El Nino does not imply drought! – Experts clarify

Linia Mashawi Gopo and Shingirai Nangombe

El Nino is a climate cycle in the Pacific Ocean with a global impact on weather patterns. It is a naturally occurring phenomenon in the equatorial region that causes temporary changes in the world’s climate. It occurs when sea surface temperatures in the central and eastern tropical Pacific Ocean become substantially warmer than average.

During the El Nino phase, the relationship between winds and ocean currents in the Pacific Ocean changes, with an impact on weather conditions around the world, especially snow, rainfall, and temperature.

The 2015–16 El Nino phenomenon posed as the strongest ever on record, thereby surpassing the 1997–98 El Nino, which was recorded as the strongest till now.

Research is showing that climate change is causing more frequent El Nino occurrences; however, it is important to note that El Nino itself is not climate change. El Nino events are a prominent feature of climate variability with global climatic impacts.

The season 1997-98 The El Nino episode has been referred to as the climate event of the 20th century because of the enormous and severe effect it had on weather globally. Extreme El Nino episodes disrupt global weather patterns, affecting the amount of rainfall in that particular season, tropical cyclone activity, and other extreme weather events the world over.

The relationship between El Nino and rainfall over Zimbabwe is misunderstood by many, and most people are of the view that El Nino implies drought, but is this correct?

Normally, El Nino is associated with reduced rainfall in mostly the southern parts of southern Africa, including Zimbabwe.

However, a closer analysis of the past El Nino years in relation to Zimbabwe rainfall was undertaken. It is quite interesting to note that out of the 30 years El Nino years that occurred in the past 70 years, only eight (38 percent) had above-normal rainfall while 13 (62 percent) had below-normal rainfall.

These statistics clearly show that the greater number of El Nino episodes led to below-normal rainfall; however, the eight episodes where above-normal rainfall was received during an El Nino episode explain that the relationship between an El Nino episode and below-normal rainfall is not one-to-one.

An El Nino episode does not translate into below-normal rainfall (meteorological drought). However, the fact that 62 percent of the El Nino years had below-normal rainfall shows that most of the El Nino years may result in a meteorological drought (below-normal rainfall).

Seasonal climate forecasting is not only guided by El Nino; it is just one of the many indicators that are critically assessed and monitored when coming up with a seasonal climate forecast; hence, El Nino should not be looked at in isolation. This explains the reason why there are El Nino years with above-normal rainfall.

El Nino is NOT the only seasonal climate forecast indicator. The other seasonal climate forecast indicators include, but are not limited to, sea surface temperatures (SSTs) globally, prior heating before the start of the rainfall season, the behaviour of the winds during the winter season, and persistent westerly cloud bands at the start of the season.

A close assessment of these indicators: prior heating – a very hot September and October are signs of a good summer rainfall season for Zimbabwe, while persistent cool south-easterlies that extend into September and October are signs of a poor rainfall season.

On the other hand, persistent westerly cloud bands in October and November are a sign of good rains over Zimbabwe. Thus, it is of paramount importance to understand that El Nino is just one of the seasonal climate forecast indicators that should not be looked at in isolation.

Looking at a few of the indicators besides the El Nino, they were showing a tendency towards a poor rainfall season over Zimbabwe, which is what the country is experiencing, and below-normal rainfall is highly likely to continue up to the end of the summer rainfall season.

Lastly, it is important to note that the worst meteorological drought was experienced during the 1991–92 summer rainfall season, which was not even an El Nino episode.

Inasmuch as the 1997–98 El Nino was strong, the rainfall performance over Zimbabwe was not bad. This serves to strengthen the argument that El Nino and meteorological drought (below normal rainfall) are not a one-to-one relationship: El Nino does not imply drought!

Linia Mashawi Gopo is the Deputy Director Public Weather Services and Zimbabwe Weather Services Principal meteorologist while Shingirai Nangombe is a former Meteorologist at Meteorological Services Department (MSD) in Zimbabwe

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