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- Title
Extreme Compound and Seesaw Hydrometeorological Events in New Zealand: An Initial Assessment.
- Authors
Bennet, Morgan J.; Kingston, Daniel G.; Cullen, Nicolas J.
- Abstract
Attention is increasingly being turned toward land atmosphere interactions within the wider hydrological cycle when investigating extreme hydrometeorological events. This is particularly the case with the identification of compound and seesaw events. To do so, accurate soil moisture data are essential. Here, soil moisture from three reanalysis products (ERA5‐Land, BARRA and ERA5) is compared to station observations from 12 sites across New Zealand, for an average timespan of 18 years. Soil moisture data from all three reanalyses are used to investigate land‐atmosphere coupling with gridded (observational) precipitation and temperature. This enables compound (co‐occurrence of hot and dry) and seesaw (rapid transitions from dry to wet) events to be identified and examined. No best performing reanalysis data set for soil moisture is evident (median Pearson's r range: 0.78–0.81). All reanalyses successfully capture the seasonal and residual component of soil moisture, but not the observed soil moisture trends at each location. Strong coupling between soil moisture and temperature occurs in all three reanalyses across the predominately energy‐limited regions of the lower North Island and entire South Island. Consequently, these regions reveal a high frequency of compound event occurrence and potential shifts in land states to a water limited phase during compound months. A series of seesaw events is also detected for the first time in New Zealand (terminating approximately one‐fifth of drought events), with a high frequency of seesaw event occurrence detected in previously identified areas of atmospheric river (AR) activity. Plain Language Summary: Extreme hydrometeorological events can be very damaging, with two examples being compound and seesaw events. Compound events include examples such as concurrent droughts and heat waves, while seesaw events represent rapid shifts from dry (drought) periods to wet (flood) periods. Understanding how these events start, operate and stop can therefore be extremely helpful to allow us to prepare for them, and reduce their effects. Soil moisture is an essential variable to examine when trying to improve our understanding of these events, as it can help us to understand the interactions between the land (soil) and atmosphere (precipitation and temperature). Therefore, having accurate soil moisture information is an important goal. This study investigates how well soil moisture is represented across New Zealand from three products, revealing all to be similar in their performance. The study then investigates the land‐atmosphere interactions across New Zealand, revealing "hot spots" of strong land atmosphere interaction during dry months. Compound events show a high occurrence in traditionally wet environments, indicating changes in the land state during drought phases. Rapid transitions from dry to wet are revealed in areas previously identified as being exposed to extreme rainfall. Key Points: Reanalysis soil moisture captures seasonal and residual components of observed soil moisture for New ZealandCompound events highlight potential changes to land states in energy limited climates during growing seasonsSeesaw events are implicated in the termination of approximately one‐fifth of drought events
- Subjects
NEW Zealand; SOUTH Island (N.Z.); NORTH Island (N.Z.); LAND-atmosphere interactions; SOIL moisture; ATMOSPHERIC rivers; HYDROLOGIC cycle; HEAT waves (Meteorology); DROUGHTS
- Publication
Journal of Geophysical Research. Atmospheres, 2023, Vol 128, Issue 21, p1
- ISSN
2169-897X
- Publication type
Article
- DOI
10.1029/2022JD038346