Differentiating forms of mass movement

Differentiating forms of mass movement

by Sean Singh -
Number of replies: 4

Hello,

I was interested in the different methods used to cross check the data, as well as different types of mass movement that were detected. I am still waiting for the webinar to be posted so I can make references to specific slides, but it seemed that one set of measurements was detecting the massive movement of carbon mass from trees into the atmosphere via vast forest fires, some intentional, others not so much, which do happen to be in similar areas as droughts. Seeing as the new normal of a year long fire season is caused by widely distributed drought conditions.
As noted here:
https://www.fs.fed.us/features/year-round-fire-season
https://www.latimes.com/opinion/editorials/la-ed-carr-fire-wildfires-climate-change-20180730-story.html

I am just saying the GRACE data can be used for more than measuring the hydro logical cycle, but also other aspects of climate change.

In reply to Sean Singh

Re: Differentiating forms of mass movement

by Yannick Schillinger -
Dear Sean,

thank you for your contributions and questions! Please be informed that the webinar recording as well as the presentation slides are now available from the course page.

Kind regards,
Yannick
In reply to Sean Singh

Re: Differentiating forms of mass movement

by Helena Gerdener -
Dear Sean,

thank you, you are totally right when saying that GRACE can be used for more than the hydrological cycle.,

The aspect with the carbon mass change is a very interesting one It would be great if you could say to which slide you refer.

Generally, I think that the resolution of GRACE probably might be too coarse to see the carbon mass change from the trees to the atmosphere due to forest fires. Do you have some numbers about this carbon mass change? It would be interesting to know, if the spatial extent of the forest fires and the resulting mass change is large enough.

Another point that comes to my mind is that droughts are events, which are long lasting (from a few months to years) and also slow developing. A drought mostly begins with a precipitation deficit and/or high evapotranspiration. This can the propagate into the hydrological storages, first the surface storages and then subsurface storages. Forest fires are more short and sudden events. So if the carbon masses are really large enough to see them in the GRACE time series, I assume that we would have a very sudden change in the time series. This could be a very interesting point to look at.

Kind regards,
Helena
In reply to Helena Gerdener

Re: Differentiating forms of mass movement

by Sean Singh -
Looking at Helmholtz presentation, side 10. In my opinion this displays a large disturbance in the amazon, this seems to accord with slash and burn farming. Because replacing forest with farmland does not normally cause significant disruptions in the water cycle, because the plants change. But still transpire water.
Which is different from what is noted from the cost of Argentina, which is experiencing a loss of snow melt water, which was also clustered only around the mountain range. A result of snow melting earlier in the season.

Looking at slide 8 of Helena’s presentation, notice that a lot of anomalies occur in northern russia, near Siberia ? Same for some parts of Europe ? Those are not farming areas, those are wilderness areas. Which also have been subject to quite a few unchecked forest fires because there is no fire dept in those areas. As for what is noted in northern Canada, another large section of wilderness, also many fires but due to the size being much larger than the fires, my guess is that those are depicting permafrost melt, not drought, I don’t think drought conditions are typically associated with the northern wilderness of both Canada, Greenland and russia/siberia. However I could be wrong about the fires in those areas being as extensive, much more likely what we are seeing is vast amounts of permafrost melt, which is releasing both methane directly, as well as methane being produced by vast tracts of microorganisms. More likely than carbon transport from fires, this is a possible canary in the coal mine for the https://en.wikipedia.org/wiki/Clathrate_gun_hypothesis or maybe a smoking gun ?So the areas with drought and farming, actually depicted less extreme changes, most likely because of being offset by irrigation.

I also have some questions about slide 11, the only graph where details are intelligible, is from 2002, the rest are too small to make out the details. Mostly to point out that india has done the worst job in water management and has been overly reliant on aquifers. So it shows an increase in territrial water which my guess is irrigation, but those aquifers are less than half full now, and the water from that as well as monsoons, typically get washed into the ocean instead of refilling the aquifers, so there is more rain yes, however the rapid urban development did not come with sewers or water management, combined with high clay content in many areas, results in water being drained into the ocean instead of replenishing aquifers. The same dynamic affects all major agricultural areas with the only exception being parts of the EU and Japan.
In reply to Sean Singh

Re: Differentiating forms of mass movement

by Helena Gerdener -
Dear Sean,

(Answer to paragraph 1:)

It is unclear whether slash and burn and related land cover changes affect water storage on a scale visible in GRACE. Anyway, since the maps are not deseasoned, what we see here is predominantly the seasonal cycle in total water storage which has a wide span between wet and dry season, which was already shown to be large in some papers (e.g. Wahr et al. 2004; Crowley et al. 2008). Thus the change in the gravity field can likely be explained by the seasonal cycle.


(Answer to paragraph 2:)

The figures show drought indicators derived from total water storage deficits. For analysing trends one would need to look at trend maps which are available in the literature. For attributing observed trends or changes to individual drivers like snow melt, permafrost change or land surface change (fires) one would need to conform the observed data with model simulations. There are plenty of studies in the literature.


(Answer to paragraph 3:)

The map shows loss of total water storage (surface, groundwater, etc) over 15 years which is a short timespan. Using model simulations, several published studies have attributed these changes to unsustainable use of groundwater over India, and this has been confirmed from groundwater well observations, so there is a high confidence. For other regions of the world, trends have been observed with GRACE but it is often difficult to attribute them so causes – this could be changes in agricultural practice like irrigation but also be natural climate variability.

Cheers,
Helena