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4DModeller / tblakes

project repo for tibetan lakes
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what happened in 2015 to lake growth? #6

Open mnky9800n opened 10 months ago

mnky9800n commented 10 months ago

If we look at 2015, there is an explosion in lake growth but i dont know why.

below i show 2014, 2015, 2016 for the water balance in square kilometers for high mountain asia:

image

image

image

As you can see there is a huge increase in lake growth in 2015 that doesn't align with the amount of growth in other years.

mnky9800n commented 10 months ago

TODO:

  1. show the original raw data plots for this time period
  2. how does precipitation change during htis time period?
  3. how does temperature change during this time period?
mnky9800n commented 10 months ago

image you can also see this in the aggregate data, here i have plotted the water balance in km^2 for each catchment as a black line per year, and then the mean of all catchments as the red line. The error bars are 1 standard deviation.

mnky9800n commented 10 months ago

There is no equivalent decline time

mnky9800n commented 10 months ago

https://www.nature.com/articles/s43247-022-00520-8

figure 2.a here also confirms it but i think they are only looking at ice dammed lakes in this paper

mnky9800n commented 10 months ago
image

here you can see the raw data from GEE and you can see the green (2015 growth) is much more prevalent than the cyan (2014 growth). there are lots of examples like this. there is also more runoff from lakes.

Two things to check:

  1. was there more precipitation in 2015?
  2. was it warmer in 2015?
mnky9800n commented 9 months ago

Hi John, thanks.

Issue 1: yes, the southern fringe of the plateau is monsoon dominated and this is wetter. If we use absolute precipitation values it will lead to a bias I suppose. Is it not better to use annual anomalies (year precip / long term mean) as predictor for lake change? A average lake is present in average precipitation conditions , but it might grow when there is above average precip?

Issue 2: OK. Seasonal climate anomalies may also be a strong predictor, e.g. temperature / precipitation anomalies during the monsoon period for example (June to September) or spring.

Issue 3: How about checking the 2015 precip and see if this is also anomalous compared to the other years?

Cheers, Walter

mnky9800n commented 9 months ago

image it does not appear that precipitation has increased at all. not sure what to make of this.

mnky9800n commented 9 months ago

you need to look at the zscores though

mnky9800n commented 9 months ago

what happens if you extract only the catchments that have larger growth values?