South America Calling

Wet Season Coming Early for Brazil?

John Baranick
By  John Baranick , DTN Meteorologist
Eyes are focused on the start of the wet season in Brazil, which may start a little early this year according to the European weekly model. (DTN graphic)

The 2020-21 crop year was a hard one for farmers in South America to handle, especially in Brazil. A distinct wet-dry season dynamic in central Brazil allows producers to double-crop soybeans with corn. That can be a risky endeavor as corn could be in reproductive phases when the rains shut down and the dry season starts if producers are not careful or just get unlucky.

Last year was abysmal. The wet season was shortened by at least six weeks as the start of the rains came about two to three weeks late and ended a good three to four weeks early. That put pressure on double-cropped (safrinha) corn as the rains shut down just after seeds were planted, forcing plants to rely almost completely on the stored soil moisture through the column to survive the season.

A shortened wet season is a typical feature of a La Nina event as was witnessed in the 2020-2021 growing season. According to USDA Meteorologist Mark Brusberg, La Nina tends to delay the start of rains returning to central Brazil in the spring and speed up their exit in the fall.

You can find more information from Mark Brusberg's 2018 presentation about La Nina here: https://www.usda.gov/…

The length of the wet season is variable though, and not a guarantee to be shorter than normal. But the extreme we saw last season was a killer for safrinha corn in Brazil.

The second factor from La Nina is an increased risk of frost and freeze and the previous season saw both in three waves from late June through mid-July. With corn planting pushed back several weeks, these frosts and freezes came during pollination and early grain fill, dramatically reducing production.

Based on the drought and frosts, early estimates of total corn production in Brazil fell from over 109 million metric tons (mmt) in February and March to the most recent estimate at 87 mmt in the August World Agricultural Supply and Demand Estimates (WASDE) report from the USDA. That is a reduction from the prior year's record corn production of 102 mmt, or roughly 15%, and 20% from the early estimates. Many private estimates are even lower on last year's production.

So with another La Nina in store for this year's crops, Brazilian producers are looking for more encouraging signs for the start of the wet season in central Brazil. Rain during the last couple of weeks has been pretty good for Rio Grande do Sul and portions of Argentina with some occasional showers all the way up to Parana and Mato Grosso do Sul. Previously dry soils late in the winter have reversed in many of these areas as systems have been bringing scattered to sometimes widespread showers. There are still some pockets of dryness and more rainfall will be needed in these areas for corn and soybean planting, but wheat is getting moisture at a critical time as it gets further into reproduction and grain fill.

Back to central Brazil, the beginning of the wet season in Mato Grosso, the country's largest producer of both corn and soybeans, typically starts around Sept. 26. This week, there have been some isolated showers sprouting up over the state. It hasn't been enough to kick off the wet season just yet, but is an encouraging sign for local farmers that are sitting on bone-dry soils.

In the short-term, models are suggesting more of these isolated pop-up showers could be possible during the next two weeks, especially for northern and western Mato Grosso. Goias and Minas Gerais are not likely to see much in terms of pop-up shower chances over this time frame. But as we start to near the statistical average start to the wet season, at least one model is predicting it could be on time, if not early this year.

The European Centre for Medium-Range Weather Forecasts (ECMWF or European for short) produces a twice-weekly forecast that has been showing precipitation at or above normal around the end of September for at least the last two weeks. Now that we are getting close to the start of the wet season, we can take this forecast a little more seriously. In the attached image, there is a noted above-normal rainfall signal throughout central Brazil in the fourth week of the month with an end date of Sept. 26, the statistical average start date. This may indicate that showers are expected to be more numerous over at least Mato Grosso on time or slightly early. This signal shows up for the following week as well, an unusual, but not impossible, occurrence during La Nina.

Not every model agrees, however. The American CFS model during the same time period has near- to below-normal precipitation through the end of September. But it does start the precipitation up in early October. That is a sign that even if the European model is a bit too aggressive in starting the wet season, a delay is not likely to be long. Last year, wet season rains did not start until mid-October.

All things considered, producers in Brazil are hoping that models are correct, especially those that double-crop soybeans with corn. Because if La Nina indeed causes an early end to the wet season in the fall, much of the crop may still get through at least pollination before the rains shut down, limiting the potential harm to safrinha corn.

John Baranick can be reached at john.baranick@dtn.com

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