The cost of mismanaging crop heat stress with irrigation: Evidence from the mid-south USA

Field level data from a voluntary water use reporting program in the Delta region of Mississippi (MS), USA, provides empirical evidence that crop growers increase the amount of groundwater pumped for irrigation during periods of high temperature (degree days above 32 C). Regression analysis reveals that growers apply excess irrigation to cope with high temperature conditions while growing season evapotranspiration and precipitation are not significant factors in their decision of how much irrigation to apply. The existing literature indicates that excess water does not alleviate the harmful effect of extreme heat, making the excess irrigation wasteful and costly. Additional degree days above 32 C are associated with a 4.6 mm increase in irrigation depth (46 m3ha−1). This result may be partially explained by the fact that most farmers use visual cues (such as leaf folding which correlate with air temperature) to initiate irrigation events regardless of soil moisture contents. To quantify the impact of this mismatch, we estimate that shifting the underlying sensitivity in the farmers’ minds by 1 C would reduce groundwater pumpage by 800862 mega liters across the Delta region of Mississippi, USA. The monetary cost of mismanaging heat stress with excessive irrigation is estimated at a minimum of over US$33 million per year. We further identify two additional possible distortions affecting the demand for irrigation groundwater: (i) overestimated benefits from irrigation; and (ii) underestimated groundwater pumping cost. The policy implication is that more efforts and incentives should be placed for programs that affect the producers’ water management mindset, such as "Master Irrigator" programs that will reduce or eliminate the identified groundwater distortions and optimize benefits from irrigation.