Current condition review - Rainfall is ‘near’ normal in China this season, so why am I concerned about corn (and soybean) production?


Here at aWhere, we monitor the agricultural earth with a weather station’s worth of daily data every 9km – yes, every 9km we construct a virtual weather station. These observed data are current through yesterday and we provide 7 days (and up to 15 days) worth of hourly data for each of these virtual weather stations – forecasts are updated every 6 hours.

What we are seeing right now – mid July of 2017 – is a conversation about crop health based on ‘near normal rainfall’ in China and some rainfall deficits – and inferred drought stress - in western Iowa and southern Illinois. This is a critical growth stage for corn - reproduction – and drought stress can have a significant and lasting negative impact on yield. Missing from maps and narrative of this precipitation driven explanation is the significant increase in PET over China (much hotter than normal temps) whereas the corn belt is mostly seasonal or even cooler-than-normal temperatures and thus lower than normal PET. So while the corn areas of China have received a normal amount of rainfall, that’s not the whole story.

Detailed examination of some 12,000 of aWhere’s weather stations ALL representing the commercially important corn growing areas of China, the following maps and charts tell a story worth ‘watching’ for the corn crop. We will be utilizing the Precipitation (P) to Potential EvapoTranspiration (PET) ratio as a sound indicator of conditions for crop health. See for details of PET.

The dashed black line schematically represents the main corn growing areas of China. Looking at the next 7 day forecast, this area is to be significantly drier than normal leveraging the P/PET index.

Corn China 170717 e.pngThe actual (for 2017) P/PET over the past 30 days indicates that ~50% of the corn area has a ratio of P/PET of less than 1.0 with 37% less than 0.80.   At less than 0.80, the corn crop is already on the edge of significant drought stress and ‘flash drought’ conditions are forming.

We’ve shown P/PET ratio over the next 7 days compared to the normal (above, first map & chart) for this time of year – and Chinese corn areas are dry to significantly drier than normal. Looking at the current P/ET for this 7-day forecast (below) really brings out the upcoming ‘flash’ drought stress: 65% of China’s maize crop is forecasted to have considerable stress over these next 7 days. Also, note, on the map, that what rainfall is expected in the corn area, is occurring over the same area that has had some decent precipitation the past 30 days…

Corn China 170717 d.png

Yes, temperatures over China’s corn area are forecasted to be significantly hotter than normal (see below) – and thus more atmospheric thirst.   Rainfall over the corn area is expected to be about ‘normal’, but with temperatures much higher than normal, actual crop conditions are likely to be significantly more stressful.

Corn China 170717 c.png



Maximum daily temperatures over the corn area as compared to the last 10 year average (the ‘normal’ or LTN): 42% of the corn area to experience temperatures more than 5’C warmer than normal.


The precipitation over the corn area of China is forecast to be about normal – a little dry but not alarmingly so. The key to the crop’s health will be in the actual PET that takes place; where rains actually fall (and how much) and yes, in the soil moisture reserves.

Corn China 170717.pngCorn China 170717 b.png
The soil moisture reserves will be the subject of another report as the spring in China was very dry.

aWhere July 18, 2017 Update: the current Chinese corn (and soybean) crop are under a flash drought watch.

Topics: Agronomic Insight

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