Impacts of Climate Warming on the Spatiotemporal Dynamics of Agro-Climatic Boundaries

This study aimed to elucidate the spatiotemporal evolution patterns of agroclimatic boundaries under climate warming and their impacts on grain yield, thereby providing a scientific basis for optimizing agricultural layouts and formulating climate change adaptation strategies.

Using meteorological data from 495 national stations in China (1961-2020), the spatiotemporal changes of major agroclimatic boundaries before and after climate abrupt changes were explored, including the January 0 ℃ isotherm, ≥10 ℃ accumulated temperature isopleth of 4500 ℃, and 200, 400, and 800 mm precipitation isopleths, via methods such as Mann-Kendall change-point detection and contribution rate analysis. Their migration patterns and quantified their contribution rates to grain yield per unit area were further characterized.

(1) Abrupt changes were detected in the national average January temperature in 1987, the ≥10 ℃ accumulated temperature in 2002, and precipitation in 2015, with post-change increases of 0.96 ℃, 251.19 ℃, and 53.58 mm, respectively. (2) Following the abrupt change in January mean temperature, the 0 ℃ isotherm shifted northward overall. Its eastern segment (Shaanxi, Henan, Anhui, Jiangsu, and Shandong) exhibited significant fluctuations with a northward migration amplitude of 1.5° latitude. (3) After the abrupt change in ≥10 ℃ accumulated temperature, the 4500 ℃ accumulated temperature isopleth expanded northward, with its eastern segment (Shaanxi, Hebei, and Shandong) showing pronounced northward migration. The northernmost boundary shifted from central Hebei Province (38.9 °N) pre-mutation to traversing the Beijing-Tianjin-Hebei region (39.7 °N) post-mutation, while the western segment (Xinjiang and Gansu) showed gentle changes. (4) Precipitation isohyets exhibited a northward and westward migration trend in some regions: the 200 mm precipitation isopleth extended westward by approximately 3.0° longitude in Inner Mongolia, shrinking arid areas; the 400 mm precipitation isopleth shifted northward by about 5.5° latitude in Inner Mongolia, expanding semi-humid regions northward; and the 800 mm precipitation isopleth moved northward by around 2.5° latitude in Sichuan Province, expanding humid regions northward. (5) The contribution rates of ≥10 ℃ accumulated temperature and precipitation to meteorological grain yield per unit area increased after the abrupt change, with precipitation showing the highest contribution rate of 27.10%, while the contribution rate of January mean temperature decreased post-mutation.

After the abrupt change driven by climate warming, China's January 0 ℃ isotherm and the ≥10 ℃ accumulated temperature isopleth of 4500 ℃ have shifted northward overall, with the segment east of Shaanxi Province being particularly pronounced. The 200 and 400 mm precipitation isohyets have shifted northward and westward in the Inner Mongolia region after the abrupt change. The 800 mm precipitation isohyet has moved southward in Nanyang (Henan) and Bozhou (Anhui), while the remaining segments have shifted northward, among which the segment in central Sichuan Province showed a significant northward migration (by approximately 2.5° latitude). In the fluctuation zones of agroclimatic boundaries, changes in hydrothermal conditions have promoted an increase in grain yield per unit area.