A virtual station multi-year time series graph (click on the image at the left to
see a sample graph) shows the sea surface temperature (SST) time series and coral
bleaching Degree Heating Weeks (DHW) time series over the time period from
Jan 2001 to present for each selected reef site. SST is shown in the center portion of
the graph, using the vertical axis on the left. DHW is shown in the bottom portion
of the graph, using the vertical axis on the right. The legend for the curves is given in
the top portion of the graph. The multi-year graph is created from the same time series
data as the single-year graphs,
however, it provides a convenient way to compare the time series between years.
In the graph, the time series of SST and DHW for the current year is plotted as a thick black solid line. The time series for the year with the warmest summer that caused the most significant mass coral bleaching event at the reef site is plotted in a thick red solid line. No thick red solid line is used if there has been no mass bleaching event at the reef site since 2001. If no DHW time series is visible for a particular year, the DHW value is zero throughout that year.
The corresponding thermal stress condition related to coral bleaching for the current year is color-coded and plotted below the time series. The thermal stress condition is categorized in the five bleaching alert levels defined by Coral Reef Watch's Satellite Bleaching Alert:
|
Stress Level No Stress Bleaching Watch Bleaching Warning Bleaching Alert Level 1 Bleaching Alert Level 2 |
Definition HotSpot <= 0 0 < HotSpot < 1 1 <= HotSpot and 0 < DHW < 4 1 <= HotSpot and 4 <= DHW < 8 1 <= HotSpot and 8 <= DHW |
At Bleaching Alert Level 1, some bleaching is expected at the site within a few weeks of the alert. An accumulation of 8 DHWs triggers a Bleaching Alert Level 2, at which point widespread bleaching and some coral mortality are likely.
The monthly mean SST climatologies (dark-blue crosses) are also plotted to show the "normal" SST conditions at the site. The time of the climatologically warmest months are usually the peak bleaching season.
The time series were extracted from a 50 km satellite water pixel surrounding or close to the selected reef site. A map showing the selected reef site and its satellite pixel is accessible by clicking on the reef name in the title of this page. Bleaching HotSpots are SST anomalies exceeding the maximum monthly mean SST (MMMSST, dashed light-blue line). The MMMSST is the maximum of the twelve monthly mean SST climatology values, and the Coral Bleaching Threshold SST (solid light-blue line) is defined as the MMMSST plus one degree Celsius. Both the MMMSST and Coral Bleaching Threshold SST are location-specific. DHW, in units of degree Celsius-weeks, are the accumulation of bleaching HotSpot anomalies during the previous 12 weeks whenever the SST equals or exceeds the coral bleaching threshold SST at the pixel. For more details on the methodology for calculating these data, please visit our methodology page.
