西南地区土壤湿度与气候之间的互馈效应

土壤湿度控制着陆气之间的水热交换,与气候具有互馈效应。为了揭示中国西南地区土壤湿度与气候之间的关系,基于39年GLDAS数据,采用线性倾向估计、偏相关等方法探究了该区域土壤湿度与降水、气温的时空规律及相关性,分析了土壤湿度记忆性(Soil Moisture Memory,SMM)的空间分布及季节特征。主要结论如下:(1) 1979—2017年,西南地区仅表层(0—10cm)年平均土壤湿度呈显著减少趋势(P 0.001),气候倾向率为0.7 kg/m2/10 a,年降水量呈不显著增加趋势,而年平均气温呈显著的增加趋势(P 0.001)。(2)多年平均状态下,表层与更深层(10—40、40—100、100—200 cm)的土壤湿度呈相反的空间格局,中层(10—40、40—100 cm)土壤湿度最高。(3)基于像元的偏相关系数表明研究区土壤湿度总体上与降水关系更密切,二者呈正相关,但在0—10 cm,部分地区相关性不显著。(4)西南地区SMM总体上以60—90 d为主,且SMM均值以夏季最长,其次为冬季和春季,秋季最短;同时,对比各深度的SMM,发现0—10 cm的土壤湿度对整个西南地区长期的气候预测具有更好的代表性。研究结果可为研究西南地区陆-气相互作用以及气候预测与模式评估等提供参考依据。

Relationship between soil moisture and climate and its memory in Southwest China

Soil moisture controls the water and heat exchange between the land and atmosphere, and has mutual feedback effects with climate. To reveal the relationship between soil moisture and climate in Southwest China, this study analyzed the spatial-temporal regularity and correlation of soil moisture with precipitation and temperature, using linear tendency estimation and partial correlation, respectively, based on 39-year GLDAS data, and determined the spatial distribution and seasonal characteristics of soil moisture memory (SMM). The main conclusions were as follows:(1) from 1979 to 2017, the annual average soil moisture in the surface layer (0-10 cm) of Southwest China showed a significant decreasing trend (P < 0.001), the climatic tendency rate was 0.7 kg/m²/10 a, the annual precipitation showed no significant increasing trend, but the annual average temperature showed a significant increasing trend (P < 0.001); (2) under the multi-year average condition, the spatial pattern of soil moisture in the surface layer was opposite to that in the deeper layer (10-40, 40-100, 100-200 cm), and the soil moisture in the middle layer (10-40, 40-100 cm) was the highest; (3) pixel-based partial correlation coefficients show that soil moisture in the study area is generally more closely related to precipitation, and are positively correlated, but at a depth of 0-10 cm, the correlation was not significant in some areas; (4) SMM in Southwest China was mainly 60-90 days, the mean SMM of the study area was the longest in summer, followed by winter and spring, and the shortest in autumn; meanwhile, compared with other SMM depths, soil moisture at a depth of 0-10 cm was more representative for long-term climate prediction in Southwest China. The results from this study could provide a reference for the study of land-air interaction, climate prediction, and model assessment in Southwest China.