Spatiotemporal variation characteristics of drought trend at annual of wheat-maize in the North China Plain based on SPEI_Kc index

The North China Plain (NCP) is an important wheat-maize production region in China with limited water resource. Drought is one of major agro-meteorological disasters for the local agricultural production. This study introduced crop coefficient Kc into calculation of Standardized Precipitation Evapotranspiration Index (SPEI) to analyze drought condition. The method was compared with the two methods including SPEI based on Thornthwaite (SPEI_TW) and Penman-Monteith (SPEI_PM). Multi-year meteorological data in the North China Plain were obtained. The applicability of these three SPEI indexes in the annual drought assessment of wheat-maize was assessed based on historical disaster data. The spatial and temporal distributions and variations of annual drought during both winter wheat and summer maize growth season from 1961 to 2017 were analyzed. To understand the effect of climate change on wheat-maize, the study further analyzed the results at the key growth period scale and the annual scale. The results showed that SPEI_KC could be a better index than SPEI_TW and SPEI_PM to evaluate crop drought. Compared with the observed actual disaster data, SPEI_KC had the best applicability to assess annual scale of wheat-maize drought among the SPEI_TW index and SPEI_PM index in the North China Plain. For the condition with right evaluation when the drought was present, the average accuracy of SPEI_Kc index in representing meteorological stations was up to 76.13%, which was 11.11 and 5.55 percent points higher than SPEI_TW index and SPEI_PM index, respectively. For the condition with right evaluation when the drought was not found, the accuracy of SPEI_KC index was 85.67%, which was 1.36 and 0.13 percent point higher than SPEI_TW index and SPEI_PM index, respectively. Spatial distribution of drought during the key growing period and the growth season of wheat and maize showed highly similar rules: light drought frequency at the key growing period and the growth season of wheat was high in the north of Heibei Province and serve drought frequency was high in the North China Plain; moderate drought frequency at the key growing period and the growth season of wheat was high in the north of Heibei Province. The drought intensity was strong in the northwest of the North China, weak in the southeast, mainly in the Henan. The average frequency of light drought was higher than 33.08%, the frequency of moderate drought was 10.08%, the average frequency of severe drought was higher than 6.14%. The drought frequency in the North China Plain showed a slight decreasing trend. The frequency of light drought increased at majority timescale and moderate drought and severe drought decreased at all of time scale. Moreover, the drought frequency decreased during the key growing period of wheat and the growing season of wheat and maize, and increased during the key growing period of maize and wheat-maize rotation. Our study revealed the temporal and spatial variation and the characteristics and causes of meteorological drought in North China Plain, and provided reasonable measures to deal with climate change.