<p>Human activity, namely irrigation, more strongly shapes the Po Plain's groundwater supply than natural dynamics like snowpack or precipitation, according to a new study led by ESPM researchers.</p>
Farmers across the fertile expanse of northern Italy’s Po Plain have historically relied on snowmelt from the nearby Alps to irrigate their crops. The region grew over the past century into both a critical breadbasket for Italy and one of the largest water users in the European Union.
As climate changes and drought intensifies, a new analysis led by researchers at the University of California, Berkeley, reveals that the amount of water stored in underground aquifers has markedly declined between 2015 and 2022. The study, which was published today in Nature Water, found that human activity—namely irrigation—more strongly shapes the region’s groundwater supply than natural dynamics like snowpack or precipitation.
To conduct their research, the authors leveraged data reported by NASA’s Gravity Recovery and Climate Experiment (GRACE) satellites and from a network of more than 1,000 underground observation wells to calculate fluctuations in the amount of groundwater stored in underground aquifers. While their study showed a recent decline in the Po Plain’s groundwater stores, they also found a surprising twist: irrigated areas within the region are actually more resilient against this decline due to groundwater recharge linked to irrigation practices.
“When we started this research, we were expecting irrigation to have a negative implication on groundwater level because groundwater is often used to supplement dwindling surface water reserves in times of drought,” said senior author Manuela Girotto, an associate professor in the Department of Environmental Science and Policy Management. “But in this region, we found the opposite.”
When snow melts in the Alps, the runoff feeds into rivers and lakes, which, in turn, supply water for irrigation. “But irrigation water across the Po Plain is applied very inefficiently, meaning that more water is being used than is needed for the crops,” said lead author Grace Carlson, a postdoctoral researcher in Girotto’s lab. During the irrigation season, which lasts from May through September, only half of the water distributed to farmland is retained in the soil and used by crops.
“The rest of the water runs off or percolates into the underlying aquifer. Because irrigation continues even during drought, this makes irrigated areas more resilient,” Carlson added.
While irrigation helps some regions maintain a high water table, areas that lack this form of irrigation experience more severe declines in groundwater due to the lack of groundwater recharge. The authors are concerned that the groundwater balance of the Po Plain may continue to shift under climate change.
“There are important questions that still need to be asked about the sustainability of these irrigation practices into the future, as surface water supplies are likely to be negatively impacted by changing snow accumulation and melt in the Alps,” said Carlson.
The study was done in collaboration with international scientists from the Italian National Research Council and the University of Milano-Bicocca. Additional UC Berkeley co-authors include former undergraduate research assistant Andrew Wilder, BA ’23 Data Science, and Destinee Whitaker, an HBCU-Berkeley Environmental Scholars for Change program participant who conducted summer research with Girotto in 2023.
Read the full study online in Nature Water