One manifestation of our warming atmosphere is increased variability in rainfall – we’ve all seen the headlines of extreme rains and subsequent flooding. However, most of the farmers’ stories go untold as they struggle to make sense of shifting rainfall patterns. Adaptation is needed in agriculture and it will start with accurate, localized information services to empower farmers know when the rains are sufficient to support a crop – and planting is advised. World leaders are seeing the need to leverage innovation to Adapt Our World – NOW (See https://gca.org/global-commission-on-adaptation/report for more details).
Increasingly variable rains have created enormous challenges across rainfed food production systems in southern Africa. But what does this variability look like? There are many ways to examine ‘variability’. In the map below we take a time-aggregate view of 5 months, November through March, to capture the bulk of the rainy period across most of southern Africa. Total rainfall during this period is a simple view as is the total seasonal ratio of precipitation (P) to potential evapotranspiration (PET). P/PET is a useful and highly interpretable indicator of water availability for plants (P or precipitation) relative to the evaporative demand of the environment (PET).
P/PET ratios less than 1.0 indicate that there is less rain than evaporative demand. As an index, maize production is difficult even with adaptive agronomics (drought tolerant seed and adapted agronomic practices) when P/PET falls below 0.80. P/PET ratios between 0.80 and 1.0 and higher, indicate sufficient water for most rainfed agriculture. Within a simple total season aggregate, the distribution of the rains play a key part in the actual success of a crop.
Southern Africa – and here I’ll call out Zimbabwe, Zambia, Malawi and Mozambique – have experienced some incredible variability over the past decade. This variability creates serious problems for farmers… aWhere’s foundation database of daily weather from 2006 onwards offers an extraordinary asset to explore risk, variability, and their impact across all segments of every agricultural value chain. The map below shows the average P/PET for the period November through March, for each rainy season since the 2006-2007 season. Over 128,000 virtual weather stations were processed for this analysis. This information is becoming the de-facto source to understand how a warming atmosphere is impacting agriculture. The simple seasonal average hides within-season rainfall variability (e.g., early or late onset, mid-season drought) but these visuals stimulate a host of questions around agriculture and where to invest to reduce risk, increase farm incomes and ensure food security.
For a sense of variability, the animation below provides a view of each November through March total seasonal P/PET from the 2018-2019 season (last year) back to the 2012-2013 season. We show the minimum P/PET that occurred during the 2006 through 2019 period as well as the standard deviation of the P/PET index.
Given increased rainfall variability, farmers struggle to invest in a crop. When we look at the average seasonal P/PET for productive regions (ranging from 0.80 and 1.2) and where the seasonal P/PET range exceeded 0.80 we can see where farming is at risk due to variability. Farmers in these areas expect adequate rains but with wilder variability in recent seasons the impact on their income starts a vicious cycle of lower and lower investment – and lower productivity even when the rains are adequate. Farmers struggle to manage this variability – and it has been extreme the past couple years.
Farmers in Southern Africa face increasing uncertainty in the rainfall that drives rural economies. Images below highlight interannual variability over the past 13 rainy seasons. Charts like these can be easily produced for every location in southern Africa as each of the 128,000 virtual weather stations has complete weather data to drive agriculture decisions. Farmers, input and service providers, commodity traders, processors, retailers and governments all need these weather and analytical tools to become economically resilient and adapt to climate change. We are excited by the ability to provide these resources to AdaptOurWorld to ClimateChange – especially to empower smallholder farmers.