Recent Decline of Irrigation-Induced Cooling Effect Over the North China Plain in Observations and Model Simulations

Irrigation over the North China Plain (NCP) has been demonstrated to lower temperature by altering the surface energy budget. During past decades, the concurrence of irrigated area variation and reduced irrigation intensity prompted our investigation into whether there has been a temporal change in irrigation cooling effect over the NCP, which is largely unknown. Using historical observations in 1979-2018, we detect a shift in the cooling effect occurring around 1995, when the expansion of irrigated area was going to slow down and water-conserving irrigation technology was boomingly introduced. After this time, the accelerated process of cooling effect (-0.0045 degrees C year(-1)) switches to a decelerated one (0.0089 degrees C year(-1)). Regional climate simulations also show a pronounced slowdown in irrigation-induced cooling with the rate of 0.0081 degrees C year(-1). The irrigation-induced cooling is expected to be weaker with the persistent reduction in agricultural water use and contribute to a more rapid warming.

Automated summary

Irrigation activities over the North China Plain have been found to lower temperature by altering the surface energy budget. However, our investigation reveals a shift in the cooling effect around 1995, coinciding with changes in irrigated area expansion and water-conserving irrigation technology. The subsequent deceleration in irrigation-induced cooling is expected to contribute to a more rapid warming.