Spatiotemporal variation of dry-wet climate during wheat growing seasons from 1961 to 2020 in China

As the intensity of climate change increases, global warming continues to affect the hydrological cycle and precipitation characteristics. Changes occur at various locations owing to interregional differences in the intensity and distribution of precipitation and evapotranspiration. To determine the dry-wet climate distribution during the wheat growing season in wheat planting regions of China and the changes that have occurred over the past 60 years, we analyzed the temporal and spatial variation characteristics of China’s dry-wet climate over the inter-annual and inter-decadal periods from 1961 to 2020 (P1: 1961–1990; P2: 1991–2020). To explore how dry-wet climate changes, a series of dry-wet indices, such as effective precipitation, crop water demand, and water surplus and deficiency (difference between effective precipitation and crop water demand) were used. A Standardized Precipitation Evapotranspiration Index was used in this study for drought risk assessment in cropping regions. In this study, 524 meteorological stations with 60-year data records of China’s wheat planting regions were selected and divided into ten wheat planting regions. These regions are as follows. Spring wheat: Northeast China Spring Wheat Region, NES; Northern Inner Mongolia Spring Wheat Region, NIMS; Northwest China Spring Wheat Region, NWS; Northern Xinjiang Spring Wheat Region, NXJS. Winter wheat: Northern China Winter Wheat Region, NW; North China Plain Winter Wheat Region, NCW; Middle-Lower Reaches of Yangtze River Winter Wheat Region, MLYRW; Southwest China Winter Wheat Region, SWW; South China Winter Wheat Region, SCW; Xinjiang Winter Wheat Region, XJW. The results showed that precipitation exceeded the crop water requirements during the wheat growing season in the SCW, SWW, and MLYRW regions over the past 60 years. Other regions experienced water deficits during the wheat growing season, with XJW (443 mm) and NXJS (495 mm) exhibiting the highest water deficit values. Estimates of effective precipitation, crop water demand, water surplus and deficit for the national wheat growing season ranged from 2.0–1320.0, 156.0–832.0, and 828.0–1081.0 mm, respectively. Both values showed a clear zonal distribution from southeast to northwest. In this study, drought frequency was calculated as 35.2%–59.6% for the national wheat growing season; it was more than 50.0% in the spring wheat regions and MLYRW regions. The frequencies of mild, moderate, and severe droughts during the wheat growing seasons were 18.7%–46.0%, 0–21.5%, and 1.7%–11.6%, respectively. The analysis showed that during the wheat growing season, effective precipitation volatility increased from 1961 to 2020, and crop water demand decreased and then increased again. The NCW and NW regions exhibited a drying climate, while the other regions showed a wetting climate trend. Further analysis revealed interregional differences in the climatic mechanisms of the wet-dry crisis in wheat planting regions. In NES, NIMS, NXJS, and XJW regions, effective precipitation increased and crop water demand decreased. Meanwhile, in MLYRW, effective precipitation and crop water demand increased, but the increase in precipitation was higher than that in crop water demand. Interdecadal variability in effective precipitation indicated a modest rising tendency; crop water demand declined in the P1 period and grew in the P2 period, whereas water surplus and deficit increased in the P1 period and decreased in the P2 period, respectively. This study makes an essential contribution to the research on the proper response of agriculture to climate change by showing the temporal and spatial variations of the dry-wet climate in China’s wheat regions.