La Niña predicted to weaken. What does it mean for us?
Zimbabwe’s Department of Meteorological Services (MSD) shares an annual national rainy season forecast in September following the Southern Africa Regional Climate Outlook Forum (SARCOF). Both of these assess and forecast climate patterns for the upcoming 2024/2025 rainfall season.
The Zimbabwean MSD’s forecast was shared here, on this platform, back in September, and below, a reminder of what our weather experts predicted:
“The 2024/2025 rainfall season coincides with a weak La Niña phase. There are prospects of better rainfall for the country from the second sub-season until the end of the forecast period, which spans from November-March. The forecast for the 2024/2025 rainfall season is based on the accumulated rainfall for each sub-season, without taking into consideration its temporal distribution.
“The rainfall forecast for the 2024/2025 season covers the months October 2024 to March The forecast is demarcated into four sub-seasons, October-November-December (OND), November-December-January (NDJ), December-January-February (DJF) and January-February-March (JFM).
“The main global climate driver, the El Niño Southern Oscillation (ENSO), is currently in the neutral phase and is expected to transition into a weak La Niña phase starting October 2024 reaching a peak in the DJF sub-season. The La Niña phase has a higher chance of normal to above-normal rainfall over the southern parts of the SADC region including Zimbabwe.
“However, the country is expected to receive normal to below-normal rainfall for the period October 2024 to December 2024. An improvement in the rainfall performance is expected for the sub-seasons November-December-January (NDJ) 2024-2025, December-January-February (DJF) 2024-2025 and January-February-March (JFM) 2025 with normal to above-normal rainfall anticipated across the country.
“Above-normal rainfall is defined as rainfall amount exceeding 125% of the long-term average (normal rainfall) of the climatic period from 1981-2010; below-normal is defined as rainfall amount less than 75% of the long-term average; normal to below-normal rainfall falls within 75% to 100% range of the long-term average; while normal to above-normal rainfall is defined as rainfall amounts falling within 100 to 125% range of the long-term average.
The period October 2024 to March 2025 is the main rainfall season over most parts of the country.
International weather bureau La Niña forecast
The ENSO Outlook is currently at La Niña Watch. This assessment is based on climate model forecasts and recent atmospheric and oceanic conditions in the Pacific.
According to latest data from the alert system for the El Niño-Southern Oscillation (ENSO) from the Australian Government’s Bureau of Meteorology (bom.gov.au), “the ENSO Outlook is currently at La Niña Watch, meaning there remain some signs that a La Niña may form later in 2024. A La Niña Watch does not guarantee that a La Niña will develop and the chance of a La Niña event developing in the coming months has decreased compared to recent outlooks.
“This assessment is based on climate model forecasts and recent atmospheric and oceanic conditions in the Pacific. Atmospheric and oceanic indices are currently within ENSO-neutral thresholds.
“The Bureau's model suggests surface sea temperatures (SSTs) are likely to remain within the ENSO-neutral threshold (-0.8 °C to +0.8 °C) throughout the forecast period.
Four of 6 international climate models also suggest SSTs will remain within the ENSO-neutral range. Only one suggests SSTs in the tropical Pacific are likely to exceed the La Niña threshold (below -0.8 °C) from November to January, with another forecasting SSTs to briefly exceed the threshold, but only during December and January.
“If a La Niña were to develop, it is likely to be relatively weak (in terms of the strength of the SST anomaly) and short-lived, with all models forecasting neutral values by February.”
Although this does not necessarily mean the southern African region will be affected by drought this season, in recent years we have come to see how much our rain seasons can be affected by El Niño and La Niña events. Following last year’s rainy season (officially declared a drought by the President of Zimbabwe, HE, ED Mnangagwa earlier this year), our agricultural sector have been pinning their hopes on favourable rains this season. The agricultural sector annually contributes an average 17% to our GDP, according to the World Bank.
How reliable are forecasts and how accurate are they? Opinion is generally that “Long-range weather forecasting refers to predictions made about weather patterns several weeks or months in advance. Medium-range forecasts predict weather patterns for the next 7-10 days. Short-range forecasts predict weather for the next several hours to two days. Short range forecasting relies on the facets of weather (humidity, temperature, wind speed and direction, air pressure, cloud cover, precipitation, etc.) over a short period of time, often measured in hours. Although each of the facets of weather can be impacted by many things, such as terrain, over the short-term, they don’t usually vary a great deal over only a few hours, so the forecasts are generally fairly accurate.
“The longer the forecast period, though, the more variations and changes are likely to occur. For example, for several days, the wind may be no more than a breeze that is blowing in a northeastern direction. Abruptly, the wind can change direction and strength, even reversing itself, and this normally has an impact on all other facets of weather. Because of the variables involved, long-range forecasting is normally not very accurate and the longer the period of time, the less accurate it tends to become.
“It boils down to this; a forecast that is for the weather in a given location a few hours after the forecast is made is likely to be correct more often than not. A forecast made for the same location for a week after the forecast is made is likely to change substantially in that intervening week.
“For this reason, long-term forecasts are definitely a work in progress and often change over time. Look at the forecast for your location 10 days from now. Tomorrow, look at the same forecast for the next 10 days. You are likely to see several changes in the prediction over that period of time.”
As we saw with our national maize yields, the economic impact of weather is significant and weather variations cause fluctuations in annual yield size. According to the government our 2024 maize yield of 635,000 metric tonnes was 60 per cent lower than the 10-year average. With a deficit between yield and consumption, the balance has needed to be made up with imports, primarily from South Africa.
According to FEWSNET, “Corn (maize) is the main staple food and the single most important crop in Zimbabwe. Corn production in Zimbabwe is dominated by smallholder farmers who have limited access to irrigation technologies. As a result, more than 90 percent of corn production is entirely dependent on rainfall.
“In the past, Zimbabwe depended on neighboring countries like South Africa and Zambia for corn imports. In MY 2023/24, Zimbabwe imported almost 640,000 MT of corn from South Africa. However, with South Africa’s corn crop also impacted by the drought, dropping by almost 20 percent, and Zambia set to import at least 1.0 MMT of corn to meet domestic demand, supply in the southern Africa region will be tight in MY 2024/25. Hence, Zimbabwe will have to source some corn on the global market. The Zimbabwean government announced that it plans to obtain corn, with the support of private millers, from Brazil, Russia, Argentina, and the United States. While Zimbabwe allows genetically engineered (GE) corn imports, shipments must be quarantined before being milled into corn meal, the national staple.”
Our winter wheat crop yield is not affected by rain to the extent that maize is as wheat is irrigated. Factors affecting our wheat yields primarily boils down to crop management (such as fertiliser and agrochemical regimes, irrigation, pest management).
Climate change is causing disruptions and some effects of it are unavoidable. Farmers need to adapt to a world with more erratic weather patterns and extreme weather events like droughts. By adapting their practices, capacitated farmers can navigate the challenges of a changing climate.
