Drought-Rich Periods Are More Likely Than Flood-Rich Periods in Brazil

IF 4.6 1区 地球科学 Q2 ENVIRONMENTAL SCIENCES
Vinícius B. P. Chagas, Pedro L. B. Chaffe, Günter Blöschl
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Abstract

Streamflow exhibits persistent decadal variability; however, it is unclear if the magnitude and spatial extent of these variabilities are symmetric for droughts and floods. Here, we examine drought-rich and flood-rich periods in 319 streamflow gauges in Brazil from 1940 to 2020. Drought- and flood-rich periods are detected by computing annual streamflow minima and maxima time series and using scan statistics to verify if events exceeding a threshold follow a Bernoulli process. We contrast streamflow time clustering with rainfall, evaporation, water abstraction, the Atlantic Multidecadal Oscillation (AMO), and the Pacific Decadal Oscillation (PDO). We detected a higher spatial frequency of drought- than flood-rich periods. For 5-year return period thresholds, drought-rich periods are observed in 81% of the basins, 16.7 times the false positive rate (4.8%) and 4.7 times flood-rich periods (17%). This asymmetry is linked with sharp increases in water abstractions since the 1990s and a higher prevalence of rainfall-poor periods (41% of gauges) compared to rainfall-rich (22% of gauges), which we interpret as being further amplified into drought-rich periods due to an interannual persistence of water storage deficits. Brazil experienced a dry period until the 1960s, extensive flooding in the 1980s, and record low flows from the 2000s onward. Drought and flood-rich periods are well aligned with rainfall clustering, water abstractions, the AMO and PDO. Droughts-rich periods are more frequent in shorter time scales (several years to one decade) and flood-rich periods in longer time scales (a few decades). Our findings highlight the nonlinearity and asymmetry of drought and flood change at decadal scales.
巴西出现干旱多发期的可能性大于洪水多发期
溪流表现出持续的十年变异性;然而,这些变异性的程度和空间范围是否在干旱和洪水中对称尚不清楚。在此,我们研究了 1940 年至 2020 年巴西 319 个流量计的干旱多发期和洪水多发期。通过计算年度溪流最小值和最大值时间序列,并使用扫描统计来验证超过阈值的事件是否遵循伯努利过程,从而检测出干旱和洪水多发期。我们将溪流时间聚类与降雨、蒸发、取水、大西洋十年涛动(AMO)和太平洋十年涛动(PDO)进行了对比。我们发现干旱多发期的空间频率高于洪涝多发期。在 5 年重现期阈值下,81% 的流域观测到干旱多发期,是假阳性率(4.8%)的 16.7 倍,是洪涝多发期(17%)的 4.7 倍。这种不对称性与 20 世纪 90 年代以来取水量的急剧增加以及降雨稀少期(41% 的水文站)高于降雨丰富期(22% 的水文站)有关。巴西在 20 世纪 60 年代之前经历了干旱期,20 世纪 80 年代经历了大洪水,21 世纪以来则出现了创纪录的低流量。干旱和洪水多发期与降雨集群、取水量、AMO 和 PDO 非常吻合。在较短的时间尺度上(几年到十年),干旱多发期更为频繁,而在较长的时间尺度上(几十年),洪水多发期更为频繁。我们的研究结果凸显了十年尺度上干旱和洪水变化的非线性和非对称性。
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来源期刊
Water Resources Research
Water Resources Research 环境科学-湖沼学
CiteScore
8.80
自引率
13.00%
发文量
599
审稿时长
3.5 months
期刊介绍: Water Resources Research (WRR) is an interdisciplinary journal that focuses on hydrology and water resources. It publishes original research in the natural and social sciences of water. It emphasizes the role of water in the Earth system, including physical, chemical, biological, and ecological processes in water resources research and management, including social, policy, and public health implications. It encompasses observational, experimental, theoretical, analytical, numerical, and data-driven approaches that advance the science of water and its management. Submissions are evaluated for their novelty, accuracy, significance, and broader implications of the findings.
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