The sensitivity of maize evapotranspiration to vapor pressure deficit and soil moisture with lagged effects under extreme drought in Southwest China

Abstract

Evapotranspiration (ET) is regulated by vapor pressure deficit (VPD) and soil moisture (SM) which are expected to change in global climate change. Understanding the impacts of VPD and SM on maize ET is essential for global food security and water cycle. Here, we estimate the actual maize ET in Southwest China during 2001–2011 based on Mapping Evapotranspiration at High Resolution with Internalized Calibration (METRIC) model using remote-sensing data and reanalysis data. Then, we define the extreme drought events in 2009–2011 using the smoothed standardized anomaly of the three-month Standardized Precipitation Evapotranspiration Index (SPEI) to investigate the responses of maize ET to VPD and SM during extreme drought events in Southwest China. We detected the lag times of maize ET responses to VPD and SM, and then analyzed the sensitivity of maize ET to VPD and SM with lagged effects. We found pervasive lagged responses of maize ET with a shorter lag time of VPD (1.12 ±0.006 months, P < 0.05) than SM (1.28±0.006 months, P < 0.05). We analyzed the lag times of maize ET in relation to elevation, temperature, and precipitation to investigate the abiotic impacts on the lagged responses and found the lagged responses were more prevalent in areas at higher altitudes with lower temperatures but there was less variation across precipitation gradients. Maize ET was more sensitive to VPD than SM with lagged effects. High VPD enhanced maize ET under sufficient SM but during an extreme drought event, maize ET might be dramatically reduced due to SM depletion in spite of high VPD. The study highlights the significance of atmospheric water demand for crop water consumption under extreme climate events.