Characterization and Propagation of Historical and Projected Droughts in the Umatilla River Basin, Oregon, USA

Abstract

Climate change is expected to have long-term impacts on drought and wildfire risks in Oregon as summers continue to become warmer and drier. This paper investigates the projected changes in drought characteristics and drought propagation in the Umatilla River Basin in northeastern Oregon for mid-century (2030–2059) and late-century (2070–2099) climate scenarios. Drought characteristics for projected climates were determined using downscaled CMIP5 climate datasets from ten climate models and Soil and Water Assessment Tool to simulate effects on hydrologic processes. Short-term (three months) drought characteristics (frequency, duration, and severity) were analyzed using four drought indices, including the Standardized Precipitation Index (SPI-3), Standardized Precipitation-Evapotranspiration Index (SPEI-3), Standardized Streamflow Index (SSI-3), and the Standardized Soil Moisture Index (SSMI-3). Results indicate that short-term meteorological droughts are projected to become more prevalent, with up to a 20% increase in the frequency of SPI-3 drought events. Short-term hydrological droughts are projected to become more frequent (average increase of 11% in frequency of SSI-3 drought events), more severe, and longer in duration (average increase of 8% for short-term droughts). Similarly, short-term agricultural droughts are projected to become more frequent (average increase of 28% in frequency of SSMI-3 drought events) but slightly shorter in duration (average decrease of 4%) in the future. Historically, drought propagation time from meteorological to hydrological drought is shorter than from meteorological to agricultural drought in most sub-basins. For the projected climate scenarios, the decrease in drought propagation time will likely stress the timing and capacity of water supply in the basin for irrigation and other uses.

摘要

随着夏季持续增暖变干,气候变化可能会对美国俄勒冈州的干旱和野火风险产生长期且深远的影响。本文研究了本世纪中叶(2030-2059年)和本世纪末(2070-2099年)气候变化情景下俄勒冈州东北部尤马蒂拉河流域干旱特征和干旱传播的变化。本文基于10个CMIP5气候模式降尺度数据和SWAT模型模拟的结果来研究该地区干旱特征的未来变化。本文采用4个短期(3个月)干旱指数来研究干旱特征(频率、持续时间和严重程度),这4个干旱指数为标准化降水指数(SPI-3)、标准化降水-蒸散发指数(SPEI-3)、标准化径流指数(SSI-3)和标准化土壤湿度指数(SSMI-3)。结果表明,短期气象干旱预计将变得更加普遍,SPI-3干旱事件的频率将增加高达20%。短期水文干旱预计将变得更加频繁,且更加严重、持续时间更长,SSI-3干旱事件的频率平均增加11%,平均持续时间增加8%。 同样地,未来短期农业干旱预计将变得更加频繁,SSMI-3 干旱事件的频率平均增加28%,但持续时间略有缩短(平均减少4%)。 从历史上看,大多数流域从气象干旱到水文干旱的干旱传递时间比从气象干旱到农业干旱的传递时间短。未来预估而言,不同类型间干旱传递时间的缩短可能会影响流域灌溉和其他用途的供水时间和能力。