Novel Along‐Track Processing of GRACE Follow‐On Laser Ranging Measurements Found Abrupt Water Storage Increase and Land Subsidence During the 2021 March Australian Flooding. Issue 11 (4th November 2021)

• Record Type: Journal Article
• Authors: Han, Shin‐Chan; Yeo, In‐Young; Khaki, Mehdi; McCullough, Christopher M.; Lee, Eunjee; Sauber, Jeanne
• Is Part Of: Earth and space science. Volume 8:Issue 11(2021)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2021-11-04
• Subjects: GRACE Follow‐On -- flood -- GPS; Space sciences -- Periodicals; Geophysics -- Periodicals; 500.5
• DOI: 10.1029/2021EA001941
• Languages: English
• ISSNs: 2333-5084

Abstract

Abstract: Following extreme drought during the 2019–2020 bushfire summer, the eastern part of Australia suffered from a week‐long intense rainfall and extensive flooding in March 2021. Understanding how much water storage changes in response to these climate extremes is critical for developing timely water management strategies. To quantify prompt water storage changes associated with the 2021 March flooding, we processed the low‐latency (1–3 days), high‐precision intersatellite laser ranging measurements from GRACE Follow‐On spacecraft and determined instantaneous gravity changes along spacecraft orbital passes. Such new data processing detected an abrupt surge of water storage approaching 60–70 trillion liters (km 3 of water) over a week in the region, which concurrently caused land subsidence of ∼5 mm measured by a network of ground GPS stations. This was the highest speed of ground water recharge ever recorded in the region over the last two decades. Compared to the condition in February 2020, the amount of recharged water was similar but the recharge speed was much faster in March 2021. While these two events together replenished the region up to ∼80% of the maximum storage over the last two decades, the wet antecedent condition of soils in 2021 was distinctly different from the dry conditions in 2020 and led to generating extensive runoff and flooding in 2021. Plain Language Summary: The monthly mean snapshots of global gravity field and surface mass variation ("mascon") from the GRACE and GRACE Follow‐On spacecraft missions are problematic to accurately quantify abrupt water storage changes and flooding by intense rainfall. This study demonstrates a new use of the GRACE Follow‐On data to measure immediate water storage changes by computing instantaneous gravity change along spacecraft orbital passes. This new application is also shown for low‐latency (a few days) data processing to assess surface mass changes immediately after extreme events. The results found that the eastern parts of Australia experienced the highest speed of ground water recharge ever recorded in the region and the wet antecedent condition of soils yielded extensive flooding in 2021. Key Points: New GRACE Follow‐On gravity data processing quantified prompt changes in water storage by the heavy rainfall and flooding in March 2021 The eastern Australia experienced the highest speed of ground water recharge and wet antecedent soils were responsible for extensive flooding in 2021 The study demonstrated the feasibility of rapid processing (1–3 days) for immediate assessment of mass changes from extreme events