Fallowed Heat Island: High surface temperature from fallowed agricultural lands increases nearby water demand and reduces crop yield.

Md Minhazul Kibria, Adeyemi A Adebiyi , John Abatzoglou

Agricultural land fallowing is a practice of temporarily idling farmlands to maximize soil water storage, restore plant nutrients, and minimize soil erosion hazards. Despite the benefits of land fallowing, it remains unclear to what extent it affects nearby crop productivity. Here, we show that one such effect is through the fallowed heat island, a concept similar to urban heat island, whereby exposed fallowed agricultural lands absorb solar radiation and retain heat more than their surrounding irrigated croplands. Using high-resolution satellite based surface temperature and evapotranspiration information over California’s Central Valley, we find that the fallowed heat island effects raise the summer surface temperature of nearby agricultural fields by as much as 6°C. In addition, this effect also results in a significant evapotranspiration deficit of up to -60 mm in the adjacent agricultural croplands, corresponding to almost 40% additional water demand compared to ideal conditions. Furthermore, we also find that the compound temperature-moisture effects of the fallowed heat island result in a reduction of up to 5% in corn crop yield relative to the county-level baseline. Overall, our findings have significant implications for sustainable water management policies and for spatially informed agricultural planning that considers changes in local microclimates.