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Anthony M. DeAngelis, Hailan Wang, Randal D. Koster, Siegfried D. Schubert, Yehui Chang, and Jelena Marshak

MERRA-2, as described in section 2c , is shown in (a)–(c). The Z scores are computed as anomalies normalized by the standard deviation over 1999–2015. The box indicates the core drought region (105°–83°W, 33°–50°N), which is used for computing regional averages throughout the paper. The causes of the 2012 flash drought have been extensively studied yet remain an active area of research. While there is substantial evidence for a connection between North American drought and sea surface

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Lu Su, Qian Cao, Mu Xiao, David M. Mocko, Michael Barlage, Dongyue Li, Christa D. Peters-Lidard, and Dennis P. Lettenmaier

Abstract

We examine the drought variability over the Conterminous United States (CONUS) for 1915-2018 using the Noah-MP land-surface model. We examine different model options on drought reconstruction including optional representation of groundwater and dynamic vegetation phenology. Over our 104-year reconstruction period, we identify 12 great droughts that each covered at least 36% of CONUS and lasted for at least 5 months. The great droughts tend to have smaller areas when groundwater and/or dynamic vegetation are included in the model configuration. We detect a small decreasing trend in dry area coverage over CONUS in all configurations. We identify 45 major droughts in the baseline (with a dry area coverage greater than 23.6% of CONUS) that are, on average, somewhat less severe than great droughts. We find that representation of groundwater tends to increase drought duration for both great and major droughts, primarily by leading to earlier drought onset (some due to short-lived recovery from a previous drought) or later demise (groundwater anomalies lag precipitation anomalies). In contrast, representation of dynamic vegetation tends to shorten major droughts duration, primarily due to earlier drought demise ( closed stoma or dead vegetation reduces ET loss during droughts). On a regional basis, the U.S. Southwest (Southeast) has the longest (shortest) major drought durations. Consistent with earlier work, dry area coverage in all subregions except the Southwest has decreased. The effects of groundwater and dynamic vegetation vary regionally due to differences in groundwater depths (hence connectivity with the surface) and vegetation types.

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Yaling Liu, Dongdong Chen, Soukayna Mouatadid, Xiaoliang Lu, Min Chen, Yu Cheng, Zhenghui Xie, Binghao Jia, Huan Wu, and Pierre Gentine

connection between SM and crops. Simulating cropland carbon fluxes such as soil organic carbon (SOC) decomposition and soil respiration, which are closely affected by SM. Evaluating the effects of alternative cropping pattern on water and carbon fluxes, which may inform regional and local decision making pertaining to environmental and agricultural policies. c. Limitations and uncertainties The extrapolation of the NN model outside the range of training conditions may be the major uncertainty source of

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Richard Seager, Jennifer Nakamura, and Mingfang Ting

national economy. Often not recognized, drought also has serious impacts on the mental health of farming families and people in agricultural communities with long-lasting effects [see U.S.-based review by Vins et al. (2015) ]. Improved understanding and forecasting of drought at least provides the possibility of improved anticipation of, and adaptation to, drought conditions with potential benefits for people and society. Understanding the physical causes of droughts in North America, and the relative

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Chul-Su Shin, Bohua Huang, Paul A. Dirmeyer, Subhadeep Halder, and Arun Kumar

. 2019 ). Regional land surface states (e.g., soil moisture, snow cover, vegetation properties, etc.) also contribute to drought severity and development (e.g., Higgins et al. 1998 ; Schubert et al. 2007 ; Koster et al. 2017 ). In particular, positive feedbacks between land and atmosphere can exacerbate or prolong dry anomalies, playing a role in maintaining droughts (e.g., Durre et al. 2000 ; Fischer et al. 2007 ; Koster et al. 2009 ; Kam et al. 2014 ; Dirmeyer et al. 2015 ; Fernando et al

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