Multicomponent Satellite Assessment of Drought Severity in the Contiguous United States From 2002 to 2017 Using AMSR‐E and AMSR2

Abstract

The Advanced Microwave Scanning Radiometer for the Earth Observing System and Advanced Microwave Scanning Radiometer 2 sensors (AMSR) have provided multifrequency microwave measurements of the global terrestrial water cycle since 2002. A new AMSR surface wetness index (ASWI) was developed by analyzing the near‐surface atmospheric vapor pressure deficit (VPD), surface volumetric soil moisture (VSM), and land surface fractional open water (FW) time series from an established AMSR Land Parameter Data Record (LPDR). The ASWI allows for multicomponent and independent satellite assessments of near‐surface drought conditions by exploiting the weighted anomalies of VPD, VSM, and FW. Comparisons between ASWI and more traditional drought metrics, including the Palmer moisture anomaly index (PDSI‐Z) and the U.S. Drought Monitor, showed generally consistent classifications of drought severity for three major droughts over the Contiguous United States since 2002. The AWSI showed moderate (0.3 ≤ R ≤ 0.7 for 56% of area) to strong (R > 0.7 for 29% of area) correlations with the PDSI‐Z during the summer months (June–August) from 2002 to 2017. ASWI and PDSI‐Z differences were attributed to AMSR retrieval uncertainties and the different aspects of drought represented by the indices. Comparisons between ASWI and the Gravity Recovery and Climate Experiment drought severity index (GRACE‐DSI) showed strong correspondence (R = 0.61) in regions where possible long‐term total water storage changes occurred. The sole reliance of the ASWI on satellite microwave remote sensing and continuing AMSR2 operations enables effective global monitoring of drought conditions while providing new information on the atmosphere, soil, and surface water components of drought.

Synergistic Satellite Assessment of Global Vegetation Health in Relation to ENSO‐Induced Droughts and Pluvials

“…For mapping drought severity, the negative ASWI values were grouped into five drought intensity classes ranging from exceptional drought (D5) to abnormally dry (D1) conditions, as follows: D5: −2.0 or less; D4:−1.5 to −1.99; D3: −1.0 to −1.49; D2: −0.5 to −0.99; and D1: −0.25 to −0.49. Positive ASWI values were similarly grouped into five pluvial intensity classes ranging from exceptional (W5) to abnormally (W1) wet conditions: W5: 2.0 or greater; W4: 1.5 to 1.99; W3: 1.0 to 1.49; W2: 0.5 to 0.99; and W1: 0.25 to 0.49 (Du et al., 2019).…”

Global terrestrial water storage and drought severity under climate change

“…These conventional indices have been used in monitoring and projecting 32,34 meteorological, agricultural, and hydrological droughts 35 . 86 Recently, a new drought index, the TWS drought severity index (TWS-DSI 5 ), has been employed to examine droughts 36,37 in relation to the vertically-integrated water storage as opposed to the individual storages or fluxes used in conventional indices. Previous studies 5,36,37 89 have demonstrated that TWS-DSI correlates with the conventional indices in regions with long-90 term water storage change, but provides an integrated measure, especially by capturing the 91 effects of slow-responding terms (i.e., deep soil moisture and groundwater).…”

“…Previous studies 5,36,37 89 have demonstrated that TWS-DSI correlates with the conventional indices in regions with long-90 term water storage change, but provides an integrated measure, especially by capturing the 91 effects of slow-responding terms (i.e., deep soil moisture and groundwater). Further, an 92 increasing number of TWS-based drought studies have shown that a synergistic combination of 93 TWS and traditional drought indices can provide crucial insights about drought impacts on 94 hydrologic systems and vegetation growth 6,36,37 , because TWS directly responds to changes in precipitation, integrates soil moisture, and modulates runoff generation, hence encompassing the three aforementioned drought types 36 . However, since previous TWS studies have focused on historical droughts [3][4][5][6]20 , the changes in future droughts due to TWS change and variability remain unexamined.…”

Remote Sensing of Environmental Changes in Cold Regions: Methods, Achievements and Challenges

“…Surface water (SW) over inland areas is a key component of the water and energy cycles, covering about three percent (4.46 million km 2 ) of Earth's land [177]. The dynamics of SW in cold land regions are closely linked to terrestrial water storage changes [178], flood and drought events [179], seasonal thawing and the spring flood pulse [180], microtopography, underlying geology and permafrost conditions [181]. SW changes are also occurring in Arctic-boreal wetlands, lakes, rivers, and streams as permafrost degrades with regional climate warming [29,180,182]; surface subsidence during the initial stages of permafrost degradation leads to increased inundation, while later stages of permafrost thaw lead to surface drying and reduced wetland extent as drainage pathways increase [27].…”