Abstract
Drought during the early vegetation growing season (spring through early summer) is a severe natural hazard in the large cropland over North America. Given the recent increasing severity of climate change manifested as surface warming, there has been a growing interest in how warming affects drought and the prospect of drought. Here we show the impact of boreal warming on the spring and early summer drought over North America using Cyclostationary Empirical Orthogonal Function analysis. Northern Hemispheric warming, the leading mode of the surface air temperature variability, has led to a decrease in precipitation, evaporation and moisture transport over the central plain of North America. From a quantitative assessment of atmospheric water budget, precipitation has decreased more than evaporation and moisture transport, resulting in increased (decreased) moisture in the lower troposphere (land surface). Despite the increased moisture content, relative humidity has decreased due to the increased saturation specific humidity arising from the lower-tropospheric warming. The anomaly patterns of the soil moisture and Palmer Drought Severity Index resemble that of the anomalous relative humidity. Results of the present study suggest a credible insight that drought in the main cropland will intensify if the anthropogenic warming continues, exacerbating vulnerability of drought.
Highlights
Surface warming due primarily to the anthropogenic forcing has been observed to be significant, over the Northern Hemispheric continents
Combining the cyclostationary empirical orthogonal function (CSEOF) loading vector and the corresponding principal component (PC) time series shows how the spatial patterns of warming have amplified in North America
The long-term warming over NH is a robust phenomenon in much of the North America region considering the overall positiveness of the CSEOF loading vector and a clear increasing trend in the PC time series
Summary
Surface warming due primarily to the anthropogenic forcing has been observed to be significant, over the Northern Hemispheric continents. The global warming has become a serious issue in the context of its long-term climatic effects such as addressed above and because of its impact on the characteristics of weather extremes[7,8,9,10,11]. The latter affects the life on the earth significantly. This study aims to understand spring to early summer drought mechanism over the central plain of North America due to the overall Northern Hemispheric warming. The CSEOF analysis is a powerful method of assessing the space-time evolution of climate variability and its relationship with a chosen target phenomenon[29,30]
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