After summer of extreme heat, Chinese growers consider advanced shading and cooler growing locations

Chinese investors are looking to advanced shading and even high altitutude and other cooler locations for plots for future greenhouse projects.  

Temperatures in Shanghai and across China broke records and have got people thinking newly about how to respond. 

Some Shanghai residents were forced into underground air raid shelters during a period of 40 °C days in July and August.  

This kind of thing isn’t just happening here. Many of my Climate Consultant colleagues at Svensson are reporting the effects of a period (September 2023 – August 2024) which globally saw the hottest June to August, as well as the hottest day on record. Overall the entire 12-month period saw a global average surface temperature that was 1.64 °C above pre-industrial levels*.

These temperatures are meant to ring alarm bells. They’re above the so-called “defense line” temperature increase of 1.5 °C.

It’s also kind of illegal.

Remember, 196 governments signed a legally binding agreement (at the 2015 COP climate meeting) to pursue efforts to limit global temperature increases to 1.5 °C above pre-industrial levels.

On a recent trip, I visited growers of lettuce and leafy greens. The spoke about serious quality issues, including leaf burn and heat stress on account of the unprecedented weather.

They know they have to change the way they do things. And they are. They were talking about new heat-resistant crop varieties and changing from tomatoes to water melons. They’re testing chilling irrigation water, which has a cooling effect when the leaves are close to the water (think lettuce). For the future, some are discussing moving production to other cooler regions of China, and yes, altitudinal farming is a topic at the moment. 

It’s hard to build greenhouses on mountains of course, but consider that much of the greenhouse growing in Mexico, for example, is done in Bajío, Jalisco or Michoacán at altitudes above 1000 meters. You can see why they’re thinking this way.  

Greenhouse in Ciudad Guzmán, Jalisco, located at an altitude of 1,550 meters above sea level, where advanced climate control technologies enhance crop production

It’s not that Chinese growers have not considered the changing climate before.

For ten years or so it has been standard for glass greenhouses here to have a frame above the greenhouse. It’s a trellis for the wire bed of a shade screen. Initially growers encountered problems with access for cleaning machines, but more recently the frames have been raised to allow the machines beneath the screens. Inside the greenhouse below, the growers are using at least two screens.

The high temperatures here in Shanghai were also accompanied by very high humidity. That meant that you couldn’t just increase ventilation. When the air coming in is hot and humid, it doesn’t promote plant transpiration like hot dry air does because it is already saturated with moisture. We’ve been writing a fair bit about humidity in recent posts, for example here.

The growers I met were exploring actively cooling the greenhouse. They’d found that fogging and pad and fan systems were not enough to bring temperatures down this summer.

And they are already planning changes in their climate screens. Some have realized that there is an opportunity to use the PARperfect system inside and below the outdoor screens to bring the total amount of light entering down below the typical amount recommended for the crop.

A high trellis above a high roof means additional shade screens can be employed to reduce temperatures inside the greenhouse, cleaning equipment can operate below the trellis, and a benefit is that thrips don't generally fly at this height. In total, five layers of screen are used. Photo courtesy of Tianjin Binhai International Flower Science & Technology Park.

This isn’t really the ideal amount of light, but since stressed hot plants with closed stomata are not using light for productive growth anyway, it’s important to simply reduce temperature.

The PARperfect system cuts total light, but ensures that the light that is coming in is as beneficial and homogenous as possible. You can reduce temperatures and that can be absolutely critical.

All told, this summer has really got people thinking differently here in China. They’re looking for new solutions and now even new plots of cooler land.

What’s your experience?

I’m curious to hear from you, whatever region you are in, how you have been coping with the hot weather this last summer? Have you considered outdoor screens or are you buying new heat-resistant varieties? Are you even looking at installing cooling systems or starting over with a semi-closed greenhouse system? And what about plots of land in cooler, high altitudes, is that something that’s also on the radar of owners and investors where you operate? I look forward to your insights—feel free to share your thoughts here.

*http://climate.copernicus.eu/surface-air-temperature-august-2024