29 March 2024

In northern China, spring irrigation mitigates effects of heat waves

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A good irrigation strategy is crucial as the increasing frequency of extreme events favors floods and droughts. Photo: Global Water Forum CC BY 2.0 DEED Attribution 2.0 Generic

Combination of spring and summer irrigation “reduces the frequency and intensity of extreme heat events by 6.5 days and 1°C,” according to a Chinese study

by Matteo Cavallito

 

Soil irrigation conducted in spring seems to reduce the impact of summer heat waves by helping to maintain higher soil moisture levels. This is suggested by research published in the journal Geophysical Research Letters.

“Based on partial correlation analysis of data products,” the study explains, “we find positive correlations between spring and summer soil moisture, suggesting that spring irrigation-induced water surplus persists into the following summer and affects regional climate by impacting surface energy partitioning.”

The study

The survey, conducted by researchers at Hohai University in China, focused on irrigation practices conducted between March and May and those carried out between June and August in the North China Plain, one of the most intensively irrigated areas in the country, notes a statement released by the authors.

This is a critically important agricultural area that covers 400,000 km2 and in which wheat crops in winter and corn crops in summer alternate between seasons. The area alone contributes more than a third of the country’s production (37 percent).

Researchers analyzed soil moisture patterns at plant root level since 1980. They also combined the data with a forecast model to simulate the effect of water usage on the impact of extreme summer heat waves from 2004 to 2018. Three scenarios were studied: without irrigation, both spring and summer irrigation, and spring intervention only.

Irrigation in spring reduces the impact of summer heat.

Simulated regional averages of extreme heat waves show a temperature of 35.8°C and a duration of 21.7 days. The positive impact of spring irrigation, the authors observe, reduced the intensity of summer heat waves by lowering temperature by 0.29°C and duration by 2.5 days. Even more significant are the results of combining spring and summer irrigation practices.

Indeed, the latter combination, the study reports, “significantly reduces the frequency and intensity of summer extreme heat events by approximately −6.5 days and −1.0°C, of which spring irrigation contributes about 38% and 30%, respectively.”

The effect of so-called soil moisture memory, which is shown in the ability to maintain higher moisture levels between seasons, is crucial. Similar patterns in this regard have been observed in the southern Great Plains, the Huang-Huai-Hai Plain, and the south-central areas of the Yangtze River Basin.

Climate change makes extreme events increasingly frequent

The research takes on particular value in today’s picture of increasing frequency of extreme events that can promote floods and droughts. The intensification of heat waves, the authors note, is facilitated by climate change and poses a threat to agricultural yields.

In this context, in addition to alleviating water stress in the subsequent summer months, the authors point out, applying more water in the spring can reduce the wastage of the resource favored by evaporation in the summer.

“Our findings underline the importance of irrigation-induced climate impacts in mitigating extreme heat events and emphasize that climate change adaptation planning in terms of irrigation must account for cross-seasonal climatic effects,” the research concludes.