mean intensified and exponential rural poverty and food and nutrition insecurity. Only you, our food producing farmers, can prevent a future catastrophe! Farmers would be wise to base their agricultural production planning on scientifically-based seasonal weather forecasts. Disclaimer The ARC-ISCW and its collaborators have obtained data from sources believed to be reliable and have made every reasonable effort to ensure accuracy of the data. The ARC-ISCW and its collaborators cannot assume responsibility for errors and omissions in the data nor in the documentation accompanying them. The ARC-ISCW and its collaborators will not be held responsible for any consequence from the use or misuse of the data by any organisation or individual. For further information please contact the following: Obed Phahlane PhahlaneO@arc.agric.za Mahlatse Phuthi MahlatseP@daff.gov.za Kentse Setshedi KentseS@daff.gov.za Adri Laas ISCWinfo@arc.agric.za 5