Assessing the impacts of temperature extremes on crop production in the Adda River basin

Climate change is driving an alarming rise in extreme weather events, including heatwaves, droughts, and floods. Among these, heatwaves stand out as the deadliest, with profound and widespread impacts across multiple sectors. Europe is emerging as a global heatwave hotspot, with heatwave frequency increasing almost four times faster than other northern midlatitudes. Agriculture is the most vulnerable sector to temperature extremes, making adaptation measures essential to support food security worldwide.  

In this work, we investigate the impacts of temperature extremes on agricultural productivity in the Adda River basin in northern Italy, in order to inform the design of adaptation strategies and to respond to projected mid-to-long-term climate change. We first simulate historical crop yields using a detailed, process-based model of the agricultural districts. Then, we use correlation analysis and the Patient Rule Induction Method to identify key drivers of crop failure. These drivers include various indices that quantify the occurrence and intensity of heatwave and drought events. Numerical results suggest that the two most important indices are the number of days above the climatology 90th percentile (NDQ90) in June, calculated with daily maximum temperature, and the nighttime Heat Wave Magnitude Index (HWMI), calculated with daily minimum temperature.  

Lastly, we evaluate the projected evolution of these two indices using six CMIP6 climate models across four climate change scenarios. To integrate climate information independently of specific scenarios, models, or periods, we analyze the ensemble of future projections by focusing on two Global Warming Levels (GWLs) calculated with respect to each model’s pre-industrial global temperature, 1.5 °C and 4.0 °C. These are compared to a baseline at a GWL of 0.69 °C corresponding to the warming level of the climatology used to compute the indices from reanalysis data. Our results show that, while both indices are projected to grow considerably relative to the reference period, HWMI displays the greatest increments, with an ensemble average that increases 21-fold when moving from GWL 0.69°C to 4.0 °C. For NDQ90 in June this variation is from 3.40 to 17.09, indicating that, on average, more than half the days in June will experience extreme maximum temperatures at GWL 4.0 °C. These trends suggest the opportunity to replace some of the crops currently cultivated in the area, primarily maize, with more heat-tolerant varieties, such as soy or cereals, in order to ensure a more reliable production in the coming years and decades.