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The 2022/23 harvest is being influenced, for the third time in a row, by the La Niña climate phenomenon.
The 2022/23 harvest is being influenced, for the third time in a row, by the La Niña climate phenomenon. It has been operating in the Equatorial Pacific Ocean since 2020 and its effects are observed in Rio Grande do Sul, with a reduction in the volume and frequency of precipitation and temperatures that, at times, have been below average in the State.
This brief bulletin provides information on the variables precipitation and air temperature, from August to November 2022, for RS. Regarding precipitation, it is observed that the accumulated volumes in August and October 2022 were similar (Figure 1). However, it was only in August that precipitation was closer to Climatological Normal (NC).
Figure 1 (see above). Precipitation occurred in August, September, October and November 2022 (top panels) and percentage of precipitation occurred, in relation to the Climatological Normal, for August, September, October and November 2022 (bottom panels), in Rio Grande do Sul The Climatological Normal is from INMET, with the reference period of 1991-2020. (Data source: INMET)
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In general, the months of September, October and November 2022 had rainfall below the NC in RS. The positive side of this is that rice sowing progressed well within the recommended season. According to Irga surveys, around 76% of the area had already been sown by 4/11, that is, within the recommended season, which is one of the main factors for obtaining high productivity. The downside is that some crops needed to be “bathed” for the plants to emerge. As a result, producers used up water from the reservoirs, which, if it doesn't rain to replace it, could be lacking to maintain the water level in the crops.
Regarding temperatures, we heard a lot that this year was colder. But colder compared to what? Analyzing the data, it was observed that in the months of August, September, October and November 2022, the average air temperatures were not lower than the NC, on the contrary, the average temperatures in the months of August, September and October were above the NC , in a large part of the Southern Half of RS. It was only in November that the average air temperature was close to NC in the Southern Half (Figure 2).
Figure 2. Anomaly of maximum, minimum and average air temperatures, for the months of August, September, October and November 2022, in Rio Grande do Sul. The Climatological Normal is from INMET, with the reference period of 1991-2020 . (Data source: INMET)
But why then did it seem like temperatures were lower? When comparing the temperatures of these four months of 2022, with those of 2021, it can be observed that, in fact, the temperatures were lower in 2022, compared to the same period in 2021.
Figure 3. Difference between the maximum, minimum and average air temperatures observed in the months of August, September, October and November 2021 and 2022, in the state of Rio Grande do Sul. (Data source: INMET)
From the maps, it can be seen that August was on average, between -1 and -2 °C colder than in 2021. The month of September 2022 was colder, throughout RS, compared to 2021, with values between - 2 and -3 °C, in most of the Southern Half of RS. October had similar temperatures between the two years, as did November, in the Southern Half of the State (Figure 2).
Figure 4. Average daily air temperature, from August to November, for the years 2021 and 2022, for some locations that have a meteorological station, in the Southern Half of RS. Data source: INMET
From the daily average temperature graphs (Figure 4), it can be seen that the biggest peaks were recorded during August 2021. Another point to highlight is that, during the analyzed months of 2022, there were not as many peaks or temperature fluctuations, as in the previous year. And, finally, the point that draws a lot of attention in the graph, the low temperature peak at the beginning of November 2022. It can be seen that the average air temperature was very low, in the seven meteorological stations analyzed.
This cold, considerably late, had some effects on rice crops, mainly. It is known that the rice plant grows and develops based on air temperature. Due to the lower temperatures, there were some reports of crops being delayed a little. The cold, combined with the application of pre-emergent herbicide, causes phytotoxicity in rice seedlings, which also delays the plant's development. There were some reports of more yellowish plants (Figure 5).
Figure 5. Photos of rice seedlings after the episode of low temperatures at the beginning of November 2022. The photos are from the bioclimatic experiment, at the Irga de Cachoeirinha (A,B) and Santa Vitória do Palmar (C,D) experimental stations ). Photos: Jossana Cera and Roberto Wolter.
With the subsequent increase in air temperature from December until the end of the harvest, this delay in development may be compensated, but this will only be verified later, close to harvest.
Source: agrolink
