Research papersClimate change effects on reference crop evapotranspiration across different climatic zones of China during 1956-2015

- Temperatures increased, but relative humidity, wind speed and sunshine hour decreased.
- More generally decreasing trends than increasing trends in annual ET0 were found.
- Abrupt changes were detected in 1990s in the MPZ, while in 1980s in the other zones.
- Relative humidity was the most sensitive climatic variable except for the MPZ.
- Increasing ET0 after 1985 increases crop water demand and aggravates water shortage.

Global climate change has been an increasing challenge to agricultural ecosystems, which will significantly affect the reference crop evapotranspiration (ET0) and subsequently crop water requirements. In this study, the temporal trends and magnitudes of key climatic variables and the accompanying effects on ET0 during 1956-2015 were evaluated at 200 meteorological stations across the temperate continental zone (TCZ), temperate monsoon zone (TMZ), mountain plateau zone (MPZ), and subtropical monsoon zone (SMZ) of China. Results show that maximum and minimum temperatures have increased significantly over the past 60 years, whilst relative humidity, wind speed and sunshine hour exhibited significant decreasing trends across all climatic zones. The overall decreasing trends in annual ET0 were more pronounced than the increasing trends, whereas more increasing trends were found in spring and winter. Abrupt changes for climatic variables and ET0 series were detected in 1990s in the MPZ, while in 1980s in the other climatic zones mainly due to the aggregated emission of greenhouse gases and air pollution from energy consumption in recent decades. Relative humidity was the most sensitive climatic variable in all climatic zones except for the MPZ where ET0 was most sensitive to sunshine hour. However, ET0 had different responses to changing climatic variables in different regions and climatic conditions. The negative contribution of wind speed to the decrease in ET0 was greater than the other climatic variables in the TCZ and the TMZ, whilst the significant increase in minimum temperature and the decrease in sunshine hour contributed most to increasing ET0 in the MPZ and to decreasing ET0 in the SMZ, respectively. Although ET0 displayed a generally decreasing trend during 1956-2015, there was a significantly increasing trend from 1985 to 2015 across China except for the SMZ, especially in the arid and semi-arid zones of China during dry seasons (spring and winter). This may lead to the increase in crop water requirements and aggravate the water shortage in these areas in view of the increase in ET0 in response to ongoing climate change.