基于改进SPEI与CMIP6多模式的中国耕地干旱暴露度预估

Projection of Drought Exposure for Cropland in China Based on Modified SPEI and CMIP6 Multi-model Ensembles

摘要:

气候变化加剧使得干旱成为威胁中国国家粮食安全的重大挑战，为保障国家粮食安全与农业可持续发展，迫切需要对我国耕地的干旱暴露风险进行深入研究。传统干旱评估方法因忽略CO2对植被气孔导度的动态调控作用，可能系统性高估了未来干旱风险。本研究基于CO2生理效应的改进标准化蒸散发指数(SPEI（CO2))与CMIP6多模式数据，通过Sen+MK趋势检验、暴露度评估模型和气候-土地利用双因子可加性分解法，系统量化了历史时期（1961—2022年）及未来情景（SSP1-2.6、SSP2-4.5和SSP5-8.5）中国九大农业区的干旱趋势、耕地暴露度及其驱动贡献。结果表明：1961—2022年SPEI与SPEI(CO2)干旱化趋势网格占比分别为77%和64%，未来2023—2100年SPEI呈微弱干旱化趋势（Sen斜率为-0.0013a-1），而SPEI(CO2)呈微弱湿润化趋势（Sen斜率为0.0011a-1），其中北方干旱半干旱区(NASR)和青藏高原区(QTP)差异最为显著。至21世纪末，SPEI和SPEI(CO2)表征下SSP5-8.5情景对应全国0.25°网格的耕地平均暴露度由57km2/a下降为10km2/a，且北方干旱半干旱区(NASR)暴露度峰值下降最为显著。归因分析显示，气候变化主导了未来耕地暴露度变化，近期(2021—2040年)和未来中期(2041—2060年)的降水增加降低了暴露风险，而未来远期(2081—2100年)温度上升驱动了暴露度上升。CO2效应通过抑制蒸散发，在未来远期逆转了SSP2-4.5和SSP5-8.5情景下主要农业区的干旱化趋势。

Abstract:

Climate change intensification has made drought a major threat to food security of China. To safeguard food security and ensure sustainable development of agriculture, it is imperative to conduct in-depth research on drought exposure risks to croplands of China. Traditional drought assessment methods may systematically overestimate future drought risk due to neglect of the dynamic regulatory effects of CO2 (SPEI(CO2)) on stomatal conductance of vegetation. An improved standardized precipitation evapotranspiration index incorporating physiological effects of CO2 was integrated with multi-model data of CMIP6. Using the Sen slope estimator, Mann-Kendall test, an exposure assessment model, and an additive decomposition method considering both climate and land use factors, drought trends, cropland exposure, and driving contributions were systematically quantified across nine major agricultural regions of China during the historical period (1961—2022) and future scenarios (SSP1-2.6, SSP2-4.5, and SSP5-8.5). Results showed that during 1961—2022, grids exhibiting an increasing trend of drought accounted for 77% and 64% for SPEI and SPEI(CO2), respectively. For the future period (2023—2100), SPEI indicated a weak trend of drought intensification (Sen slope: -0.0013a-1), while SPEI (CO2) suggested a weak trend of humidification (Sen slope: 0.0011a-1), with the most significant differences observed in the northern arid and semiarid region (NASR) and Qinghai-Tibet Plateau (QTP). By the end of the 21st century, the national average cropland exposure (based on 0.25° grids) under SSP5-8.5 was estimated at 57km2/a for SPEI and 10km2/a for SPEI (CO2), with NASR showing the most significant reduction in peak exposure. Attribution analysis revealed that climate change dominated dynamics of future cropland exposure: increased precipitation in the near term (2021—2040) and mid-term (2041—2060) reduced risk of exposure, whereas rising temperatures in the long term (2081—2100) amplified exposure. The effect of CO2 suppressed evapotranspiration and reversed intensification of drought in major agricultural regions under SSP2-4.5 and SSP5-8.5 scenarios during 2081—2100.