Climate change and pesticides

According to current research at the Rossby Centre at the Swedish Meteorology and Hydrology Institute (SMHI), climate change will result in a wetter and warmer climate, with rainfall and temperature predicted to increase more during the winter months. Extreme high intensity rainfall events are also predicted to become more frequent.

This diagram shows mean monthly precipitation in January (1961-1990) and the predicted increase in mean precipitation during two future 30-year periods, according to SMHI’s regional climate scenarios for Sweden based on IPCC emissions scenario A2 and the GCM model ECHAM4.

Climate change can increase the risk of diffuse losses of pesticides to the environment, i.e. mainly those losses occurring from agriculture. This is likely to be a result of indirect effects, i.e. how climate change will affect pesticide use. Changes in the amount and intensity of precipitation can increase the risk of leaching in the form of increased flow through macropores in the soil, but also in the form of surface runoff following high-intensity precipitation events, though this may be counteracted by increased temperature allowing for a faster decomposition rate.

There are several different conceivable indirect effects of climate change:

1. Changes in the amount and intensity of rainfall can increase the risk of leaching in the form of increased flow through macropores in the soil, but also in the form of surface runoff following high-intensity rainfall events. An increase in temperature could counteract the leaching of pesticides by resulting in a higher degradation rate, but in certain regions higher temperature could cause drought, which would inhibit pesticide degradation. Soil organic carbon content is very important for binding pesticides to the soil and it can be expected to decrease in a future warmer climate, which is positive from a leaching perspective, although higher temperatures will mean that organic material is broken down more quickly in certain areas. The combined impact of these factors on the risk of pesticide leaching is difficult to predict and can be expected to vary between different regions.
2. A longer growing season can allow earlier application of pesticides, which can be beneficial since there is a longer time available for degradation. However, autumn spraying can also be expected to be delayed owing to the greater area of winter crops grown, which may increase leaching, as precipitation in autumn/winter is predicted to increase.
3. Changes in land use, changes in crop rotations and the introduction of new varieties will change the need for pesticides.
4. Higher moisture and higher temperature will increase the pressure from pests, and probably result in an altered weed flora, which is expected to increase the need for pesticides. Most of the pesticides used within agriculture today are herbicides, but climate change may result in a greater need for insecticides and fungicides in the future.

Research and advisory services are incredibly important tools when it comes to reducing the use of pesticides, particularly in light of climate change, and it is therefore important to start at an early stage. Environmental monitoring of pesticides will continue to be important and may need to be intensified, with denser sampling during the growing season and also during the winter season, and with more ‘type areas’ farther north in the country.