Propagation in the Drought Cascade: Observational Analysis Over the Continental US

Abstract

Persistent deficits in meteorological, hydrological and ecological variables define different types of drought that are often linked together in a cascade. The drought cascade is an emergent phenomenon in the climatic system. A quantitative evaluation of the drought cascade based on observations is both a rigorous test of how different components of numerical Earth System models interact with one‐another and a useful tool for practitioners concerned with drought impacts on water resource and ecosystem services. In this study the drought cascade is characterized over the continental US using remote sensing data and in situ observations. Remote sensing fields of coincident vegetation photosynthesis and above‐ground biomass anomalies are introduced into the cascade to assess the role of the terrestrial biosphere within the cascade. The propagation of the diverse drought types, in terms of amplitude‐dampening and phase‐delays, are quantified. It is shown that woody and herbaceous vegetation have contrasting responses to prolonged soil moisture deficit that is traceable to access and storage of water as well as the dual effects of water‐ and light‐limitation. The observations also show that prolonged precipitation deficit in itself is not adequate to trigger the intense soil moisture and vegetation stress responses and that excessive atmospheric evaporative demand needs to be coincident with the precipitation anomalies.

Understanding the Propagation of Meteorological Drought to Groundwater Drought: A Case Study of the North China Plain

“…Similar to Entekhabi [55], our study is based on long-term observational data. Meanwhile, we focus on how meteorological drought affects groundwater systems.…”

“…However, these studies did not involve the North China Plain nor did they deeply analyze the response of groundwater systems to meteorological drought. In drought propagation research, previous studies mostly relied on methods like the maximum correlation coefficient method [64] and traditional lag cross-correlation analysis [55], which depend on the linear relationship between variables. If the propagation of drought involves nonlinear processes, these methods have limitations in quantifying the drought transmission time.…”

“…If the propagation of drought involves nonlinear processes, these methods have limitations in quantifying the drought transmission time. Additionally, the drought delayed time calculated by Entekhabi [55] is based on the difference in the start time of groundwater drought and meteorological drought, and the degree of drought attenuation is calculated based on the area enclosed by the drought process curve and the drought threshold. However, the start time of drought is not always so clear, and the selection of different drought indices and different threshold levels will bring uncertainty to the results.…”

“…Given the thresholds R 0 and R 1 , when the drought index is less than R 0 , it is a negative excursion, and when it is greater than R 0 , it is a positive excursion. If the duration of negative trips exceeds a certain length (usually 2 months or more) [55], a drought event is considered to have occurred and is labeled as a drought; if the negative trip lasts only 1 month and the drought index < R 1 , drought is also considered to have occurred and is labeled as a drought event; if the interval between two droughts is only 1 month and the drought index < 0, the two negative excursions are combined as a drought event; and if none of the above three conditions are satisfied, the event cannot be labeled as a drought event [56]. In this study, the drought frequency (DF) is determined by counting the number of times mild or more severe droughts occurred during the research period.…”

“…After successfully pairing two types of drought events, the peak time (PT), peak intensity (PI), and drought duration (DD) are calculated, respectively. To further understand the propagation process of meteorological drought to groundwater drought, including cumulative [58], delayed [59], attenuation [55], and prolonged [60] aspects, this study calculated the peak lag time (PLT), attenuation scale factor (ASF), and extension scale factor (ESF) between meteorological and groundwater droughts across various meteorological drought time scales (Supporting Information Figure S2). PLT, ASF, and ESF are quantitative indicators of delayed, attenuation, and prolonged effects, respectively.…”