Researchers have made a fascinating discovery that the place rainfall derives from—the land or the sea—has huge bearing on how well crops will grow. Rain arising from the ocean, they found, is more reliable, whereas crops relying mainly on land-derived rainfall are more likely to struggle with unpredictability and drought. 

Their study delves into what lies behind this land/ocean divide, and started with 16 years of satellite rainfall data, spanning the period between 2003 and 2019. Paired with rainfall models, the satellite data enabled the researchers to trace back where regional rainfall originated from: either through evaporation from the sea surface or from soils, forests, and other ecosystems on land. 

Then, looking at key crops like maize, wheat, soybeans, and rice, and measuring traits like vegetation greenness that can be detected by satellites—greenness being a good proxy for growth levels—they determined how rainfall patterns affected the growth and yields of those crops.

This revealed that when the share of land-derived rainfall makes up 36% or more on croplands, they tend to suffer more. Two examples are the US Midwest and parts of East Africa, regions that both rely more heavily on rainfall that arises specifically from local land-based sources. The researchers found that crops in these regions are more likely to experience lower rainfall levels, more drought, and reduced productivity. 

The study also notes that 40% of global maize and 60% of global wheat crops—two of the world’s staple crops—receive most of their rainfall from land-based evaporation, showing how consequential fluctuations in this rainfall variety could be. 

Meanwhile, regions that receive less of their rainfall from the land and more from marine sources tended to experience more consistent rainfall patterns, leading to more stable growth and yields. 

The factor behind this phenomenon, it seems, is the ongoing degradation of key rainfall reservoirs on land. Deforestation, often to make way for farmland, shrinks the acreage of dense, vapor-producing vegetation. Soils that become more exposed through erosion and poor farming methods are then less capable of locking in moisture that can later be evaporated to seed rainfall. 

As these habitats are eroded, they become a less reliable source of moisture to drive rain, which in turn becomes less consistent and abundant. 

This illustrates a concerning cycle of destruction between agriculture and the ecosystems that sustain it—but also highlights focal points for action, the researchers say. 

Knowing the regions and crops that are most dependent on land-based sources could help us identify the specific landscapes and habitats that need protection to sustain the rain—whether through forest conservation, the reestablishment of natural wetlands, and better soil preservation. As the researchers put it: “Protecting these ecosystems isn’t just about biodiversity—it’s about sustaining agriculture.”

Jiang, Y. & Burney, J. A. “Crop water origins and hydroclimate vulnerability of global croplands.” 

Image: Based on Brocken Inaglory via Wikimedia Commons