澜沧江——湄公河流域干旱趋势及其对生态系统碳固定的影响

Drought trend and its impact on ecosystem carbon sequestration in Lancang-Mekong River Basin

全球变暖导致干旱事件频发,强度不断增大,对陆地生态系统碳收支产生了重大影响。本文评估了2000—2019年澜沧江—湄公河(澜湄)流域的干旱趋势,并通过标准化异常指数(SAI)、标准化降水蒸散指数(SPEI)、潜在蒸散(PET)、饱和水汽压差(VPD)和土壤水分(Soil_w)评价了干旱对该流域净生态系统生产力(NEP)的影响。结果表明:①2000—2019年澜湄流域向暖干化发展,主要受降水减少的影响,近1/4的区域遭受了中度以上干旱,其中2009—2016年间干旱事件频发,干旱热点地区位于澜沧江上游和湄公河中下游地区;②尽管澜湄流域碳汇整体上随着气候变暖而增加,但干旱年份植被光合作用降低,生态系统呼吸增加,导致2005年、2010年和2019年湄公河流域生态系统碳源汇发生转变,其中2010年干旱使得GPP减少5.68%,生态系统呼吸增加3.15%,NEP呈现重度异常;③干旱对流域NEP普遍具有滞后效应,整体滞后时间为1~4个月,面积占比为57.82%;④不同水文气候要素对NEP的影响表现出显著的空间差异,其中澜湄流域NEP与VPD整体呈负相关,云南省、缅甸西部、柬埔寨和越南南部的NEP与SPEI呈正相关,而青藏高原NEP主要受到土壤干旱的影响。干旱对澜湄流域生态系统碳固定的影响存在显著的空间异质性,量化干旱对碳固定的影响可以为气候变暖背景下澜湄流域不同地区的生态管理提供参考。

Global warming leads to increased frequency and severity of droughts,profoundly affecting the carbon budget of terrestrial ecosystems.We conducted a comprehensive assessment of drought trends within the Lancang-Mekong River Basin(LMRB)and quantified the impacts of standardized precipitation evapotranspiration index(SPEI),potential evapotranspiration(PET),vapor pressure deficit(VPD)and soil moisture(Soilw)on net ecosystem productivity(NEP)using geographically weighted regression(GWR)method.The GWR analysis demonstrated that drought indices have a significant impact on NEP.From 2000 to 2019,with the decrease of precipitation,LMRB experienced a rise in temperature and a drop in humidity,leading to moderate or extreme drought in around 25%of the LMRB,especially between 2009 and 2016.Drought hotspots were identified in the upper reaches of the Lancang River and the middle and lower reaches of the Mekong River.Drought events in 2005,2010,and 2019 altered the carbon source/sink of the Mekong River Basin ecosystem by decreasing plant photosynthesis and increasing ecosystem respiration.In 2010,for example,drought reduced GPP by 5.68%and increased ecosystem respiration by 3.15%,resulting the anomalies of NEP.The impact of drought on NEP in the LMRB often exhibited a lag effect,with an overall lag duration of 1 to 4 months,covering approximately 57.82%of the area.Spatial differences of the influence of different hydroclimatic factors on NEP were observed.NEP was negatively correlated with VPD in the LMRB,and positively correlated with SPEI in China's Yunnan province,western Myanmar,Cambodia and southern Vietnam.The NEP in the Qinghai-Tibet Plateau was mainly affected by soil drought.This study highlights the significant spatial heterogeneity in the impact of drought on ecosystem carbon sequestration within the LMRB,providing essential insights for ecological management in drought-affected areas.